1 Reasonable determination of construction scale
For a mine, it is necessary to build sewage pipe network and sewage treatment plant by stages according to the overall planning and drainage planning of the mine, and implement it by stages according to the water environment protection goal, and gradually put it in place.
(1) At present, sewage treatment plants are being built in some coal mine industrial sites and residential areas. The land acquisition and repeated construction for two times have increased investment, resulting in high operating energy consumption, high management cost, scattered technical force and high cost per ton of water treatment. Generally speaking, mine industrial sites are not far from residential areas, so it is more reasonable to jointly build a sewage treatment plant with a certain scale. Considering the drainage from the residential area to the industrial site, the pipeline is buried too deep, so a sewage lifting pump station can be set in the middle, or a sewage treatment plant can be built in the middle section between the industrial site and the residential area. Taking the co-construction model can not only save investment, but also greatly reduce operating costs.
(2) At present, when many new mines are designed, according to the specifications and overall efficiency, the number of labor capacity is small. However, after the actual completion of the coal mine, a large number of laborers are recruited. With the development of the coal mine, a large number of outsiders flood in, which increases the water consumption and sewage volume of the coal mine. Therefore, for the design of new coal mine sewage treatment plant, the retention coefficient should be considered in the construction scale.
(3) Because the quality and quantity of coal mine sewage vary greatly, it is directly related to the investment, operating expenses and cost-effectiveness of the project to reasonably determine the design sewage quantity and quality. Considering the production sewage and domestic sewage as a whole, we can't leave much room to avoid increasing investment and making the equipment idle or inefficient.
2 coal mine sewage treatment design common process
Generally speaking, different coal mines have different requirements for effluent, so the treatment degree should be determined according to the requirements of China's environmental protection department to ensure the effluent quality. Because nitrogen and phosphorus in domestic sewage are eutrophic, sewage treatment needs the effect of nitrogen and phosphorus removal.
The water quality of coal mine sewage is similar to that of ordinary urban sewage, but it is different from urban sewage (urban sewage often contains some industrial wastewater). Its characteristics can be summarized as follows: the water quality and quantity change greatly, the pollutant concentration is low, the sewage has good biodegradability and the treatment difficulty is small.
In 1980s, when designing coal mine sewage treatment plants, activated sludge method was widely used. Because the organic matter content in sewage is too low, microorganisms can't get the minimum nutrition in operation, so they can't form activated sludge and can't run. The same problem exists in oxidation ditch sewage treatment process. The returned activated sludge can't flow back, which makes the original oxidation ditch system become a zonal advection sedimentation tank with additional aeration, which can't meet the required treatment target.
Since 1990s, great achievements have been made in the research, development and application of new technologies for wastewater biological treatment, and many new technologies have emerged. The common characteristics of these new technologies are: high efficiency, stability, energy saving, nitrogen and phosphorus removal and other functions. Typical processes are:
(1)A2/O process is the abbreviation of anaerobic, anoxic and aerobic biological nitrogen and phosphorus removal process, which was developed by American experts on the basis of anaerobic-aerobic phosphorus removal process (A/O) in 1970s.
(2) Short for 2)SBR sequencing batch activated sludge process, which is an activated sludge sewage treatment technology operated by intermittent aeration, is also called sequencing batch activated sludge process. In fact, SBR is the earliest activated sludge process, which appeared in the United States in the 1970s. After 20 years of research, development and innovation, the principle of variable volume activated sludge process and biological selector is organically combined to become an improved SBR process.
(3)BAF process, that is, biological aerated filter process, is a new type of microbial attached sewage treatment technology developed in the early 1990s. It can complete biological treatment and solid-liquid separation at the same time, and become a combined process with nitrogen and phosphorus removal functions by adjusting the structure of the filter.
Treatment of coal mine sewage by 3BAF process
3. 1 process
Biological aerated filter (BAF) was first developed in Europe and America, and it is widely popular in developed countries such as Europe, America and Japan. In recent years, it has been applied in dozens of domestic sewage treatment plants. Such as Dalian, Cixi, Xinhui and Yangling, are also used in the treatment of domestic sewage in Shanxi coal mines.
This technology integrates filtration, adsorption and biological metabolism. Sewage enters the filter material layer from the bottom of the filter, and an aeration system with oxygen supply is arranged at the lower part of the filter material layer for aeration, so that gas and water flow in the same direction. In the filter, 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 accumulated filter material layer and microbial membrane, partial denitrification can be realized at the same time of nitrification, and the effluent from the upper part of the filter can be directly discharged from the system.
3.2 Process characteristics
As a new membrane wastewater treatment process, BAF has the following advantages compared with the traditional activated sludge process and contact oxidation process:
(1) has higher biological concentration and higher organic load. Biological aerated filter (BAF) adopts coarse porous spherical filter material, which provides a better growth environment for microorganisms, is easy to film and run stably, and can keep more biomass between the surface and the filter material. The microbial biomass per unit volume is much higher than that of activated sludge process (up to 10 ~ 15g/L). High concentration of microbial biomass increases the volume load of BAF, reduces the tank volume and floor space, and makes BAF.
Lower it.
(2) The process is simple and the effluent quality is good. Due to the mechanical interception of the filter material, the adsorption of microorganisms on the surface of the filter material and the viscous substances produced by metabolism, the effluent SS is very low, generally not exceeding15 mg/L. Due to regular backwashing, the biofilm can be effectively updated, which is characterized by thin biofilm and high activity. Sometimes, even if biological treatment fails, its physical mechanism can still ensure high-quality effluent in a short time. The effluent treated by biological aerated filter can not only meet the discharge standard, but also be reused.
(3) Strong impact load resistance. Because the high concentration of microorganisms is distributed in the whole filter, it is not as sensitive to the changes of organic load and hydraulic load as traditional activated sludge, and there is no sludge bulking problem.
(4) High oxygen transmission efficiency. The oxygen utilization rate of biological aerated filter can reach 20%-30%, and the aeration rate is obviously lower than that of general biological treatment. The main reasons are:
1 Due to the small particle size of the filter material, bubbles are continuously cut into small bubbles in the rising process, which increases the gas-liquid contact area and improves the utilization rate of oxygen;
In the rising process of bubbles, due to the blocking and partition of filter materials, bubbles must pass through the gaps of filter materials, which prolongs their residence time and is also beneficial to oxygen mass transfer;
Theoretical research shows that the oxygen in BAF can directly penetrate into the biofilm, thus speeding up the transmission speed of oxygen and reducing the oxygen supply.
(5) easy film hanging and quick start. The debugging time of BAF is short, usually only 7 ~ 12 days, and there is no need to inoculate sludge, so it is domesticated by natural membrane hanging. Because microorganisms grow on the surface of rough and porous filter media, they are not easy to lose, which makes their operation and management simple. BAF can be closed when it is not used for a short time, and can resume normal operation in a short time once the influent is aerated, which shows that BAF is very suitable for sewage treatment in some areas with large water volume changes.
(6) The flora structure is reasonable. In the traditional activated sludge process, the distribution of microorganisms is relatively uniform, but different dominant strains are formed from top to bottom in BAF, so that carbon removal, nitrification/denitrification can occur in one tank.
(7) High degree of automation. Due to the development of related industrial technology, some advanced automation equipment, such as liquid level sensor, online dissolved oxygen analyzer, timer, frequency converter, microcomputer, etc., has successfully realized the automation of operation and management of BAF system.
The biological aerated filter system can detect the water quality, water quantity and dissolved oxygen concentration in sewage online, and adjust the aeration time conveniently through the PLC control system to control the oxygen supply of the fan to achieve the best operation. The PLC system can automatically backwash the filter.
(8) Good denitrification effect. Through the combination of filters with different functions or the distribution of different functional areas in the same filter, the filter can carry out nitrification and denitrification while removing carbon. Its principle is that by artificially creating an aerobic and facultative biological environment in two groups of filters or the same filter, not only can the general organic matter and suspended matter be removed, but also it has a good denitrification function.
In the aeration stage of the primary filter (C/N tank) and the secondary filter (N tank), it is necessary to constantly adjust the dissolved oxygen level to make it reach a higher level (about 2 ~ 3mgo2/L), while in the DN tank, it is necessary to make it reach a lower level (about 0.2 ~ 0.5mgo2/).
Reuse of effluent from 4BAF process
As we all know, the shortage of water resources has become a worldwide problem. China is also facing the reality of water shortage. 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 utilization of limited water resources. After treatment and disinfection, coal mine sewage can be used for greening, washing and industrial water. Using BAF process to treat coal mine sewage, the effluent quality is stable, which is superior to the general traditional biological treatment process. After disinfection, the effluent can be reused as reclaimed water.
Biological aerated filter (BAF) process has the characteristics of small volume, less land occupation, high efficiency, good effluent quality, simple process and convenient operation and management. In actual operation, centralized control and manual automatic control can be realized. After the practical application of several projects, it has become increasingly mature, and its effluent can reach the standard of reclaimed water reuse after disinfection. It is understood that at present, the direct investment of 1m3 sewage in China is about 1000 yuan, while the BAF process can be controlled around 500 yuan, and it can save nearly 4/5 of the occupied area. The quality and quantity of coal mine sewage vary greatly, the concentration of pollutants is low, and the sewage has good biodegradability, so BAF process is more suitable.
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