Abstract
Effects of the hydraulic retention time (HRT) and loading rate on thermophilic methane fermentation of the organic fraction of municipal solid waste (OFMSW) were investigated by using a semi-continuous flow completely-mixed reactor. The experiment was conducted at a temperature of 55 °C and a constant influent TS level of 10% by changing the HRT from 5 days to 30days. The results indicate that the HRT of thermophilic digester could be shortened to 5 days without significant decrease in both the organic matter degradation and methane production, and that the digester was successfully operated at the high loading rate up to 31 kg-CODCr·m-3·d-1. The removal efficiencies of TS, VS and total CODCr were, respectively, in the ranges of 73-78%, 76-78%, and 72-75%, and 1 kg of influent TS produced about 0.75 m3 of digestion gas with the methane content of 57-59%. The Stoichiometric formula of the methane fermentation of OFMSW was identified as: C17H29O10N + 6.5H2O → 9.25CH4 + 6.75CO2 + NH4+ + HCO3-, which is in accordance with the experimental results of this study. The first-order reaction was found suitable for describing the degradation of the OFMSW, and kinetic constants for TS, VS and total CODCr were summarized in a table. It is suggested that the applicable HRT for the high-solids digestion of OFMSW could be shortened to at least of 7.5 days, corresponding to the CODCr loading rate of 20 kg-CODCr·m-3·d-1, by adding mineral nutrient to the feed. In addition, the relationships between HRT and various operation parameters were determined quantitatively based on the experimental results.
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