What are the main treatment methods of rural sewage?

Rural life is becoming more and more urbanized, and domestic sewage mainly comes from toilet washing water, kitchen washing water, washing machine drainage, shower drainage and other drainage. According to the concentration of pollutants in water, it can be divided into two parts: black water (toilet flushing water) and gray water (the rest of the drainage water).

Unit treatment technology of rural domestic sewage

In recent years, rural domestic sewage treatment processes are different, but they are all different combinations of each unit treatment technology. Practical technologies for rural sewage treatment include septic tanks, sewage purification biogas digesters, ordinary aeration tanks, sequencing batch reactors, oxidation ditches, biological contact oxidation tanks, constructed wetlands, land treatment and ecological ponds. According to the functional requirements of the receiving water body, combined with the economic situation, infrastructure, complete natural environmental conditions and drainage destination in rural areas, the treatment technology suitable for the local area is selected.

1. Pretreatment technology

Rural domestic sewage sources are many and scattered, so it is suggested to follow the principle of rain and sewage diversion. Rainwater is collected separately through pipes or drains, and then directly discharged into the ecosystem for treatment or irrigation of farmland. For the collection and pretreatment of domestic sewage, it is suggested to keep septic tanks or septic tanks near the villagers' doors. Septic tank can not only collect sewage, but also remove some organic matter through microbial metabolism.

A new septic tank is built, and the process flow is separation tank-septic tank-acidification tank-oxidation tank-discharge. The process has the advantages of no power, low energy consumption, small floor space and good effluent quality. However, septic tanks have some disadvantages, such as being difficult to clean, producing malodorous gas and blocking pipes. Sichuan drainage authorities suggested using grid grit chamber instead of septic tank, which can remove large debris before sewage is connected to municipal pipe network to prevent blockage, and the biodegradability of sewage will not be affected. It is easier to achieve this goal by reasonably transforming the pit near the villagers' entrance.

Qing Zhipeng and others designed the pretreatment device of grid grit chamber to remove large debris and grit, which not only achieved good results, but also reduced the construction cost.

2. Biological treatment technology

Biological treatment technology is to use the metabolism of microorganisms to transform dissolved or colloidal organic pollutants in sewage into stable and harmless substances. The content of organic matter in rural domestic sewage is relatively high, and the content of toxic and harmful substances is low. Biological treatment is often the core of the treatment process. At present, the technology of treating domestic sewage by biological unit has matured, and many new processes have been continuously developed. Biological treatment technology includes anaerobic treatment and aerobic treatment.

3.2. 1 anaerobic biological treatment technology

Anaerobic biological treatment technology does not need aeration and oxygenation, and produces less sludge. It is a low-cost and easy-to-manage sewage treatment technology, which can meet the technical requirements of rural domestic sewage treatment. The common processes in rural sewage treatment include anaerobic biofilter and compound anaerobic treatment technology.

3. Anaerobic biofilter

Anaerobic biofilter is a sealed tank, in which fillers are placed, and sewage enters from the bottom and is discharged from the top. The process has the advantages of low energy consumption, simple operation, strong treatment capacity, high microbial concentration in the filter, no need to set up mud-water separation equipment, low effluent ss and so on. The existing problems are high filter material cost, easy plugging and thick biofilm, so the concentration of suspended solids in influent must be strictly controlled. Ma Chuanjun and others used oyster shell as filter material to study the treatment effect of anaerobic biofilter on domestic sewage at low temperature in spring. The results show that the sewage temperature is 14? 16 C, influent COD concentration is 500? When the dosage is 600 mg/L and the hydraulic retention time is 1.4 h, the COD removal rate can reach 83%.

4. Composite anaerobic treatment technology

Combined anaerobic treatment technology combines the advantages of anaerobic sludge bed reactor and anaerobic biofilter, which is a new technology to treat domestic sewage in concentrated residential areas. This technology has the advantages of good treatment effect, low energy consumption, low operation cost and convenient operation and management. The compound anaerobic reactor developed by Shanghai Municipal Engineering Design and Research Institute adopts the anaerobic treatment combined process mode, which has good treatment effect on rural domestic sewage in Shanghai.

5. Aerobic biological treatment technology

Aerobic biological treatment technology is a method to treat pollutants by aerobic microorganisms (including facultative microorganisms) under aerobic conditions, and the removal rate can reach more than 90%, which is generally suitable for villages with good economic conditions or high requirements for effluent. Aerobic processes suitable for rural domestic sewage treatment include biological rotary drum, biological rotary table, SBR, biological filter and oxidation ditch.

6. Biological contact oxidation tank

Biological contact oxidation tank is a biofilm method. In this technology, sewage is soaked in all fillers, and pollutants are removed by biofilm attached to fillers during the three-phase contact of oxygen, sewage and fillers. The biological contact oxidation tank is convenient to operate and manage, and is more suitable for rural areas.

In China, biological contact oxidation technology has been studied and applied in some towns and villages with limited land use, low temperature in winter, good economic conditions or high water demand, such as Puxin Village, Luogang District, Guangzhou, Dongbei Village and Zhao Jia Village, Dai Nan, Taizhou City, Jiangsu Province, and Qukou Township, Pingluo County, Ningxia.

7. small tentacles (same as small bristles)

Sequencing batch activated sludge process (SBR), also known as intermittent activated sludge process, integrates regulating tank, aeration tank and sedimentation tank without sludge reflux system. The process has the advantages of simple operation, low investment, stable effect, difficult expansion of sludge, strong impact load resistance and strong nitrogen and phosphorus removal ability. It is suitable for the treatment of small and medium-sized domestic sewage in rural areas of Gao Quan with developed economy, tight land use, large water quantity change and high water quality.

The integrated airlift SBR process was used to treat rural domestic sewage with low carbon-nitrogen ratio. The effluent water quality indexes of COD, NH/-N, TN and TP all reached the secondary requirements of GB 189 18—2002. Yan et al. SBR with rice husk as carrier has good simultaneous nitrification and denitrification characteristics, and the removal rates of organic matter and ammonia nitrogen are 90.46% and 95.64% respectively. Domestic sewage was treated by SBR process in Zhu Jin Village, Nanbaixiang, ouhai district, Wenzhou City, Zhejiang Province. The monitoring results of the project for two years show that the removal rates of COD, BOD5, NH3-N and TP in the effluent reach 80.0%, 93.3%, 90. 1% and 9 1. 1% respectively, and the overall operation effect is stable.

8. Biological aerated filter

BAF (biological aerated filter) is the third generation biological filter which combines the advantages of biofilm process and activated sludge process. BAF can remove organic matter, harmful substances, nitrogen and phosphorus; Small floor space, low capital investment, low energy consumption and operating costs.

Yang Wenlan and others used upflow biological aerated filter to treat rural domestic sewage. The research shows that under the process conditions of hydraulic retention time of 3.2h and gas-water ratio of 5: 1, CODcr, NH3-N, BOD5 and SS all meet the first-class discharge standard of GB 8978- 1996.

9. Ecological treatment technology

Ecological treatment technology can be well combined with the natural and geographical conditions in rural areas, such as abandoned ponds, beaches and abandoned land, so the capital investment is low; There is no need to add chemicals in the operation process, and the operation cost is low; The output of sludge is small, which can reach the agricultural reuse standard and reduce the secondary pollution if properly treated; The process is stable in operation and has strong impact load resistance, which can make the sewage discharge reach the standard stably, and the effluent can be directly reused for farmland irrigation or rural miscellaneous water. The technologies used for rural domestic sewage treatment at home and abroad mainly include constructed wetland, underground infiltration, artificial rapid infiltration and ecological pond.

10. Constructed wetland

The main body of constructed wetland is composed of soil and fillers filled according to a certain grade, and aquatic plants are planted on the bed surface, forming a unique ecosystem. There have been many successful examples at home and abroad. The combined process of biological filter tower and constructed wetland has obvious removal effect on organic matter, nitrogen and phosphorus in rural domestic sewage treatment.

In Europe, subsurface flow systems are widely used, and wetland plants such as reed, calamus and cattail are planted. In rural communities with a population of nearly 65,438+0,000, this system is often secondary treatment.

1 1. Underground infiltration

Underground infiltration is to control the sewage into the taxi layer with a certain depth from the surface, a certain structure and good diffusion performance, so that the sewage can move around under the capillary infiltration and infiltration of soil to achieve the purpose of purification. Zhangshu Village, Luodian Town, Baoshan District, Shanghai adopts underground infiltration system to treat domestic sewage, and the effluent reaches the first-class B standard of GB 189 18—2002. The whole treatment system has low construction cost and basically does not need maintenance.

12. Artificial rapid infiltration

During the operation of the rapid infiltration system, sewage is periodically filled and stopped in the infiltration field, and the anaerobic and aerobic alternate operation state formed in the soil layer is beneficial to the removal of nitrogen and phosphorus. Three-stage series artificial rapid infiltration system was used to treat domestic sewage. The average removal rates of COD and ammonia nitrogen were 79.65% and 94.47% respectively, and the effluent reached the first-class A discharge standard of GB 189 18—2002.

13. Ecological pond

Ecological pond is an ecological sewage treatment technology developed from oxidation pond, which is mainly used for secondary advanced treatment of sewage. It is a natural or artificial pond that uses the natural purification ability of water to treat sewage. Driven by solar energy as the initial energy, organic matter is removed by the bacteria and algae strengthening system, and aquatic plants, aquatic products and waterfowl are recycled as resources. The purified sewage can also be recycled as reclaimed water resources to realize the recycling of sewage treatment, which is the development direction of ecological treatment. High efficiency algae pond system was used to treat rural domestic sewage in Taihu Lake area. The average removal rates of COD, ammonia nitrogen and phosphorus exceeded 70%, 93% and 55% respectively.

Combined treatment process of rural domestic sewage

In rural domestic sewage treatment, unit process often has certain limitations. At present, there are many kinds of rural domestic sewage treatment processes at home and abroad, which are mainly divided into four types: anaerobic+ecological process, aerobic+ecological process, anaerobic+aerobic process and anaerobic+aerobic+ecological process. At present, the domestic sewage treatment process is mature, and there are many integrated equipment and combined treatment technologies. However, due to its characteristics of dispersion, small scale and difficulty in concentration, the treatment of domestic sewage in rural areas in China cannot be extended and replicated from the sewage treatment technology and design parameters in large and medium-sized cities, resulting in high project investment and operating costs. Rural domestic sewage treatment technology must follow the principle of "low investment, low energy consumption, simplicity and high efficiency" and adopt intelligent and fool-like operation mode.

As early as the early 1960s, Japan developed an integrated purification tank technology to treat small and medium-sized scattered domestic sewage, which played an important role in improving the rural water environment at that time. In recent years, Australia has developed a "sewage circulation system combining filtration, land treatment and pipeline drainage" called "filtration" technology, which combines sewage treatment with farmland irrigation needs.