Information on biological contact oxidation operation and management

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This post was last written by li* Edited by ch1968 on 2010-8-30 20:33 (1) Characteristics of the contact oxidation method 1) Compared with other biological treatment methods, the contact oxidation method has the following characteristics: high BOD volume load, large sludge biomass, relatively high treatment efficiency, and strong adaptability to incoming water impact load (hydraulic impact load and organic concentration impact load). The treatment time is short. Therefore, under the condition of treating the same amount of water, the required equipment is smaller, so it occupies a small area. It can overcome the problem of sludge expansion. The biological contact oxidation method, like other biofilm methods, does not have the problem of sludge expansion. For those sewage that is prone to expansion by the activated sludge method, the biological contact oxidation method particularly shows its superiority. Bacteria that are prone to expansion in the activated sludge method (such as jersey bacteria, etc.), in the contact oxidation method, not only do not expand, but also can give full play to their strong decomposition and oxidation capabilities. It can operate intermittently. When a power outage or other sudden accident occurs, the biofilm has strong adaptability to intermittent operation. After a long period of parking, bacteria and protozoa can enter a dormant state in order to adapt to the adverse conditions of the environment. Once the environmental conditions improve, the microorganisms start to grow and metabolize again. Some people have tested that even if the operation is stopped for a month and then restarted, the biofilm can return to normal within a few days. Maintenance and management are easy, and there is no need to flow back sludge. Since microorganisms attach to the filler to form biofilms, the peeling and growth of the biofilm can automatically maintain a balance, so there is no need to flow back sludge, and the operation is very convenient. The amount of remaining sludge is small. 2) The contact oxidation method has the above advantages and is an efficient biochemical treatment method. The principle analysis of its efficient treatment is as follows: High biological activity (low mud age). In the contact oxidation tanks used in China, most of the aeration devices are located under the filler, which not only provides sufficient oxygen, but also agitates the biofilm, accelerates the renewal of the biofilm, and improves the biological activity. If we look at the "sludge age", the "sludge" of the activated sludge method The "average mud age" of the biofilm in the first-stage oxidation tank is 1 to 2 days. Due to the low average mud age, the microorganisms are always working at a high level of activity. According to the oxygen consumption rate measurement, the oxygen consumption rate of a biofilm with filamentous bacteria of the same wet weight is 1.81 times higher than that of the activated sludge method. The mass transfer conditions are good, and the metabolism of organic matter by microorganisms is relatively fast. In the contact oxidation method, due to the agitation of the air, the sewage in the entire oxidation tank flows between the fillers, causing a greater relative speed between the biofilm and the water flow, speeding up the medium renewal on the bacterial surface, enhancing the mass transfer effect, speeding up the biological metabolism, and shortening the treatment time. It is beneficial to the growth of filamentous bacteria. In the contact oxidation tank with fillers, it is very beneficial to the growth of filamentous bacteria. The presence of filamentous bacteria can improve the decomposition ability of organic matter. The oxygenation efficiency is high. The filler in the contact oxidation method can improve the oxygenation effect. The power efficiency is above 3kgO2/kwh, which is 30% higher than the aeration without filler. The oxygenation efficiency is high, and the oxidation rate of organic matter increases accordingly. There is a higher biological concentration. Generally, the sludge concentration of the activated sludge method is 2~3g/L, while the contact oxidation method can reach 10~20g/L. Due to the high concentration of microorganisms, * * The BOD5 volume load and treatment efficiency are improved. Due to the large biomass, low-concentration sewage can be effectively treated; and because the filler surface is conducive to the growth of nitrifying bacteria, it can adapt to the requirements of ammonia nitrogen nitrification in sewage. 3) Although the biological contact oxidation method has many advantages and is an efficient biochemical treatment structure, there are also some shortcomings: The thickness of the biofilm increases with the increase of the load. If the load is too high, the biofilm will be too thick, causing blockage of the filler. Therefore, the load should not be too high, and flushing measures to prevent blockage should be taken. A large number of metazoans (such as rotifers) are produced. Metazoa can easily cause large pieces of biofilm to fall off instantly, which can easily affect the quality of the effluent. Fillers and supports often lead to increased construction costs. (2) Structure of the contact oxidation tank 1) Pool body In addition to purifying sewage, the role of the pool body must also consider the installation of fillers, water distribution, gas distribution and other facilities. When the pool volume is small, a circular steel structure can be used, and when the pool volume is large, a rectangular reinforced concrete structure can be used. The plane size of the pool body can meet the requirements of water distribution, uniform gas distribution, filler installation, and convenient maintenance and management. The bottom wall of the pool must have a frame to support the filler and a support for the water and air inlet pipe. The thickness of the pool body is calculated according to the structural strength requirements of the pool. The height is calculated by the filler, water and gas distribution layer, stable water layer and super height. At the same time, the air supply pressure or lifting height of the oxygenation equipment must also be taken into consideration. Generally, the total pool height is about 3.5 to 6.0m. 2) Filler Filler is a place for biofilm to inhabit. It is a carrier of biofilm and also has the function of intercepting suspended solids. Therefore, carrier filler is the key to the contact oxidation tank and directly affects the efficiency of the biological contact oxidation method. The requirements of the carrier filler are: easy for biofilm to adhere, large specific surface area, and large void ratio , small flow resistance, high strength, good chemical and biological stability, durable, strong ability to intercept suspended substances, does not dissolve harmful substances, does not cause secondary pollution, has a similar specific gravity to water, avoids overloading of the oxidation tank, can form a uniform flow rate between fillers, is cheap and easy to obtain, and is convenient for transportation and construction. At present, synthetic resins are mainly used as fillers in China, such as hard polyvinyl chloride plastics, polypropylene plastics, epoxy fiberglass, epoxy paper honeycomb and other hard fillers; a variety of novel soft fillers, semi-soft fillers, elastic biological ring fillers and floating fillers have also been developed. These fillers account for about 55 to 60% of the construction cost of the biological contact oxidation system. Therefore, the carrier filler is directly related to the economic effect of the contact oxidation method. 3) It is very important for the water and gas distribution device to contact the oxidation tank and distribute water and gas evenly. It has a great relationship with exerting the filler function and improving the working efficiency of the oxidation tank. The role of the gas supply is threefold: ① To make the biological contact with the dissolved oxygen in the oxidation tank is generally controlled at 4 to 5m g/L; ② Stir fully to form turbulent flow, which is conducive to even distribution of water. The more turbulent the flow, the higher the contact efficiency between the treated water and the biofilm, the mass transfer efficiency is good, and the treatment effect is better; ③ Prevent the clogging of the filler and promote the renewal of the biofilm. At present, the commonly used gas distribution methods in production include ejector (water ejector) oxygen supply, perforated tube gas distribution, aeration head gas distribution, etc. Water distribution methods are divided into two types: forward flow and counter flow. Down flow means that the water inlet and the gas supply are in the same direction, and the water and gas in the oxidation tank flow in the same direction. In this process, the filler is not easy to block, the biofilm renewal is better, and it is easier to control. ; Counter flow means that the water inlet and the air supply direction are opposite, and the water and air in the pool flow in reverse and relative directions. The gas-liquid contact conditions are good, which increases the contact area between air, water and biofilm, so the removal effect is good. However, due to the small hydraulic erosion effect of the water inlet part, the biofilm on the filler is not easy to fall off and renew. In China, the downstream process is usually used. (3) Commonly used processes and their selection. There are usually two treatment processes for biological contact oxidation, namely one-stage method (one biological contact oxidation) and two-stage method (two contact biological oxidation). Practice has proved that under different conditions, these two systems have their own characteristics, and their economic and applicability ranges are briefly introduced as follows: 1) The one-stage method is also called the one-oxygen-one-sedimentation method. The raw water first passes through the regulating tank, then enters the biological contact oxidation tank, and then flows into the secondary sedimentation tank for mud and water separation. The treated upper water is discharged or further treated, and the sludge is regularly discharged from the secondary sedimentation tank. Although this process sometimes causes short circuits in the oxidation tank, the thickness of the biofilm on the filler of the entire tank is almost the same, the BOD load is roughly the same, and it has the characteristics of complete mixing. The ratio of nutrients (F) to the weight of active microorganisms (M) is low, and the growth of microorganisms is in a declining stage. At this time, the proliferation of microorganisms is no longer limited by their own physiological functions, but is dominated by the amount of nutrients in the sewage. 2) The two-stage method is also called the dioxide secondary precipitation method. The purpose of using the two-stage method is to increase the biological oxidation time, improve biochemical treatment efficiency, and at the same time be more adaptable to changes in raw water quality and stabilize the treated water quality. After the raw water is adjusted by the regulating tank, it enters the first biological contact oxidation tank, and then flows into the intermediate sedimentation tank for mud and water separation. The upper water continues to enter the second contact oxidation tank, and finally flows into the secondary sedimentation tank, where the mud and water are separated again, and the effluent is discharged. The sludge in the sedimentation tank is regularly discharged. In the two-stage process, it is necessary to control the microorganisms in the first stage oxidation tank to be in a higher F/M condition. When F/M>2.1, the microbial growth rate can be in an increasing stage. At this time, the nutrients far exceed the needs of microbial growth. Microbial growth is not affected by nutritional factors and is only limited by its own physiological functions. Therefore, microorganisms reproduce quickly, have strong vitality, and have a high ability to adsorb and oxidize organic matter, which can improve treatment efficiency. In order to maintain microbial growth, Bioenergy is under higher F/M conditions, the BOD load increases accordingly, and the concentration of organic matter in the treated water must be higher. In the second-stage oxidation tank, appropriate F/M conditions must be controlled as needed, generally around 0.5. At this time, the microorganisms are in the endogenous respiration stage after the growth rate decline stage. It can be seen that the microbial working conditions of the two-stage process are similar to the push-flow activated sludge method or the activated sludge AB method. The above are two basic processes. As practice changes, these two processes can be changed accordingly: for example, the contact oxidation tank can be divided into compartments without an intermediate sedimentation tank and operated according to a push-flow type. After the oxidation tank is divided into compartments, the microorganisms in each compartment can be more adapted to the load conditions, and the microorganisms can be cultivated and tamed specifically to improve the overall treatment efficiency. From the comparison of the above two methods, it can be seen that the one-stage method is simple and easy to operate, and saves investment, but its BOD degradation ability is not as good as the two-stage method. The two-stage method has good treatment effect and can shorten the total time required for biological oxidation, but it increases the treatment equipment and maintenance management work, and the investment is higher than that of the one-stage method. Generally speaking, when the organic load is low and the hydraulic load is large, the two-stage method is used. It is better to use the one-stage method. When the organic load is high, it is more appropriate to use the two-stage method or the plug-flow method. Tests have shown that the volume ratio of the first contact oxidation tank to the second contact oxidation tank in the two-stage method should be 7:3. In the plug-flow process, the cells can be divided according to the conditions of BOD change (the first cell is the largest and then gradually decreases); it can also be divided according to the hydraulic load (each cell is of equal size).