Municipal wastewater treatment plant process?

Municipal wastewater treatment plant process is very important, the initial intention is to better treat sewage, reduce the discharge of harmful substances, the most critical is the process to do a good job in order to solve the problem. Zhongda consulting on the urban wastewater treatment plant process and you introduce.

Construction of urban wastewater treatment plant is the inevitable trend of water resources utilization and water pollution control, is the inevitable result of the requirements of sustainable development. The choice of sewage treatment plant process is directly related to the construction costs and operating costs, the treatment effect is good or bad, the size of the footprint, the management of the convenience of the key issues. Therefore, in the design of sewage treatment plant, must do a good job of comparing the process program to determine the best program.

Treatment plant process is to achieve the required degree of treatment under the premise of the organic combination of sewage treatment units. Determine the main basis for the sewage treatment plant process is to achieve the degree of treatment, and the degree of treatment depends mainly on the self-purification capacity of the water body to receive treated sewage or treated sewage outlets. Therefore, the specific conditions of each region and city are different, different needs, the choice of process is also different. According to statistics, the most used process in the world is the activated sludge method, of which there are different modes, such as the traditional activated sludge method, stage aeration, aeration and sedimentation tanks, A B method, A O method and so on. Of course, there are also other methods such as: biofilm method, physical and chemical methods, as well as natural treatment methods, oxidation ponds and so on. Each treatment process has its own characteristics and scope of adaptation, should be based on a variety of different local conditions and requirements to choose the form of treatment.

1 Activated sludge method

Activated sludge method is the artificial strengthening of water self-purification, is to make the microbial population in the aeration tank is suspended, and sewage contact and make it purified method. Including the standard activated sludge method, STEP aeration method, long time aeration method, segmented aeration method, limit aeration method and AB method, such as the traditional activated sludge method modification and AO method, AOO and so on. In recent years, the development of efficient nitrogen and phosphorus removal process. At present, the activated sludge method is dominant, suitable for the treatment of domestic sewage accounted for a large proportion of urban sewage, but with the development of new processes such as the AO method, AOO method, AB method, etc., for the treatment of industrial wastewater composition of higher sewage treatment effect has also been improved.

1.1 traditional activated sludge method

Advantages: ① not suitable for physical and chemical methods of wastewater treatment, BOD removal rate of up to 95% or more. ② construction investment is high, but the power cost of treatment is low.

Disadvantages: the required residence time is long, the equipment is huge, the infrastructure investment is large, so we have to add a variety of structures, so that a variety of structures to increase the volume, so that the area of the treatment plant to increase, increase the management personnel and management difficulties.

Direction of development: ① in order to waste water system components, concentration uniformity, revaluation of pretreatment, re-examination of the adjustment tank. ② Explore the selection of strains of activated sludge microbial system. ③ Activated sludge process equipment to introduce instrumentation and the development of management indicators.

1.2 Intermittent activated sludge method

In recent years, with the continuous expansion of the city scale and the development of the town itself, the sewerage facilities have been shown in large cities to small and medium-sized cities, rural towns, small-scale sewage treatment facilities gradually increased, small towns in rural areas for the improvement of the living environment conditions of the requirements of more and more urgent.

Small-scale sewage treatment facilities and large-scale treatment facilities, compared to its natural and social conditions are very different, therefore, must be studied and adopted for small-scale sewage treatment facilities to replace the large-scale treatment in the past. Small-scale sewage treatment should have the following characteristics: ① easy operation and management; ② easy maintenance; ③ low construction costs; ④ good quality of effluent. After years of practice of some domestic and foreign sewage treatment plants (e.g. Ohara-cho Sewage Purification Plant in Chiba Prefecture, Japan), the intermittent activated sludge method has proved to be a treatment method that can satisfy these conditions.

Intermittent activated sludge method is a treatment tank for aeration, sedimentation, discharge of treated water, so that the equipment is simplified, miniaturized, the flow pattern in the tank is clear, easy to run and manage, unmanned operation can be achieved, for the inflow of wastewater load changes, there is a buffer capacity, stable performance, not only to remove the organic matter and suspended solids and nitrogen removal effect is good. Intermittent activated sludge method is representative of the way, generally set up two aeration and sedimentation tanks, continuously into the mixed sewage, each staggered half cycle for operation, running a cycle of 6h, week after week, repeatedly.

1.3 AB process method

AB process method, also known as adsorption biodegradation method, is the first in Germany in the mid-seventies, is a modification of the traditional activated sludge method, from many sewage plant data show that the process in the treatment of difficult to degrade industrial wastewater or higher concentration of municipal wastewater treatment, it is compared with the ordinary activated sludge method, there are special purification mechanism and the superiority of many aspects. Multi-faceted superiority, it is the traditional activated sludge method of aeration tank is divided into two sections - A section and B section, A section of the organic material adsorption, absorption, oxidation of the three ways, the first two play a major role, while the B section of the latter two play a role, especially oxidation occupies a major position.

From the process flow point of view, the main features of the AB process are: ① AB process does not set up a primary sedimentation tank, sewage through the fine grating, sand sedimentation tank directly into the A section of the aeration tank; ② set up an intermediate settling tank, so that the A section and B section sludge is strictly separate, separate backflow, to maintain their respective bacterial characteristics; ③ AB process of the A section of the aeration and adsorption tank to run at high loads, the age of the sludge is shorter, the B section of the aeration tank to run at low loads; ④ AB process of the A section of the aeration and adsorption pool with high loads, short age sludge, B section of the aeration pool with low AB process A section of the aeration tank can be run according to the components of the sewage partially aerobic or aerobic operation to improve the biochemical properties of sewage, which greatly reduces the load of the B section of the aeration tank. Therefore, the total volume of two sections of aeration tank of AB process is significantly reduced compared with the aeration tank of traditional activated sludge method; ⑤ Due to the differences in the operating conditions of A and B sections of AB process, which lead to different metabolic functions of microbial communities in the two sections, A and B sections are equipped with sludge reflux equipment, but according to the research of experts and some sewage factories' actual operation (e.g. North Central Wastewater Treatment and Purification Ltd. in the city), the process generally remains better than the traditional activated sewage. In general, it still saves the infrastructure investment and power consumption than the traditional activated sludge method, the higher the concentration of sewage, the more investment and power consumption is saved, and the superiority is more obvious.

1.4 AO method and AOO method

AO method and AOO method is a new process of biological denitrification and phosphorus removal developed in recent years, compared with the traditional chemical and biological denitrification and phosphorus removal, it is also effective in improving the effluent indicators of BOD, COD, SS. AO method is the abbreviation of anoxic, aerobic, AOO method is the abbreviation of anaerobic, anaerobic and aerobic, the denitrification is accomplished in anoxic section, phosphorus removal requires anaerobic section. AO method mainly removes nitrogen, AOO method can remove nitrogen and phosphorus at the same time. Both processes require full aeration of sewage, so that the nitrogenous organic matter is fully nitrified, so it is necessary to reduce the sludge load, extend the aeration time and increase the amount of air blowing. According to the practice of Tianjin Dongjiao Wastewater Treatment Plant and Shenyang City North Wastewater Treatment Plant, the use of A O process than the traditional living sludge process of aeration pool volume, the second sedimentation tank volume, return sludge volume, air blower volume and the number of aeration devices are increased by about double, and because of the process requires a relatively low sludge load, otherwise not enough to achieve aerobic stabilization of sludge, so the AO method will bring about a substantial increase in infrastructure investment and power consumption. AOO method in front of the anoxic section there is also an anaerobic tank, in order to achieve the effective removal of phosphorus, infrastructure costs and power consumption than the AO process is higher.1/2 12NextEndPage

2 Biofilm method

Biofilm treatment of wastewater is a kind of aerobic biological treatment technology along with the activated sludge method. It is an artificial enhancement of soil self-purification, a method of making microbial groups attached to other objects in the form of a membrane on the surface and allowing it to come into contact with sewage to purify it. Including biofilter, biological turntable, biological contact oxidation method and other forms. Advantages: ① strong adaptability to changes in water quantity and quality; ② in low water temperature conditions, but also able to maintain a certain degree of purification; ③ suitable for solid-liquid separation; ④ able to deal with low concentrations of sewage; ④ low cost of power, the amount of sludge produced is small. Disadvantages: ① low load, large footprint, not suitable for treatment of large amounts of sewage; ② filter material is easy to clog; ③ produce filter flies, affecting environmental health; ④ biofilm regeneration management is relatively complex. Only a few sewage treatment plants in China to use the process, the city of Yinjiabao sewage treatment plant is one of the earlier use of the process of sewage treatment plant, from more than thirty years of experience in operation and management, the process is indeed low operating costs, but the biofilm is easy to fall off, and is not easy to cultivate, to a certain extent, increasing the difficulty of management.

3 oxidation pond

Oxidation pond is a simple structure, easy to maintain and manage, sewage purification effect is good, energy-saving sewage treatment method. Oxidation ponds on the sewage purification process and natural water self-purification process is very similar to the sewage in the pond after a long period of slow flow, storage, through the metabolic activities of microorganisms, so that the sewage in the degradation of organic pollutants, sewage is purified. According to statistics, the world has nearly 5 0 countries using oxidation ponds for sewage treatment. Oxidation ponds have some relatively prominent advantages: ① can make full use of the terrain, engineering simplicity, infrastructure investment; ② to achieve sewage resources, so that the combination of sewage purification and utilization; ③ sewage treatment costs are low. But the oxidation pond also has certain shortcomings: ① large area; ② sewage purification effect is not stable; ③ sludge should be removed in a timely manner; ④ floating oil should be removed in a timely manner.

Oxidation ditch is also widely used in the world, the city's northern suburbs of sewage purification plant in 2OO6 years, also used the Aubert oxidation ditch process, after a year of trial operation, the treatment effect basically reaches the original design indexes, the removal of nitrogen is very high, but the removal of phosphorus is generally effective. Oxidation ditch process relative to the ordinary activated sludge method, improve the mixed liquid sludge concentration (M L s s), reduce the amount of residual sludge generation. There are many forms of oxidation ditches: carrousel type, triple ditch type, combined construction type, and so on. Generally with mechanical aerator striking the water surface and oxygenation, the aerator has a horizontal axis rotating brush type, oxidation ditch water depth of about 3 m, the maximum depth of water does not exceed 3.6 m. Some oxidation ditch using disk or vertical axis inverted umbrella aerator. Three ditch type oxidation ditch in some sewage plant is applied, such as Xiangzhou purification plant, Shenzhen sewage plant, this oxidation ditch not set up another secondary sedimentation tank, inlet and outlet water through the program timed switching both aeration and sedimentation function, do not need to sludge reflux, saving energy and land construction costs, but due to the aeration of the equipment utilization rate is low, increasing the cost of equipment.

Since there can be no reflux sludge device operation and management is simple, and oxidation ditch has some of the advantages of oxidation ponds, and overcomes the oxidation pond covers an area of large, unstable treatment effect and other shortcomings, the application of certain development. Combined oxidation ditch is developed in recent years a series of modification of the general term, they are characterized by sedimentation ponds and oxidation ditch, water intake and aeration are continuous and unchanged, it has the advantages of other oxidation ditch at the same time, to achieve the infrastructure cost savings, low operating costs, management and simple and convenient. But no matter what form of oxidation ditch, due to the water depth can not be too large a restriction, in part of the aerator is running at full capacity, resulting in its development has been affected.

4 sequential batch aeration (SBR method)

Sequential batch aeration (SBR) is an ancient process, initially in a pool of intermittent water intake, intermittent aeration, and then sedimentation, drainage, sludge discharge, treatment process is quite simplified. Such as the use of delayed aeration of the SBR method, but also eliminates the sludge digestion, biogas storage and utilization processes, the entire sewage plant requires only a few structures. At present, China is only in some small-scale urban sewage plant applications, the size of 10 0(~ n3 per day, but because of its outstanding simplicity, has shown the advantages of simple management, stable operation, etc., attracted widespread attention. The process is not only simple, but also has a strong adaptability to changes in water quantity and quality, can eliminate the need for regulating pools, there is no danger of sludge expansion, sludge settling is good, can be denitrification and phosphorus removal, good quality of effluent, occupies an area of province, under a certain scale of the cost of provincial, low operating costs. Its disadvantage is that the water, aeration inversion frequently, and due to the discharge device, the process has not yet been formed in the country, the development of certain restrictions, has not been able to promote. However, it is still two very potential process, gradually receiving attention.

SBR process has developed rapidly in recent years, there have been a variety of modifications, the following types are currently in common use: ① traditional intermittent water intake, intermittent aeration, this type of adaptability to changes in the quantity and quality of water, the amount of water changes in the water type sewage plant is most suitable. ② continuous water intake, intermittent aeration, no control of the water intake, but it must not affect the precipitation. ③ double pools in series, continuous water intake, continuous aeration of the front pool, after the pool of intermittent aeration, from the back of the pool to the front pool back to the pool of the mixture in order to maintain the sludge concentration. The latter two forms are continuous water intake, can be used for larger sewage treatment plants.

5 Internal treatment of sewers

Sewage contains microorganisms and easily assimilated organic matter, so if the sewage is in an aerobic state (the presence of dissolved oxygen), most of the organic matter is gradually oxidized to carbon dioxide or converted into new bacterial cells. When the sewage is transported for a long time in the pressure pipe, the supply of oxygen in the atmosphere is interrupted, and the remaining dissolved oxygen is quickly used up, and after a short time the special microorganisms begin to reduce the sulfate to hydrogen sulfide, and thus the sewage at this time is known as putrefactive sewage. When this sewage comes into contact with the air again, hydrogen sulphide is released and oxidized to sulphate on the walls of the sewers, thus causing serious hazards and corrosion. In the UK, at least 50 sewers have successfully used oxygen sprayed into the sewers to prevent this corrosion and damage. However, the oxidizing effect of this oxygen is partly affected by the microorganisms in the suspended sewage and the biofilm growing on the surface of the sewer trunk, and the amount of oxygen is large, and the cost is about 25 times higher than that of other methods. So this technology is only applicable to certain conditions, but they can still be used as an effective complementary method to reduce the load of overloaded sewage treatment plants. In our country at present there is no example of the use of this method, this is due to the method of investment is too huge, our current economic conditions can not be reached. But I station on the city's sewers for more than ten years of monitoring information, if you can thoroughly implement who pollutes, who manages the policy, the drainage of large households to take up part of the responsibility for the water environment of the city as a whole is not to be ignored.

6 Conclusion

Through the comparison of the above processes, we can easily see that, in terms of treatment effect, usually activated sludge method of higher treatment efficiency, biofilm law is lower, in the activated sludge method, SBR method, oxidation ditch method, AB method, etc., higher treatment efficiency. When the concentration of organic matter in the sewage is high, processes such as AB method and AO method are more favorable. When the concentration of organic matter is low, oxidation ditch, SBR method and other delayed aeration processes have obvious) advantages. The traditional activated sludge method has a wide range of adaptation, high and low organic concentration can be well adapted, when the advantages of other processes are not obvious, the traditional sludge method is often the best process. When the effluent has special requirements for nitrogen and phosphorus removal, according to the different requirements, the use of AO method, AOO method and other methods to achieve nitrogen or phosphorus removal or simultaneous nitrogen and phosphorus removal. From the point of view of investment, activated sludge method is more than other methods, biofilm method, oxidation pond less, but the biofilm method has more stringent requirements on the management of oxidation ponds and poor sanitation, but also pollution of groundwater. In terms of floor space, the traditional activated sludge method, oxidation pond covers a larger area. Currently from the world's sewage treatment, large-scale sewage plants with traditional activated sludge method, small sewage plants in the oxidation ditch accounted for a large proportion.

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