Domestic sewage treatment has always been a difficult problem in urban residential quarters where urban sewage pipe network has not been laid or reached, or where urban sewage treatment plants have not been built. Septic tank sedimentation and anaerobic fermentation, which were commonly used in the past, can remove suspended solids and parasitic eggs to a certain extent, but BOD5 removal rate is very low, and it does not have the function of nitrogen and phosphorus removal, which can no longer meet the needs of water pollution prevention and water environment protection. In recent years, the technology of small sewage treatment stations and sewage treatment equipment suitable for residential quarters has developed rapidly. This paper intends to discuss the achievements in this respect and put forward opinions on the existing problems.

Domestic sewage treatment; Technology development; Problem discussion

Domestic sewage treatment has always been a difficult problem in urban residential quarters without laying urban sewage pipe network or impossible to reach, or without establishing urban sewage treatment plants. Septic tank sedimentation and anaerobic fermentation, which were commonly used in the past, have a certain purification effect on suspended solids and parasitic eggs, but the purification rate of BOD5 is very low, and it has no function of nitrogen and phosphorus removal, which can no longer meet the needs of water pollution prevention and water environment protection. In recent years, the technology of small sewage treatment stations and sewage treatment equipment suitable for residential quarters has developed rapidly. This paper intends to discuss the achievements in this respect and put forward opinions on the existing problems.

Keywords domestic sewage treatment; Technical development; Problem research

1. technology development The evolution of domestic sewage treatment technology in residential quarters has gone through the process from single process to combined process. From the point of view of whether it is aerobic or not, it develops along the track of "anaerobic → aerobic → anaerobic+aerobic → anaerobic+anoxia". As far as the removal object is concerned, the early technology can only remove SS substances, but the current process also has the function of nitrogen and phosphorus removal. The following describes several commonly used processing technologies and equipment.

1. 1 biological contact oxidation method. Biological contact oxidation is a sewage biological treatment technology between activated sludge process and biofilm process, which has both advantages. Its main structure is a biological contact oxidation tank, which is filled with fillers. The oxygenated sewage flows through the submerged packing at a certain speed, forming a biofilm on the packing. Sewage is in extensive contact with biofilm. Under the action of microorganisms on the biofilm, organic pollutants are removed and sewage is purified. Because the pool has good environmental conditions suitable for microbial habitat and proliferation, the biofilm is rich in biota, long in food chain, high in microbial concentration, strong in activity, free from sludge bulking, low in sludge production and easy to precipitate. In addition to effectively removing organic matter, biological contact oxidation has many purification functions. If properly operated, it can also remove oxygen and phosphorus. The key part of biological contact oxidation method is filler. Traditional honeycomb plastic pipes are easy to be blocked, and now suspended soft fillers and suspended or semi-suspended spherical fillers are often used, which can effectively prevent blockage, with large area and good treatment effect. Biological contact oxidation is one of the technologies used in the treatment of domestic sewage in residential quarters earlier. The main process flow is: raw sewage → primary sedimentation tank → contact oxidation tank → secondary sedimentation tank → disinfection tank → discharge primary sedimentation tank. The two secondary sedimentation tanks are vertical sedimentation tanks, and the rising flow rates are 0.6 ~ 0.8 mm/s and 0.3 ~ 0.4 mm/s respectively. Trapezoidal straight pipe packing is used, and jet aeration is used in the central corridor of the tank. Gas-water ratio10:1~12:1,residence time 2.5~3.3h, average designed influent BOD5=200mg/L, effluent BOD5 = 20mg/L. ..

1.2 two-stage activated sludge process. Two-stage activated sludge process, abbreviated as AB process. This law regards sewage pipelines and sewage treatment plants as sewage treatment systems. Its technological characteristics are: no primary sedimentation tank, high load in section A, low load in section B, sludge in sections A and B flowing back respectively, making full use of microorganisms in sewage pipelines, creating good environmental conditions for dominant microbial populations growing in different periods, giving full play to their functions, having strong impact load resistance and stable treatment effect. The main process flow is: raw sewage → grid → top aeration regulating tank →A-level aeration tank →A-level sedimentation tank →B-level sedimentation tank → discharging this kind of equipment. Self-priming jet aerator, unsupported sludge suspended biological filler, lateral flow inclined plate sedimentation tank and other advanced technologies are adopted. The removal rate of BOD5 is 90%, and that of COD is 80%.

1.3 sequencing batch activated sludge process. Sequencing batch activated sludge process, abbreviated as SBR process. In principle, the main process equipment of SBR method has only one gap reactor, which can be divided into five stages: water inflow, reaction, precipitation, drainage and idle in one operation cycle. Great progress has been made in the development of decanter, the key equipment of SBR process. At present, there are three commonly used decanters: siphon type, rotary type and sleeve type. SBR process is simple and cost-saving. The ideal push-flow process has the advantages of large thrust, high efficiency, flexible operation mode, good nitrogen and phosphorus removal effect, no sludge bulking, impact load resistance and strong treatment capacity. The main process flow is: raw sewage → regulating tank →SBR reaction tank → disinfection tank → effluent of a sewage treatment station in Shanghai adopts this process flow. The designed average flow rate is 750m3/d, the influent water quality BOD5 = 200mg/LSS = 250mg/L, TN = 40mg/L, NH4+= 20mg/L, and the effluent water quality meets the wastewater discharge standard in the upper reaches of Huangpu River, namely

1.4 anaerobic biofilter. Anaerobic biofilter is an anaerobic biofilm treatment device with filler as microbial carrier. Anaerobic microorganisms grow on the surface of the carrier. When the sewage passes through the fixed bed formed by the carrier from bottom to top, under the action of anaerobic microorganisms, the organic matter in the sewage can be anaerobically decomposed and biogas can be produced. There are many varieties of anaerobic biofilter, and the filler develops rapidly. Its technological process is as follows: water inflow → sedimentation tank → anaerobic digestion tank → anaerobic biofilter → exhaust pipe → oxidation ditch → air inlet and exhaust well → sewage enters anaerobic digestion tank for hydrolysis and acidification after pretreatment in sedimentation tank, which can improve the biodegradability of sewage and create conditions for subsequent treatment. Under the action of ventilation system, the biofilter is in an aerobic state, which prevents the production of methanogens in sewage, so that the whole system is still in an acidic stage, while the dissolved oxygen in the oxidation ditch can generally be stabilized at 1.5 ~ 2.8 mg/L, and the sewage is further aerobic treated here. The essence of this process is similar to that of A/O process, except that facultative anaerobic biofilter strengthens the anaerobic stage. The pumping system is the key to the treatment process. Its main advantages are no energy consumption, low cost, simple management, no noise, no peculiar smell, fast film formation, less excess sludge, good effluent quality and stable operation effect.

2. Discussion on the problem As far as the treatment technology of domestic sewage in residential quarters is concerned, the mature technology and technology of urban sewage treatment can be adopted at present, but the treatment of domestic sewage in residential quarters has its own characteristics and should be considered.

2. 1 The sewage flow in the residential area is small and the biodegradability is good, so the biofilm treatment technology should be given priority. Biofilm method has the advantages of rich biological phase, high microbial concentration, long food chain, no sludge bulking and good sludge settling performance, and is suitable for a small amount of sewage treatment. With the adoption of new packing, the blocking problem that was worried in the past has been basically solved.

2.2 Due to the shortage of residential land, priority should be given to the sewage treatment process covering the whole province, and certain measures should be taken in the design. Now it is generally designed to be underground or semi-underground, forming a pattern that the underground is a sewage treatment station and the ground is a green space or flower bed, which can beautify the environment. However, in this design, attention should be paid to buried depth, lifting equipment, ventilation requirements and odor treatment.

2.3 Due to the limitation of the number and professional quality of community managers, priority should be given to processes that are convenient to operate, maintain and manage, and efforts should be made to improve the automation of operation and management.

2.4 The construction period of residential quarters is tight, and the transformation of sewage treatment facilities from structures to equipment seems to be an inevitable trend. Assembled sewage treatment equipment is adopted, which has the advantages of simple installation, short construction period and easy maintenance. Daya Bay Nuclear Power Station introduced a small sewage treatment station from France. The main equipment is all parts, which are assembled on site. Among them, the heating pool and sedimentation pool are composed of 10 small pieces, which can be completed in only 20 days from earthwork excavation to debugging. Domestic small sewage treatment equipment manufacturers have mushroomed, but the good and the bad are mixed. Most manufacturers are weak in design, research, testing and testing, and the product quality is difficult to guarantee, and the after-sales service is poor [3]. The state should strengthen supervision and management in this regard.

2.5 With the improvement of effluent quality requirements, it is difficult for a single process to meet the needs, and combined sewage treatment technology and equipment have been developed. At present, there are mainly multi-stage aerobic treatment, anaerobic+aerobic treatment and anaerobic+anoxic treatment. Anaerobic biological treatment has broad prospects in reducing energy consumption and recovering bioenergy. Organic matter in sewage itself has certain potential energy. In anaerobic treatment, on the one hand, aeration is not needed, which can reduce energy consumption; On the other hand, its biogas can be recycled for heating and heating in residential areas, forming an ecological balance system in residential areas, which is an ideal development trend.

3. Conclusion Domestic sewage treatment station in residential quarters has played a positive role in preventing pollution and protecting water environment. Although the development trend of urban sewage treatment is centralized treatment rather than decentralized treatment, the author believes that in some small and medium-sized cities in China, small domestic sewage treatment stations will still exist for a long time, so we should attach great importance to their technical development and equipment development.

refer to

[1] Cyndi Luo, Claire Kuo, Zhang Daqun, Characteristics Analysis of Anaerobic Sequencing Batch Reactor (ASBR). Water supply and drainage, 1997.4.

Stone. Introduce a small sewage treatment station. Water supply and drainage, 1993.8.

[3] Cao Ruiyu, Gu Guowei, Huang Juwen and so on. Development and analysis of combined domestic sewage treatment equipment. China water supply and drainage, 1997.4.

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