Optimum Ratio of Chicken Manure and Napier Grass in Single Stage Anaerobic Co-digestion

This study examined an optimum ratio of chicken manure to Napier grass (Pennisetum purpureum, Schum.) for single stage anaerobic digestion in batch reactor. Carbon to nitrogen (C/N) ratio of chicken manure was 8.22 and Napier grass was 39.35. The anaerobic digestion experiments for 5 ratios of chicken manure to Napier grass of 1:0, 3:1, 1:1, 1:3, and 0:1 were conducted using hydraulic retention time of 48 days and total solids were controlled at 2%. The mixed organic materials of chicken manure to Napier grass of 1:1 achieved a high methane percentage of 64.4% and also remained stable for anaerobic digestion. Single material in anaerobic digestion: chicken manure or Napier grass did not yield maximum methane production. C/N ratio of chicken manure was not suitable for anaerobic digestion because excessive nitrogen could inhibit the growth of methane-forming bacteria. Anaerobic digestion of Napier grass presented low stability due to high VFA accumulation in the system from hydrolysis of cellulose in the grass.