Study On Performance Of Circulated Moving Carrier Biofilm Reactor

Moving Bed Biofilm Reactor (MBBR) is a new and efficient biofilm reactor for wastewater treatment and has shown many advantages. However, the carrier movement in MBBR is not homogeneous, which results in a large dead space. A new reactor called Circulated Moving Carrier Biofilm Reactor (CMCBR) was designed by changing the operation manner and reactor configuration of MBBR. By theoretical analysis and experimental research, following conclusions could be drew:(1) The experimental test with tap water indicated that the flow pattern of CMCBR was similar to that of the ideal completely mixed reactor. The physical and chemical characters in different region were almost the same.(2) The reactor configuration, the ratio of carrier volume to total volume and the aeration mode had large influence on the hydraulic characteristics of CMCBR.The circulation and mixing state in the reactor were shown to relate with the gas flow rate, the gap between the board and the bottom of reactor and the liquid height above the board. After all the factors were taken into account, 250mm was recommended for both the gap between the board and the bottom of reactor and the liquid height above the board. 2 to 3 was suggested for the ratio of the raising area to down-coming area.With increase of the ratio of carrier volume to total volume, oxygen transfer coefficient gradually became larger. After the effect of carrier volume on circulation rate and reactor investment was considered, 50% was suggested for the ratio of carrier volume to total volume.With increase of oxygen supply, the use of oxygen was improved. But a strong aeration led to a decrease of oxygen utilization ratio. The suitable ratio of gas flow rate to water flow rate was about 10:1.(3) Hydraulic retention time (HRT) is one of the key parameters which have effect on removal efficiency. When HRT was set at 2 hours, 3 hours and 4 hours, respectively, the COD removal was 71.7%, 84% and 87.7%. The suitable HRT was 3 hours after both the reactor efficiency and economical factor were considered.(4) CMCBR was suitable to treat domestic wastewater. When the COD concentration was 320-650mg/l and HRT was 4h, the COD removal efficiency was about 87.7%, and the effluent COD concentration was less than 100mg/l, which satisfied the national standard for wastewater discharge.The reactor had a high toleration to COD loading shock and it could keep the effluent quality stable.(5) Compared with other biofilm reactors, the biomass in CMCBR was low, and the high efficiency resulted from the high microbial activity.