The MBR process studied in this paper can be obtained by combining biological treatment and membrane separation technology. With the increasingly strict standards for sewage discharge, the number of underground sewage treatment plants is increasing. The combination of MBR and A2O process not only has a good inhibitory effect on reversible pollution, but also can alleviate the problem of membrane pollution. Therefore, the discussion is focused on the operation problems faced by the process, It plays a very positive role in the development of sewage treatment plant and even the whole industry.
1. A20 + MBR process introduction/p>
& nbsp; The main problem facing contemporary society is the scarcity of land resources, which is also the background of the proposal and promotion of underground sewage treatment plant. The technology of sewage treatment in underground treatment plant is naturally different from that in traditional treatment plant. It is a general trend to innovate the process and technology.
As a representative of activated sludge process, A20 emphasizes the use of microorganisms to degrade organic matter, and its phosphorus and nitrogen removal effects are more prominent. A20 + MBR means that after the MBR tank is added in the aerobic area corresponding to A20 tank, it replaces the secondary sedimentation tank for mud water separation. It can not only effectively save land, but also separate mud and water from high concentration sewage, so that the front-end biochemical treatment process section can increase the sludge concentration to more than 8g / L, effectively improve the load of biochemical reaction tank, so as to achieve the purpose of overall land saving. The construction cost of buried sewage treatment plant is higher than that of traditional methods. Choosing land-saving process can effectively reduce the construction cost. Therefore, with the shortage of urban land resources, more and more urban sewage treatment plants choose MBR membrane process.
Of course, the shortcomings of this process are also very obvious. For example, the sludge discharge is uneven, so that the safety of the membrane can not be guaranteed, and the effect of biological phosphorus removal is always different from that expected. The treatment object of a sewage treatment plant is domestic sewage, which has been successfully transformed from the early activated sludge method to A20 + MBR. The sludge is deeply dehydrated by using the high-pressure plate and frame filter press. The moisture content of the treated sludge is maintained below 60% (as shown in Figure 1).
It can be seen from the information provided in Figure 1 that the process of sewage treatment is as follows: before entering the pump room, install a coarse grid, which can effectively intercept floating and suspended solids, provide comprehensive protection for the water pump, avoid the blockage of valves or pipe fittings, and ensure the normal operation of subsequent systems. Then, fine grids that can intercept solid substances and small floating objects are set to minimize the impact of external factors on the sludge and biological treatment system that has been officially put into operation. Aeration grit chamber and membrane grid have their own functions. Aeration grit chamber can remove grease, inorganic sand and scum, while membrane grid can block the way of fiber and hair entering the reactor. In addition, the combined biochemical tank is composed of two series, both of which have the conditions for independent operation. Any combined biochemical tank can be divided into MBR tank, aerobic area, anaerobic area and anoxic area. The flow ejector and diversion wall are set in the middle of the tank body, and the disinfection equipment is set inside the water outlet pipeline, so as to truly use sodium hypochlorite to kill pathogenic microorganisms in the contact tank in a large range.
2. Analysis of operation problems and Countermeasures
The layout of the sewage treatment plant discussed in this paper is semi underground. First, the structure is covered with concrete, and then the concrete cover is Afforested by covering soil. After a period of operation, the plant summarized the problems encountered, mainly including:
2.1 membrane fouling
The main operation problem faced by MBR process is membrane pollution, which is closely related to operation cost and effluent quality. If the density of membrane wire is too high, it will be difficult to shake off pollutants during purging, which is not conducive to cleaning and will increase the cost.
At this stage, the solutions for small-scale trial mainly include electric pollution suppression, in-situ chemical cleaning and the use of nano material films. Restricted by the cost and technical maturity, the above countermeasures cannot be popularized in a large scale in a short time. Based on this, the staff put forward the following schemes: firstly, reducing the membrane wire density can reduce the difficulty of shaking off pollutants, and maintain the power consumption within a controllable range by reducing the number of pollution times; Secondly, if the number and density of membrane filaments remain unchanged, the above purpose can be achieved by increasing the floor area; Finally, set the sedimentation tank inside the MBR tank to ensure that the sewage has been precipitated before passing through the membrane wire, which can also avoid the attachment of a large number of pollutants to the membrane wire. Of course, the floor area of the membrane tank will become larger. This requires the plant to weigh the advantages and disadvantages, determine the solutions that meet its own needs, and solve the problem of membrane pollution.
2.2 chain fracture
There are thrusters in the anoxic tank and anaerobic tank, and the chain hoist connecting the thruster is mainly used to lift the thruster to facilitate subsequent maintenance. Under normal circumstances, the chains are in an environment full of water, and the corrosion is obvious. When they are in motion, there must be friction between different chains. After a period of time, the corroded chains will break. To repair the broken chain, professionals are usually required to salvage the broken end by diving. The cost and difficulty are self-evident< br /> Considering various factors, the staff put forward the following countermeasures: replace the original chain with professional chain, add the grab hook at the end of the chain, and set the lifting ring on the ejector. The professional chain does not need to be used in daily work. At this time, it can be stored in the maintenance workshop. When there is a maintenance demand, the grapple can be used to hook the lifting ring to ensure that the ejector can be lifted out of the water as soon as possible and shorten the time required for maintenance. It has been proved that this can maintain the operating cost and difficulty within the ideal range by reducing the number of chain breaks.
<2.3 Aeration tray failure
The main material of the biochemical tank built by the plant is reinforced concrete. On the basis of all closure, the top plate is covered with soil for greening. The manhole is set on the top plate. The blower room and membrane grid room are located on the top of the tank. It is obvious to all that it is difficult to maintain the aeration plate. Generally speaking, the premise for the maintenance of the aeration tray is to completely empty the aerobic tank instead of 20000m & sup3; The aerobic tank with large volume has slow ventilation and slow drainage. When the water level reaches a certain height, the blower will automatically stop the operation of the aeration system. It is because of the above reasons that a large number of harmful and toxic gases are generated in the drainage process. For example, methane and methyl mercaptan. In order to ensure their own safety, maintenance personnel need to maintain and repair the aeration plate in strict accordance with industry regulations, which not only needs to invest a lot of cost, but also remains difficult< br /> There are two practical and effective solutions to the failure of aeration plate: first, modify the automatic control program to ensure that aeration always exists in the process of water level decline, and avoid the generation of harmful and toxic gases by alleviating anaerobic and anoxic conditions; Second, if conditions permit, the sewage treatment plant can choose to separate the aerobic tank to reduce the difficulty of maintenance and treatment
3. Effluent not up to standard
(1) The total nitrogen exceeds the standard.
Due to the problem that the total nitrogen of effluent exceeded the expectation in the trial operation, after comprehensive consideration of various factors, the staff decided to add methanol, sodium acetate, organic wastewater and other carbon sources to the anoxic tank. With the increase of carbon source, the operating cost has increased slightly. How to make the deoxidation efficiency reach the ideal level has naturally become the focus of attention. The research scheme mainly emphasizes two aspects: first, under the guidance of fine management, on the basis of increasing the volume of anoxic tank, control the do value of aerobic tank; Second, multi-point influent uses raw water carbon source and anoxic environment to improve the denitrification efficiency of the system, which has a significant effect.
（2）Excessive Escherichia coli。
E. coli exceeding the first-class a standard occasionally occurs. The inspection results show that the main reason for this problem is the leakage of the membrane wire. The simple membrane wire fracture usually does not cause the leakage of the membrane wire. This is because the suction force of the produced water makes the middle of the broken membrane wire shrivel. After a large amount of sludge blocks the membrane wire, the way of sewage flowing into the produced water pipeline is completely blocked. The leakage point appears near the interface of the membrane box, and the pluggable membrane box is adopted by the factory, which is characterized by easy disassembly and assembly, but the deformation and dislocation of the rubber gasket are common. Once the operating pressure exceeds the limit, there will be leakage. In order to completely solve the above problems, the most effective way is to give up the plug-in joint and choose the screw joint. The joint can be fastened by rotation. In addition, if there are special needs, the staff can increase the thickness of the gasket as appropriate. Although it is difficult to disassemble it, the leakage problem can be solved. Of course, the test results also prove the above conjecture. If the treatment plant selects the screw joint, even if sodium hypochlorite is not used for disinfection, the E. coli in the effluent still meets the standard.
3、epilogue
Whether from the technical or economic point of view, A2O + MBR technology has ideal feasibility, and its development potential and space are self-evident. For the buried treatment plant, in order to reduce the difficulty of operation and management, the staff need to consider mainly membrane tank layout, component cleaning, etc. In addition, we should pay attention to the purpose of using this technology to treat sewage, not only to ensure that it meets the discharge standards, but also to reduce energy consumption and help achieve sustainable development and related goals.
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