Effects of anaerobic digestion and aerobic treatment on the reduction of gaseous emissions from dairy manure storages

Effects of anaerobic digestion and aerobic treatment on the reduction of gaseous emissions from dairy manure storages were evaluated in this study. Screened dairy manure containing 3.5% volatile solids (VS) was either anaerobically digested or aerobically treated prior to storage in air-tight vessels. Anaerobic digestion was carried out using a mesophilic anaerobic sequencing batch reactor operated at a hydraulic retention time of 20 days and an organic loading rate (OLR) of 1 gVS/(L times d). Aerobic treatment was achieved using an aerobic reactor operated at a hydraulic retention time (HRT) of 10 days and an OLR of 2 gVS/(L times d). The treated manure was put into the storage on a daily basis for a period of 180 days. All the gases produced during this period were captured and analyzed for methane, carbon dioxide and volatile organic compounds (VOCs). Untreated manure was stored and analyzed in the same way as the treated manure and used as a control for comparison. The results show that low amounts of gases were produced during the first 84 days of storage in both treated and untreated manure, but increased significantly after this time point. The generally expected positive impacts of anaerobic and aerobic treatment on the reductions of methane and VOCs were confirmed in this study. However, the effects of anaerobic and aerobic treatment varied over the time of storage, especially for VOCs. The results of this study indicate that to achieve significant reductions in VOC emission the storage time of anaerobic digester or aerobic reactor effluent should be limited to no more than 100 days.