With the development of the township enterprises and farming industry and the improvement of the living standards of farmers, the amount of water and sewage in the countryside is increasing. Is expected to 2010 China's urban sewage emissions will reach 270 tons. With the implementation of national energy conservation and emission reduction policies, the pollution caused by domestic sewage in rural areas is becoming more and more attention. Report on a survey of the Ministry of construction completed in January 2005 "rural living environment current situation and problems of display: China is representative of 43 counties in nine provinces of 74 villages, 96% of the villages no drainage channels, random discharge of sewage of production and living, seep into the ground or discharged into the adjacent rivers, resulting in large areas of water pollution. 2006 in the central policy of the call, the new rural construction is booming all over the country. How to control domestic sewage discharge in the new rural construction is a topic of concern. According to our hospital on the experience accumulated in the suburbs of Beijing Rural Planning and farm house design project of rural sewage treatment as briefly discussed in this paper.

Selection of sewage treatment method

Should fully consider the local natural, economic and social conditions, according to local conditions, the use of investment province, operating costs and low energy consumption, maintenance and management, treatment effect of the sewage treatment process.

The 1.1 housing is relatively dispersed area with three decentralized sewage treatment tank format form. At present many rural areas in China by three format septic tanks sewage treatment, Beijing suburban rural areas according to the standard of the Beijing Municipal Health Village will household toilet flushing, three format, septic tanks, pools of subsequent infiltration wells, penetrate to the soil drainage. Toilet main structure is divided into two parts on the ground and underground, on the part of the toilet, size is generally 1440x1440mm; underground septic tank, structure size 3720x1680mm, high 1120mm. three format septic tank volume ratio to 2:1:3. Basic 100mm thick pea gravel concrete, walls, the first grid and the second grid partition walls 240mm. The second and the third grid partition can is 120mm wall, the inner wall of the pool by 1:3 cement mortar rendering, and then the 1:2 cement mortar. See Figure 2, 1. Rural three squares septic tanks and urban septic tanks are different, the city of 1 ~ 3# septic tank is two squares, 4 ~ 9# septic tank using is format. Rural three format of the three lattice of some seepage, treated water is directly poured farmland; some do not render, the third lattice water seep directly into the underground. Three format septic tanks toilet flushing water inlet COD value is in 2000 above, the COD removal rate is about 35%, 15cm thick soil layer on COD removal rate was 70%. Based on the above data, rural toilet sewage septic tank treatment again by 15cm thick soil layer can basically meet the requirements of the national integrated wastewater discharge standard "level 3 emission, but natural water emissions will still environmental pollution of water bodies. Therefore, countries and relevant departments should consider the technical transformation of three format septic tanks so that it can handle on water depth.

1.2 in the village area residents can be divided according to the region Baotuan were set up small sewage treatment equipment, using biochemical treatment method. Biochemical treatment is the use of microbial metabolism, the pollutants in the sewage degradation, transformation and stability, so that the process into a harmless. The treatment cost is relatively low, and the operation management is more convenient, and the treatment method has two types: aerobic treatment and anaerobic treatment. Common methods of aerobic activity sludge, oxidation pond, oxidation ditch, biofilter and rotating biological contactor, contact oxidation and aerobic biological fluidized bed; common methods of anaerobic treatment with anaerobic pond, anaerobic digestion, up flow anaerobic sludge bed and anaerobic filter etc.. Small treatment equipment is recommended in the rural area. Small processing equipment has MBR integrated treatment equipment, double biological membrane - micro flocculation filtration equipment, aeration - soft fiber filtration of domestic sewage integration equipment, etc.. Japan's rural sewage treatment mainly uses the membrane bioreactor, the use of small domestic sewage purification equipment, sewage treatment equipment is small in size, simple operation and operation. The sludge from the sewage can be transported to the field for fertilizer. At present, there are 8 million small purification devices installed in Japan, the service population of 36 million, the lack of drainage system in the rural areas of more applications, relatively mature technology.

1.2.1 working principle introduced the membrane bioreactor technology integrated membrane treatment and biological treatment technology advantages. Membrane bioreactor using membrane separation equipment will be activated sludge biochemical reaction tank and high molecular material cut and keep, thus greatly improving the concentration of activated sludge, hydraulic retention time (HRT) and sludge retention time (SRT) can control respectively, and the reactor difficult degradation material continuously in response, are effective for degradation of organic compounds, the porosity is less than or equal to 0.08 micron film will clean water and impurities separated completely, effluent SS value tends to zero. Vast majority of bacteria, microbes, the heat source, the virus along with its carrier a trapped in the sewage, subsequent disinfection means to do for the sterilization of double insurance, to avoid the traditional process may appear quality problem, effluent water quality is fully guaranteed. Its pre-processing and post-processing are extremely simple, so it occupies a small area and can be controlled by programmed control. MBR sludge concentration (MLSS) can reach 30 ~ 20000mg/l above, so the organic matter in the MBR is its oxidative decomposition, basic does not produce sludge, little mud, does not produce secondary pollution, only using simple PLC technology for automatic control, membrane pollution alarm and open the corresponding backwashing facility can be programmed management of the water level. The membrane bioreactor is mainly composed of a tank body, a membrane module, a blast aeration system, a pump and a pipeline valve instrument.

Compared with the traditional biological treatment technology, the 1.2.2 technology has obvious advantages: (1) the equipment is compact, the area is small; the concentration of sludge in the bioreactor can be increased by 2 ~ 5 times, and the volume load can be greatly improved. (2) the water quality of the effluent is good, and can be used directly. (3) in the biological treatment unit, the sludge concentration is high, the sludge age is long, and the removal rate of the organic matter is high. (4) the removal efficiency of nitrogen and phosphorus is higher. (5) the operation is simple and easy to control, easy to realize automatic control operation, no need of professional personnel operation, simple management and so on.

1.3 large villages combined in a larger population, relatively concentrated in rural areas can be a village, or is close to several villages in the combination of centralized sewage treatment plant, as far as possible the use of wastewater land treatment system and method with artificial wetland, high rate Algae Pond, land infiltration filter system, unpowered anaerobic treatment system and sys fast biological treatment technology, "filter" sewage treatment system (filtering land and underground pipe drainage combined sewage reuse systems) and other types. Sewage land treatment system is under the condition of artificial control, the use of soil microbial plant composition of the ecological system to make the sewage purification treatment method. When the sewage is purified, the nutrient material in the water can be recycled, so that the sewage is harmless and resource. Land treatment process is slow filtration, rapid infiltration of overland flow, wetlands, subsurface infiltration system and the basic process of the fifth can consist of several complex processing system. Wastewater land treatment system generally consists of the following parts: sewage pretreatment facilities; sewage regulation and storage facilities; sewage transportation, water distribution and control system; land purification field; purifying water collection and utilization system. Among them, the land purification field is the core link. At present domestic new rural construction application is successful is soil complex ecological sewage treatment system --- underground ditch pattern soil sewage treatment technology.

1.3.1 working principle of underground ditch pattern sewage land treatment technology is refers to the use of natural purification ability of plants and soil purification and biological artificial system combining the sewage purification efficiency, low energy consumption, low cost of sewage treatment system. Trench sewage treatment technology from Japan, the application in Japan has more than thirty years of history. Sewage water interception first through the filter bed biological filler and soil composition, filtration of the sewage and sewage interception in small suspension; the soil capillary infiltration diffusion principle and siphon phenomenon as the sewage flow power, the colloidal particles, the solid particles in the sewage that pollutant dissolution, filtration and separation quickly and effectively in the physical and chemical adsorption the soil under the action of the soil, and by anaerobic and aerobic microbial organic substances in the sewage to strengthen the decomposition, a simple C, N, P and other inorganic substances, and the nature of the material circulation in the soil for planting plants in the absorption and utilization, maintain the ecological system of nature. Therefore, it is also called land sewage treatment technology as the natural ecological treatment technology. The mechanism of sewage purification is soil capillary action, soil adsorption, filtration, biological degradation of modified soil, and plant uptake in soil.

The working process of 1.3.2 wastewater by raw water grille grit removal of bulk to regulation pool dirt and inorganic particulate matter in the sewage, are regulated, and the water quality of water, a water ascending into the ditch type land treatment system by regulating pond, water distribution system will be uniformly dosed into the filtration sewage treatment unit, in the filtration processing unit through the redistribution of filler layer, the soil capillary rise to the surrounding medium layer (modified soil or plant root zone), after the biochemical effects of soil physical, chemical and microbiological effects, and plant surface soil in absorption and utilization, purification and deodorization, purified water by collecting direct reuse or discharge system. The waste land sewage treatment system is composed of three parts: A water distribution system; B filtration treatment system: the core treatment section of this process; the C water collection system. See figure 4.

1.3.4 process characteristics

(1) advanced ecological water treatment technology, no noise, odor pollution, system can be integrated with the surrounding environment, and truly realize the ecological concept of the residential area of green, energy saving and environmental protection. (2) operating costs are low, only for the traditional process operating costs of 1/5. (3) can be carried out modular decentralized treatment design, to achieve the nearest treatment of sewage, the nearest reuse, while saving investment in pipe network, it is conducive to the comprehensive planning of the rural network. (4) the anti shock load capacity is strong, the system runs stably and reliably. (5) there is no equipment room to save the cost of construction investment. (6) the effluent quality reached the urban sewage regeneration use urban miscellaneous water quality "(GB/T189202002) and" urban sewage regeneration use of landscape and environmental water quality "(GB/T189212002 as prescribed in the water quality standards.

2 existing problems:

2.1 in the choice of rural domestic sewage treatment process should be according to the degree of the raw water quality, drainage quantity and treatment should be achieved, local topography, climate and other natural conditions, operation and management technologies and capital reserves, can use space and operating costs low to choose suitable treatment process.

2.2 China's rural domestic sewage treatment work started late, there is no scale. It is not completely suitable for the domestic and foreign technology, and it is not completely suitable for the domestic. China's scientific research institutions, independent research and development of many different kinds and advanced technology of the domestic sewage treatment device, but for rural to say, high efficient, low investment, low running cost of technology really is applicable to the construction of new countryside.