CHARACTERIZATION OF POULTRY LITTER  
 
FOR STORAGE AND PROCESS DESIGN 
 
Except where reference is made to the work of others, the work described in this thesis is 
my own or was done in collaboration with my advisory committee.  This thesis does not 
include proprietary or classified information.  
 
_________________________________________________ 
Matthew Bernhart 
Certificate of Approval: 
 
 
 
_______________________                                            _________________________ 
John Fulton            Oladiran Fasina, Chair                                          
Assistant Professor                                                           Assistant Professor 
Biosystems Engineering                                                   Biosystems Engineering 
 
 
 
 
 
_______________________                                            _________________________ 
Mario Eden                                                                       Yifen Wang 
Assistant Professor                                                           Assistant Professor 
Chemical Engineering                                                      Biosystems Engineering 
 
 
 
 
 
 
 
________________________ 
                                                Joe F. Pittman 
                                                Interim Dean 
                                                Graduate School 
CHARACTERIZATION OF POULTRY LITTER 
 
FOR STORAGE AND PROCESS DESIGN 
 
Matthew Bernhart 
 
 
A Thesis  
Submitted to 
the Graduate Faculty of  
Auburn University  
in Partial Fulfillment of the  
Requirements for the  
Degree of  
Master of Science 
 
 
Auburn, Alabama 
August 4, 2007 
 
 
 
 
iii
CHARACTERIZATION OF POULTRY LITTER  
 
FOR STORAGE AND PROCESS DESIGN 
 
 
Matthew Bernhart 
 
 
Permission is granted to Auburn University to make copies of the thesis at its discretion, 
upon request of individuals or institutions and at their expense.  The author reserves all 
publication rights.  
 
 
 
    
 
____________________________ 
                                                                Signature of Author 
 
 
____________________________ 
                                                               Date of Graduation 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
iv
VITA 
 
Matthew Bernhart, son of Edward J. and Jill K. Bernhart, was born April 27, 1982 
in Leesburg, Virginia.  He graduated from Bishop Denis J. O?Connell High School in 
Arlington, Virginia.  He then attended North Carolina State University in Raleigh, North 
Carolina until August, 2002.  He then transferred to Auburn University in Auburn, 
Alabama where he graduated with a Bachelor of Science degree in Chemical Engineering 
in May, 2005.  He then began the graduate program at Auburn University in Chemical 
Engineering in August of 2005. 
 
 
 
 
 
 
 
 
 
 
 
 
v
THESIS ABSTRACT 
THE CHARACTERIZATION OF POULTRY LITTER  
FOR STORAGE AND PROCESS DESIGN 
Matthew Bernhart 
Masters of Science, August 4, 2007 
(B.S., Auburn University, 2005) 
116 Typed Pages 
Directed by Oladiran Fasina 
 
 Concern over the world?s dependence on nonrenewable fossil fuels as the primary 
source of energy is continually increasing.  This has led researchers, industry officials 
and government agencies to begin to aggressively investigate the use of alternative and 
renewable energy resources such as biomass.  Poultry litter, a combination of 
accumulated chicken manure, feathers, and bedding materials (obtained from broiler 
houses), is a potential biomass feedstock.  In this study some of the characteristics of 
poultry litter (such as bulk density, particle density, compressibility, compaction and 
flowability) that are important for its storage and process design were examined.  It was 
found that moisture content significantly affected the bulk density, particle density, and 
porosity of poultry litter.  An average tap bulk density of 0.580 g/ml and Hausner ratio of 
vi
1.070 were obtained and were not affected by moisture content.  Based on 
compressibility results, poultry litter was found to have good or excellent flow when 
pressures less than 12 kPa were applied to poultry litter samples at moisture contents of 
26.0% (w.b.) and below.  The fit of the GAB equation to poultry litter?s equilibrium 
moisture isotherm (at 25
o
C) indicated that the monolayer moisture content for poultry 
litter is 5.8% (d.b.), implying that biochemical degradation occurs when the litter is 
stored at a moisture content greater than 5.8% (d.b.) or 5.5% (w.b.).  To enhance storage 
and transportation, the effect of moisture content and pressure on the compaction of 
poultry litter was investigated.  The initial density of the compacts, the energy required 
for compaction and the strength of the resulting compacts (after two months storage) 
were significantly affected by the moisture content of the samples and the pressure 
applied during compaction.  However, the density of the compacts after two months 
storage was only significantly affected by the pressure applied during compaction.  
Increasing the moisture content of the poultry litter reduced its flowability (hence 
increased particle cohesion) from easy flowing (flow index of 6.369) at a moisture 
content of 10.3% (w.b.) to very cohesive/non-flowing (flow index of 1.871) at a moisture 
content of 30.9% (w.b.).  The adhesion of poultry litter to the milled steel surface was 
reduced when the surface was modified.  The carbon coated steel surface had the least 
adhesion in comparison to the aluminum surfaces and mirror finished steel surface.  The 
findings from this study can be used to design and/or select optimal equipment and 
facilities to handle, store and transport poultry litter for value-added utilization. 
vii
ACKNOWLEDGEMENTS 
 The author would like to thank the Chemical and Biosystems Engineering 
departments for their collaboration in this project.  The author would also like to give 
very special thanks to Dr. Oladiran Fasina for patiently teaching him the field of Bulk 
Materials Handling and helping him construct this thesis.  The author would also like to 
thank Dr. Yifen Wang for his suggestions to reexamine data when it was necessary.  The 
author would like to thank Dr. John Fulton, and Dr. Mario Eden for their input and 
support.  Finally, the author would like to thank his parents and his girlfriend, Elizabeth 
Elliott, for their patience and support during this endeavor.  
 
 
 
 
 
 
 
 
 
 
 
viii
Style manual or journal used: Publication format 
 
Computer software used: Microsoft Word, Microsoft Excel, SAS 9.1 Statistical program,  
 PolyMath 5.1 Nonlinear regression program 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ix
TABLE OF CONTENTS 
LIST OF FIGURES .......................................................................................................... xii 
LIST OF TABLES........................................................................................................... xiii 
CHAPTER 1. INTRODUCTION ........................................................................................1 
CHAPTER 2. LITERATURE REVIEW .............................................................................4 
            2.1 Bioenergy...........................................................................................................4  
            2.2 Poultry litter .......................................................................................................5 
                        2.2.1 Poultry litter as a fertilizer ..................................................................6 
                        2.2.2 Poultry litter as an energy source........................................................7 
                        2.2.3 Poultry litter for use as activated carbon...........................................10 
                        2.2.4 Composition analysis........................................................................10 
            2.3 Physical Properties...........................................................................................12 
                        2.3.1 Size....................................................................................................13 
                        2.3.2 Bulk density ......................................................................................14 
                        2.3.3 Particle density..................................................................................15 
                        2.3.4 Porosity .............................................................................................15 
                        2.3.5 Hausner ratio.....................................................................................15 
                        2.3.6 Compressibility.................................................................................16 
                        2.3.7 Equilibrium moisture relationships...................................................16 
            2.4 Compaction of Poultry Litter...........................................................................18 
            2.5 Flowability .......................................................................................................20 
            2.6 Summary..........................................................................................................26 
            2.7 References........................................................................................................27 
CHAPTER 3. MOISTURE DEPENDENT PHYSICAL PROPERTIES OF POULTRY 
LITTER..............................................................................................................................33 
            3.1 Introduction......................................................................................................33 
            3.2 Methods and Materials.....................................................................................35 
                        3.2.1 Preparation ........................................................................................35 
                        3.2.2 Particle size distribution....................................................................35 
                        3.2.3 Poured bulk density...........................................................................37 
                        3.2.4 Tap bulk density................................................................................37 
                        3.2.5 Particle density..................................................................................38 
                        3.2.6 Porosity .............................................................................................39 
                        3.2.7 Hausner ratio.....................................................................................39 
                        3.2.8 Mechanical compressibility ..............................................................39 
                        3.2.9 Equilibrium moisture isotherm .........................................................40 
                        3.2.10 Data Analysis..................................................................................41 
            3.3 Results and Discussion ....................................................................................42 
                        3.3.1 Moisture contents..............................................................................42 
x
                        3.3.2 Particle size distribution....................................................................42 
                        3.3.3 Poured bulk density...........................................................................44 
                        3.3.4 Tap bulk density................................................................................45 
                        3.3.5 Particle density..................................................................................45 
                        3.3.6 Porosity .............................................................................................46 
                        3.3.7 Hausner ratio.....................................................................................47 
                        3.3.8 Compressibility.................................................................................47 
                        3.3.9 Equilibrium moisture isotherm .........................................................49 
            3.4 Conclusion .......................................................................................................51 
            3.5 References........................................................................................................52 
CHAPTER 4. COMPACTION OF POULTRY LITTER..................................................55 
            4.1 Introduction......................................................................................................55 
            4.2 Methods and Materials.....................................................................................57 
                        4.2.1 Preparation ........................................................................................57 
                        4.2.2 Compaction.......................................................................................57 
                        4.2.3 Data analysis .....................................................................................59 
            4.3 Results and Discussion ....................................................................................60 
                        4.3.1 Density of poultry litter compacts.....................................................60 
                        4.3.2 Density of poultry litter compacts after 2 months ............................63 
                        4.3.3 Breakage force of poultry litter compacts.........................................64 
                        4.3.4 Specific energy for poultry litter compaction ...................................65 
            4.4 Conclusion .......................................................................................................67 
            4.5 References........................................................................................................68 
CHAPTER 5. FLOWABILITY OF POULTRY LITTER.................................................69 
            5.1 Introduction......................................................................................................69 
            5.2 Methods and Materials.....................................................................................71 
                        5.2.1 Preparation ........................................................................................71 
                        5.2.2 Flowability ........................................................................................71 
                        5.2.3 Wall friction......................................................................................73 
                        5.2.4 Data analysis .....................................................................................73 
            5.3 Results and Discussion ....................................................................................74 
                        5.3.1 Moisture contents..............................................................................74 
                        5.3.2 Flowability ........................................................................................74 
                        5.3.3 Wall friction......................................................................................76 
            5.4 Conclusion .......................................................................................................79 
            5.5 References........................................................................................................80 
CHAPTER 6. CONCLUSION...........................................................................................81 
CHAPTER 7. FUTURE WORK........................................................................................83 
APPENDICES ...................................................................................................................85 
            Appendix A. Physical Property Data.....................................................................86 
                        Table A.1 Particle size distribution of poultry litter ..................................86 
                        Table A.2 Bulk density ..............................................................................86 
                        Table A.3 Particle density..........................................................................86 
                        Table A.4 Tap bulk density........................................................................86 
                        Table A.5 Porosity of poultry litter............................................................87 
                        Table A.6 Hausner ratio of poultry litter ...................................................87 
xi
                        Table A.7 Compressibility of poultry litter................................................88 
                        Table A.8 Equilibrium moisture isotherm (25
o
C) raw data for  
                                         poultry litter ..............................................................................89 
            Appendix B. Compaction Data..............................................................................90 
                        Table B.1 Poultry litter compaction data set 1...........................................90 
                        Table B.2 Poultry litter compaction data set 2...........................................91 
                        Table B.3 Poultry litter compaction data set 1 after 2 months storage......92 
                        Table B.4 Poultry litter compaction data set 2 after 2 months storage......93 
                        Table B.5 Poultry litter compact?s percent decrease in density after 2 
                                        months........................................................................................94 
                        Table B.6 Breakage force of compacts after 2 months storage .................95 
                        Table B.7 Specific energy required for compaction of poultry litter.........95  
            Appendix C. Flowability Data ...............................................................................96 
                        Table C.1 Flow function data for poultry litter..........................................96 
                        Table C.2 Cohesion and angle of internal friction of poultry litter ...........97 
                        Table C.3 Wall friction flow function data and angle of wall friction for  
                                         poultry litter with milled steel...................................................97 
                        Table C.4 Wall friction flow function data and angle of wall friction for  
                                         poultry litter with milled aluminum..........................................97 
                        Table C.5 Wall friction flow function data and angle of wall friction for  
                                         poultry litter with mirror finished aluminum............................98 
                        Table C.6 Wall friction flow function data and angle of wall friction for  
                                         poultry litter with carbon coated steel.......................................98 
                        Table C.7 Wall friction flow function data and angle of wall friction for  
                                         poultry litter with mirror finished steel.....................................98 
            Appendix D. Equipment Photos ............................................................................99 
                        Figure D.1 Texture analyzer with compression cell and tight fitted  
                                           piston.......................................................................................99 
                        Figure D.2 Clamped compaction die filled with poultry litter below a  
                                          plunger attached to the crosshead of the texture analyzer  
                                          before compaction..................................................................100 
                        Figure D.3 Poultry litter compact removed from compaction die...........101 
                        Figure D.4 Annular shear cell..................................................................102 
                        Figure D.5 Wall friction samples.............................................................103 
 
 
 
xii
LIST OF FIGURES 
Figure 2.1 Jenike shear cell................................................................................................21 
Figure 2.2 Yield locus plot ................................................................................................22 
Figure 2.3 Flow function graph .........................................................................................23 
Figure 2.4 Jenike shear cell with wall sample ...................................................................24 
Figure 2.5 Annular shear cell tester ...................................................................................25 
Figure 3.1 Particle size distribution of poultry litter at various sieve apertures ................43 
Figure 3.2 Effect of moisture content on the poured bulk density of poultry litter ...........44 
Figure 3.3 Effect of moisture content on the particle density of poultry litter ..................46 
Figure 3.4 Effect of moisture content on the porosity of poultry litter..............................47 
Figure 3.5 Effect of moisture content and pressure on the mechanical compressibility  
                  of poultry litter .................................................................................................48 
Figure 3.6 Effect of moisture content on the relative humidity of poultry litter (25
o
C)....50 
Figure 4.1 Effect of moisture content and pressure on the density of poultry litter  
                  compacts ..........................................................................................................61 
Figure 4.2 Effect of moisture content and pressure on the density of poultry litter  
                  compacts ..........................................................................................................62 
Figure 4.3 Effect of moisture content and pressure on the density of poultry litter   
                  compacts after 2 months storage......................................................................63 
Figure 4.4 Effect of moisture content and pressure on poultry litter compact?s breakage 
                  force after 2 months storage.............................................................................64 
Figure 4.5 Effect of moisture content and pressure on the specific energy required for 
                  the compaction of poultry litter........................................................................65 
Figure 5.1 Flow function graph of poultry litter................................................................74 
Figure 5.2 Wall friction flow functions of 20.0% moisture content (w.b.) poultry litter ..77 
 
 
 
 
 
 
 
xiii
LIST OF TABLES 
Table 3.1 Summary of moisture contents used for various physical property tests ..........42 
Table 3.2 Particle size distribution of poultry litter ...........................................................43 
Table 5.1 Flow index of poultry litter at various moisture contents..................................75 
Table 5.2 Wall friction flow index of 20.0% moisture content (w.b.) poultry litter..........78 
 
 
 
 
1
CHAPTER 1. INTRODUCTION 
 A significant amount of companies, businesses, governmental agencies, and 
institutions are beginning to invest in alternative energy because of the current high cost 
of energy obtained from fossil fuels.  Energy production through biomass, which is 
abundant in this country and can be used as a carbon based fuel, is one of the promising 
renewable energy options being vigorously pursued in the US because of its positive 
environmental implications.  In order for the large scale use of biomass as an alternative 
energy source to be realized in the US, more research must be done to characterize its 
physical properties.  Without the knowledge of these properties, optimal design and 
selection of equipment and facilities to handle, store, and transport biomass cannot be 
achieved.  
Poultry litter is one of the biomass feedstocks that can be utilized as a renewable 
resource for bioenergy production in the US.  Poultry litter is a combination of 
accumulated chicken manure, feathers, and bedding materials found in broiler houses.  
The bedding materials are often made up of wood shavings, sawdust, wheat (Triticum 
aestivum L.) straw, peanut (Arachis hypogaea L.) hulls, or rice (Oryza Sativa L.) hulls 
(Edwards and Daniels, 1992).  These broiler houses are located in concentrated areas 
across the country.  Estimates indicate that about 11 million tons of poultry litter is 
generated in the country annually (Gollehon et al, 2001). 
2
Poultry litter has a calorific value of 13.5 GJ/ton, about half that of coal (Abelha 
et al, 2002).  Because of this there are plans around the world (e.g. Western Australia, 
Ireland, Britain) and in the U.S. to build large scale powerstations that use poultry litter as 
its feedstock (http://www.eprl.co.uk/profile; http://www.fibrowattusa.com).  Poultry litter 
also has the potential to be used for the production of methane and the production of 
activated carbon for water purification purposes (Hills and Ravishanker, 1984; Safley et 
al, 1987; Lima and Marshall, 2004).   
Poultry litter is, however, a bulk solid.  The effective design and selection of 
storage, transportation and processing facilities and equipment of bulk solid materials 
requires information on its physical and flow properties and the effects of moisture on 
these properties.  This information is currently lacking for poultry litter. 
 Traditionally, poultry litter is utilized in places of production as a fertilizer partly 
because of the expensive cost of transporting the low-density litter.  The utilization of 
poultry litter for bioenergy and other value added applications will require that the litter 
be transported over long distances.  Compaction or agglomeration of the litter will 
significantly reduce the cost of transportation.  Other benefits such as low dust 
generation, minimal spread of pathogens, and a more uniform product can also be 
realized by compacting the litter. 
 Therefore, the main objective of this study is to investigate some of the properties 
of poultry litter that are crucial for process design and value added utilization.  To 
achieve this, the following specific tasks were carried out:  
(1) Characterization of the physical properties (particle size distribution, bulk 
density, tap bulk density, particle density, porosity, Hausner ratio, 
3
compressibility, and equilibrium moisture relations) of poultry litter and the effect 
of moisture content on these properties, 
(2) Optimization of the compaction of poultry litter for effective transportation for 
off-site utilization, and   
(3) Characterization of the flow properties (flow function, cohesion, internal angle of 
friction, wall friction flow function, and angle of wall friction) of poultry litter 
and the effect of moisture content on these properties. 
Chapters 3, 4, and 5 of this thesis each contain separate studies corresponding to 
the three tasks above: chapter 3 is on the moisture dependent physical properties of 
poultry litter; chapter 4 is on the compaction of poultry litter; and chapter 5 is on the 
flowability of poultry litter.  Each chapter has a separate set of sections (introduction, set 
of objectives, methods and materials, results and discussion, conclusion, and references).   
 
 
 
 
 
 
 
 
 
 
 
4
CHAPTER 2. LITERATURE REVIEW 
2.1 Bioenergy 
The need to obtain energy from sources other than fossil fuels is becoming more 
apparent everyday.  Oil prices hit record highs in April 2006 (rising to over $74 per barrel 
in New York trading) and are expected to increase.  In 2002, the price of oil was roughly 
$28 per barrel (www.washingtonpost.com).  These prices already far exceed projections 
from the Department of Energy, which only predict the price of petroleum in 2010 to be 
$48.24 per barrel.  These increases in price make research into the use of biomass as an 
alternative energy source a necessity.  In addition to this, the total renewable energy 
generation in the United States is projected to grow by 1.7% per year due to expected 
improvements in technology, higher prices of fossil fuels, and extended tax credits 
provided by both the federal government?s Energy Policy Act of 2005 and other state 
renewable energy programs (http://www.eia.doe.gov/oiaf/aeo/index.html). Because of all 
these factors, bioenergy has future economic potential. 
 Bioenergy is defined as energy derived from biomass.  This includes biopower 
(electricity or industrial process heat or steam generated from biomass or intermediate 
byproducts), energy from biobased transportation fuels, and energy from biomass 
materials that are used for process or space heating.  Biomass is defined as organic 
materials that are plant or animal based, including but not limited to dedicated energy 
5
crops, agricultural crops and trees, food, feed and fiber crop residues, aquatic plants, 
forestry and wood residues, agricultural wastes, biobased segments of industrial and 
municipal wastes, processing by-products and other non-fossil organic materials (ASABE 
Standard S593, 2006). 
 Biomass is a renewable energy source and is very friendly to the environment 
especially when compared to fossil fuels.  The combustion and regrowth of biomass is a 
process which recycles atmospheric carbon.  As a result, biomass power contributes 
virtually zero net emissions of CO
2
.  Fossil fuels on the other hand contribute over 
600,000 kg (or 660 tons) of CO
2
 for every gigawatt-hour of energy produced (Easterly 
and Burnham, 1996).  
 
2.2 Poultry Litter 
Poultry litter is a combination of accumulated chicken manure, feathers, and 
bedding materials.  The bedding materials are often made up of wood shavings, sawdust, 
wheat (Triticum aestivum L.) straw, peanut (Arachis hypogaea L.) hulls, or rice (Oryza 
Sativa L.) hulls (Edwards and Daniels, 1992).  In the United States close to 11 million 
tons of poultry litter is produced annually (Gollehon et al, 2001).  Approximately, 2.7 
million tons of broiler litter were produced in the state of Alabama in 2004.  The 
production of broilers has continued to increase every year.  Between 2002 and 2005 the 
number of broilers in the US increased from 8.59 billion to 8.87 billion 
(http://usda.mannlib.cornell.edu).  This implies that the production of poultry litter will 
continue to rise.  Therefore, it is urgent that value added utilization methods are identified 
for poultry litter. 
6
2.2.1 Poultry litter as a fertilizer 
Poultry litter is nutrient rich with typical N:P:K ratios of 6:2:3, which make it an 
excellent fertilizer (Nicholson et al, 1996).  Unfortunately, in broiler producing states 
such as Alabama, Arkansas, Delaware, Georgia, Maryland, Mississippi, North Carolina, 
West Virginia, and Virginia, broiler houses are typically found in small concentrated 
areas.  Large amounts of poultry litter are therefore produced in these areas that are 
beyond the fertilizer requirements of the neighboring agricultural areas (Ndegwa et al, 
1991).  The result is excessive use of poultry litter in some cropping systems that has 
resulted in reports of nitrate contamination of ground water in some of these areas (Bitzer 
and Sims, 1988).  Improperly dispensed poultry litter can contribute to air pollution with 
the release of CH
4
, NH
3
, H
2
S, amides, volatile organic acids, mercaptans, esters, and 
other compounds (Sweeten et al, 2003).   
As a result of the problems mentioned in the previous paragraph regarding the 
disposal of poultry litter, the environmental regulation agencies in these areas are 
beginning to examine the methods being used to dispose poultry litter more carefully.  In 
the state of Alabama the application of manure on pastureland and cropland in north 
Alabama is prohibited by ADEM (Alabama Department of Environmental Management) 
for most of the fall and winter months of the year (November 15 to February 15) 
(Mitchell and Tyson, 2002).  In Maryland, the Quality Improvement Act was passed in 
1998.  It contains regulations concerning the application of manures and inorganic 
fertilizers to crops.  This has already caused some Delmarva counties in the state of 
Maryland to realize the need to investigate alternative uses of broiler litter due to the 
excessive amounts they produce (Carr, 1998). 
7
2.2.2 Poultry litter as an energy source 
Air-dried poultry litter samples have a typical calorific value of 13.5 GJ/ton about 
half that of coal (Abelha et al, 2002).  Despite this, several countries around the world 
have started utilizing poultry litter as a renewable energy resource.  For example in 
Ireland, a small scale fluidized bed combustor that uses poultry litter or a poultry litter 
and peat mixture (50% of each) as feedstock is being installed to heat poultry houses 
(Abelha et al, 2002).  Energy Power Resources Limited in the United Kingdom is 
currently operating three large scale power stations that are run on the combustion of 
poultry litter as the primary biomass. Each of these plants also produces ash which is sold 
as a safe alternative to super phosphate fertilizers.  The plant in Eye, UK consumes 
140,000 tonnes of poultry litter to produce 12.7 MW of power annually.  The plant in 
Westfield, UK consumes 110,000 tonnes of poultry litter to produce 9.8 MW of power 
annually.  The plant in Thetfield, UK consumes 420,000 tonnes of poultry litter to 
produce 38.5 MW of power annually (http://www.eprl.co.uk/profile).    
Fibrowatt LLC, which runs Energy Power Resources Limited in the UK, is 
planning more litter powered plants to the US.  In early 2007, it plans to launch a power 
plant run on turkey litter in Minnesota.  This will be the first plant of its kind in the US 
and it will consume 700,000 tons of turkey litter to produce 55 MW of power annually.  
Plans to build similar plants that are run on poultry litter and forest residue mixtures 
(approximately 2:1)  are being developed in Mississippi, and Maryland with an annual 
poultry litter consumption and power production estimates of 200,000-300,000 tons and 
40 MW, and 200,000-300,000 tons and 30-40MW (http://www.fibrowattusa.com). 
8
The major benefit of poultry litter as an energy source is the low amount of 
emissions it produces when combusted.  As stated earlier there are no net CO
2 
emissions 
in its use (Easterely and Burnham, 1996).  Furthermore, with proper optimization of the 
combustion process CO emission levels can be controlled and lowered to permissible 
levels (Abelha et al, 2002; Henihan et al, 2003; Zhu and Lee, 2004).  It is also recognized 
that SO
2 
emissions always remain low because poultry litter has a low sulfur content.  
These emissions are even further lowered as ash is produced because the Ca in it acts to 
retain the small amounts of SO
2
 that are released in the process (Abelha et al, 2002).  
Whenever poultry litter was used by itself or in conjunction with other energy sources, 
NO
x
 emissions were always considered low in comparison to other methods of energy 
production (Sweeeten et al, 2003; Sami et al, 2000; Zhu et al, 2004; Albeha et al, 2002; 
Henihan et al, 2003). 
Coal produced 32% of the nation?s energy in 2004, and is projected to continue to 
increase its production to 38% of the nation?s energy by 2030 
(http://www.eia.doe.gov/oiaf/aeo/index.html).  Using poultry litter in conjunction with 
coal appears to be a very attractive option.  The co-firing of coal and biomass is 
advantageous for many reasons.  It reduces fossil fuel based CO
2
 and it reduces NO
x
.  
Biomass can be cheaper than coal.  It can also potentially reduce the soil, water, and air 
pollution that may be associated with excess amounts of waste by creating an economic 
method for waste disposal (Sweeten et al, 2003).  The majority of NO
x 
emissions from 
coal-fired plants come from fuel N
2
 reacting with oxygen at high temperatures.  Poultry 
litter when optimally used with the coal in staged co-combustion can drastically reduce 
these emissions by avoiding this reaction (Sami et al, 2000).  
9
The co-combustion of poultry litter with other energy sources, such as natural gas, 
has also been explored.  At optimal operating conditions, the co-combustion of poultry 
litter with natural gas in an advanced swirling fluidized bed combustor can have a carbon 
combustion efficiency of 89%, providing a cost effective disposal system for farmers 
with excess waste.  This was also shown to be another low emission environmental 
friendly system for the production energy (Zhu and Lee, 2004). 
  Poultry litter can also be used to make energy by converting it into methane, 
which is a gas that can be used as a fuel.  Putting poultry litter through an anaerobic 
digester in order to form methane gas has been a well established process (Hills and 
Ravishanker, 1984; Safley et al, 1987).  Kinetic models have been created for this process 
relating gas yield to influent concentration and retention time of the digester (Webb and 
Hawkes, 1985).  The economic analysis for anaerobic digestion of poultry litter done by 
Collins et al (2002), suggests that areas with large concentrations of broilers could 
possibly support a commercial size operation for the production methane, provided that a 
disposal fee for the poultry wastes brought to a facility was put in place, or if the digested 
solid effluent could be sold as a fertilizer (market value above that of the original poultry 
litter). 
Combustion of only poultry litter can also be carried out, provided that the 
moisture content of the litter is less than 25%.  A fluidized bed was used by Abelha et al 
(2002) to combust poultry litter.  As with the co-combustion methods, the pure poultry 
litter combustion method resulted in the formation of NO
x
 well below EU standards and 
all heavy metals in the ash were also below EU standards.  Through process optimization 
CO emissions were also reduced to acceptable levels.  Henihan et al (2003) further 
10
reported that the same fluidized bed system can be used for poultry litter with moisture 
contents greater than 25% if the poultry litter was mixed (1:1 ratio) with peat. 
 
2.2.3 Poultry litter for use as activated carbon  
Another example of a value added product that can be obtained from poultry litter is 
activated carbon.  Activated carbon is obtained by charring the litter to at least 700
o
 C 
resulting in the formation of a lattice-like carbon particle structure in the poultry litter.  
The activated carbon produced can then used for the adsorption of impurities in 
wastewater (Lima and Marshall, 2004).  The present demand for activated carbon in the 
US is 420 million lbs a year and the demand has been growing by 3% yearly.  Activated 
carbon for the adsorption of impurities in wastewater is currently being manufactured 
with bituminous coal and coconut shells.  Coal is an expensive non-renewable resource 
and coconut shells are not readily available in the US.  Poultry litter is an inexpensive 
renewable resource that is produced in mass quantities in the US making its use a viable 
option (Lima and Marshall, 2004). 
 
2.2.4 Composition analysis 
The exact elemental composition of poultry litter can vary  depending on the 
management style in the poultry house.  The major elements found in poultry litter are 
carbon, nitrogen, phosphorus, and potassium.  In addition to these elements, lesser 
amounts of Ca, Mg, Cu, Fe, Mn, and Zn have also been detected in poultry litter (Sistani 
et al, 2003).  Since poultry litter is traditionally used as a fertilizer, research regarding the 
compositional make up of poultry litter has mainly focused on its fertilizing nutrients: 
11
nitrogen, phosphorus, and potassium.  The typical N:P:K ratios of poultry litter are 6:2:3 
(Nicholson et al., 1996).   
The concentration of carbon in poultry litter will however become much more 
important if litter is to be used as a renewable fuel.  This is because its combustion 
involves the exothermic chemical reaction of a fuel or organics, which by definition 
contain carbon, with oxygen.  The reaction usually produces heat, CO
2
, H
2
O, and NO
x
, 
along with lesser amounts of by products depending on the fuel being combusted 
(Zumdahl and Zumdahl, 2007).  Furthermore, the amount of methane and activated 
carbon that can be produced using poultry litter is also dependent on the amount of 
carbon present.  Zhu and Lee (2004) reported that the poultry litter used in their 
combustion was 13.71 weight percent fixed carbon.  They also reported a moisture, 
volatile, and ash contents of 15.02, 40.35, and 30.92 weight percents, respectively. 
It should also be noted that the elements observed in the poultry litter may be 
distributed with different concentrations depending on the areas throughout the material 
that are sampled.  A study of the concentration of nitrogen, phosphorus, and potassium 
according to particle size revealed that, while the phosphorous and potassium had 
relatively the same concentration throughout, the nitrogen did not.  The fine particulate 
was found to contain a higher concentration of nitrogen (Ndegwa et al, 1991).  
Unfortunately, there was no mention of how carbon varied with particulate size. 
As one might expect, fecal coliforms (bacteria that inhabit the intestinal tract of 
warm-blooded animals and indicate the presence of bacterial pathogens), such as 
Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, and Citrobacter 
freundii, have been found in poultry litter.  The levels of fecal bacteria are primarily 
12
affected by moisture, temperature, and pH.  In order to decrease the amount of fecal 
bacteria in poultry litter, it is recommended that the poultry litter be stacked and aged.  
Within 8 days it was observed that the fecal coliforms reduced to below detectable levels 
(Hartel et al, 2000).  An evaluation of broiler litter microbial composition did not detect 
the presence of pathogens, such as Salmonella, Escherichia coli, Compylobacter spp., 
Yerersinia spp., Listeria spp., or toxigenic staphylococci.  However, bacteria associated 
with the degradation of wood and the cycling of nitrogen and sulfur, such as Globicatella 
sulfidofaciens, Corynebacterium ammoniagenes, Corynebacterium urealyticum, 
Clostridium aminovalericum, Arthrobacter sp., and Denitrobacter permanens, were 
found (Lu et al, 2003).   
 
2.3 Physical Properties 
Poultry litter is a bulk solid.  Bulk solids are composed of many particles of 
varying sizes (and possibly slightly varying shape), chemical composition, and densities, 
that are randomly grouped together in order to form a bulk (Woodcock and Mason, 
1987).  Therefore, the characterization of bulk solid behavior will involve characterizing 
the individual particles that comprise the bulk material.  Individual  particle properties of 
interest include particulate size, shape, particle density, particle size distribution, and 
particle surface area, while the bulk properties needed to characterize poultry litter 
include bulk density, porosity, flow properties, compressibility, strength properties, 
moisture content, and water activity.  Knowledge of these properties is needed to 
optimize the conditions required to process, store, and handle bulk materials.  This will in 
13
turn result into saving in handling costs, improved utilization of men, machines, and 
space, and reduced amounts of material wastage (Shamlou, 1988). 
 
2.3.1 Size 
Size is considered the most important characteristic of particulates.  This is 
because it is directly used to calculate properties such as surface area, and volume.  It 
should be mentioned that size is always represented as a distribution because the shape 
and size of the particulates vary throughout a bulk solid.  Methods that are used to 
measure the size of bulk biological materials include sieving, digital imagery analysis and 
a laser based system.  Sieving is the simplest and the cheapest and is therefore mostly 
used for size determination.  ASABE standard S319.3 (ASABE, 2003) is often used to 
estimate the average size and distribution of agricultural materials.  
Ndegwa et al (1991) reported that the chemical composition of poultry litter 
varied with particle size.  Their experiment divided the poultry litter into three distinct 
fractions: the fine fraction, the middle fraction, and the coarse fraction.  They had a fine 
fraction that was made up of particulate that had particle sizes less than #20 mesh screen 
(0.83 mm).  This portion of the material was a uniform brown powdery material that had 
the ability to clump together when squeezed.  Manure, small amounts of split feeds, and 
saw dust were believed to be the contents.  The middle fraction consisted of particulate 
that had particle sizes between the #20 (0.83mm) and the #6 (3.3 mm) mesh screens.  
This fraction was largely made up of small wood chips, saw dust, and some unidentified 
small flaky materials.  The largest particulate in the poultry litter was found in the coarse 
fraction.  These particles were too large to fit through the #6 (3.3 mm) mesh screen.   
14
2.3.2 Bulk density 
In general bulk density is obtained by measuring the mass of a material that 
occupies a container of known volume.  The method of filling the sample container will 
determine the type of bulk density that is measured and the qualifier used when 
discussing the measurement (Woodcock and Mason, 1987).  Traditionally, there are three 
different types of bulk densities.  These are aerated, poured, and tap (Barbosa et al, 2005).   
Aerated bulk density is a measure of the material?s density when its particulates 
are in their most loosely packed form.  The complicated approach used to obtain aerated 
bulk density can be found in Barbosa et al (2005).  Because of the amount of 
complication involved most researchers do not measure the aerated bulk density of 
particulates. 
The poured bulk density is the most common type of bulk density that is 
measured.  This is obtained by pouring a sample into a container of known volume.  The 
ratio of the mass of the material that filled the container to the size of the container is 
taken as the poured bulk density (Barbosa et al, 2005).   
The tap bulk density is the ratio of the mass of the material to its volume after it 
has been closely packed together.  Packing is achieved by repeatedly dropping the sample 
from a height of 14mm according to ASTM Standard B527 (ASTM 2005).  
Quantifying the effect of moisture content on the poured and tapped bulk density 
is crucial to the behavious of biological materials during storage, handling and 
transportation (Barbosa et al, 2005).   
 
 
15
2.3.3 Particle density 
There are two types of particle density- apparent and true.   True particle density 
is the mass of the particulate divided by its volume excluding open and closed pores.  
Apparent particle density is different only in that it includes the volume of closed pore 
within its calculation of the particulate volume (Woodcock and Mason, 1987).  
Measurement of the true density is often achieved by means of a helium pycnometer 
(Vianna et al, 2002).  Apparent particle density is best obtained from size measurements 
of the particles.  
 
2.3.4 Porosity 
Porosity is a function of the poured bulk density and the true particle density.  It is 
the amount of space in a bulk solid that is not occupied by a particulate and it is 
sometimes referred to as voidage.  Porosity can be a good prediction of the sphericity or 
irregularity of the particles in a bulk solid.  If particles are spherical, their porosity is on 
average around 0.4, while more irregular shapes have higher porosity values (Woodcock 
and Mason, 1987). 
 
2.3.5 Hausner ratio 
The Hausner ratio is a function of the tap and poured bulk density (Equation 2.1).  
The Hausner ratio is often used to indicate how easily a powder is fluidized (Geldart et al, 
1984). 
o
n
R
H
?
?
=      (2.1) 
16
Where the ?
n
 is the tap bulk density after n number of taps and the ?
0
 is the poured bulk 
density (Hayes, 1987).   Powders that are easily fluidized have Hausner ratios less than 
1.25, while those that have fluidization problems have Hausner ratios greater than 1.4 
(Geldart et al, 1984).  The Hausner ratio is affected by particle shape and size.  Attempts 
have therefore been made to develop equations that relate the Hausner ratio as a function 
of the deviation of particulates from ideal spheres (Guo et al, 1980) including an index of 
powder shape based on the Hausner ratio (Kostelnik and Beddow, 1970).   
 
2.3.6 Compressibility 
 Unintentional compression of bulk solids is undesirable during their storage,  
handling and transportation, because it often leads to flow problems.  The compression of 
bulk solids may be due to vibrations (e.g. during transportation), due to the weight above 
it (sometimes called mechanical compression) (e.g. during storage), or a combination of 
both.  Tap bulk density is often used to quantify the vibrational compressibility of a 
material.  The mechanical compressibility of a material is usually quantified from the 
results obtained from a piston cylinder arrangement that is attached to the cross head of a 
universal testing machine such as a texture analyzer.  A known force is applied to the 
bulk powder and the mechanical compressibility of the powder is obtained from the 
resulting data (Barbosa et al, 2005). 
 
2.3.7 Equilibrium moisture relationships 
 Biomass materials such as poultry litter are hygroscopic in nature and will 
therefore exchange moisture with their surrounding environment.  Knowledge of 
17
equilibrium moisture behavior is needed to prevent the spoilage of poultry litter during 
storage, which may reduce the fuel value and quality of the litter (Jenkins, 1989). 
 There are at least 77 different equations that have been developed to model 
moisture sorption isotherms (Bruin and Luyben, 1980).  One of the most commonly used 
models is the Guggenheim-Anderson-de Boer or GAB equation (Equation 2.2) (Rao and 
Rizvi, 1986). 
)**)1(1)(*1(
***
ERHKCERHK
RHKCM
EMC
o
?+?
=   (2.2) 
 
where EMC is the equilibrium moisture content (g water/g solids), ERH is the 
equilibrium relative humidity (decimal), M
o
 is the monolayer moisture content (%), C is 
the constant related to monolayer sorption heat, and K is the constant related to 
multilayer sorption heat (ASAE Standard D245.5, 2000).   
The GAB equation is a refinement of Brunauer-Emmett-Teller (BET) equation. It 
assumes layered localized physical adsorption of moisture with no lateral interaction just 
as the BET equation does.  It differs from the BET equation in that the added third 
parameter assumes that the multilayer molecules interact with the sorbent with an energy 
level range somewhere between the monolayer molecules of the solid and the bulk liquid.  
When the third parameter is unity, the GAB equation simplifies to the BET equation.  In 
addition, instead of being limited to water activities between 0.05 and 0.45 as is the case 
with the BET equation, the GAB equation can be used for water activities between zero 
and 0.9 (Rao and Rizvi, 1986).  As stated by Van den Berg (1984), the GAB equation?s 
major advantages are its theoretical background, its accuracy for describing sorption rates 
18
over almost the entire range of water activities, its simplicity in only using three 
parameters, its constants have physical meaning, and the fact that its parameters can be 
broken down into Arrhenius style equations when temperature effects are to be included 
in the model. 
 
2.4 Compaction of Poultry Litter 
Agglomeration is the process of using short range physical forces to form larger 
entities from smaller particulate (Pietsch, 2002).  For agglomeration to be effective, the 
bonds formed between the particulates must be strong enough to prevent breakage during 
storage, handling and transportation of the agglomerate.  Some of the advantages of a 
agglomerated or compacted material include 
(a) Improving storage and handling characteristics (Colley et al, 2005), 
(b) Handling a material with a lower dust content, thereby reducing primary and 
secondary pollution.  Biosecurity is also important to poultry litter during 
transportation.  Poultry litter that is transported from a place of production to a 
place of utilization might result in exposure in pathogen contamination in 
communities between these two areas (Fasina et al, 2006). 
(c) Increasing bulk density and lowering bulk volume thus reducing the cost  
required to store and transport poultry litter, 
(d) Handling a material of defined size, shape and weight, and 
(e) Improving product appeal. 
There have been several efforts to densify poultry litter by pelletization (McMullen et al, 
2005; Lichtenberg et al, 2002).  McMullen et al. (2005) reported that pelleting can be 
19
used to increase the density (hence decrease the amount of space required for storage and 
/or transportation) by more than three fold.  Pelletizing is however an expensive process 
(about $50-$60 per ton) because of the high amount of energy required for the 
processing.  Pelleting is therefore not economical for compacting agricultural wastes. 
Moreover due to the energy requirements of the pellet mill and the complexity involved 
in operating a pellet mill, it is not feasible for every broiler farmer to own a pellet mill. 
Colley et al (2005) reported that the pressure required to pelletize (4.9 to 7.9 mm 
diameter) poultry litter ranged from 8 to 22 MPa (1172 to 3256 psi).  This resulted in 
pellets with particle densities of 1350 kg/m
3
 to 1450 kg/m
3
 (84.2 lb/ft
3
 to 93.7 lb/ft
3
). 
Densification methods such as baling and cubing are less costly and less energy 
intensive when compared to pelleting.  In general, cubes and bales have smaller densities 
than pellets.  Bales and cubes typically  have densities of 161 kg/m
3
 and 870 kg/m
3
 (10 
lb/ft
3
 and 54 lb/ft
3
), respectively (Sokhansanj and Turhollow, 2004).   
Cubing is a volume reduction agglomeration process that uses pressure, it is 
similar to pelleting except that lower pressures are applied.  As the name implies, cubes 
are formed with a square cross section of chopped biomass, typically varying from 12.7 
to 38.1 mm (Sokhansanj and Turhollow, 2004).   
Baling is a process that combines compression and packing (tying with ropes or 
wrapping) operations, it is typically used for grassy or fibrous-like materials that are 
stringy in nature (Badger, 2003).  The property of compaction is therefore crucial to the 
development and design of baling equipment.  Poultry litter is not stringy and therefore 
the low-cost volume reduction method that can be developed is limited to pressure 
agglomeration. Bale dimensions are roughly 44 in by 49 in (Badger, 2003).   
20
2.5 Flowability 
Flowability of poultry litter is also very important to the efficient design of large-
scale storage and conveying systems for poultry litter.  Flowability is influenced by other 
bulk properties such as bulk density, porosity, and compressibility.  Flowability is a 
measure of the cohesiveness and adhesiveness of bulk solids.  Bulk solids with strong 
cohesion have particles that have a tendency to ?stick? to one another due to strong 
attractive forces between the particles. Bulk solids with strong adhesion have particles 
that have a tendency to ?stick? to the walls of storage containers.  The cohesiveness and 
adhesiveness of a bulk material are obtained from flowability tests.  In general, moisture 
content significantly influences the cohesiveness and the adhesiveness of bulk solid 
materials (Woodcock and Mason, 1987). 
Bulk solids that are stockpiled in silos for storage purposes are often gravity 
discharged from the bottom of the silo at the time of use.  The two types of flow that 
occur in the silo are mass flow and funnel flow.  During mass flow, all the particles move 
when the outlet is opened thereby resulting in uniform flow.  In funnel flow only some of 
the material moves when the outlet is opened while the rest remains stagnant.  This may 
lead to problems such as rat holing, increased segregation, and a tendency of degradation 
over time of the stationary region.  Therefore funnel flow is only desired during the 
storage and discharge of coarse, free-flowing non-degrading bulk solids.  Mass flow bulk 
solids can also develop problems such as arches.  When arches form within silos flow is 
halted.  There are two types of arches mechanical and cohesive.  Mechanical arches form 
when large particles interlock with one another.  Cohesive arches form when small 
particles consolidate due attractive forces and become stable.  Flow problems such as 
21
ratholing and arching can result in structural failure and damaging of silos.  These flow 
problems can be avoided if results from the material?s flowability test is taken into 
account during the design and selection of silos, bins, and hoppers (Shamlou, 1988). 
Although properties such as particle size and moisture content do affect 
flowability, there is no strong mathematical relationship between these properties and 
cohesiveness and adhesiveness.  Wall friction is one of the most important parameters in 
determining whether mass flow or funnel flow will occur.  Jenike?s mathematical 
analyses that uses data from wall friction tests is often used to determine the minimum 
hopper angle and the opening size for a mass flow system (Fitzpatrick et al, 2004). 
In order to quantify the flowability and the cohesiveness of bulk solids, 
measurements of a material?s shear strength is normally carried out.  This test was 
developed by Jenike in 1964 and it involves a tangential shear cell (Figure 2.1) that 
measures the shear stress (?) of a material while varying the pressure (?) applied to the 
top of the material.  At a given normal force (V = A?), the tangential force (S = A?) 
would increase until the material would fail or shear.  The shear strength was obtained 
from the tangential force required to fail the material.  
 
Figure 2.1 Jenike shear cell (Zulfiqar et al, 2006) 
 
22
The yield locus is obtained from the plot of the normal force vs. the shear force.  
The flowability of a material is then obtained from the yield locus graph (Figure 2.2).   
 
Figure 2.2 Yield locus plot (Klausner et al, 2000) 
 
For any shearing to take place the angle of internal friction (?) for that material must be 
overcome.  Graphically the angle of internal friction is equal to the angle of the yield 
locus.  No deformation or flow of the material can occur as long as S < V tan ?, but once 
S = V tan ?, slip takes place. If a material is free flowing, the plot of the graph intersects 
at the origin.  If the material is cohesive the graph begins at a point where S > 0 when V 
= 0 (Jenike, 1964).  For example, Figure 2.2 shows that the polymer powder is cohesive.  
The silica powder is free flowing in nature.  Its angle of internal friction is smaller than 
that of the polymer powder. 
 The flow function graph is obtained by plotting the ultimate yield stress (UYS; 
Equation 2.3) vs. major consolidating stress (MCS; Equation 2.4) of a material (Figure 
2.3).  The UYS and MCS are calculated by using the data in a series of yield locus plots.  
This type of graph is very good at characterizing flow and the inverse of the slope of this 
line is a materials flow index (Fitzpatrick et al, 2004; Teunou et al, 1999).  These values 
are mathematically defined as follows: 
23
( )
?
?
cos
sin12 +
=
c
UYS      (2.3) 
()
?
?
?
???
tan
sin1
cos
cossin
2
2222
cAA
MCS ?+
?
?
?
?
?
?
?
?
??
=   (2.4) 
Where 
?
?
tan
c
A +=                                         
and c is cohesion defined as ? at ? = 0. 
 
 
Figure 2.3 Flow function graph (Fitzpatrick et al, 2004) 
 
By replacing the base container of the shear cell with a sample of the wall (Figure 
2.4) that will be used for storage container and then applying the same method, Jenike 
(1964) was also able to find the wall yield locus (WYL) and the kinematic angle of 
friction between a bulk solid and a channel wall (??).   
 
24
 
Figure 2.4 Jenike shear cell with wall sample (Iqbal and Fitzpatrick, 2006) 
 
From his research, Jenike (1964) also found some general trends regarding the 
flowability of bulk solids.  He discovered that bulk solids in silos tended to gain strength 
over time i.e. the value of S at V = 0 is increased.  He attributed this to the compaction of 
the material increasing with moisture content.  The compaction of the material was 
attributed to an escape of entrained air, external vibrations that cause the rearrangement 
of particles, the break up and softening of particles resulting in an increase of 
cohesiveness.  While the migration of water and evaporation of water led to changes in 
moisture content over time, he also found that bulk solids which contained a range of 
sieve sizes including fine and coarse, such as poultry litter, generally had their flow 
properties governed by the fine fraction. 
Jenike?s work culminated with the development of equations for calculating the 
minimum outlet dimension of a channel (B in meters; Equation 2.6) and the diameter 
needed for a pipe to carry a given bulk solid (D in meters; Equation 2.7) as follows: 
?
?
A
VH
B
)'(
=      (2.6) 
Where H(??) (kg) is found within graphs he developed based on the slope of the angle of 
the channel, V (m
3
) is the normal load, A is the area (m
2
), and ? is the bulk weight (kg). 
25
?
?
A
VG
D
)(
=      (2.7) 
Where G(?
t
) (kg) is found within graphs he developed based on the angle (
o
) of friction 
between the bulk solid and the wall, V is the normal load (Pa), A is the area (m
2
), and ? is 
the bulk weight (kg) (Jenike, 1964). 
Although the use of Jenike?s shear cell is well established its limitation is that the 
tests cannot be automated.  Therefore this has led to the development of the rotational 
shear testers (Figure 2.5). 
 
 
Figure 2.5 Annular shear cell tester (Fitzpatrick et al, 2004) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
26
2.6 Summary 
 New uses of poultry litter as a renewable energy source through many different 
processes are currently being investigated and appear to be environmentally safe methods 
for energy production.  Poultry litter also has the potential to be digested into methane 
and to be carbonized into activated carbon for adsorption of impurities in wastewater.  By 
understanding the physical properties and the flowability of poultry litter efficient 
materials handling can be achieved and optimal storage and process facilities can be 
developed.  This, in turn, will cause savings to handling costs, improved utilization of 
manpower, machines and storage space, and reduced amounts of material wastage.  
Furthermore, the development of an economical large scale agglomeration procedure for 
poultry litter will be crucial to its value-added utilization in the bioenergy economy. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
27
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28
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Guo, A., Beddow, J.K., Vetter, A.F. 1985. A simple relationship between particle shape 
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30
Lima, I.M., Marshall, W.E. 2004. Granular activated carbons from broiler manure: 
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69(2): 901-908. 
 
Malave-Lopez, J., Barbosa-Canovas, G.V., Peleg, M. 1985.  Comparison characteristics 
of agglomerated coffee during taping. Journal of Texture Studies  24(3): 253-258. 
 
McMullen, J., Fasina, O. O., Wood, C. W., Feng, Y. 2005.  Storage and handling 
characteristics of pellets from poultry litter. Applied Engineering in Agriculture 21(4): 
645-651. 
 
Mitchell, C.C., Tyson, T.W. 2002.  Spreading manure in winter. Have the rules changed? 
Bulletin No. 5-04-02. pp. 3, Auburn University, Auburn, Alabama: Alabama Cooperative 
Extension System Bulletin.  
 
Moreyra, R., Peleg, M. 1981. Effect of equilibrium water activity on bulk properties of 
selected food powders. Journal of Food Science  46(6): 1918-1922. 
 
NASS. 2006. Poultry ? Production and Value: 2005 Summary. Washington, DC: USDA 
National Agricultural Statistics Service. Available at: http://usda.mannlib.cornell.edu/ 
Accessed: 7 March 2007. 
 
Ndegwa, P. M., Thompson, S. A., Merka, W. C. 1991. Fractionation of poultry litter for 
enhanced utilization. Transactions of the ASAE 34(3): 992-997. 
 
Nicholson, F. A., Chambers, B. J., Smith, K. A. 1996.  Nutrient Composition of Poultry 
Manures in England and Wales. Bioresource Technology 58(3): 279-284. 
 
Peleg M. 1978. Flowability of food powders and methods for its evaluation-a review. 
Journal of Food Process Engineering, 1: 303-328. 
 
Pietsch, W.  2002. Agglomeration Processes ? Phenomena, Technologies and Eqiupment. 
Weinheim, Germany: Wiley VCH. 
 
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Dekker, Inc. 
 
Safley, L. M., Vetter, R. L., Smith, L. D. 1987.  Management and operation of a full-scale 
poultry waste digester. Poultry Science 66: 941-945. 
 
Sami, M., Annamalai, K., Wooldridge, M. 2000.  Co-firing of coal and biomass fuel 
blends. Progress in Energy and Combustion Science 27(2): 171-214. 
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Shamlou, P. A.  1988. Handling of Bulk Solids: Theory and Practice.  London, UK: 
Butterworth-Heinemann. 
 
Sistani, K. R., Brink, G. E., McGowan, S. L., Rowe, D. E., Oldham, J. L. 2003.  
Characterization of broiler cake and broiler litter, the by-products of two management 
practices. Bioresource Technology 90(1): 27-32. 
 
Sokhansanj, S., Turhollow, A.F. 2004. Biomass densification and cubing operation costs 
for corn stover. Applied Engineering in Agriculture  20(4): 495-499. 
 
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Theoretical aspects. In Water Activity: Influences on Food Quality, NewYork, NY: 
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32
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Company. 
 
 
 
 
 
 
 
 
 
 
 
 
 
33
CHAPTER 3. MOISTURE DEPENDENT PHYSICAL PROPERTIES OF 
POULTRY LITTER 
3.1 Introduction 
Poultry litter is a combination of accumulated chicken manure, feathers, and 
bedding materials found in broiler houses.  The bedding materials are often made up of 
wood shavings, sawdust, wheat (Triticum aestivum L.) straw, peanut (Arachis hypogaea 
L.) hulls, or rice (Oryza Sativa L.) hulls (Edwards and Daniels, 1992).  In the United 
States, close to 11 million tons of poultry litter is produced annually (Gollehon et al, 
2001).  Unfortunately, the production of poultry litter occurs in concentrated areas in the 
states that are noted for broiler production (Alabama, Arkansas, Delaware, Georgia, 
Maryland, Mississippi, North Carolina, West Virginia, and Virginia; Ndegwa et al, 
1991). 
Presently, the most common use for poultry litter is application to cropland as a 
fertilizer because of its typical N:P:K ratios of 6:2:3 (Nicholson et al, 1996).  However, 
the large amounts of poultry litter created in small areas are beyond the fertilizing needs 
of the neighboring agricultural areas (Ndegwa et al, 1991).  The result is the excessive 
use of poultry litter on these lands that has resulted in ground water and surface water 
problems as excess nutrients run off of the land or leach into the ground water supplies, 
respectively (Moore et al, 1998; Wood et al, 1999).  Therefore, environmental regulating 
34
agencies in these states are beginning to examine the methods used for the 
disposal and the utilization of poultry litter.  For example, in the state of Alabama, the 
application of manure on pasture land and crop land in north Alabama (a large broiler 
producing region) is prohibited by ADEM (Alabama Department of Environmental 
Management) between November 15 and February 15 (Mitchell and Tyson, 2002). 
The environmental implications of the prolonged use of poultry litter as a 
fertilizer has led to various studies into the non-fertilizing value-added utilization of 
poultry litter such as bioenergy feedstocks (Abelha et al, 2002), methane production 
(Safley et al, 1987) and activated carbon production (Lima and Marshall, 2004).  These 
value added uses will require that appropriate equipment and facilities be designed and 
selected to store, handle, and transport poultry litter, hence the need to quantify the 
physical properties of poultry litter (Shamlou, 1988).  Several studies have shown that 
moisture content has a significant affect on the physical properties of biological materials 
(Balasubramanina, 2001; Nimkar and Chattopadhyay, 2002; Barbosa et al, 2005).  
Therefore the objectives of this study were to:  
(1)  Quantify the effect of moisture on bulk density, particle density, tap density,  
 Hausner ratio, and porosity of poultry litter, 
(2)  Quantify the effect of moisture and applied pressure on the compressibility of  
 poultry litter, and  
(3)  Determine the equilibrium moisture isotherm of poultry litter at a temperature  
 of 25
o
C. 
 
 
35
3.2 Methods and Materials 
3.2.1 Preparation 
 The poultry litter sample (with a hard wood shaving bedding) used in this study 
was obtained from a local poultry farmer in Lee County, Alabama.  The litter was stored 
in the laboratory at 25
o
C before use.  Physical property tests were carried out on poultry 
litter samples within the moisture content range of 10% to 30%.  To adjust the moisture 
content of a sample to the desired level, the poultry litter was either dried in an oven set 
to 60
o
C (to reduce the moisture content of the sample), or a known quantity of water was 
added and mixed with the poultry litter in a mixer for 15 minutes.  In both cases the 
samples were stored in an air tight container for 24 hours to allow moisture equilibration 
to take place.  The moisture content of each sample was then verified by a moisture 
analyzer (Model IR-200, Denver Instruments, Arvada CO).  The actual moisture content 
values used for the physical property tests can be found in section 3.3.1. All moisture 
contents are reported in wet basis unless otherwise noted.   
 
3.2.2 Particle size distribution 
 Particle size distribution was determined according to ASABE Standard S319.3 
(ASABE, 2003).  This procedure involved placing 100 grams of material on the top sieve 
of a nest of successively smaller sieves and recording the weight of material retained on 
each sieve after the test was complete.  For this analysis, 7 U.S. Series test sieves plus a 
pan with aperture sizes ranging from 1.700 to 0.212 mm were used.  The nest of test 
sieves was shaken for ten minutes in a Sieve shaker (Model CL 340, Soil Test 
Engineering Test Equipment Co., Evanston, IL), after which, the nest of sieves were 
36
removed from the sieve shaker.  The mass of material retained on each sieve was then 
recorded.  This procedure was done in triplicate.  The determination of the geometric 
mean diameter (d
gw
) of the sample and the geometric standard deviation of particle 
diameter (S
gw
) was carried out according to the ASABE Standard S319.3 (ASABE, 2003) 
(Equations 3.1 ? 3.3):  
 
                                    
?
?
?
?
?
?
?
?
?
?
?
?
=
?
?
=
=?
n
i
i
n
i
ii
gw
W
dW
d
1
11
)log(
log     (3.1) 
 
                                 
2/1
1
1
2
log
)log(log
?
?
?
?
?
?
?
?
?
?
?
?
?
=
?
?
=
=
n
i
i
n
i
gwii
W
ddW
S    (3.2) 
 
                                 ( )[ ]
1
log
1
log
1
loglog
2
1 ?
??
?= SSdS
gwgw
   (3.3) 
Where, d
gw
   = geometric mean diameter or median size of particles by mass (mm) 
             S
log 
 = geometric standard deviation of log normal distribution by mass in ten     
bases logarithm (dimensionless) 
             S
gw
  = geometric standard deviation of particle diameter by mass (mm) 
             W
i
   = mass on i
th
 sieve (g) 
              n    =  number of sieves plus one pan 
              
i
d   =  nominal sieve aperture size of the i
th
 sieve (mm) 
37
3.2.3 Poured bulk density 
Bulk density was determined by a bulk density measurement apparatus (Burrows 
Co., Evanston, IL) and according to ASABE Standard S269.4 (2002).  This method 
involves pouring the bulk solid into a container (volume of 947 mm
3
) from a funnel.  The 
material was leveled across the top of the surface of the container and weighed.  The bulk 
density (?
b
) of the poultry litter ?was taken as the mass of sample in the container (m
c
) 
divided by the volume of the container (V
c
) (Equation 3.4).  This procedure was 
performed in triplicate. 
                                                               
c
c
b
V
m
=?      (3.4) 
 
3.2.4 Tap bulk density 
The tap bulk density of the material was measured using an automated tap density 
tester (Model TD-12, Pharma Alliance Group Inc., Vencia, CA) according to the ASTM 
Standard B 527 (ASTM, 2005).  A 250 ml graduated cylinder was filled with poultry 
litter and weighed using a balance accurate to 0.01 g (Model PE3600 DeltaRange, 
Mettler-Toledo, Heightstown).  The cylinder was then placed in the tap density tester.  
For each run, the cylinder was initially tapped 500 times at a rate of 300 taps per minute.  
Each tap consisted of the cylinder being raised by 14 mm and then dropped under its own 
weight.  After the first 500 taps, the new volume was entered into the machine.  The 
cylinder was then tapped 750 times, and the new volume was recorded.  If the difference 
in volume after the 500 taps and after 750 taps was greater then 2%, the process was 
38
repeated, otherwise the experiment was completed and the new sample volume was 
recorded.  The tap bulk density (?
t
) of the poultry litter ?was taken as the mass of sample 
in the container (m
c
) divided by the volume of the sample after the completion of the 
tapping (V
t
) (Equation 3.5).  This procedure was performed in triplicate. 
t
c
t
V
m
=?      (3.5) 
3.2.5 Particle density 
The particle density of the poultry litter was measured by gas comparison 
pycnometry (Model AccuPyc 1330, Micromeritics Instrument Corp, Norcross, GA) 
where a known quantity of helium under pressure was allowed to flow from a previously 
known reference volume into a cell containing a sample of the material.  By applying the 
ideal gas law to the pressure change from the reference cell to the sample cell, the 
pycnometer calculates the volume of the material in the sample cell.  Particle density (?
p
) 
was taken as the ratio of the mass of material in the sample cell (m
p
) to the volume (V
p
) 
measured by the pycnometer (Equation 3.6).  Sample mass was obtained with a digital 
balance accurate to 0.001 grams (Model AR3130, Ohaus Corp., Pinebrook, NJ).  This 
procedure was performed in triplicate.   
p
p
p
V
m
=?      (3.6) 
 
 
 
39
3.2.6 Porosity 
 
Porosity is the percentage of the total container volume occupied by air spaces 
when a bulk solid is placed in a container (Woodcock and Mason, 1987).  Porosity is 
mathematically defined by Equation 3.7 and was calculated using the average bulk and 
particle densities that were obtained for each sample. 
                                                                
p
b
?
?
? ?=1      (3.7) 
 
3.2.7 Hausner ratio 
Hausner ratio quantifies the change in the volume of a sample subjected to the tap 
bulk density test described in Section 3.2.4.  It is mathematically defined by Equation 3.8 
and was calculated as the ratio of the average tap bulk density to the poured bulk density 
at each moisture content.   
b
t
r
H
?
?
=      (3.8) 
 
3.2.8 Mechanical compressibility 
 A texture analyzer (Model TA-HD, Stable MicroSystems, Surrey, UK) was used 
to measure the mechanical compressibility of poultry litter.  The measurement system 
consisted of a compression cell (internal diameter of 49.55 mm and height of 101.83 mm) 
and a close-fitting piston (49.00 mm in diameter) that was attached to the crosshead of 
the texture analyzer (see Appendix D Figure D.1).  Before each test, a sample of known 
weight (using a balance accurate to 0.01 g (Model PM4600, DeltaRange, Mettler-Toledo, 
40
Heightstown) was loaded into the compression cell.  The piston was used to compress the 
sample within the cell at a speed of 1 mm/s until a consolidating pressure of 1.5, 3, 6, 9, 
12, or 15 kPa was achieved.  This procedure was done in duplicate.  The force (hence the 
pressure) impacted on the sample by the moving crosshead of the texture analyzer and the 
distance traveled (hence the compression of the sample) were automatically recorded by 
the software supplied by the manufacture of the texture analyzer.  Mechanical 
compressibility (in percent; Equation 3.9) was calculated. 
   
?
?
?
?
?
?
?
?
?=
?
?
?
?
?
?
?
? ?
=
bf
bi
i
fi
V
VV
Cm
?
?
1100100     (3.9) 
 
3.2.9 Equilibrium moisture isotherm 
A water activity instrument (HygroLab 2 - H3, Rotronic Instrument Corp., 
Huntington, NY) was used to obtain the equilibrium moisture isotherm of poultry litter at 
a temperature of 25
o
C.  To conduct a test, each sample (about 20g) was placed in the 
sample holder of the water activity instrument.  The water activity probe was placed on 
top of the sample holder thereby forming a sealed measurement system. The probe was 
equipped with a small fan that circulates air within the sample container, a thin film 
capacitance sensor that was capable of measuring relative humidity from 0 to 100%  
(with an accuracy of ? 1.5%) and a platinum RTD (resistance temperature detector) 
temperature probe (with an accuracy of ?0.3?C).  The measurement system was then 
transferred to a temperature controlled-chamber (Model ESL-2CA, ESPEC North 
America, Inc., Hudsonville, MI) set at 25?C to ensure a constant environmental 
temperature during the measurement process.  The relative humidity and dry bulb 
41
temperature output from the water activity meter was continuously recorded on a 
personal computer until equilibrium was reached (usually less than 4 hrs).  The moisture 
content of a sample at a measured ERH (or water activity) was taken as the equilibrium 
moisture content of that sample.  The equilibrium moisture isotherm experiment was 
carried out in triplicate. 
3.2.10 Data analysis 
 
Regression analysis was performed on poured bulk density, tap bulk density, 
particle density, porosity, Hausner ratio, and compressibility data sets using the proc reg 
function in SAS statistical software package (Version 9.1, SAS Institute Inc., Cary, NC, 
2002-2003) and plotted with the experimental data using Microsoft Excel (Microsoft 
Office XP Professional, 2005).  A nonlinear regression was performed on the water 
activity data set using PolyMath statistical software package (Version 5.1 build 230, 
Mordechai Shacham, Michael B. Cutlip, Michael Elly, 2007) and then plotted with the 
experimental data using Microsoft Excel (Microsoft Office XP Professional, 2005). 
 
 
 
 
 
 
 
 
 
42
3.3 Results and Discussion 
3.3.1 Moisture contents 
 The original intention of this study was to measure the physical properties of 
poultry litter at moisture contents of 10%, 14%, 18%, 22%, 26%, and 30% (w.b.).  
However, it was found that these exact moisture contents are practically impossible to 
obtain.  Because of this, the moisture content of the sample at the time of measuring a 
physical property was recorded.  It should be mentioned that none of the actual moisture 
contents vary more than 2% from the target moisture contents.  The moisture contents 
used for each of the physical property measurements is summarized in Table 3.1. 
 
Table 3.1 Summary of moisture contents used for various physical property tests 
Physical Property Moisture Contents (%, w.b.) 
Bulk Density 30.6 26.1 22.0 18.1 14.2 10.3 
Tap Bulk Density 29.6 26.1 22.0 18.4 14.2 10.3 
Particle Density 30.9 26.0 22.1 18.0 13.8 10.3 
Porosity 30.7 26.1 22.0 18.0 14.0 10.3 
Hausner Ratio 30.1 26.1 22.0 18.2 14.2 10.3 
Compressibility 30.9 26.0 22.1 18.0 13.8 10.3 
Water Activity 30.6 26.7 23.6 17.7 13.4 10.1 
 
 
3.3.2 Particle Size Distribution 
 The particle size distribution of poultry litter is shown in Table 3.2 and Figure 3.1.  
Most of the particles (24.14 % and 20.19%) were retained on the bottom pan and on the 
43
sieve with an aperture of 0.850 mm, respectively.  The geometric mean diameter (d
gw
) 
and the geometric standard deviation (S
gw
) of poultry litter were calculated to be 0.841 
mm and 0.251 mm, respectively (Equations 3.1-3.3).  Particle sizes below 0.400 mm 
(40% of the poultry litter) are considered fine and highly compressible.  Fine particles are 
also associated with decreased flowability because of their increased compressibility 
(Tabil and Sokhansanj, 1997; Mani et al 2003).  
 
Table 3.2 Particle size distribution of poultry litter 
U.S. Sieve 
No. 
Sieve Aperture Size 
(mm) 
Distribution 
(%) 
12 1.700 16.41 
20 0.850 20.19 
30 0.595 15.39 
40 0.425 8.08 
50 0.297 9.01 
60 0.250 3.80 
70 0.212 2.98 
Pan 0.000 24.14 
 
 
0
5
10
15
20
25
30
35
0.0 0.5 1.0 1.5 2.0
Seive Aperature Size (m m )
P
a
r
t
ic
l
e
 S
iz
e
 
D
is
t
ib
u
t
i
o
n
 (
%
)
 
Figure 3.1 Particle size distribution of poultry litter at various sieve apertures 
44
3.3.3 Poured bulk density 
 The poured bulk density of poultry litter ranged from 0.550 g/ml to 0.533 g/ml 
within the moisture content range of 10.3% and 30.6% (Figure 3.2).  In general, the 
poured bulk density decreased with increases in the moisture content.  This implies the 
bulk poultry litter volumetrically expands faster than the increased weight when the 
moisture content of the litter is increased.  The implication of this is that in process 
design applications, the amount of volume that will be required to store poultry litter will 
increase as moisture increases.  The following equation (Equation 3.10) describes the 
relationship between bulk density (g/ml) and moisture content (%, w.b.). 
2
0.0000373M- 0.000919M 0.540 +=
b
?   R
2
 = 0.875  (3.10) 
0.50
0.51
0.52
0.53
0.54
0.55
0.56
5152535
Moisture Content (%, w.b.)
D
e
ns
it
y
 (
g
/m
L)
Experimental Data
Predicted Value
 
Figure 3.2 Effect of moisture content on the poured bulk density of poultry litter 
 
It should be mentioned that the poured bulk density of poultry litter (0.50 g/ml) is 
significantly higher than the values that are typically obtained for agricultural materials 
(less than 0.20 g/ml) (Balasubramanian, 2001; Deshpande et al, 1993; Fasina and 
45
Sokhansanj, 1992; Nimkar and Chattopadhyay, 2001).  This is because of the relatively 
high amount of minerals present in poultry litter.  The response of poultry litter?s bulk 
density to moisture content was also similar to those documented for the poured bulk 
density of other biological materials (Balasubramanian, 2001; Deshpande et al, 1993; 
Fasina and Sokhansanj, 1992; Nimkar and Chattopadhyay, 2001). 
 
3.3.4 Tap bulk density 
Statistical analysis showed that there was no significant (P<0.05) effect of 
moisture content on the tap bulk density of poultry litter.  The average tap bulk density of 
poultry litter was 0.580 g/ml. 
 
3.3.5 Particle density 
The particle density of poultry litter decreased from 1.623 g/ml to 1.434 g/ml as 
moisture content increased from 10.3% to 30.9%, respectively (Figure 3.3).  It is 
postulated that the volume of the particles of the litter increased at a higher rate than the 
increase in mass due to the saturation of the particles with moisture.  This trend has also 
been observed in various other biological materials (Deshpande et al, 1993; Joshi et al., 
1993; Nimkar and Chattopadhyay, 2001). Equation 3.11 was used to describe the 
relationship between the particle density (g/ml) and the moisture content (%, w.b.) of 
poultry litter.  
2
0.000177M- 0.0000658M  1.627 +=
p
? , R
2
 = 0.970  (3.11) 
46
1.45
1.50
1.55
1.60
1.65
5152535
Moisture Content (%, w.b.)
D
e
ns
it
y
 (
g
/m
L)
Experimental Data
Predicted Value
 
Figure 3.3 Effect of moisture content on the particle density of poultry litter 
 
3.3.6 Porosity 
The average porosity of poultry litter ranged from 0.63 to 0.67 at moisture 
contents of 30.7% and 10.2%, respectively (Figure 3.4).  The average porosity of 
spherical particles is 0.4, while irregular shaped particles have higher porosity values 
(Woodcock and Mason, 1987). The porosity values obtained in this study were indicative 
of the irregular and non-spherical nature of the particulates that constitute poultry litter. 
In general, the porosity of the poultry litter increased with a decrease in moisture content.  
Results presented earlier on the poured bulk density and particle density showed that the 
bulk and individual particulates of poultry litter were expanding volumetrically at a faster 
rate than it was gaining weight as it absorbed moisture.  This resulted in less air space 
between the particulates, thus the general decrease in porosity as the moisture increased.  
A similar trend was also observed with other biological materials (Joshi et al, 1993; 
47
Deshpande et al, 1993).  Equation 3.12 was used to describe the relationship between the 
porosity (decimal) and moisture content (%, w.b.) of poultry litter. 
      
2
0.0000244M- 0.000270M 0.666 ?=? , R
2
 = 0.982  (3.12) 
0.62
0.63
0.64
0.65
0.66
0.67
5152535
Moisture Content (%, w.b.)
Po
r
o
s
i
ty
Experimental Data
Predicted Value
 
Figure 3.4 Effect of moisture content on the porosity of poultry litter 
 
3.3.7 Hausner ratio 
Statistical analysis showed that there was no significant effect (P < 0.05) of 
moisture content on the Hausner ratio of poultry litter.  The average Hausner ratio of 
poultry litter was 1.070.  This value was less than the critical value of 1.25 thereby 
indicating that poultry litter can be easily fluidized. 
 
3.3.8 Compressibility 
 The percent compressibility of poultry litter ranged from 2.4% to 18.1%, with 
sample moisture contents and applied pressures of 10.2% and 1.5kPa, and 30.9% and 
15kPa, respectively (Figure 3.5).  The percent compressibility increased with moisture 
48
content and applied pressure.  Similar trends have been documented for other biological 
materials (Barbosa et al, 2005).  Fayed and Skocir (1997) used compressibility values to 
classify the flowability of a material.  Percent compressibility values between 5-15% 
indicated excellent flow, and 12-16% indicated fair to passable flow.  Based on this 
classification, except for poultry litter samples of 30.9% moisture content compressed to 
pressures of 12 and 15 kPa, poultry litter has good or excellent flow. Equation 3.13 was 
developed to relate the mechanical compressibility (%) to the moisture content (%, w.b.) 
and pressure (kPa) of poultry litter. 
  )3.3821log(0.00568M 0.164M3.312- 
2
?+++=Cm , R
2
 = 0.948  (3.13) 
0
4
8
12
16
20
0 2 4 6 8 10121416
Pressure (kPa)
C
o
mp
r
essi
b
ilit
y
 (
%
)
M=10.3% M=13.8%
M=18.0% M=22.1%
M=26.0% M=30.9%
 
Figure 3.5 Effect of moisture content and pressure on the mechanical 
compressibility of poultry litter 
 
 
 
 
49
3.3.9 Equilibrium moisture isotherm 
 Since equilibrium relations for biological materials are often represented in dry 
basis moisture contents, Equation 3.14 was used to convert the wet basis moisture content 
values to dry basis moisture contents values (ASAE Standard D245.5, 2000). 
)100(
*100
W
W
D
MC
MC
MC
?
=     (3.14) 
Where MC
D
 is the percent dry basis moisture content and MC
W
 is the percent wet basis 
moisture content.   
Figure 3.6 shows that the equilibrium moisture relation curve for poultry litter is 
type II (sigmoidal in shape).  This is typically obtained for biological materials (Labuza, 
1984; Erbas et al., 2005).  The ERH (on the x axis) is often used to determine the amount 
of moisture that is available for microbial activity, enzymatic activity and chemical 
reaction.  When the ERH is above 0.8, there is sufficient moisture in the material to 
promote mold growth (30% moisture content dry basis or 24% moisture content wet basis 
for poultry litter).  Bacterial growth is often associated with materials stored at moisture 
contents that are at equilibrium with relative humidity of 90% and above (corresponding 
to 30% moisture content wet basis or 43% moisture content dry basis for poultry litter) 
(Wilhelm et al, 2004). 
The GAB equation (Equation 3.15, ASAE Standard D245.5, 2000) was fitted 
(using the non-linear regression procedure in PolyMath 5.1 Software) to the experimental 
equilibrium moisture sorption isotherm data. 
)**)1(1)(*1(
***
ERHKCERHK
ERHKCM
EMC
o
?+?
=   (3.15) 
50
Where EMC (MC
D
) is the equilibrium moisture content (g water/g solids), ERH is the 
equilibrium relative humidity (decimal), M
o
 is the monolayer moisture content (g water/g 
solids), C is the constant related to monolayer sorption heat, and K is the constant related 
to multilayer sorption heat.  A good fit of the GAB equation to the experimental data was 
obtained with R
2
 value of 0.917. The estimated values of M
o
, C, and K were 0.0583, 
3031, and 0.955, respectively.  These values illustrated the presence of a monolayer (at a 
moisture content 5.8% dry basis), with strongly bound water molecules (C>>1), and a 
multilayer that had characteristics comparable to bulk liquid (K~1) (Quirijns et al, 2005).  
The monolayer moisture content is the moisture content that is optimal for the stability of 
the biological materials during storage (Moraga et al, 2006).  The equilibrium relative 
humidity that was calculated to be in equilibrium with the monolayer moisture content is 
1.9%. Beyond this value, deteriorative reactions are accelerated in the product.  Therefore 
the maximum stability for poultry litter stored at 25
o
C will be obtained at a moisture 
content of 5.8% (d.b.) or 5.5% (w.b.).  
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
2040608010
Equilibrium Relative Humidity (%)
M
o
i
s
tu
r
e
 C
o
n
te
n
t (%
,
 w
.
b.
) 
Predicted Value
Experimental Data
 
Figure 3.6 Effect of moisture content on the relative humidity of poultry litter (25
o
C) 
 
51
3.4 Conclusion 
It can be concluded from this study that moisture content significantly affects the 
physical properties of poultry litter.  Based on particle size analysis, 40% of the poultry 
litter was considered to be fine and highly compressible.  Other physical properties such 
as the poured bulk density, particle density and porosity decreased while the 
compressibility increased with increases in moisture content.  The porosity indicated that 
poultry litter?s particles were irregular and non-spherical in shape.  The average tap bulk 
density and Hausner ratio were not affected by moisture content and had average values 
of 0.580 g/ml and 1.070, respectively (which indicated easy fluidization).   
The compressibility of poultry litter was affected by both pressure and moisture 
content with a maximum compressibility percent of 18.0% obtained at a moisture content 
of 30.8% and a pressure 15 kPa.  As moisture content increased the compressibility was 
found to increase. 
The equilibrium moisture isotherm data was found to follow the model used in the 
GAB equation, where constants M
o
, C, and K were found to be 0.0583, 3031, and 0.955, 
respectively, with a R
2
 value of 0.917.  Based on the estimated monolayer moisture 
content, it was found that when poultry litter was stored at a temperature of 25
o
C, 
minimum biochemical degradation of the litter will occur when the relative humidity of 
the environment is about 1.9%. 
 
 
 
  
52
3.5 References 
Abelha, P., I.Gulyurtlu, D. Boavida, J. S. Barros, I. Cabrita, J. Leeahy, B. Kelleher, M.  
Leahy. 2002. Combustion of poultry litter in a fluidised bed combustor. Fuel 82(6):  
687-692. 
 
ASABE Standard. 2000. D245.5 Moisture relationship of plant based agricultural 
products. St. Joseph, MI: ASABE. 
 
ASABE Standard. 2002. S269.4 Cubes, pellets, and crumbles ? Definitions and methods 
for determining density, durability, and moisture content. St. Joseph, MI: ASABE. 
 
ASABE Standard. 2003. S319.3 Method of Determining and Expressing Fineness of Feed 
Materials by Sieving. St. Joseph, MI: ASABE. 
 
ASTM Standards. 2005. B 527. Standard Test Method for Determination of Tap Density 
of Metallic Powders and Compounds. West Conshohocken, PA: ASTM. 
 
Balasubramanian, D. 2001. Physical properties of raw cashew nut. Journal of 
Agricultural Engineering Research 78(3): 291-297. 
 
Barbosa-Canovas, G. V., Ortega-Rivas, E., Juliano, P., Yan, H. 2005.  Food Powders: 
Physical Properties, Processing, and Functionality.  New York, NY: Kluwer 
Academic/Plenum Pub. 
 
Deshpande, S.D., Bal, S., Ojha, T.P. 1993. Physical properties of soybean. Journal of 
Agricultural Engineering Researc 56(2): 89-98. 
 
Edwards, D. R., Daniels, T.C. 1992. Environmental impacts of on-farm poultry waste 
disposal ? a review. Bioresource Technology 41(1): 9-33. 
 
Erbas, M., Ertugay, M. F., Certel, M. 2005.  Moisture absorption behavior of semolina 
and farina. Journal of Food Engineering 69(2): 191-198. 
 
Fasina, O.O., Sokhansanj, S. 1992.  Hygroscopic moisture absorption by alfalfa cubes 
and pellets. Transactions of the ASABE 35(5): 1615-1619. 
 
Fayed, M.E., Skocir, T.S. 1997. Mechanical Conveyors: Selection and Operation. 
Lancaster, PA: Technomic Publishing Company Inc.  
 
Joshi, D.C., Das, S.K., Mukherjee, R.K. 1993. Physical properties of pumpkin seeds, 
Journal of Agricultural Engineering Research  54(3): 219-229. 
 
Labuza, T.P., Kaanane, A., Chen, J.Y. 1985. Effect of temperature on moisture sorption 
isotherms and water activity shift of two dehydrated foods, Journal of Food Science  50: 
385-391. 
53
 
Lima, I.M., Marshall, W.E. 2004. Granular activated carbons from broiler manure: 
physical, chemical and adsorptive properties. Bioresource Technology. 96(6):699-706. 
 
Mani, S., Tabil, L. G., Sokhansanj, S., Roberge, M. 2003. Mechanical properties of corn 
stover grind, An ASAE/CSAE Meeting Presentation, Paper No. 0.36090, 2003 
ASAE/CSAE Annual International Meeting, Sponsored by ASAE, July 27-30, Las Vegas 
Convention Center, Las Vegas, NV. 
 
Mitchell, C.C., Tyson, T.W. 2002.  Spreading manure in winter. Have the rules changed? 
Bulletin No. 5-04-02. pp. 3, Auburn University, Auburn, Alabama: Alabama Cooperative 
Extension System Bulletin.  
 
Moraga, G., Martinez-Navarrete, N., Chiralt, A. 2006. Water sorption isotherms and 
phase transitions in kiwifruit. Journal of Food Engineering  72(4): 147-156. 
 
Moore, P. A., Jr., Daniel, T. C.,  Sharpley, A. N.,  Wood, C. W. 1998. Poultry manure 
management. In Agricultural Uses of Municipal, Animal, and Industrial Byproducts, 60-
77. Washington, D.C.: USDA Agricultural Research Service. 
 
Ndegwa, P. M., Thompson, S. A., Merka, W. C. 1991. Fractionation of poultry litter for 
enhanced utilization. Transactions of the ASAE. 34(3): 992-997. 
 
Nicholson, F. A., Chambers, B. J., Smith, K. A. 1996.  Nutrient Composition of Poultry 
Manures in England and Wales. Bioresource Technology. 58(3): 279-284. 
 
Nimkar, P.M., Chattopadhyay, P.K. 2001.  Some physical properties of green gram, 
Journal of Agricultural Engineering Research. 80(2): 183-189. 
 
Quirijns E.J., van Boxtel, A.J.B., van Loon, W.K.P., van Straten, G. 2005. Sorption 
isotherms, GAB parameters and isosteric heat of sorption. Journal of Science of food 
Agriculture.  85(11): 1805-1814. 
 
Safley, L. M., Vetter, R. L., Smith, L. D. 1987.  Management and operation of a full-scale 
poultry waste digester. Poultry Science. 66: 941-945. 
 
Tabil, L.G., Sokhansanj, S. 1997. Bulk properties of alfalfa grind in relation to its 
compaction characteristics. Applied Engineering in Agriculture. 13(4): 499-505. 
 
Wilhelm, L.R., Suter, D.A., Brusewitz, G.H. 2004. Food & Process Engineering 
Technology. St. Joseph, MI: ASABE. 
 
Wood, B. H., Wood, C. W., Yoo, K. H., Yoon, K. S., Delaney, D. P. 1999. Seasonal 
surface runoff losses of nutrients and metals from soils fertilized with broiler litter and 
commercial fertilizer. Journal of Environmental Quality. 28(4): 1210-1218. 
 
54
Woodcock, C. R., Mason, J. S. 1987. Bulk Solids Handling: An Introduction to the 
Practice and Technology.  Glasgow, Scotland: Blackie and Son Ltd. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
55
CHAPTER 4. COMPACTION OF POULTRY LITTER 
4.1 Introduction 
Compactibility is defined as the ability of a bulk solid to be agglomerated into a 
tablet of specified strength.  This differs from compressibility in that compressibility 
involves the ability of a bulk material to decrease in volume under pressure (Leunberger 
and Jetzer, 1984).  Compressibility studies are therefore useful in diagnosing flow 
problems in bulk solids while the main focus of compactibility studies is to enhance 
storage and handling properties of bulk solids through increased density of the material 
(Demirbas, 1999).   
Poultry litter is a lightly dense material (bulk density is less than 500 kg/m
3
 ? see 
results in section 3.3.3 of this thesis).  This makes it costly to transport poultry litter from 
production sites to areas where it could be effectively utilized for value-added 
applications such as in bioenergy and bioproduct applications (Colley et al, 2005).  
Biosecurity is also a concern when poultry litter is to be transported over long distances.  
Poultry litter is dusty, and is known to contain pathogens such as E. Coli (Nandi et al, 
2004).  Thus, during transportation, pathogen infected dust maybe released into the 
atmosphere. This in turn could lead to the spreading of poultry-related diseases in 
locations where the litter is transported through.  This biosecurity problem could be 
considerably minimized if the poultry litter is densified because this would reduce the 
dispersion of dust and dust-laden microbes during transportation (Fasina et al, 2006). 
56
Traditionally, agricultural materials are densified into pellets, cubes, and bales.  
Pellets are the densest of these agglomerates and therefore require the maximum amount 
of energy input.  This high energy input translates into high costs ($50-$60 per ton), 
which prevent the process from being economical and practical for every broiler farmer 
to purchase and operate a pellet mill (Fasina et al, 2006).  Similar to the production of 
pellets, pressure agglomeration is used to manufacture cubes except that lower pressures 
are used.  Production of cubes is presently limited to forage crops such as alfalfa.  As the 
name implies, cubes are usually in the forms of a square cross section of chopped 
biomass (Sokhansanj and Turhollow, 2004), and typically vary from 12.7 to 38.1 mm 
dimensionally. 
Baling is a process that combines compression and packing (tying with ropes or 
wrapping) operations, it is typically used for grassy or fibrous-like materials that are 
stringy in nature (Badger, 2003).  Poultry litter is not stringy and therefore the low-cost 
volume reduction method that can be developed for poultry litter is limited to pressure 
agglomeration. Bale dimensions are roughly 44 in by 49 in (1026mm x 1040mm; Badger, 
2003).   
The objective of this study is to optimize the compaction of poultry litter for 
efficient transportation and off-site utilization.  This will be achieved by  
(1)  Determining the effect of moisture content on the minimum pressure required to  
compact poultry litter, and  
(2)  Determining the energy required to compact poultry litter. 
 
 
57
4.2 Methods and Materials 
4.2.1 Preparation 
This experiment was conducted with fresh poultry litter that was obtained from a 
local poultry farmer in Lee County, Alabama.  The methodology described in section 
3.2.1 for adjusting the moisture contents of poultry litter was also used in this study.  
Compaction of poultry litter was carried out on samples conditioned to the following 
moisture contents: 16.5%, 21.7%, 24.2%, 26.1%, 29.0%, 31.7%, 35.1%, 37.7%, and 
41.4%, wet basis.   
 
4.2.2 Compaction 
 The compaction apparatus consisted of a 27.3 mm diameter die.  The die had a 
length of 135.2 mm and was composed of two semicircular halves that were bound 
together by three to eight clamps depending on the pressure applied.  Before each test, the 
inside of each half was lubricated with vegetable oil to minimize the amount friction 
between the poultry litter and the die.  The two halves were then clamped together and 
the die was filled with poultry litter.  A plunger (25.6 mm diameter, 124.6 mm length) 
attached to the crosshead of the texture analyzer (model TA-HDi, Stable Microsystems, 
Surrey, UK) was used to compress the sample at a speed of 1 mm/s until the desired force 
was reached (see Appendix D Figure D.2).  The compacted sample was held in a creep 
mode (i.e. constant force) for a period of 60s after the desired force was reached.  
Compaction forces of 50 kg, 100 kg, 150 kg, 200 kg, 250 kg, 300 kg, 350 kg, 400 kg, 450 
kg, and 500 kg (corresponding to pressures of 0.84, 1.7, 2.5, 3.4, 4.2, 5.0, 5.9, 6.7, 7.5, 
and 8.4 MPa) were applied on the samples at the various moisture contents.  Force and 
58
deformation data were automatically acquired and stored by the software provided by the 
manufacturer of the texture analyzer.  The force-deformation data was used to calculate 
the energy expended during the compaction process.  Once compaction was completed, 
the agglomerated sample was removed from the die (see Appendix D Figure D.3) and 
stored in the laboratory (temperature of 22
o
C and a relative humidity of 45%) for a period 
of 2 months. 
A digital vernier caliper (Solar ABSOLUTE Digimatic Caliper, Model CD-S6?C, 
Mitutoyo Corporation, Japan)  was used to measure the length and the diameter, while a 
digital balance accurate to 0.001 grams (Model AR3130, Ohaus Corp., Pinebrook, NJ) 
was used to measure the mass of freshly made and stored compacts.  The density of the 
samples were calculated from the ratio of mass to volume (obtained from length and 
diameter measurements).  In addition, the strength of some compact samples (those that 
were adjusted to moisture contents of 31.7% to 41.4%) was also obtained by means of a 
12.7 mm diameter round probe (Model TA-23, Texture Technologies, Scarsdale, NY).  
The compact was placed on a flat plate in its natural position (i.e. radial dimension was in 
the same direction as that of the compressive force).  The probe (attached to the 
crosshead of the texture analyzer) was then used to compress the compact at a speed of 1 
mm/s.  The force required to rupture the compacts was obtained from the maximum force 
in the force deformation curve. All of the procedures outlined above were carried out in 
duplicate. 
 
 
 
59
4.2.3 Data analysis 
Regression analysis was performed using the proc reg function in SAS statistical 
software package (Version 9.1, SAS Institute Inc., Cary, NC, 2002-2003) and plotted 
with the experimental data  using Microsoft Excel (Microsoft Office XP Professional, 
2005). 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
60
4.3 Results and Discussion 
4.3.1 Density of poultry litter compacts 
 Initially, compaction was carried out on samples with moisture contents ranging 
from 16.5% to 29.0 % (w.b.) with a pressure range of 5.0 to 8.4 MPa.  A preliminary 
evaluation showed that:  
(a) The agglomeration of poultry litter was not achieved at applied pressures less than 
5.0 MPa,  
(b) Poultry litter has to be compacted to a minimum density of 765.6 kg/m
3
  
(Figure 4.1), and  
(c) The density of agglomeration after compaction increased with moisture content.   
 
Regression analysis showed that within the moisture content range of 16.5% to 29.0% 
(w.b.) and the pressure range of 5.0 to 8.4 Mpa, the following relationship (Equation 4.1) 
can be used to predict the density (kg/m
3
) of compacts as a function of moisture content 
(%, w.b.) and pressure (MPa). 
61
700
800
900
1000
1100
1200
1300
4.555.566.577.588.59
Pressure (MPa)
De
n
s
i
t
y
 (
k
g
/
m
3
)
21.7% 24.2%
16.5% 26.1%
29.0% Predicted Value
 
 
Figure 4.1 Effect of moisture content and pressure on the density of poultry litter 
compacts  
 
 
)log(*187.075M*20.343159.994 ?? ++=
compact
, R
2
 = 0.907  (4.1) 
 
Similar plots were obtained by Demirbas (1999) and Mani et al (2006) for biomass 
feedstocks. 
 Based on the above results a second set of compaction tests was conducted at 
higher moisture values (31.7% to 41.4%, w.b.) with the hypothesis that less energy would 
be required to compact poultry litter at higher moisture contents, since moisture is acting 
as a binder during the compaction process.  Statistical analysis (P<0.05) showed that the 
densities from the second set of experiments were not significantly different from those 
obtained by the first set of experiments.  However, the following observations were made 
from the second set of compaction tests:   
62
(a) It was possible to produce poultry litter compacts at pressures less than 5 MPa. 
Successful agglomeration occurred at pressures as low as 0.84 MPa.  It should be 
recalled that compaction was not possible below 5 MPa for samples with moisture 
contents less than 29.0%. 
(b) At moisture contents greater than 37.6% and pressures greater than 5 MPa, it was 
extremely difficult to compact poultry litter.  This is because the samples began to 
exhibit fluid like (or slurry) behavior at these higher pressures and therefore could 
not be contained within the die.   
(c) Within the pressure range of 0.84 to 5.9 MPa the density (kg/m
3
) of the compacts 
increased logarithmically with increases in applied pressure (MPa) and increased 
linearly with increases in the moisture content (%, w.b.) of the samples (Figure 
4.2 & Equation 4.2). 
600
700
800
900
1000
1100
1200
01234567
Pressure (MPa)
D
e
ns
i
t
y
 (k
g/
m
3
)
31.7% 35.1%
37.7% 41.4%
Predicted Value
 
 
Figure 4.2 Effect of moisture content and pressure on the density of poultry litter 
compacts 
  
)log(*125.778M*7.363574.570 ?? ++=
compact
, R
2
 = 0.831  (4.2) 
 
63
4.3.2 Density of poultry litter compacts after 2 months 
After two months of storage the compacts equilibrated to the environment and 
each had an equal moisture content of 9.4% (w.b.). Figure 4.3 shows the density of all the 
compacts (set 1 & 2) after two months of storage. 
300
400
500
600
700
800
900
01234567
Pre ssure  (MPa )
D
e
ns
i
t
y
 (
k
g/
m
3
)
16.5% 21.7%
24.2% 26.1%
29.0% 31.7%
35.1% 37.7%
41.4% Predicted Value
dsf
 
 
Figure 4.3 Effect of moisture content and pressure on the density of poultry litter 
compacts after 2 months storage  
 
 
Despite the fact that moisture content and pressure significantly affect the density to 
which the compacts can be made (Figure 4.1 & 4.2), this was not the case for compacts 
that have been stored for two months under laboratory conditions.  Statistical testing 
(P<0.05) showed that within the moisture range of 16.5 to 41.4% (w.b.) only pressure had 
a significant affect on the density of the stored compacts.  The average density values 
obtained at the various moisture contents were therefore averaged, and an exponential 
relationship was obtained between the compact density (kg/m
3
) and the applied pressure 
(MPa) (Equation 4.3). 
)log(*241.101190.592 ?? +=
compact
, R
2
 = 0.710  (4.3) 
64
The density of the compacts decreased by an average of 23.5% during the two 
month period.  This is because of two reasons: 
(a) The samples equilibrated with the laboratory conditions to an average moisture 
content of 9.4% (w.b.). 
(b) The compacts relaxed (or expanded in size) over the two month period. 
  
4.3.3 Breakage force of poultry litter compacts 
Figure 4.4 shows that the average force required to rupture the compacts (after 2 
months of storage) vary from 16.6 N to 357.0 N.   
0
50
100
150
200
250
300
350
400
01234567
Pressure (MPa)
For
c
e
 (
N
)
31.7%
37.7%
41.4%
Predicted Value
 
 
Figure 4.4 Effect of moisture content and pressure on poultry litter compact?s 
breakage force after two months storage 
 
 
Despite the fact that the moisture had no significant effect on density of the compacts 
after 2 months of storage, the force (N) required to rupture the compacts was significantly 
influenced by moisture content (%, w.b.) in a linear fashion and by pressure (MPa) in an 
logarithmic fashion (Equation 4.4). 
)log(*108.220M*0.46250.917 ?++=
breakage
F , R
2
 = 0.707 (4.4) 
65
It is well known in the field of agglomeration that moisture can act as a film and bridge 
forming binder by coating particles thereby improving the natural adhesion of the 
particles to each other (Pietsch, 2002). 
 
4.3.4 Specific energy for poultry litter compaction 
The specific energy required to form agglomerates of poultry litter ranged from 
0.190 kJ/kg to 1.763 kJ/kg within the moisture content range of 16.5% to 41.4% (w.b.) 
and applied pressure range of 0.84 MPa to 5.9 MPa (Figure 4.5).   
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
01234567
Pressure (MPa)
S
p
eci
f
i
c E
n
er
g
y 
(
kJ/
kg
)
16.5% 24.2% 26.1% 29.0%
31.7% 35.1% 37.7% 41.4%
 
 
Figure 4.5 Effect of moisture content and pressure on the specific energy required 
for the compaction of poultry litter 
 
 
This is significantly lower than the specific energy required to produce pellets from 
biomass feedstocks (typically 19 kJ/kg to 90kJ/kg; Colley et al, 2005).  By substantially 
increasing the moisture content, it is therefore feasible to reduce the energy required to 
compact biomass feedstocks by nine fold.  The required energy (kJ/kg) increased with 
applied pressure (MPa) and decreased with moisture content (%) in a linear fashion as 
follows (Equation 4.5): 
66
?*0.204M*0.0108-0.479 +=E     (4.5) 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
67
4.4 Conclusion 
 It can be concluded that both the pressure applied and the moisture content of the 
poultry litter at the time of compaction significantly affect the density of the compact and 
the energy required for the compaction.  After two months of storage, the density of the 
compacts were only significantly affected by the amount of pressure applied during 
compaction while the moisture content no longer had any significant affect.  However, 
the force required to rupture the compacts after 2 months of storage was significantly 
affected by both the moisture content and the pressure applied.  It was found that when 
the moisture content of poultry litter was increased to as high as 37.7% the energy 
required to compact the litter in comparison to the energy required for pelleting was 
reduced by nine fold.  Based on the results from this study, it is recommended that 
poultry litter be compacted at a moisture content of 37.7% and a pressure of 5.0 MPa.      
  
    
 
 
 
 
 
 
 
 
 
68
4.5 References 
Badger, P.C. 2003. Biomass transport systems. In : Encyclopedia of Agricultural, Food 
and Biological Engineering, 94-98. New York, NY: D.R. Marcel Dekker, Inc. 
 
Colley, Z., O. O. Fasina, D. Bransby, Wood, C. W. 2005. Compaction Behavior of 
Poultry Litter and Switchgrass, An ASAE/CSAE Meeting Presentation, Paper No. 
056053, 2005 ASAE/CSAE Annual International Meeting, Sponsored by ASAE, July 17-
20, Tampa Convention Center, Tampa, FL. 
 
Demirbas, A. 1999. Physical properties of briquettes from waste paper and wheat straw 
mixtures. Energy Conversion & Management 40(4): 437-445. 
 
Fasina, O.O., Fulton, J., Srivastava, P., Wood, W., Owsley, F. 2006. Volume reduction 
technologies for transporting poultry litter, An ASABE Meeting Presentation at the 2006, 
Paper No. 066173, ASABE Annual International Meeting 2005, Sponsored by ASABE, 
July 17-20, Portland Convention Center, Portland, OR.  
 
Leuenberger, H., Jetzer, W. 1984. The compactibility of powder systems ? a novel 
approach. Powder Technology 37: 209-218. 
 
Mani, S., Tabil, L.G., Sokhansanj, S. 2006.  Effects of compressive force, particle size 
and moisture content on mechanical properties of biomass pellets from grasses. Biomass 
and Bioenergy  30(7): 648-654. 
 
McMullen, J., Fasina, O. O., Wood, C. W., Feng, Y. 2005.  Storage and handling 
characteristics of pellets from poultry litter. Applied Engineering in Agriculture 21(4): 
645-651. 
 
Nandi, S., Maurer, J., Hofacre, C., Summers, A.O. 2004. Gram-positive bacteria are a 
major reservoir of Class 1 antibiotic resistance integrons in poultry litter. Proceedings of 
National Academy of Sciences 101(18): 7118-7122. 
 
Pietsch, W.  2002. Agglomeration Processes ? Phenomena, Technologies and Eqiupment. 
Weinheim, Germany: Wiley VCH. 
 
Sokhansanj, S., Turhollow, A.F. 2004. Biomass densification and cubing operation costs 
for corn stover. Applied Engineering in Agriculture 20 (4): 495-499. 
 
 
 
 
 
69
CHAPTER 5. FLOWABILITY OF POULTRY LITTER 
5.1 Introduction 
 Flowability is the mathematical representation of a material?s cohesiveness and 
adhesiveness.  Cohesiveness refers to the material?s internal friction within itself and 
adhesiveness refers to the material?s friction against surfaces it may be touching.  Each of 
these characteristics determine how easy or difficult a material will flow when handled, 
stored, and/or transported  (Woodcock and Mason, 1987). 
 Most bulk solids are stored in bins or silos.  Poultry litter may have to be stored in 
these types of equipment if it is going to be utilized at off-production sites.  This will 
require the proper design and selection of bins and silos that will enable poultry litter to 
be easily unloaded from them (Shamlou, 1988).  The Jenike Shear cell is the best known 
machine that is used to measure material?s flowability.  Flowability data provides 
information that are applied to strength and flow, feeder loads and power requirements, 
gravity flow blenders, purge bins, and pneumatic dense-phase conveying, all of which are 
required for proper storage silo design (Wilms, 1999).  Improper flow and design such as 
rat holing and arches can be avoided, when storage bins and silos are properly designed.  
 The objectives of this study were to:  
(1) Measure the flowability, cohesion, and internal angle of friction of poultry litter at  
 moisture contents (w.b.) of 10%, 18%, 22%, 26%, and 30%, and  
70
(2)  Measure the wall friction and the wall angle of friction of poultry litter on  
milled aluminum, mirror finished aluminum,  milled steel, mirror finished steel, 
and carbon coated steel.  
71
5.2 Methods and Materials 
5.2.1 Preparation 
 The methodology described in Section 3.2.1 to adjust the moisture contents of 
samples was used.   
 
5.2.2 Flowability 
An automated shear tester (ShearScan TS12, Sci-Tec Inc., Worthington, Ohio) 
was used to quantify the flow behavior of the samples. The shear cell was of the annular 
split cell type that consisted of a base ring with attached inner and outer sides, upper 
floating inner and outer rings, and a twisting lid (see Appendix D Figure D.4). The 
diameters of the outer and inner rings were 110 mm and 55 mm, respectively. The height 
of the upper and bottom rings were 18 mm and 12 mm, respectively. To run a sample, the 
space between the outer and inner rings of the shear cell was loaded with the sample to be 
tested.  The cell containing the poultry litter was then placed on the base of the shear 
tester, and the cell lid was placed carefully on top of the sample.  
The software provided by the manufacturer of the shear tester was then activated. 
This caused the load head, which houses the normal load cell, to move down until it made 
contact with the cell lid. A compression load was then applied at a rate of 7.5 mm/min 
until the preset normal load was reached (consolidating stress). With the normal (or 
consolidating) stress applied, the load head began to twist the cell lid at a speed of 2.5 
mm/min. This motion caused the sample to shear. The shear stress was measured by the 
shear load cell and continued to increase until it reached the steady-state point. When the 
steady-state point was reached, the load head lifted to reduce the load to a preset point. 
72
The shear motor then started, and the maximum shear stress required for the sample to 
fail was monitored and recorded. The maximum shear stress was measured for multiple 
loads (25%, 35%, 45%, 55%, 65%, and 75% of the consolidating stress). A plot of the 
maximum shear stress versus normal stress produces a line called the yield locus at that 
consolidating stress. Consolidating stresses of 1.5, 3, 6, 9, and 12 kPa were used for all 
the samples.  The Mohr-Coulomb equation (Equation 5.1) was used to estimate the 
cohesion and angle of internal friction: 
??? )tan(+= c     (5.1) 
Where ? = shear stress (kPa) 
? = normal stress (kPa) 
? = angle of internal friction (
o
) 
c = cohesion strength (kPa). 
Using the software provided by the manufacturer of the shear tester, each yield 
locus was used to calculate the unconfined yield stress (UYS; Equation 5.2) and the 
major consolidating stress (MCS; Equation 5.3) of each sample.  Two yield loci for each 
consolidating stress (10 yield loci for each sample) were used to make a flow function (a 
plot of the UYS vs. MCS) for each sample.  This was used to obtain the flow index of the 
poultry litter samples.   
( )
?
?
cos
sin12 +
=
c
UYS      (5.2) 
()
?
?
?
???
tan
sin1
cos
cossin
2
2222
cAA
MCS ?+
?
?
?
?
?
?
?
?
??
=   (5.3) 
73
Where
?
?
tan
c
A += , and c is the cohesion defined as ? at ? = 0. 
5.2.3 Wall friction 
The methodology and equipment described in the previous section to quantify the 
flowability of poultry litter were used in this section for the wall friction and the wall 
angle of friction determination except that the bottom section of the shear cell that 
previously contained poultry litter was replaced with a solid material that was 
manufactured for a given wall material of interest (i.e. milled aluminum, mirror finished 
aluminum, milled steel, mirror finished steel, and carbon coated steel; see Appendix D 
Figure D.4). 
Therefore instead of developing the yield locus, the wall yield locus was 
developed from the normal load-shear stress data.  Further analysis was carried in the 
fashion described in the previous section.  
 
5.2.4 Data Analysis 
 
All of the regression analysis and plots of the data were created using Microsoft 
Excel (Microsoft Office XP Professional, 2005). 
 
 
 
 
 
 
74
5.3 Results and Discussion 
5.3.1 Moisture contents 
 The flowability tests for poultry litter were carried out on samples of the 
following moisture contents: 10.3%, 18.0%, 22.1%, 26.0%, and 30.9%, wet basis.  While 
the wall friction test was carried out on a sample of 20.0% moisture content, wet basis. 
 
5.3.2 Flowability 
  The flow function plots (Figure 5.1) or the plots of the ultimate yield stress 
(UYL) vs. the major consolidating stress (MCS) at different moisture contents indicate 
that the flowability of poultry litter reduces as moisture content increases.   
R
2
 = 0.858
R
2
 = 0.854
R
2
 = 0.872
R
2
 = 0.749
R
2
 = 0.518
0
2
4
6
8
10
12
14
16
18
20
10203040
MCS (kPa)
UYL
 (kP
a)
M=10.3%
M=18.0%
M=22.1%
M=26.0%
M=30.9%
Fitted (M=30.9%)
Fitted (M=22.1%)
Fitted (M=26.0%)
Fitted (M=18.0%)
Fitted (M=10.3%)
 
 
Figure 5.1 Flow function graph of poultry litter 
 
75
This is confirmed from the values of the flow index (obtained from the inverse of the 
slope of the linear fit of the UYL vs. MCS plot; Table 5.1).   
 
Table 5.1 Flow index of poultry litter at various moisture contents 
 
M.C. % (w.b.) Flow Function (FF) Flow Index (FI) Characteristic Flow 
30.9 0.535 1.871 Very cohesive/non-flowing 
26.0 0.367 2.727 Cohesive 
22.1 0.309 3.239 Cohesive 
18.0 0.224 4.474 Easy flowing 
10.3 0.157 6.369 Easy flowing 
 
 
 
Based on the flow index values, poultry litter conditioned to moisture contents of 18.0% 
and below can be classified as easily flowing materials, while poultry litter at a moisture 
content of 30.9% and above are considered very cohesive and non-flowing.  This implies 
that flow aids will be required to discharge high moisture content poultry litter from 
storage bins, silos, or hoppers. 
This is not surprising since the results reported in section 3.3.8 of this thesis 
showed that poultry becomes more compressible with increased moisture contents. Thus 
when the same load is applied to samples of high and low moisture contents, the high 
moisture content sample compresses more than the lower moisture content sample.  The 
result is that more force is required to shear the high moisture content sample.  Teunou 
and Fitzpatrick (1999) also found similar results when they compared the flow functions 
of flour (at 12.0% moisture content), tea (at 6.5% MC), and whey (at 4.0%MC).  They 
concluded from their study that the flour with the highest moisture content had the most 
difficult flow and that whey with the lowest moisture content had the easiest flow. 
76
The cohesion and internal angle of friction of poultry litter was not significantly 
affected by the moisture content of the samples.  The average cohesion of poultry litter at 
normal stresses of 1.5, 3, 6, 9, and 12 kPa were 0.4, 0.6, 1.1, 1.7, and 2.1 kPa, 
respectively.  These values are similar to some agricultural materials.  Teaunou and 
Fitzpatrick (2000) measured approximately the same range of cohesion values in whey.  
Pressure did not have a significant affect on the internal angle of friction.  The average 
internal angle of friction was 42.1
o
.   
 
5.3.3 Wall friction 
 For the wall friction tests a poultry litter sample of 20.0% moisture content was 
tested on milled aluminum, mirror finished aluminum, milled steel, mirror finished steel, 
and carbon coated steel.  Wall friction flow function graphs for each of the materials were 
developed through an excel spreadsheet (Figure 5.2).   
77
R
2
 = 0.9608
R
2
 = 0.8856
R
2
 = 0.9092
R
2
 = 0.9321
R
2
 = 0.9958
0
1
2
3
4
5
6
7
8
9
0 5 10 15 20 25 30
MCS (kPa)
UY
S
 (
kP
a)
Milled Steel
Milled Aluminum
Mirror Finished Steel
Carbon Coated Steel
Mirror Finished Aluminum
Fitted (Milled Steel)
Fitted (Milled Aluminum)
Fitted (Mirror Finished Aluminum)
Fitted (Carbon Coated Steel)
Fitted (Mirror Finished Steel)
 
Figure 5.2 Wall friction flow functions of 20.0% moisture content (w.b.) poultry 
litter 
The worst flow for poultry litter was obtained on the milled steel surface.  
However, the flow of poultry litter significantly improved when the steel surface was 
modified by either carbon coating or by mirror finishing.  A better response to improve 
flow was obtained by the carbon coating the steel rather then mirror finishing it.  A study 
looking at the flow properties of biomass and coal blends also reported having better flow 
after modifying the steel surfaces tested.  In the study conducted the worst flow occurred 
on a milled mild steel surface and improved flow was observed on a stainless steel 304 
with 2B finish surface (Zulfiqar et al, 2004).     
Figure 5.1 also shows that poultry litter flows better on a milled aluminum surface 
in comparison to a milled steel surface.  However, modifying the milled aluminum 
surface by mirror finishing did not improve the flow of poultry litter.  This may be 
78
because thin aluminum oxide films are known to readily form on the metal?s surface 
(Kresse et al, 2005). Each sample was made from the same aluminum and only differed 
in finish.  It is hypothesized that the data is indicating that the type of finish has no effect 
on the wall friction because an aluminum oxide film of uniform friction has been formed 
on the surface of each sample.  This may explain why these findings are in contrast to the 
significant improvement in the flow of poultry litter on the modified steel surfaces 
explained in the previous paragraph. 
The average angle of wall friction for each of the materials, milled aluminum 
(37.9
o
), mirror finished aluminum (32.5
o
), milled steel (26.6
o
), mirror finished steel 
(35.1
o
), and carbon coated steel (30.7
o
), was calculated.  These angles can be used to 
insure mass flow out of gravity flow devices, such as silos and hoppers.  
The results above were confirmed by the flow index (obtained from the inverse of 
the slope of the linear fit of the UYL vs. MCS plot; Table 5.2).  The flow index data 
indicated that all of the materials appear to have low adhesion with poultry litter.  Milled 
steel was the only material with some adhesion but it was not close to being non-flowing.  
The optimal material appears to be the carbon coated steel because it allowed the easiest 
flow to occur. 
 
Table 5.2 Wall friction flow index of 20.0% moisture content (w.b.) poultry litter 
 
Material Flow Function (FF) Flow Index (FI) Characteristic 
Flow 
Milled steel 0.387 2.584 Adhesive 
Mirror finished aluminum 0.211 4.739 Easy flowing 
Milled aluminum 0.154 6.494 Easy flowing 
Mirror finished steel 0.107 9.346 Easy flowing 
Carbon coated steel 0.083 12.048 Free flowing 
79
5.4 Conclusion 
 This study found that poultry litter?s moisture content greatly affected its 
flowability.  Flowability reduced with increases in moisture content.  The carbon coated 
steel surface gave the least resistance to flow, while the milled steel gave the greatest 
resistance.  Modifying the milled aluminum surface by mirror finishing did not change 
the flowability of poultry litter on that surface. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
80
5.5 References 
Fitzpatrick, J. J., Barringer, S. A., Iqbal, T. 2004.  Flow property measurement of food 
powders and sensitivity of Jenike?s hopper design methodology to the measured values. 
Journal of Food Engineering 61(3): 399-405. 
 
Kresse, G., Schmid, M., Napetschnig, E., Shishkin, M., Kohler, L, Varga, P. 2005. 
Structure of the ultrathin aluminum oxide film on NiAl(110). Science 308(5727): 1440-
1442. 
 
Shamlou, P. A.  1988. Handling of Bulk Solids: Theory and Practice.  London, UK: 
Butterworth-Heinemann. 
 
Teunou, E., Fitzpatrick, J. J. 2000.  Effect and storage time and consolidation on food 
powder flowability. Journal of Food Engineering 43(2): 97-101. 
 
Wilms, H. 1999.  Equipment design based on solids flowability data. Powder Handling 
and Processing 11(1): 37-42. 
 
Woodcock, C. R., Mason, J. S. 1987. Bulk Solids Handling: An Introduction to the 
Practice and Technology.  Glasgow, Scotland: Blackie and Son Ltd. 
 
Zulfiqar, M., Moghtaderi, B., Wall, T.F. 2004. Flow properties of biomass and coal 
blends. Fuel Processing Technology 87(4): 281-288. 
 
 
 
 
 
 
 
 
 
 
 
 
81
CHAPTER 6. CONCLUSION 
It can be concluded from this study that moisture content significantly affects the 
physical properties, compaction and flowability of poultry litter.  According to particle 
size analysis, 40% of the poultry litter can be considered to be fine and highly 
compressible.  Physical properties such as the poured bulk density, particle density and 
porosity decreased with increases in moisture content.  The porosity values indicated that 
poultry litter?s particles were irregular and non-spherical in shape.  The average tap bulk 
density and Hausner ratio were not affected by moisture content and had average values 
of 0.580 g/ml and 1.070, respectively (which indicated easy fluidization).   
The compressibility of poultry litter was affected by both pressure and moisture 
content with a maximum compressibility percent of 18.0% obtained at a moisture content 
of 30.8% and a pressure 15 kPa.   
The equilibrium moisture isotherm data was modeled with the GAB equation, 
where constants M
o
, C, and K were found to be 0.0583, 3031, and 0.955, respectively, 
with a R
2
 value of 0.917.  The estimated monolayer moisture content of poultry litter 
indicated that biochemical degradation of the litter will occur when the relative humidity 
and temperature of the environment were 1.9% and 25
o
C, respectively.   
Both the pressure applied and the moisture content of the poultry litter at the time 
of compaction significantly affected the density of the compact and the energy required 
82
for the compaction.  Increase in moisture content resulted in an increase in the density of 
the compacts and a decrease in the energy expended during compaction. After two 
months of storage, the density of the compacts were only significantly affected by the 
amount of pressure applied during compaction while the original moisture content no 
longer had any significant affect.  However, the force required to rupture the compacts 
after 2 months of storage was significantly affected by both the moisture content and the 
pressure applied. Based on the results from this study, it is recommended that poultry 
litter be compacted at a moisture content of 37.7% (w.b.) and a pressure of 5.0 MPa.   
Poultry litter?s moisture content significantly affected its flowability.  Flowability 
reduced with increases in moisture content.  The carbon coated steel surface gave the 
least resistance to flow, while the milled steel gave the greatest resistance.  Modifying the 
milled aluminum surface by mirror finishing did not change the flowability of poultry 
litter on that surface. 
 
 
 
 
 
 
 
 
 
 
83
CHAPTER 7. FUTURE WORK 
 This study provides useful information about the physical properties, compaction 
and flowability of poultry litter that will aid in the design or selection of optimal 
equipment and facilities to handle, store and transport poultry litter.  Still, more research 
can be done to better understand the material. 
 More information on poultry litter?s particle size distribution is needed.  The sieve 
analysis completed in this study found that the largest percentage of the particles 
(24.14%) was retained on the bottom pan.  Additional sieve analysis should be done to 
get a distribution of the particles smaller than 0.212 mm.  The top sieve (with an aperture 
of 1.700 mm) also retained a large percentage (16.41%) of the poultry litter. This 
indicates that additional sieve analysis should be done on particles bigger than 1.700 mm.  
If this additional sieve analysis was carried out the error bars on the Figure 3.1 could 
considerably decrease and a more thorough size distribution could be provided. 
 The data provided in the Chapter 4 on the compaction of poultry litter should be 
taken into consideration and applied to a larger compaction process in order to produce 
larger agglomerates, such as cubes.  The process of cubing poultry litter should be looked 
at rather than baling because poultry litter is not stringy in nature, and therefore would 
not benefit from baling.  Research into the optimal compaction of poultry litter through 
cubing would allow for the densification of more material per process making it a more 
economical and efficient method for large scale compaction. 
84
Additional tests on the flowability of poultry litter should also be completed.  
These tests should be done on samples with moisture contents (w.b.) between 18% and 
22%, and between 26% and 30%.  These additional tests could be used to find the exact 
moisture contents where the flow of the poultry litter changes from easy to cohesive, and 
from cohesive to very cohesive/non-flowing, respectively.  With additional research a 
more complete understanding of poultry litter?s physical properties, compaction and 
flowability could be obtained. 
Therefore, future research objectives could include:  
(1)  Developing a more complete particle size distribution of poultry litter through   
       further sieve analysis, 
(2) Applying the small scale compaction data provided here to optimize the large 
scale compaction of poultry litter through cubing, and  
(3) Measuring the flowability of poultry litter at smaller moisture content increments 
between 18% and 22%, and between 26% and 30%, in order to find  the exact 
point where the flow of poultry litter transitions from easy to cohesive, and from 
cohesive to very cohesive/non-flowing, respectively. 
 
   
 
  
 
 
 
85
APPENDICES 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
86
Appendix A. Physical Property Data 
 
Table A.1 Particle size distribution of poultry litter  
US Seive No. Aperture (mm) Run 1 (%) Run 2 (%) Run 3 (%) 
12 1.700 10.66 19.64 18.94
20 0.850 17.72 21.49 21.36
30 0.595 14.87 15.50 15.81
40 0.425 8.21 8.34 7.68
50 0.297 9.98 8.36 8.69
60 0.250 4.48 3.31 3.61
70 0.212 3.85 2.38 2.70
Pan 0.000 30.23 20.96 21.21
 
 
Table A.2    Table A.3              Table A.4 
           Bulk density             Particle density        Tap bulk density 
M  
(%, w.b.) 
?
b
 
(g/ml)  
M  
(%, w.b.) 
?
p
 
(g/ml)  
M  
(%, w.b.) 
?
T 
(g/ml) 
10.3 0.550 10.3 1.623 10.3 0.591
10.3 0.547 10.3 1.596 10.3 0.589
10.3 0.541 10.3 1.597 10.3 0.589
14.2 0.541 13.8 1.601 14.2 0.595
14.2 0.548 13.8 1.612 14.2 0.587
14.2 0.546 13.8 1.588 14.2 0.564
18.1 0.546 18.0 1.567 18.4 0.561
18.1 0.542 18.0 1.562 18.4 0.581
18.1 0.542 18.0 1.570 18.4 0.584
22.0 0.546 22.1 1.550 22.0 0.586
22.0 0.549 22.1 1.559 22.0 0.579
22.0 0.542 22.1 1.554 22.0 0.565
26.1 0.538 26.0 1.488 26.1 0.581
26.1 0.535 26.0 1.507 26.1 0.576
26.1 0.536 26.0 1.487 26.1 0.574
30.6 0.534 30.9 1.491 29.6 0.578
30.6 0.534 30.9 1.473 29.6 0.577
30.6 0.533 30.9 1.434 29.6 0.581
 
 
 
87
Table A.5 Porosity of poultry litter 
M (%, w.b.) ? M (%, w.b.) ? M (%, w.b.) ? 
10.3 0.661 18.0 0.652 26.1 0.638 
10.3 0.663 18.0 0.650 26.1 0.640 
10.3 0.667 18.0 0.654 26.1 0.640 
10.3 0.655 18.0 0.651 26.1 0.643 
10.3 0.657 18.0 0.648 26.1 0.645 
10.3 0.661 18.0 0.653 26.1 0.644 
10.3 0.656 18.0 0.652 26.1 0.638 
10.3 0.657 18.0 0.650 26.1 0.640 
10.3 0.661 18.0 0.655 26.1 0.640 
14.0 0.662 22.0 0.648 30.7 0.642 
14.0 0.658 22.0 0.646 30.7 0.642 
14.0 0.659 22.0 0.651 30.7 0.643 
14.0 0.664 22.0 0.650 30.7 0.637 
14.0 0.660 22.0 0.648 30.7 0.637 
14.0 0.662 22.0 0.653 30.7 0.638 
14.0 0.659 22.0 0.649 30.7 0.627 
14.0 0.655 22.0 0.647 30.7 0.627 
14.0 0.657 22.0 0.651 30.7 0.628 
 
 
Table A.6 Hausner ratio of poultry litter 
M (%, w.b.) H
R
 M (%, w.b.) H
R
 M (%, w.b.) H
R
 
10.3 1.074 18.2 1.028 26.1 1.079 
10.3 1.080 18.2 1.022 26.1 1.086 
10.3 1.093 18.2 1.036 26.1 1.084 
10.3 1.070 18.2 1.065 26.1 1.070 
10.3 1.076 18.2 1.058 26.1 1.076 
10.3 1.089 18.2 1.073 26.1 1.075 
10.3 1.070 18.2 1.070 26.1 1.066 
10.3 1.076 18.2 1.064 26.1 1.073 
10.3 1.089 18.2 1.078 26.1 1.071 
14.2 1.099 22.1 1.074 30.1 1.082 
14.2 1.086 22.1 1.067 30.1 1.082 
14.2 1.091 22.1 1.082 30.1 1.085 
14.2 1.085 22.1 1.061 30.1 1.080 
14.2 1.072 22.1 1.055 30.1 1.080 
14.2 1.076 22.1 1.069 30.1 1.083 
14.2 1.042 22.1 1.035 30.1 1.087 
14.2 1.030 22.1 1.029 30.1 1.087 
14.2 1.034 22.1 1.043 30.1 1.091 
 
88
Table A.7 Compressibility of poultry litter 
M (%, w.b.) P (kPa) C (%) M (%, w.b.) P (kPa) C (%) 
10.3 1.5 2.44 22.1 1.5 4.37 
10.3 1.5 2.48 22.1 1.5 4.63 
10.3 3 3.05 22.1 3 6.31 
10.3 3 3.22 22.1 3 5.98 
10.3 6 4.60 22.1 6 8.46 
10.3 6 4.76 22.1 6 8.18 
10.3 9 5.77 22.1 9 10.71 
10.3 9 5.71 22.1 9 10.56 
10.3 12 6.62 22.1 12 12.03 
10.3 12 6.87 22.1 12 12.20 
10.3 15 7.20 22.1 15 13.11 
10.3 15 7.25 22.1 15 13.34 
13.8 1.5 2.87 26.0 1.5 4.80 
13.8 1.5 3.26 26.0 1.5 5.21 
13.8 3 4.05 26.0 3 7.20 
13.8 3 4.19 26.0 3 7.47 
13.8 6 6.13 26.0 6 10.18 
13.8 6 5.74 26.0 6 10.32 
13.8 9 7.03 26.0 9 12.43 
13.8 9 6.74 26.0 9 12.79 
13.8 12 7.92 26.0 12 14.19 
13.8 12 7.70 26.0 12 14.31 
13.8 15 8.48 26.0 15 15.63 
13.8 15 8.65 26.0 15 15.54 
18.0 1.5 3.96 30.9 1.5 6.99 
18.0 1.5 4.16 30.9 1.5 6.80 
18.0 3 4.95 30.9 3 9.49 
18.0 3 5.59 30.9 3 9.97 
18.0 6 7.57 30.9 6 12.97 
18.0 6 7.75 30.9 6 13.31 
18.0 9 8.28 30.9 9 15.19 
18.0 9 8.71 30.9 9 14.83 
18.0 12 8.83 30.9 12 16.39 
18.0 12 9.15 30.9 12 16.13 
18.0 15 9.64 30.9 15 17.69 
18.0 15 10.23 30.9 15 18.10 
 
 
 
 
 
89
Table A.8 Equilibrium moisture isotherm (25
o
C) raw data for poultry litter 
M (%) EMC (%, d.b.) ERH (%) 
10.09 11.22 25.51
10.09 11.22 25.86
10.09 11.22 26.76
13.42 15.50 57.25
13.42 15.50 58.10
13.42 15.50 59.24
17.68 21.48 73.79
17.68 21.48 74.57
17.68 21.48 76.01
23.64 30.96 84.87
23.64 30.96 86.07
23.64 30.96 87.41
26.70 36.43 87.73
26.70 36.43 88.72
26.70 36.43 90.37
30.58 44.05 90.84
30.58 44.05 91.51
30.58 44.05 93.21
 
 
 
 
 
 
 
 
 
 
 
 
 
90
Appendix B. Compaction Data 
 
Table B.1 Poultry litter compaction data set 1 
M (%, w.b.) P (Mpa) ? (kg/m
3
) M (%, w.b.) P (Mpa) ? (kg/m
3
) 
16.5 5.0 765.55 24.2 6.7 963.63
16.5 5.0 807.43 24.2 6.7 1014.47
16.5 5.9 867.90 24.2 7.5 1016.24
16.5 5.9 776.69 24.2 7.5 1036.57
16.5 6.7 920.44 24.2 8.4 1082.56
16.5 6.7 915.96 24.2 8.4 971.02
16.5 7.5 855.58 26.1 5.0 1019.47
16.5 7.5 912.78 26.1 5.0 1008.09
16.5 8.4 927.12 26.1 5.9 1041.50
16.5 8.4 848.59 26.1 5.9 1013.81
21.7 5.0 855.05 26.1 6.7 1084.50
21.7 5.0 887.21 26.1 6.7 1072.47
21.7 5.9 888.99 26.1 7.5 1123.85
21.7 5.9 853.63 26.1 7.5 1038.78
21.7 6.7 982.33 26.1 8.4 1020.24
21.7 6.7 999.23 26.1 8.4 1095.60
21.7 6.7 992.79 29.0 5.0 1120.45
21.7 7.5 1027.08 29.0 5.0 1061.42
21.7 7.5 930.23 29.0 5.9 1102.36
21.7 7.5 948.78 29.0 5.9 1050.14
21.7 8.4 955.10 29.0 6.7 1087.83
21.7 8.4 1046.03 29.0 6.7 1090.94
24.2 5.0 946.72 29.0 7.5 1064.28
24.2 5.0 998.21 29.0 7.5 1121.67
24.2 5.9 934.24 29.0 8.4 1172.17
24.2 5.9 953.57 29.0 8.4 1220.05
 
 
 
 
 
 
 
 
91
Table B.2 Poultry litter compaction data set 2 
M 
(%, w.b.) 
P 
(Mpa) 
? 
(kg/m
3
) 
M 
(%, w.b.) 
P 
(Mpa) 
? 
(kg/m
3
) 
31.7 0.84 842.28 37.7 0.84 791.51 
31.7 0.84 786.97 37.7 0.84 801.85 
31.7 1.7 795.44 37.7 1.7 928.49 
31.7 1.7 783.65 37.7 1.7 980.06 
31.7 2.5 942.46 37.7 2.5 1017.29 
31.7 2.5 887.58 37.7 2.5 985.77 
31.7 3.4 986.02 37.7 3.4 990.04 
31.7 3.4 927.19 37.7 3.4 1010.57 
31.7 4.2 1058.98 37.7 4.2 1080.79 
31.7 4.2 1045.87 37.7 4.2 1072.55 
31.7 5.0 996.70 37.7 5.0 1020.63 
31.7 5.0 996.15 37.7 5.0 1032.45 
31.7 5.9 1047.41 37.7 5.9 1015.22 
31.7 5.9 972.67 37.7 5.9 1036.84 
31.7 6.7 1012.72 37.7 6.7 958.99 
31.7 6.7 1019.09 37.7 6.7 1017.64 
31.7 7.5 1115.38 41.4 0.84 851.57 
31.7 7.5 1050.46 41.4 0.84 826.29 
31.7 8.4 999.57 41.4 1.7 985.38 
31.7 8.4 947.63 41.4 1.7 1007.57 
35.1 0.84 772.76 41.4 2.5 1002.05 
35.1 0.84 805.33 41.4 2.5 1074.68 
35.1 1.7 863.17 41.4 3.4 1061.84 
35.1 1.7 910.75 41.4 3.4 991.68 
35.1 2.5 972.46 41.4 4.2 1024.17 
35.1 2.5 916.53 41.4 4.2 1052.26 
35.1 3.4 1049.62 41.4 5.0 1015.59 
35.1 3.4 1027.69 41.4 5.0 1009.27 
35.1 4.2 1050.46  
35.1 4.2 1035.94  
35.1 5.0 1077.80  
35.1 5.0 1036.57  
35.1 5.9 1087.27  
35.1 5.9 1018.84  
35.1 6.7 1053.00  
35.1 6.7 1079.95  
35.1 7.5 1084.75  
35.1 7.5 1103.66  
35.1 8.4 1159.60  
35.1 8.4 1139.94  
 
 
 
92
Table B.3 Poultry litter compaction data set 1 after 2 months storage 
M (%, w.b.) P (Mpa) ? (kg/m
3
) M (%, w.b.) P (Mpa) ? (kg/m
3
) 
16.5 5.0 746.93 24.2 6.7 751.44
16.5 5.0 744.41 24.2 6.7 871.20
16.5 5.9 722.01 24.2 7.5 793.18
16.5 5.9 705.69 24.2 7.5 805.92
16.5 6.7 914.17 24.2 8.4 874.47
16.5 6.7 906.56 24.2 8.4 773.11
16.5 7.5 844.94 26.1 5.0 766.01
16.5 7.5 839.58 26.1 5.0 747.51
16.5 8.4 859.65 26.1 5.9 811.34
16.5 8.4 728.60 26.1 5.9 815.56
21.7 5.0 707.08 26.1 6.7 858.88
21.7 5.0 797.53 26.1 6.7 844.34
21.7 5.9 638.44 26.1 7.5 908.81
21.7 5.9 824.18 26.1 7.5 873.15
21.7 6.7 834.39 26.1 8.4 854.79
21.7 6.7 776.13 26.1 8.4 869.34
21.7 6.7 824.20 29.0 5.0 846.31
21.7 7.5 873.85 29.0 5.0 842.12
21.7 7.5 790.77 29.0 5.9 846.23
21.7 7.5 728.17 29.0 5.9 829.94
21.7 8.4 813.17 29.0 6.7 927.06
21.7 8.4 808.52 29.0 6.7 892.15
24.2 5.0 817.08 29.0 7.5 864.01
24.2 5.0 626.24 29.0 7.5 865.25
24.2 5.9 795.28 29.0 8.4 917.68
24.2 5.9 788.98 29.0 8.4 922.35
 
 
 
 
 
 
 
 
 
 
93
Table B.4 Poultry litter compaction data Set 2 after 2 months storage 
M  
(%, w.b.) 
P  
(Mpa) 
? 
(kg/m
3
) 
M  
(%, w.b.) 
P  
(Mpa) 
? 
(kg/m
3
) 
31.7 5.0 588.43 37.7 0.84 562.75 
31.7 5.0 716.26 37.7 0.84 559.28 
31.7 5.9 796.31 37.7 1.7 658.59 
31.7 5.9 728.76 37.7 1.7 665.26 
31.7 6.7 731.83 37.7 2.5 674.38 
31.7 6.7 759.10 37.7 2.5 688.53 
31.7 7.5 704.84 37.7 3.4 711.92 
31.7 7.5 820.86 37.7 3.4 740.94 
31.7 8.4 706.11 37.7 4.2 707.52 
31.7 8.4 654.03 37.7 4.2 804.21 
35.1 0.84 561.33 37.7 5.0 737.74 
35.1 0.84 568.15 37.7 5.0 748.91 
35.1 1.7 637.39 37.7 5.9 731.15 
35.1 1.7 625.43 37.7 5.9 703.71 
35.1 2.5 679.17 37.7 6.7 717.43 
35.1 2.5 672.94 37.7 6.7 702.64 
35.1 3.4 775.28 41.4 0.84 588.90 
35.1 3.4 781.47 41.4 0.84 513.86 
35.1 4.2 750.52 41.4 1.7 662.88 
35.1 4.2 744.84 41.4 1.7 694.99 
35.1 5.0 807.39 41.4 2.5 681.26 
35.1 5.0 755.94 41.4 2.5 738.95 
35.1 5.9 821.91 41.4 3.4 736.74 
35.1 5.9 778.71 41.4 3.4 701.75 
35.1 6.7 874.36 41.4 4.2 743.91 
35.1 6.7 777.82 41.4 4.2 749.32 
35.1 7.5 813.69 41.4 5.0 672.36 
35.1 7.5 804.19 41.4 5.0 707.39 
35.1 8.4 767.92  
35.1 8.4 803.27  
 
 
 
 
 
 
 
94
Table B.5 Poultry litter compact?s percent decrease in density after 2 months  
M (%, w.b.) P (Mpa) ?
decrease
 (%) M (%, w.b.) P (Mpa) ?
decrease
 (%) 
16.5 5.0 5.2 31.7 6.7 26.6
16.5 5.9 13.2 31.7 7.5 29.6
16.5 6.7 0.9 31.7 8.4 30.1
16.5 7.5 4.7 35.1 0.84 28.4
16.5 8.4 10.6 35.1 1.7 28.8
21.7 5.0 13.6 35.1 2.5 28.4
21.7 5.9 16.1 35.1 3.4 25.1
21.7 6.7 18.1 35.1 4.2 28.3
21.7 7.5 17.7 35.1 5.0 26.1
21.7 8.4 19.0 35.1 5.9 24.0
24.2 5.0 25.8 35.1 6.7 22.5
24.2 5.9 16.1 35.1 7.5 26.1
24.2 6.7 18.0 35.1 8.4 31.7
24.2 7.5 22.1 37.7 0.84 29.6
24.2 8.4 19.8 37.7 1.7 30.6
26.1 5.0 25.4 37.7 2.5 32.0
26.1 5.9 20.8 37.7 3.4 27.4
26.1 6.7 21.0 37.7 4.2 29.8
26.1 7.5 17.6 37.7 5.0 27.6
26.1 8.4 18.5 37.7 5.9 30.1
29.0 5.0 22.6 37.7 6.7 28.2
29.0 5.9 22.1 41.4 0.84 34.3
29.0 6.7 16.5 41.4 1.7 31.9
29.0 7.5 20.9 41.4 2.5 31.6
29.0 8.4 23.1 41.4 3.4 30.0
31.7 5.0 34.5 41.4 4.2 28.1
31.7 5.9 24.5 41.4 5.0 31.9
 
 
 
 
 
 
 
 
 
95
Table B.6 Breakage force of compacts after 2 months storage 
M  
(%, w.b.) 
P  
(Mpa) 
F  
(N) 
M  
(%, w.b.) 
P  
(Mpa) 
F  
(N) 
31.7 0.84 9.8 37.7 3.4 259.3 
31.7 0.84 23.5 37.7 4.2 277.0 
31.7 1.7 26.6 37.7 4.2 273.3 
31.7 2.5 74.6 37.7 5.0 319.7 
31.7 2.5 65.6 37.7 5.0 269.6 
31.7 3.4 141.7 37.7 5.9 344.1 
31.7 4.2 179.0 37.7 5.9 370.5 
31.7 4.2 168.2 41.4 0.84 127.7 
31.7 5.0 160.5 41.4 0.84 86.9 
31.7 5.0 183.5 41.4 1.7 260.4 
31.7 5.9 213.6 41.4 1.7 308.5 
31.7 5.9 225.1 41.4 2.5 272.2 
37.7 0.84 44.4 41.4 2.5 370.0 
37.7 0.84 50.9 41.4 3.4 414.8 
37.7 1.7 155.5 41.4 3.4 272.9 
37.7 1.7 200.0 41.4 4.2 366.6 
37.7 2.5 266.0 41.4 4.2 336.1 
37.7 2.5 255.6 41.4 5.0 257.2 
37.7 3.4 291.6 41.4 5.0 334.6 
 
 
Table B.7 Specific energy required for compaction of poultry litter 
M (%, w.b.) P (Mpa) E (KJ/kg) M (%, w.b.) P (Mpa) E (KJ/kg) 
16.5 5.0 1.380 35.1 3.4 0.763
16.5 5.9 1.710 35.1 4.2 0.972
24.2 5.0 1.091 35.1 5.0 1.086
24.2 5.9 1.335 35.1 5.9 1.168
26.1 5.0 1.124 37.7 0.84 0.205
26.1 5.9 1.398 37.7 1.7 0.504
29.0 5.0 1.161 37.7 2.5 0.590
29.0 5.9 1.318 37.7 3.4 0.698
31.7 0.84 0.216 37.7 4.2 0.889
31.7 1.7 0.440 37.7 5.0 1.011
31.7 2.5 0.686 37.7 5.9 1.374
31.7 3.4 0.913 41.4 0.84 0.233
31.7 4.2 1.012 41.4 1.7 0.404
31.7 5.0 1.216 41.4 2.5 0.645
31.7 5.9 1.407 41.4 3.4 0.837
35.1 0.84 0.190 41.4 4.2 0.812
35.1 1.7 0.452 41.4 5.0 1.106
35.1 2.5 0.651  
 
96
Appendix C. Flowability Data 
 
Table C.1 Flow function data for poultry litter 
M (%, w.b.) 10.3   18.0   22.1   
?  
(kPa) 
UYS 
(kPa) 
MCS 
(kPa) 
UYS 
(kPa) 
MCS 
(kPa) 
UYS 
(kPa) 
MCS 
(kPa) 
1.5 1.25 3.79 1.93 2.58 1.95 3.91 
1.5 1.91 4.66 2.22 3.83 2.82 6.87
3 1.00 15.63 2.72 7.57 2.80 7.09
3 2.81 7.81 2.11 8.51 1.46 7.67
6 2.72 6.17 2.84 13.85 5.12 13.85
6 3.14 32.93 2.37 13.99 4.36 19.41
9 4.65 32.82 4.19 20.83 6.10 21.15
9 4.12 18.53 3.09 21.48 9.57 22.55
12 5.57 30.45 7.22 31.12 8.04 26.79
12 10.81 36.11 10.18 31.67 9.54 28.97
 
M (%, w.b.) 26.0   30.9   
?  
(kPa) 
UYS 
(kPa) 
MCS 
(kPa) 
UYS 
(kPa) 
MCS 
(kPa) 
1.5 1.79 2.56 1.73 2.62 
1.5 1.00 3.12 1.83 2.92 
3 1.69 6.96 2.97 6.71 
3 2.71 7.92 3.64 7.30 
6 4.84 12.57 6.99 12.47 
6 8.56 14.51 8.35 13.21 
9 6.42 19.79 10.60 20.13 
9 8.00 20.91 17.97 23.92 
12 10.19 25.08 13.05 24.74 
12 8.87 26.19 12.02 28.43 
 
 
 
 
 
 
 
97
Table C.2 Cohesion and angle of internal friction of poultry litter 
? (kPa) 1.5   3   6   9   12   
M  
(%, w.b.) 
c 
(kPa) 
?  
(
o
) 
c 
(kPa) 
?  
(
o
) 
c 
(kPa) 
?  
(
o
) 
c 
(kPa)
? 
 (
o
) 
c 
(kPa)
? 
 (
o
) 
10 0.51 33.74 0.61 41.66 0.84 45.65 0.98 44.30 2.08 47.90
10 0.30 38.55 0.59 44.49 0.20 46.24 1.22 42.69 0.52 53.36
18   0.57 44.56 0.62 42.89 0.93 42.13 2.37 40.07
18 0.72 24.06 0.45 43.88 0.52 42.70 0.65 44.38 1.55 43.50
22 0.27 49.52 0.61 43.16 1.18 40.53 1.30 43.82 1.88 39.89
22 0.49 36.69 0.61 42.84 0.69 54.89 2.07 43.22 2.05 43.47
26 0.49 32.49 0.33 47.25 1.98 40.35 1.84 40.61 1.99 41.67
26 0.20 46.51 0.50 49.44 1.17 38.40 1.43 41.98 2.48 38.07
30 0.37 46.00 0.65 42.65 2.21 34.22 3.94 42.64 2.53 44.35
30 0.44 36.15 0.73 46.28 1.77 36.28 2.57 38.25 3.32 36.06
 
 
Table C.3 Wall friction flow function data and angle of wall friction  
for poultry litter with milled steel 
? (kPa) UYS (kPa) MCS (kPa) ? (
o
) 
12 7.84 18.33 27.27 
9 7.70 16.05 32.07 
6 4.34 8.96 35.43 
3 3.51 3.90 21.66 
1.5 1.68 1.86 8.95 
1.5 1.39 2.43 33.99 
 
 
Table C. 4 Wall friction flow function data and angle of wall friction  
for poultry litter with milled aluminum 
? (kPa) UYS (kPa) MCS (kPa) ? (
o
) 
12 5.38 25.17 32.66 
9 3.51 16.55 35.66 
6 3.55 12.38 45.28 
 
 
 
 
98
Table C. 5 Wall friction flow function data and angle of wall friction  
for poultry litter with mirror finished aluminum 
? (kPa) UYS (kPa) MCS (kPa) ? (
o
) 
12 2.24 16.19 28.13
9 3.70 13.93 34.60
6 2.88 10.19 30.67
3 1.55 5.26 40.24
3 2.33 5.81 28.81
 
 
Table C. 6 Wall friction flow function data and angle of wall friction  
for poultry litter with carbon coated steel 
? (kPa) UYS (kPa) MCS (kPa) ? (
o
) 
12 1.88 17.17 36.97
9 1.64 12.14 29.20
6 1.12 8.07 25.80
 
 
Table C.7 Wall friction flow function data and angle of wall friction  
for poultry litter with mirror finished steel 
? (kPa) UYS (kPa) MCS (kPa) ? (
o
) 
12 2.79 17.87 32.86
12 2.80 17.30 36.17
6 1.90 9.25 36.39
 
 
 
 
 
 
 
 
99
Appendix D. Equipment Photos 
 
 
Figure D.1 Texture analyzer with compression cell and tight fitted piston 
 
 
 
 
 
 
 
 
100
 
Figure D.2 Clamped compaction die filled with poultry litter below a plunger 
attached to the crosshead of the texture analyzer before compaction 
101
 
Figure D.3 Poultry litter compact removed from compaction die 
 
 
 
 
 
 
 
 
 
 
102
 
Figure D.4 Annular shear cell  
 
 
 
 
 
 
 
 
 
 
103
 
Figure D.5 Wall friction samples  
(Top row, left to right: milled aluminum, mirror finished aluminum;  
Bottom row, left to right: milled steel, mirror finished steel, and carbon coated steel)