Optimizing feeding composition and carbon–nitrogen ratios for improved methane yield during anaerobic co-digestion of dairy, chicken manure and wheat straw

This study investigated the possibilities of improving methane yield from anaerobic digestion of multi-component substrates, using a mixture of dairy manure (DM), chicken manure (CM) and wheat straw (WS), based on optimized feeding composition and the C/N ratio. Co-digestion of DM, CM and WS performed better in methane potential than individual digestion. A larger synergetic effect in co-digestion of DM, CM and WS was found than in mixtures of single manures with WS. As the C/N ratio increased, methane potential initially increased and then declined. C/N ratios of 25:1 and 30:1 had better digestion performance with stable pH and low concentrations of total ammonium nitrogen and free NH3. Maximum methane potential was achieved with DM/CM of 40.3:59.7 and a C/N ratio of 27.2:1 after optimization using response surface methodology. The results suggested that better performance of anaerobic co-digestion can be fulfilled by optimizing feeding composition and the C/N ratio.

► Co-digestion of multi-substrates, dairy, chicken manure and wheat straw was conducted.
► Anaerobic co-digestion was optimized by feeding composition (DM/CM) and C/N ratio.
► Higher synergetic effect showed in mixed DM, CM and WS than single manure with WS.
► C/N ratios of 25:1 to 30:1 resulted in stable pH, low ammonium nitrogen and free NH3.
► Maximize methane potential realized with DM/CM of 40.3:59.7 and C/N of 27.2:1.