Characterization of Poultry Litter for Storage and Process Design

Abstract

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 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 25oC) 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.