Study On Domestic Wastewater Treatment By High-Rate Anaerobic Hybrid Reactor

Study on domestic wastewater treatment by high-rate anaerobic biotechnology has been a hot topic. It has certain potential and practical value for the treatment of decentralized wastewater in less developed regions and villages for its high performance, low cost, easy operation and maintenance.To carry out applied research on wastewater treatment by high-rate anaerobic biotechnology, a set of high-rate anaerobic hybrid reactor with an effective volume of 20.3 liters was designed and processed. In this paper, the research was carried out with three objectives: the investigation of proper methods for its start-up, the characteristics of anaerobic granular sludge and determination of optimal parameters for its efficiency, using simulative domestic wastewater and domestic wastewater as substrate. The main research results are as follows:(1)This reactor was designed based on the inner-circulation anaerobic reactor, however, the increase of height-to-diameter ratio and circulation of outer water system made the reactor endurable for higher hydraulic surface loading, so microbes could fully contact with substrate. The setup of packing layers in the top part of reactor could dramatically improve the ability of granular sludge retention and maintain its high concentration and bioactivity of sludge.(2)The anaerobic granular sludge was cultivated through three stages, during which different strategies were taken for certain purposes. In the reactor, the sludge diameter augmented dramatically. At the first stage, the reactor was inoculated with the percentage of 87.27% of total sludge whose size is smaller than 0.18mm.At the second stage, 53.69% of total sludge size was larger than 0.425mm. At the third stage, the sludge size distribution reached a steady level and 83.66% of the total was lager than 0.425mm.(3)With the augment of sludge size, the content of bioactive substance of sludge and mechanical strength dramatically increased and settlement performance also was improved greatly with wet density increasing a bit accordingly. Specific methanogenic activity (SMA) with a mixture of glucose, sodium acetate and peptone showed a significant increase with sludge size, suggesting better establishment of syntrophic relationship in larger granular sludge. The SMA tested in dynamic experiment was 23%～85% higher than that in static experiment for sludge with the same size, showing that better hydraulic condition is favorable for sludge activity.(4)Single factor test was carried out to study the effect of temperature, HRT and circular flow on COD_Cr removal efficiency, using synthetic wastewater of 400～600mg·L^-1 as substrate. In the first experiment, with HRT set as 3h and circular flow 48±1L·h^-1,when the temperature rise to 34±1℃, average removal efficiency of COD_Cr reached 94.04%.In the second experiment, temperature was set as 34±1℃and circular flow 48±1L·h^-1,when HRT was 3h, average removal efficiency of COD_Cr could get 93.39%.In the third experiment, temperature was set as 34±1℃and HRT 3h,when circular flow was 32±1L·h^-1, average removal efficiency of COD_Cr could get 93.27% and COD_Cr concentration outflow was below 50 mg·L^-1. It was also shown that the higher circular flow was, the higher the average removal efficiency was to some extend, however, it was not economical. (5) In the forth experiment, HRT was set as 3h with temperature 34±1℃and circular flow 32±1L·h^-1, the reactor was applied to treat domestic wastewater for a month, COD_Cr removal efficiency was 42%～64%. When circular flow was increased to 48±1L·h^-1 gradually, removal efficiency rise to 68%～75% and COD_Cr concentration outflow was 100～150 mg·L^-1 steadily.