Effects of Hydraulic Retention Time and Loading Rate on High-Solids Thermophilic Methane Fermentation of the Organic Fraction of Municipal Solid Waste

摘要

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 ℃ 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 3l kg-COD_cr ·m~(-3)· d~(-1). The removal efficiencies of TS, VS and total COD_cr were, respectively in the ranges of 73-78, 76-78, and 72-75, and 1 kg of influent TS produced about 0.75 m~3 of digestion gas with the methane content of 57-59. The Stoichiometric formula of the methane fermentation of OFMSW was identified as: C_17 H_29O_10N + 6.5H_2O → 9.25CH_4 + 6.75CO_2 + NH_4~+ ＋ HCO_3~-, 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 COD_cr 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 COD_cr loading rate of 20 kg- COD_cr·m~(-3)· d~(-1), by adding mineral nutrient to the feed. In addition, the relationships between HRT and various operation parameters were determined quanti