Dry Anaerobic Digestion of Fresh Feedyard Manure: A Case Study in a Laboratory Setting

Recently, Dry Anaerobic Digestion (DAD) of solid manure has acquired increasing interest because of its robustness, flexibility, and cost-effectiveness over conventional anaerobic digestion system. A laboratory scale DAD system was fabricated, used with feedlot manure and inoculum mix at a ratio of 2:1, and was evaluated for a 40 day hydraulic retention time (HRT) under a 35±2 C digestion temperature. The main constituents of biogas identified and quantified were CH4, carbon dioxide (CO2), and nitrous oxide (N2O). The share of CH4, CO2, and other gases including N2O were 62.3, 36.3, and 0.41% of the total biogas produced, respectively. Average daily biogas yield was 0.575 L per day over a 40 day hydraulic retention time (HRT). Biogas gas production from feedlot manure also found to be varied with digestion temperature fluctuations. Initially, CO2 amount produced was higher than CH4. Later on, amount of CH4 gas production was increased over CO2 as the experiment was continued. Average concentrations of CH4 and CO2 over a period 40 day HRT were 49%, and 44%respectively. Average daily CH4 yield was 0.359 L per day based on 40 day HRT. The feedlot manure showed a VS removal of 27.4 % over 40 day HRT. Estimated specific biogas and CH4 yield were 0.053 and yield of 0.0337 L g-1 of VS removed.