Anaerobic digestion of kitchen wastes in a single-phased anaerobic sequencing batch reactor(ASBR) with gas-phased absorb of CO2

The performance of the single-stage anaerobic digestion of kitchen wastes was investigated in an anaerobic sequencing batch reactor(ASBR) with gas-phased absorb of CO2. The ASBR was operated at four chemical oxygen demand(COD) loading rates, 2.8, 5.1, 6.2 and 8.4 g/(L x d) respectively. The COD loading rate was increased with the TS concentration and HRT changing. At maximum COD loading rate of 8.4 g/(L x d), the COD, total solid(TS) removal rate and methane gas yield were 69%, 68% and 2.5 L/(L x d) respectively. The operation of the reactor with gas-phased absorb of CO2 was stable in spite of the low pH (2.6-3.9) and high concentration of TS (142 g/L) of input mixture. The output volatile fatty acid(VFA) concentration was between 2.7-4.7 g/L and had no inhibition on the methanogenic microorganism. The reactor without gas-phased absorb of CO2 became acidified when the total COD loading rate was increased to 5.1 g/(L x d). Stoichiometry of the methanogenesis for kitchen wastes showed a considerable amount of alkaline will be required to keep pH in the appropriate range for the methanogenic microorganism based on theoretical calculation. Gas-phased absorb of CO2 effectively reduced the alkaline consumption, hence avoided excessive cation into the reactor.