EVALUATION OF AN ANAEROBIC SYSTEM FOR TREATING POULTRY MORTALITIES

Abstract

An anaerobic digestion system was evaluated as an alternative for poultry mortality disposal. The bench-scalesystem consisted of an upflow anaerobic sludge blanket (UASB) reactor and three leachbeds (LB). The LBs were batch-loadedwith dead chickens and sequentially started at an average interval of 50 days. Only one LB was connected to theUASB to form a closed-loop at any one time. Leachate from the LB was fed to the UASB as influent while effluent from theUASB overflowed to the LB to maintain constant liquid volumes in both reactors. The LB-UASB pair initially functionedas a two-phase system, with the LB serving as the hydrolysis/acidification phase and the UASB serving as themethanogenic phase. Through repeated liquid recycle between the LB and the UASB, the LB eventually accumulatedenough methanogens to become methanogenic as well. Leachate concentrations from the methanogenic LB droppedrapidly. When the leachate was no longer able to sustain the UASB at high loading rates (LR), the next LB with anotherdead chicken was connected to the UASB. Digestion of the mortality was considered complete when methane productionrate from the off-line LB became marginal. When digestion in an LB was complete, the fermentation fluid in the LB wasreused to start up the next LB. The first cycle ended when digestion in the third LB was complete. Two cycles werecompleted during this study. The system satisfactorily completed treatment of seven consecutive batches of mortalities in432 days. The average CH 4 yield was 0.679 m 3 (kg dry) 1 [or 0.254 m 3 (kg wet) 1 ]. However, timings of the start-up of anLB and its subsequent connection to the UASB need to be improved to sustain the system at peak treatment efficiency.Alternatively, the system could include a fourth LB to allow more flexibility in scheduling. Additionally, a fifth LB reactorwould simplify restarting of an LB from its preceding LB being terminated. Cost estimates based on systems with oneUASB and five LBs ranged from US$118 (10 3 kg live wt sold) 1 for a 10,000 bird poultry farm to US$28 (10 3 kg live wtsold) 1 for a farm with 100,000 chickens.