Balancing of greenhouse gas emissions and economic efficiency for biogas-production through anaerobic co-fermentation of slurry with organic waste

Using the organic fraction of municipal solid waste (OFMSW) for biogas production might contribute to greenhouse gas mitigation, but emissions linked with biogas production can reduce these beneficial effects. Therefore the emissions of NH3, CH4 and N2O and costs caused by treating OFMSW by co-fermentation with slurry were calculated in detail from literature data, and strategies for reducing emissions were evaluated. Emission factors were calculated for single gases during storage and after application. The sensitivity of the calculations concerning the organic dry matter content of OFMSW, retention time and CH4-yield was analyzed. The anaerobic co-fermentation of OFMSW increased biogas yields and contributed to the reduction of CO2 emissions with 32 to 152 kg CO2 t−1 organic waste depending on application and storage techniques used for the fermentation residues. Considering a payment of 0.1 €/kWh for the electricity produced, the costs for utilization of OFMSW in slurry based biogas plants were calculated to range between 34 and 38 € t−1. Measures for mitigating greenhouse gas emissions by covering the fermentation residue stores proved to be more cost effective with 3–31 € t−1 CO2 compared to immediate harrowing or injecting the residues during field application.