BAF process sewage treatment-coal mine sewage treatment plan

In order to strengthen coal mine wastewater treatment and protect the water environment, new mines attach great importance to environmental protection and have invested a lot of money. The design department also carried out multi-process and multi-scheme comparison and exploration for domestic sewage treatment.

1. Reasonably determine the construction scale

For a mine, it is necessary to construct the sewage pipe network and sewage treatment plant in phases according to the overall planning and drainage plan of the mine. It must be implemented in phases according to the goal of water environmental protection and gradually put in place.

(1). At present, some coal mine industrial sites and residential areas each have a sewage treatment plant, two land acquisitions, repeated construction, increased investment, high operating energy consumption, high management costs, scattered technical forces, and high cost of water treatment per ton. Generally speaking, the mine industrial site and the residential area are not very far away. It is more reasonable to build a sewage treatment plant of a certain scale. Considering the drainage from the residential area to the industrial site, the pipeline is buried too deep, and the sewage lifting pump station can be set in the middle. Or requisition land in the middle of the industrial site and the residential area to build a sewage treatment plant. The joint construction method can not only save investment, but also greatly reduce operating costs.

(2). At present, many newly-built mines are designed according to specifications and full-staff efficiency. The number of labor quotas is small. However, after the actual completion of the coal mine, a large number of laborers will be recruited. As water consumption increases, so does the amount of sewage. Therefore, for the design of a new coal mine sewage treatment plant, the reserve factor should be considered in the construction scale.

(3). Due to the large changes in coal mine sewage water quality and quantity, reasonable determination of the designed sewage water quantity and sewage water quality directly involves project investment, operating costs and cost benefits. The overall consideration of production sewage and domestic sewage should not make the margin too large, and avoid increasing investment, leaving equipment idle or operating inefficiently.

For a mine, it is necessary to construct the sewage pipe network and sewage treatment plant in phases according to the overall planning and drainage plan of the mine. It must be implemented in phases according to the goal of water environmental protection and gradually put in place.

Sewage treatment and recycling plant (9)

2. Common process of coal mine sewage treatment design

Generally speaking, different coal mines have different requirements for effluent water. The degree of treatment should be determined according to the requirements of environmental protection departments in various countries to ensure the quality of effluent water. Because the nitrogen and phosphorus in domestic sewage have eutrophication effects on water bodies, sewage treatment requires the effect of nitrogen and phosphorus removal.

The quality of coal mine sewage is similar to that of general urban sewage, but is different from urban sewage (urban sewage often includes part of industrial wastewater). Its characteristics can be summarized as follows: large changes in water quality and quantity, low pollutant concentration, good sewage biodegradability, and low treatment difficulty.

During the design of coal mine sewage treatment plants, many activated sludge treatment processes were adopted in the 1980s. Due to the low organic content in the sewage, the microorganisms cannot obtain the minimum nutrients during the operation process, and the activated sludge cannot be formed. stand up. The oxidation ditch sewage treatment process also has the same problem. The activated sludge cannot be returned, which causes the original oxidation ditch system to become a belt-shaped advection sedimentation tank with additional aeration, which fails to meet the required treatment goals.

In the 1990s, many mines used the secondary biological contact oxidation method to treat domestic sewage from coal mines, with very good results. The characteristic of this process is that it can adapt to the low-concentration, large-changing sewage in the mining area, and at the same time it saves investment, and the operation and maintenance are simpler than the activated sludge method, but the method has a poor effect on nitrogen and phosphorus removal.

Since the 1990s, great achievements have been made in the research, development and application of new technologies and new technologies for biological wastewater treatment. Many new technologies have emerged. The common features of these new technologies are: high efficiency, stability, energy saving, and denitrification and phosphorus removal. Features. The more typical processes are:

  1.  A2/O process This process is short for anaerobic, anoxic, aerobic biological nitrogen and phosphorus removal process, based on the anaerobic-aerobic phosphorus removal process (A/O) by American experts in the 1970s developing.
  2.  The abbreviation of SBR process sequence batch activated sludge method is an activated sludge wastewater treatment technology operated by intermittent aeration, also known as sequential batch activated sludge method. SBR is actually the earliest activated sludge process that appeared in the United States in the 1970s. 20 years of research and development innovation, the variable volume activated sludge process and the principle of biological selector are organically combined to become an improved SBR process.
  3. BAF process, namely biological aerated filter process, is a new type of microorganism-attached sewage treatment technology developed in the early 1990s. It can complete biological treatment and solid-liquid separation at the same time. It has the ability to remove nitrogen and phosphorus by adjusting the structure of the filter. Combination of functions.

3. BAF process to treat coal mine sewage

3.1 Process flow

Biological aerated filter is the first developed in Europe and America, and is widely popular in developed countries such as Europe, America and Japan. In recent years, dozens of sewage treatment plants have been used in my country. Such as Dalian, Cixi, Xinhui, and Yangling are also used in the treatment of domestic sewage from coal mines in Shanxi.

This technology integrates various purification functions such as filtration, adsorption and biological metabolism. Sewage enters the filter material layer from the bottom of the filter tank, and the lower part of the filter material layer is equipped with an aeration system for oxygen supply for aeration, and the air and water flow in the same direction. In the filter tank, the organic matter is oxidized and decomposed by microorganisms, and NH3-N is oxidized to NO3-N; in addition, due to the anaerobic/anoxic environment in the stacked filter layer and the microbial membrane, part of the nitrification is achieved at the same time. Denitrification, the effluent from the upper part of the filter can be directly discharged from the system.

3.2 Process characteristics

BAF, as a new membrane wastewater treatment process, has the following advantages compared with the traditional activated sludge method and contact oxidation method:

(1) It has a higher biological concentration and a higher organic load. The aerated biological filter adopts coarse and porous spherical filter material, which provides a better growth environment for microorganisms, is easy to hang the membrane and operates stably, and can maintain more biomass on the surface of the filter material and between the filter material. Microbes per unit volume The amount is far greater than the amount of microorganisms in the activated sludge method (up to 10~15g/l). The high concentration of microorganisms makes BAF

The volumetric load is increased, the pool volume and floor space are reduced, and the capital construction cost is greatly reduced.

(2). The process is simple and the effluent quality is good. Due to the mechanical retention of the filter material and the adsorption formed by the microorganisms on the surface of the filter material and the viscous substances produced during metabolism, the SS of the effluent is very low, generally not exceeding 15mg/l. Due to the periodic backwashing, the biofilm can be effectively renewed, showing that the biofilm is thinner and has higher activity. Sometimes even if the biological treatment fails, its physical mechanism can still ensure high-quality water in a short period of time. The treated effluent of BAF not only meets the emission standards, but also can be used for reuse.

(3). Strong resistance to impact load. Due to the high concentration of microorganisms distributed in the entire filter tank, it is not as sensitive to changes in organic load and hydraulic load as traditional activated sludge, and there is no sludge expansion problem.

(4). High oxygen transmission efficiency. The utilization rate of oxygen in the biological aerated filter can reach 20%-30%, and the aeration rate is significantly lower than that of general biological treatment. The main reasons are: 1 due to the small particle size of the filter material, the bubbles are continuously cut into small bubbles during the ascending process, which increases the gas-liquid contact area and improves the utilization of oxygen; 2 the air bubbles are rising due to the filter material The blocking and partitioning effect of the air bubble must pass through the gap of the filter material, which prolongs its residence time, which is also conducive to the mass transfer of oxygen; 3 theoretical studies have shown that the oxygen in the BAF can directly penetrate the biofilm, thus accelerating the oxygen transmission speed , Reduce the oxygen supply.

(5). Easy to hang the film and quick start. BAF debugging time is short, generally only 7~12 days, and does not need to inoculate sludge, and adopt natural film domestication. Because microorganisms grow on the surface of the rough and porous filter material, the microorganisms are not easy to lose, making its operation and management simple. BAF can be shut down when not in use for a short period of time. Once water is supplied and aerated, it can resume normal operation in a short time. This feature shows that the biological aerated filter is very suitable for sewage in areas with large changes in water volume. deal with.

(6). The structure of the flora is reasonable. In the traditional activated sludge method, the distribution of microorganisms is relatively uniform, while in BAF, different dominant strains are formed from top to bottom, so that carbon removal and nitrification/denitrification can occur in one pond.

(7). High degree of automation. Due to the development of related industrial technology, some advanced automation equipment such as liquid level sensors, online dissolved oxygen analyzers, timers, frequency converters and microcomputers have emerged, making the operation and management automation of the biological aerated filter system smoothly realized.

The biological aerated filter system can perform online detection of influent water quality, water volume and dissolved oxygen concentration in sewage, and conveniently adjust the length of aeration time through the PLC control system, control the oxygen supply of the fan, and achieve optimized operation. PLC The system automatically backwashes the filter tank.

(8) Good denitrification effect. Through the combination of different functions of the filter or the distribution of different functional areas in the same filter, the filter can perform nitrification and denitrification while removing carbon. The principle is to artificially create aerobic and facultative biological environments in the two sets of filters or the same filter, which can not only remove general organic matter and suspended solids, but also has a better denitrification function.

In the aeration stage of the primary filter (C/N tank) and the secondary filter (N tank), the dissolved oxygen level needs to be continuously adjusted to make the dissolved oxygen reach a higher level (about 2~3mgO2/l), and the The dissolved oxygen in the DN pool can reach a lower level (about 0.2~0.5mgO2/).

The disadvantage of the BAF process is that it needs regular backwashing:

As the filtration progresses, more and more biomass is produced on the surface of the filter material, and the intercepted SS continues to increase. At the beginning, the head loss of the filter increases slowly. When the solid matter accumulates to a certain level, the head loss reaches the limit head loss. Or cause the SS to penetrate. At this time, the filter must be backwashed to remove the excessive microbial film and SS in the filter bed and restore its processing capacity.

4. Water reuse of BAF process

As we all know, water scarcity has become a worldwide problem. Sewage recycling is one of the effective ways to improve the comprehensive utilization rate of water resources, alleviate the contradiction of water shortage, reduce water pollution, and realize the sustainable use of limited water resources. After the coal mine sewage is treated and disinfected, it can be used for greening, washing, and industrial water. The BAF process is used to treat coal mine wastewater, and the effluent quality is stable, which is better than the general traditional biological treatment process. After disinfection, the effluent can be reused as reclaimed water.

5. Conclusion

The biological aerated filter process has the characteristics of small size, low land occupation, high efficiency, good water quality, simple process, convenient operation and management, etc. In actual operation, it can realize centralized control and on-site manual automatic control. It has been applied in multiple projects. , Has become mature day by day, and its effluent can reach the standard of reclaimed water after being disinfected. It is understood that the current BAF process for processing 1m3 can be controlled at about 500 yuan, and it can save nearly 4/5 of the area. The quality and quantity of sewage from coal mines vary greatly, the concentration of pollutants is low, and the biodegradability of sewage is good. BAF process is more suitable.

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