| More than 120 dry million tons of nutrient-rich animal wastes is annually produced in the U.S., which causes a series of negative environmental consequences such as odor problem, greenhouse gas emission and ground water/surface water contamination. Anaerobic digestion (AD) is one of the widely accepted animal manure management technologies that can not only control odor but also generate renewable energy biogas. Anaerobic digestion technology has advantages of robustness, feedstock flexibility, relatively simple implementation, and low capital investment in treating high-strength organic wastes. However, it is also challenged by: 1) liquid digestate has relatively high levels of chemical oxygen demand and nutrients (phosphorus and nitrogen); 2) more than 50% of carbon is still remained in the solid digestate; 3) biogas has high contents of impurities such as H2S, which requires a complicated purification prior to further uses for energy production; and 4) a relatively large quantity of CO2 in the biogas reduce the energy value of biogas and decrease the efficiency of biogas energy production. Therefore, in order to advance the application of anaerobic digestion, the goal of this study is to apply systems approaches to develop an integrated process to address the aforementioned challenges and explore alternative value-added outputs from AD. The integrated process includes anaerobic digestion of animal wastes, electrocoagulation, algal cultivation, and fungal culture for fine chemical production and CO2 utilization. Anaerobic digestion first utilizes some nutrients in animal waste to produce methane. The liquid digestate from anaerobic digestion was then treated by electrocoagulation to reclaim water. Biogas was also incorporated into the electrocoagulation to facilitate water reclamation, removal of impurities (e.g. H2S) from biogas and to improve energy efficiency. Algal cultivation was applied on the reclaimed EC water to further remove nitrogen, fix CO2, and accumulate lipid-rich algal biomass. A fungal fermentation was applied on solid digestate using the EC treated liquid digestate as the processing water to produce a value-added biopolymer -- Chitin. In addition, this study also conducted an in-depth investigation on using CO2 derived formate as both carbon and energy sources to simultaneously sequester CO2 and enhance fungal lipid accumulation. With successful completion of the study, an environmental friendly and economically feasible animal waste utilization concept has been elucidated. Consequently, implementing such system could make a major contribution to realizing sustainable animal agriculture in the near future. |
