Characterization of methanogenesis, acidogenesis and hydrolysis in thermophilic methane fermentation of chicken manure

•Thermophilic methane fermentation of chicken manure was studied at 10% TS.•Ammonia inhibition was evaluated by long time operation of continuous experiment.•Methanogenesis was more sensitive to ammonia than acidogenesis and hydrolysis.•Microbial community shifts were characterized by 16S rDNA cloning library.

The thermophilic methane fermentation of chicken manure (CM) with a total solids (TS) of approximately 10% was investigated with regard to ammonia inhibition. A gradual increase in total ammonia nitrogen to 6000 mg/L was observed in the case of raw CM fermentation. A distinct rise in VFA accumulation combined with a low methane production of 0.29 L/gVS occurred at a TAN of 4000 ∼ 5000 mg/L. Biogas production completely ceased when TAN reached 8000 mg/L after the addition of NH4HCO3. The high sensitivity of methanogenesis to TAN and free ammonia (FA) was quantitatively confirmed. The IC50 of TAN for methanogenesis, acidogenesis and hydrolysis was 5058, 5305 and 5707 mg/L at a pH value of 8.1 ± 0.2. Similar results but with a lower IC50 were obtained for FA inhibition during fermentation. The microbial community analysis revealed significant differences in hydrogenotrophic methanogens and aceticlastic methanogens before and after inhibition.

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