Promoting Nitrification in Poultry Processing Wastewater Treatment Using Microalgae and Biochar
Type of DegreeMaster's Thesis
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The exponential growth of the global population poses a need for more sustainable food production and waste remediation tactics. Waste-to-resource food production systems such as aquaponics and “poultry-ponics” may be the solution to this problem. Nitrogen-rich wastewaters from animal production systems can be used as irrigation waters for crop production when treated correctly. Because nitrate is the preferred form of nitrogen for plant growth, and ammonium is toxic to most organisms, nitrification is key to making these wastewaters suitable for plant production. The presence of algae can promote nitrification in wastewater treatment when ammonium concentrations are non-limiting. The prevailing hypothesis for this promotion is algae’s provision of a hyper-oxic environment through photosynthetic oxygenation. Preliminary data from our lab has shown evidence of nitrification promotion even in intensely aerated systems, which poses the question: are there other mechanisms by which algae promote nitrification? Objective 1 of this master’s research project devised and tested additional hypotheses for possible mechanisms. The experiments concluded that algal provision of dissolved oxygen alone is not enough to explain the nitrification promotion effects of algae. Across all experiments, the nitrate level in the supplemental oxygen treatment was never significantly greater than the control (p > 0.15). It was observed that algal extracellular excretions may play a role in this promotion. In one experiment, the algal “Spent Medium” produced nitrate concentrations of ~3X the control (p = 0.002). More isolated experiments need to be conducted in order to conclude this definitively. Further understanding of the relationship between nitrifying bacteria and microalgae could directly inform the design of sustainable food production systems such as poultry-ponics and optimize the nutrient transformation in these systems. The addition of biochar could promote interaction between algae and nitrifying bacteria by providing a solid substrate for colonization. Biochars are very easily “engineered” based on the needs of the user. So, their properties can be optimized for the wastewater treatment process. Objective 2 of this research evaluates the efficiency of two different biochars in terms of nitrification promotion. It was found that the Low Cation Exchange Capacity (CEC) Biochar had the ability to promote nitrification in poultry processing wastewater. The culture containing Low CEC Biochar was capable of producing 10X the amount of nitrate as the control culture (p = 0.002). This was true with and without the addition of algae. This research will hopefully inform the future implementation of nutrient transformation systems and encourage the use of biochar as a nitrification-promoting substrate.