Assessment of the effects of anaerobic co-digestion of water primrose and cow dung with swine manure on biogas yield and biodegradability

This study aims to investigate the potential of water primrose for biogas production in batch anaerobic digestion. To examine the ability of co-digestion with other substrates, cow dung and swine manure was chosen to mix with pretreated water primrose in a ratio of 1:1 (w/w, based on dry matter of water primrose). The pretreatment of water primrose was conducted by using sodium hydroxide at 2% concentration for one week. A modified Gompertz equation was employed to estimate parameters, including estimated biogas yield potential (Ym), maximum biogas production rate (Rm), and duration of lag phase (λ). The equation showed a good approximation of cumulative biogas production with a coefficient of determination (R2) over 0.997. The overall results indicate that all treatments had successfully produced biogas production in the range of 4285 to 6150 mL with methane (CH4) content above 50%. The maximum biogas yield of 6150 mL was obtained at co-digestion with cow dung and high methane content of 63.88%. This value was given 25.50 MJ/m3 for high calorific value (HCV) and 22.97 MJ/m3 of low calorific value (LCV).