Ammonia Removal During Food Waste Anaerobic Digestion to Increase Energy Generation and Reactive Nitrogen Recovery
Mentor: Dr. Stefan Grimberg
Department: Civil and Environmental Engineering
As part of Clarkson University’s commitment of reducing its carbon footprint the university has installed an anaerobic digester treating its cafeteria waste to generate biogas and a fertilizer for its grounds - thus avoiding landfilling while generating energy. Our preliminary lifecycle assessment research has shown the critical environmental value associated with the use of digester products to displace these fuels and fertilizers. However, there is a trade-off: nitrogen in the digestate is valued as fertilizer for land application, but its ammonia form is inhibitory to methane producing bacteria, thereby reducing biogas production. In previous research, we observed that reducing total ammonia nitrogen (TAN) from 4500 to 2500 mg/L resulted in an 80% increase in methane production. The objective of this project is to evaluate in the laboratory passive TAN removal processes. Reduction of TAN is expected to increase biogas production, while the recovered ammonia can be sold separately or custom blended with digester effluent to meet agricultural needs. Processes under consideration are membrane separation of ammonia, ammonia sorption to highly specific media or precipitation. Using a cation exchange membrane TAN recovery resulted in a 50% more methane production compared to the control digester. Long term membrane performance, however, still will need to be assessed. Overall, the preferred process will require minimal chemical/energy input while retaining TAN nutrient value.