Limiting factors for biogas production from cow manure: energo-environmental approach

The main innovation of the study is the use of a novel energo-environmental approach for investigation of biogas production, and analysis of the amount of methane and biogas produced in terms of energy production and global warming potential (GWP). Two types of reactors (laboratory-scale and semi-industrial reactors) were prepared for biogas production to perform a detailed study and for exact consideration of treatments in terms of production. Based on the results, the maximum methane production in the laboratory-scale set-up was related to a carbon/nitrogen (C/N) ratio of 30 at mesophilic temperature (35,967 ml/kg volatile solids). Accordingly, the C/N ratio in the semi-industrial reactor was considered to be 30; methane production was equal to 14/489m3 at loading rates of 237.5, 2.580 and 234.92 kg for cow manure, wheat straw and water content, respectively. The maximum biogas production occurred on day 65, from the viewpoint of energetic analysis. The highest daily net electricity production occurred on day 12, with a positive energy balance. However, considering GWP effects in the production and use of biogas, it would be better to stop production on day 48, in which case methane production would be equal to 77% of the final limit of biogas production.