Research On Two-phase Anaerobic Digestion For The Treatment Of Municipal Biowaste

The municipal biowaste including kitchen waste, vegetable waste and municipalsludge is difficult to be treated in traditional disposition process due to its highly contentof water and organic materials. In this study, treatment of municipal biowaste throughtwo-phase anaerobic digestion in high efficiency was researched.The phase separate process was successfully carried out in acidogenic phase underthe condition of HRT=5d and OLR=20kgVS·（m³·d）^-1through dynamics method.Under this condition, the acidogenic phase would form ethanol-type fermentation orbutyrate-type fermentation, but would not form propionic-type fermentation Inethanol-type fermentation, ethanol and acetic acid accounted for more than80%of thefermentation products with no biogas production, and no organic matter was removed,24.7%of VSS turned into VDS. In butyrate-type fermentation, acetic acid and butyrateaccounted for more than80%of the fermentation products,19.7%of the organicmatters were removed to product CO2and H2with a volume H2production rate about1.03m³H2·（m³·d）^-1. So ethanol-type fermentation would be better than propionic-typefermentation for the purpose of producing CH4.The fermentation type of acidogenic phase can be changed through controlling thepH value. When the pH value is within4.0-4.5, ethanol-type fermentation could occur;when the pH is within5.0-5.5, butyrate-type fermentation could occur.Fermentation types of acidogenic phase has great influence on gas production ofmethanation phase. Ethanol-type fermentation products can be quickly degraded inmethanation phase, the biogas producing rate declined linearly; butyrate-typefermentation products degrade slow in methanation phase, the biogas producing raterose at first, then declined and keep steady to a certain level.After hydrolysis and acidification in the acidogenic phase, the performance ofmunicipal biowaste in methanation phase was carried out. In methanation phase, the pHwas above7.5within the OLR of6.1^-11.2kgVS·（m³·d）^-1, there was no risk ofacidification. The butyrate-type fermentation products can reach a methane producingrate of0.56m³CH4·kgVS^-1, while the organic removal rate reached57.5%; the Ethanol-type fermentation products can reach a methane producing rate of0.63m³CH4·kgVS^-1, while the organic removal rate reached66.1%, the overall organicremoval rate in two-phase process is higher than65%..A pilot scale two-phase anaerobic digestion reactor was successfully built up.Butyrate-type fermentation occurred in the acidogenic phase. The overall organicremoval rate reached68.0%and the methane producing rate reached0.48m³·kg VS^-1,the hydrogen producing rate reached0.05m³·kg VS^-1.