Methane and carbon dioxide emissions from simulated anaerobic swine manure treatment lagoons under summer conditions

Most estimates of carbonaceous gas emissions from manure treatment lagoons are based on biogas production from anaerobic digesters, gases collected over covered lagoons, or the CH4 production potential of animal waste. More data from direct measurements are necessary for evaluating mitigation strategies. Researchers at Oklahoma State University have successfully operated a pilot-scale bioreactor consisting of four 270 L columns that recreate environmental conditions found in anaerobic lagoons as indicated by color, temperature, pH, and electrical conductivity (EC). The columns were loaded at a surface organic loading rate similar to lagoons treating manure from commercial swine farms in the state of Oklahoma (935 kg VS/ha-day). The simulated mid-to-late summer CH4 emission rate was determined to range between 200 and 300 kg/ha-day, and the CO2 emission rate ranged between 380 and 580 kg/ha-day. Approximately 65% of the total carbon applied to the surface of the lagoon simulator was recovered as CH4 and CO2 gases; however, lagoon methane production was greater than expected using chemical oxygen demand (COD) as a predictive standard. The daily patterns of gaseous emissions and volatile organic acid concentrations in the liquid suggest that CH4 production takes place across the entire depth of the reactor. Easily digestible organic matter is converted in the upper layers; more slowly digested material settles and is converted at the sludge layer. Data on day versus night emissions show that biogas had a higher proportion of CO2 during the day than during the night.