Evaluation of an anaerobic system for treating poultry mortalities

An anaerobic digestion system was evaluated as an alternative for poultry mortality disposal. The bench-scale system consisted of an upflow anaerobic sludge blanket (UASB) reactor and three leachbeds (LB). The LBs were batch-loaded with dead chickens and sequentially starred at an average interval of 50 days. Only one LB was connected to the UASB to form a closed-loop at any one time. Leachate from the LB was fed to the UASB as influent while effluent from the UASB overflowed to the LB to maintain constant liquid volumes in both reactors. The LB-UASB pair initially functioned as a two-phase system, with the LB serving as the hydrolysis/acidification phase and the UASB serving as the methanogenic phase. Through repeated liquid recycle between the LB and the UASB, the LB eventually accumulated enough methanogens to become methanogenic as well. Leachate concentrations from the methanogenic LB dropped rapidly. When the leachate was no longer able to sustain the UASB at high loading rates (LR), the next LB with another dead chicken was connected to the UASB. Digestion of the mortality was considered complete when methane production rate from the off-line LB became marginal. When digestion in an LB was complete, the fermentation fluid in the LB was reused to start up the next LB. The first cycle ended when digestion in the third LB was complete. Two cycles were completed during this study. The system satisfactorily completed treatment of seven consecutive batches of mortalities in 432 days. The average CH4 yield was 0.679 m(3) (kg dry)(-1) for 0.254 m(3) (kg wet)(-1)]. However timings of the start-up of an LB anti 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 reactor would simplify restarting of an LB from its preceding LB being terminated Cost estimates based on systems with one UASB and five LBs ranged from US$118 (10(3) kg live wt sold)(-1) for a 10,000 bird poultry farm to US$28 (103 kg live wt sold)(-1) far a farm with 100,000 chickens.