Biochar Addition in High-Solids Anaerobic Digestion of Poultry Litter

Methane produced from anaerobic digesters can be used as a renewable off-grid energy source. Poultry litter has a high methane production potential and is an abundant resource. However, it is a troublesome feedstock for methane generation due to its high nitrogen content and low moisture. In this study the impact of biochar addition on high-solids anaerobic digestion of poultry litter was investigated at three feedstock (poultry litter) to inoculant (wastewater treatment plant sludge) (F/I) ratios. The addition of biochar reduced the lag time before significant methane production commenced. The lag time for digesters with biochar decreased by 52% to 9.3 days at an F/I of 0.5, the lowest F/I ratio used. At an F/I of 2, the highest ratio used, the lag time was decreased by 53% to 14.3 days for digesters with biochar. However, the addition of biochar could not overcome ammonia inhibition and did not increase the 90-day methane yield significantly. The maximum 90-day methane yield for digesters with biochar ranged from 57.1 mL/g volatile solids (VS) to 61.8 mL/g VS, while the maximum 90-day methane yield from control digesters ranged from 55.7 to 63.5 mL/g VS. The addition of biochar appears to improve anaerobic digester performance via interactions between microorganisms and biochar, as opposed to ammonia adsorption or an increased acid-buffering capacity.