Mesophilic methane fermentation of chicken manure at a wide range of ammonia concentration: stability, inhibition and recovery.

A 12L mesophilic CSTR of chicken manure fermentation was operated for 400 days to evaluate process stability, inhibition occurrence and the recovery behavior suffering TAN concentrations from 2000 mg/L to 16,000 mg/L. A biogas production of 0.35-0.4 L/gVS(in) and a COD conversion of 68% were achieved when TAN concentration was lower than 5000 mg/L. Ammonia inhibition occurred due to the addition of NH4HCO3 to the substrate. The biogas and COD conversion decreased to 0.3 L/gVS(in) and 20% at TAN 10,000 mg/L and was totally suppressed at TAN 16,000 mg/L. Carbohydrate and protein conversion decreased by 33% and 77% after inhibition. After extreme inhibition, the reactor was diluted and washed, reducing TAN and FA to 4000 mg/L and 300 mg/L respectively, and the recovered biogas production was 0.5 L/gVS(in). The extended Monod model manifested the different sensitivities of hydrolysis, acidogenesis and methanogenesis to inhibition. VFA accumulation accompanied an increase in ammonia and exerted a toxic on microorganism.