【正文】 環(huán)境生物技術 沈陽大學 07環(huán)境工程 20239gying 3 Activated Sludge Process ? Singlestage process ? Fig. Flow diagram of anactivated sludge plant. 3 Activated Sludge Process ? Singlestage process ? An activated sludge plant is characterized by four elements: ? An aeration tank equipped with appropriate aeration equipment, in which the biomass is mixed with wastewater and supplied with oxygen. ? A final clarifier, in which the biomass is removed from the treated wastewater by settling or other means. ? Continuous collection of return sludge and pumping it back into the aeration tank. ? Withdrawal of excess sludge to maintain the appropriate concentration of mixed liquor. Twostage process ? The twostage process has several advantages. Harmful substances can be removed in the first stage, which is important for the treatment of industrial wastewater。 and in the lowload second stage, due to the high sludge age microanisms can be maintained that are able to remove slowly biodegradable anics or to oxidize ammonia. Furthermore, bulking sludge is only rarely observed in either stage. ? The disadvantages are that about twice as many clarifiers are needed as in the onestage process and that nitrogen removal, as well as enhanced biological phosphate removal, may be inhibited owing to missing anics, which are removed in the first stage. ? Single sludge carbon, nitrogen, and phosphorous removal ? In the early 1960s three different methods for nitrogen removal were demonstrated: ? postdenitrification 。 ? preanoxic zone denitrification 。 ? simultaneous denitrification 。 ? Today most newer plants are built with means for enhanced biological phosphate removal and/or equipment for simultaneous precipitation. ? Sequencing batch reactor (SBR) process ? Because of the development of reliable automatic process control and aeration systems, the SBR process today is a perfect alternative to the conventional activated sludge process. The reactor is usually equipped with an aeration system, a mixing device, a decanter to withdraw treated wastewater, an excess sludge removal device, and the process control system. Wastewater treatment is performed by a time series of process phases (fill, react, settle, decant). As in the conventional activated sludge process, the SBR process is capable of carbon, nitrogen, and phosphorous removal. It is used for both industrial and municipal wastewater . ? Special developments ? Pure oxygenactivated sludge process ? Attached growth material in activated sludge aeration tanks ? Highrate reactors ? Membrane separation of mixed liquor ? Technological and microbiological aspects ? Wastewater characteristics ? Wastewater to be treated can contain anic carbon predominantly as a single soluble substance (., an alcohol), as a mixture of soluble substances, or as a mixture of solids and numerous soluble anic substances. Many industrial wastewaters are mixtures of soluble anic substances, but some may contain mainly one anic substance. Municipal wastewater and wastewater from most food processing industries is always a mixture of soluble and particulate anic matter. ? Microbial degradation of anic carbon requires certain amounts of nitrogen, phosphorous, calcium, sodium, magnesium, iron, and other essential trace elements to grow biomass. In industrial wastewater treatment plants, missing elements have to be added. Since domestic wastewater contains all the necessary elements in excess, it is advantageous to treat special industrial wastewater together with municipal wastewater. ? The concentration of anic matter in wastewater is measured as the biochemical oxygen demand (BOD5, or BOD20, incubation period of 5 or 20 d, nitrification inhibited), chemical oxygen demand (COD), or total anic carbon (TOC). ? Environmental factors ? Dissolved oxygen ? The dissolved oxygen concentration (DO), the pH, and toxic substances in the wastewater are considered as environmental factors that may inhibit the biological reactions. ? Alkalinity and pH ? Toxic substances Thanks! 設備結構 Plant Configurations Typical Tanks for mixing and aeration Mixing tanks for denitrification can be square, rectangular, or circular and have mixers in the center or propellers （螺旋槳） (Fig. ). Rectangular tanks can be visualized as a series of square tanks. In closedloop, tanks either propellers or vertical shaft（軸） impellers（推動器） maintain the circulating flow. Finebubble diffusedair aeration(曝氣 ) systems can be installed in almost any type of tank. Tanks for vertical shaft surface aerators are either square or rectangular in which the length is a multiple of the width (Fig. ). Tanks for cyclic（循環(huán)） aeration are preferably（更好的，更可取的） circular or of closed loop type. Aeration equipment as well as appropriate mixers must be installed. Mixing can also be performed by rotating bridges on which diffusers are mounted. (Fig. ). Since the aeration is switched off cyclically（循環(huán)的） , only nonclogging aeration systems, ., membrane diffusers for fine bubble aeration are appropriate. Simultaneous nitrification and denitrification in practice is performed mainly in closedloop tanks equipped with horizontalaxis（水平的，軸） surface aerators, ., mammoth（巨大的） rotors（旋翼） or vertical shaft surface aerators, as in the carousel（轉盤） process. Simultaneous denitrification can also be performed with air diffusers arranged in ‘ fields’ in closedloop tanks . Carbon removal processes In industrialized countries today, removal of both carbon and nitrogen is increasingly required。