Anaerobic digestion is a common terminal step in wastewater treatment systems and produces valuable by-products such as biogas, a combination of carbon dioxide and methane. Biogas can be used to off-set energy costs, and along with the anaerobic co-digestion of fats, oils, and greases (FOG) has been found to increase biogas production and enables some plants to become self-sufficient and a net-exporter of energy.
Operational difficulties, such as ammonia inhibition, can prevent treatment plants from implementing anaerobic digestion. This is due to high concentrations of FOG, which includes protein, that produce ammonia at levels that may be inhibitory to the anaerobic digestion process. While ammonia is not harmful to the system in quantities smaller than 2500 mg TAN/L, concentrations larger than that can lead to inhibition.
Two different lab-scale facilities were used to seed the batch bottle experiments. One from Gresham, OR which has used FOG successfully for years and the other from Corvallis, OR which has never been exposed to FOG. The digestate was put into batch bottles in five different conditions: control, volatile fatty acid control, +500 ppm NH 4 + , +1000 ppm NH4 + , and + 1500 ppm NH4 + . Anaerobic digestion activity was monitored through daily biogas volume measurements and methane composition measurements. The results found that while the ammonia levels of the digestate were comparable, the biogas production from the Gresham digestate was much higher. These results provide insight into how ammonia inhibition, and methane production, are affected by FOG co-digestion.
Funding Statement (additional comments about funding)
This work is supported by the USDA NIFA Higher Education MSP, grant number 2016-38413-25323/project accession number .1009828, from the U.S. Department of Agriculture, National Institute of Food and Agriculture. As well as the USDA NIFA AFRI EWD REEU project grant no. and project accession no. 2020-67037-30670/1021806. It is also supported by the National Science foundation -NSF CAREER Award #1847654.