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Oxidation ditch process
Brief introduction:
As a mature activated sludge sewage treatment process, the oxidation ditch process has been widely used in the country, it is a variant of the activated sludge method, and its aeration tank is a closed ditch type, so it is different from the traditional activated sludge method in the hydraulic flow state, but a kind of circulating flow aeration ditch connected from end to end, and the sewage seeps into it to be purified.
Process characteristics:
1. The hydraulic retention time and sludge age of the pretreatment oxidation ditch are simplified than that of the general biological treatment method, the suspended organic matter can be removed more thoroughly at the same time as the dissolved organic matter, and the remaining sludge discharged has been highly stable, so the oxidation ditch can not be equipped with a primary sedimentation tank, and the sludge does not need to be anaerobic digested.
2. The floor area is small, because the primary sedimentation tank, sludge digester are omitted in the process, and sometimes the secondary sedimentation tank and sludge return device are omitted, so that the total area of the sewage plant not only does not increase, but can also be reduced.
3. The oxidation ditch with the characteristic of push-flow flow has the characteristics of push-flow, so that the dissolved oxygen concentration forms a concentration gradient along the length of the pool, forming aerobic, anoxic and anaerobic conditions. Through the reasonable design and control of the system, a better effect of nitrogen and phosphorus removal can be obtained.
4. Simplify the process of combining the oxidation ditch and the secondary sedimentation tank into an integrated oxidation ditch, and the oxidation ditch that has been developed in recent years to work alternately, so that the secondary sedimentation tank can be used, so that the treatment process is more simplified.
A/O process
Brief introduction:
The A/O process was produced in the 70s of the 20th century, and has been widely used because of its simultaneous degradation of organic matter and denitrification, and convenient operation and management. Because the sewage treatment process is determined according to the water quantity, water quality, effluent requirements and local actual conditions and other factors, small and medium-sized urban domestic sewage treatment stations generally choose A/O and other processes.
Process characteristics:
1. Advantages: high efficiency: the process has a high removal effect on organic matter and ammonia nitrogen in wastewater. When the total residence time is greater than 54h, the effluent after biological denitrification can be coagulation and precipitation, which can reduce the COD value to below 100mg/L, and other indicators also meet the emission standards, and the total nitrogen removal rate is more than 70%. The process is simple, the investment is low, and the operating cost is low, and the organic matter in the wastewater is used as the carbon source for denitrification, so there is no need to add expensive carbon sources such as methanol.
2. Disadvantages: Because there is no independent sludge reflux system, sludge with unique functions cannot be cultivated, and the degradation rate of refractory substances is low. In order to improve the efficiency of nitrogen removal, it is necessary to increase the internal circulation ratio, which increases the operating cost. In addition, the internal circulating liquid comes from the aeration tank and contains a certain amount of DO, which makes it difficult for section A to maintain an ideal anoxic state, affects the denitrification effect, and the denitrification rate is difficult to reach 90%.
A2/O process (emphasis on dephosphorization and nitrogen removal)
Brief introduction:
A2/O process is the English abbreviation of Anaerobic-Anoxic-Oxic, which is the abbreviation of anaerobic-anoxic-aerobic biological nitrogen and phosphorus removal process. The treatment efficiency of this process can generally reach: BOD5 and SS are 90%~95%, total nitrogen is more than 70%, and phosphorus is about 90%, which is generally suitable for large and medium-sized urban sewage plants that require nitrogen and phosphorus removal. However, the infrastructure cost and operation cost of the A2/O process are higher than those of the ordinary activated sludge method, and the operation and management requirements are high, so for the current national conditions of China, the process is only used when the treated sewage is discharged into a closed water body or a slow water body to cause eutrophication, thereby affecting the water supply source.
Process characteristics:
1. Pros:
The pollutant removal efficiency is high, the operation is stable, and the impact load resistance is good. The sludge has good sedimentation performance. Anaerobic, anoxic and aerobic three different environmental conditions and the organic cooperation of different types of microbial flora can have the functions of removing organic matter, denitrification and phosphorus at the same time. The denitrification effect is affected by the reflux ratio of the mixed solution, and the phosphorus removal effect is affected by the entrainment of DO and nitric acid oxygen in the reflux sludge, so the denitrification and phosphorus removal efficiency cannot be very high. This process is the simplest of the processes for simultaneous deoxidation and phosphorus removal of organic matter, and the total hydraulic retention time is also less than that of other processes in the same category. Under the anaerobic-hypoxic alternate operation, filamentous bacteria will not multiply in large numbers, and the SVI is generally less than 100, and sludge expansion will not occur. The phosphorus content in the sludge is high, generally more than 2.5%.
2. Cons:
The reaction cell volume is larger than that of the A/O denitrification process. The sludge has a large return flow rate and high energy consumption. The cost of small and medium-sized sewage plants is high. The economic benefits of biogas recovery and utilization are poor. Sludge ludate needs to be chemically phosphorus removed.
Biofilm method (for low-concentration wastewater)
Brief introduction:
The biofilm method is an artificial enhancement of the soil self-purification process, which mainly removes dissolved and colloidal organic pollutants in wastewater, and also has a certain nitrification capacity for ammonia nitrogen in wastewater. The biofilm method is widely used in the treatment of industrial wastewater.
Process characteristics:
1. Pros:
The diversity of microorganisms and the long food chain of organisms are conducive to improving the sewage treatment effect and the treatment load per unit area. The segmented operation of dominant flora is conducive to improving the degradation efficiency of organic pollutants by microorganisms, increasing the removal rate of refractory pollutants, and improving the effect of nitrogen and phosphorus removal. It has strong adaptability to changes in water quality and quantity, and its impact load resistance is enhanced. The sludge has good sedimentation performance, easy solid-liquid separation, and the remaining sludge output is small, which reduces the sludge treatment cost and thus reduces the investment cost. It is suitable for the treatment of low-concentration wastewater. Easy to maintain, convenient operation and management, low energy consumption.
2. Cons:
Compared with the activated sludge method, the biofilm method has higher requirements for ambient temperature, and too high or too low temperature will affect the activity of the biofilm, causing necrosis and shedding of the biofilm. In addition, the specific surface area of the carrier has a great impact on the effect of biofilm treatment, if the specific surface area of the selected filter material does not meet the requirements, the area of the treatment tank should be increased in order to achieve the expected treatment effect, so that the investment cost increases.
