| With the rapid progress of urbanization and industrialization, problems of high density organic wastewater pollution have become increasingly serious, how to treat this kind of wastewater has become the hot topic. Two-phase anaerobic process is an economical method to treat organic wastewater, up-flow anaerobic sludge bed(UASB) is the most frequently used reactor in the process of anaerobic biological treatment. Based on the superiority of UASB in treating organic wastewater, the difficulty to treat high density organic wastewater and the fossil fuel crisis currently, in-depth study on characteristics of producing acid and ethanol as well as the effect of hydrogen and methane recovery in treating high density organic wastewater under changing volumetric loading rate and pH using new two-phase UASB process was carried out, possibility of forming of ethanol-type fermentation under current researches and effect of start-up of two-phase anaerobic process were researched. Characteristics of the main bacterial colonies of sludge in two-stage UASB process were analyzed by fluorescence in situ hybridization(FISH). The main results are as follows:(1) In the study of effect of changing VLR on characteristics of producing acid and ethanol as well as the effect of hydrogen recovery in treating high density organic wastewater with a single-phase UASB, when the influent VLR was respectively 18 、 24 and 36kgCOD/(m3·d), the yield of butyric acid was the highest one of all organic acids. When VLR was 48kgCOD/(m3·d), the yield of propionic acid was the highest, the average yield of ethanol reached to its maximum value of 142.98mg/L, the average hydrogen production rate reached to its highest value of 887mL/d, the COD removal rate decreased to 13%. Butyric-type fermentation was easier to be formed than ethanol-type fermentation under conditions that were said to be in favor of forming ethanol-type fermentation. The best operating condition for acidogenic phase was at the VLR of 36kgCOD/(m3·d) while the corresponding HRT was 2h, the main microorganisms in UASB at last were Clostridium.(2) In the study of the influence of changing p H on metabolism in acidogenic phase under a low pH, during the process of regulating pH from 4.2 to 4.9 in single-phase UASB, butyric acid was always the main liquid product, concentration of propionic acid and valeric acid increased first and then decreased, concentration of acetic acid had been increasing and concentration of ethanol had been keeping fluctuant near 100mg/L. When pH in UASB was about 4.2, the biogas production rate was high. After the elevation of pH, the COD removal rate decreased, the relative abundance of bacteria and Clostridium in sludge reduced and the relative abundance of archaea and enterobacteriaceae increased. The fluctuation of pH did not change the major metabolic pathway from producing butyric acid to producing ethanol, the best pH for the acidogenic phase of producing acid and hydrogen was about 4.2.(3)When the acidogenic phase UASB and the methanogenic phase UASB were connected to form a two-phase anaerobic process, and the two-stage UASB process operated steadily, in the methanogenic phase UASB, the maximum biogas production rate was 740 m L/d, the maximum methane production rate was 545mL/d, the highest COD removal rate was 98%. The average energy recovery rate in second-stage UASB was 58.62%, average energy recovery efficiency of whole process was 59.4%. When the methanogenic phase was acidified, the relative abundance of bacteria, archaea, butyrate-oxidizing acetogenic bacteria Syntrophomonas spp. and propionate-oxidizing acetogenic bacteria Syntrophobacter wolinii were respectively 67.67%, 32.33%, 48.64% and 10.54%. When the process ceased, the relative abundance of various microorganisms above were 37.78%, 62.22%, 21.09% and... |
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