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.Application of multi-soil-layer system (MSL) in rural wastewater treatmentAbstract: with the continuous improvement of living in rural farmers, the water consumption of residents is increasing, rural sewage emissions will continue to increase, if not treat effectively, the water environment in rural areas will be serious deteriorated, and influence the life quality of rural residents. In this case this paper presents a decentralized sewage treatment system, multi-soil-layer system technology (MSL) application in the rural sewage treatment, this paper summarizes the new technology, you can better understand and practice, especially in the developing countries where is in need of this technology. In the foreseeable future, it can protect public health and the sustainable development of the environment, and it also provides a new way for rural sewage treatment.Key words: rural sewage; multi-soil-layering system; distributed1. IntroductionIn recent years, with the continuous development of economy, peoples living standards continue to improve, rural economic development is also very rapid, but the rural economic development and environmental development is not synchronized, serious rural water pollution. While high technical sewage treatment plants, such as centralized sewage treatment plants are involved in large investment costs, high operating costs, Because of economic constraints, such systems are less suitable for livestock farms and small communities in rural areas. While the multi-media-soil layer system(MSL) sewage treatment system, this decentralized sewage treatment system, it has less investment, low operating costs, high handling load. Besides, the utility model overcomes the defects of the prior soil percolation which is easy to be blocked from the space structure. The sewage treatment system is one kind of the purification technology of sewerage treatment soil developed in Japan in twentieth Century, the soil system will be modularized, and the module is set up around the water in the soil layer to avoid clogging, and adding natural organic materials to soil modules can improve the purification ability of the system.The MSL system consists of a Permeable layer (PL) and a soil mixing layer block (SMB), The Permeable layer is usually composed of larger particles fillers such as gravel, pumice, perlite and zeolite. Higher porosity can effectively prevent clogging of the soil water layer. At the same time, the formation of aerobic environment is conducive to organic degradation. The mixed layer soil is mainly packing soil mixed with other 20%-30% other materials such as activated carbon, wood, iron and other material or soil with local resources. The organic material added in the soil mixed layer can improve the biological decomposition and adsorption capacity of the system, and can also improve the supply of hydrogen in the process of nitrogen removal and promote the removal of nitrogen.There are many researches on MSL system treating urban sewage, livestock wastewater and river water at home and abroad. Researchers in China, Ye Hai et al1 studied the effect of surface load on polluted river water treated by multi-soil-layer system. Song Ying2 had studied the treatment effect of multi medium soil infiltration system for turtle breeding wastewater. Zou Jun3 also pointed out that multi-soil-layer material selection will have a certain impact on the domestic sewage treatment efficiency. In foreign countries, especially in Japan, Thailand and Indonesia, MSL systems have been used to handle various types of wastewater, but the domestic of this technology in sewage treatment in rural areas there is no comprehensive study, This article through to the MSL system technology processing rural domestic sewage research, in order to provide some technical support for the MSL system in the practical application of rural sewage treatment.2.1characteristics of rural sewageFor a long time, Chinas pollution control on rural attention and investment far less than the city, 96% of the villages without drainage pipe network and sewage treatment system, The random discharge of domestic sewage has become one of the main reasons for the deterioration of water quality in the basin, and is also an important factor causing the rural water environment pollution and lake eutrophication. At the same time, it seriously affects the safety of production and living in the rural areas, and seriously affects the economic development. The main features of rural sewage in China are:(1) The amount is huge and increases year by year. Statistics show that in 2002.There are 3.205 million tons of national rural domestic sewage daily emissions. The total nitrogen emission is about 283.1t, total phosphorus daily emission is about 56.6t, basically without any treatment directly discharged.(2) Water quality and water quantity fluctuation are huge. Rural sewage water is not stable, different periods have different water quality, generally do not contain heavy metals and toxic and harmful substances, but contains more synthetic detergent and bacteria, viruses.(3) More sources. In addition to human feces, kitchen generated sewage, there are household cleaning, domestic waste landfill leachate generated sewage, which will then enter the river part of the sewage, will cause greater pollution.(4) Low treatment rate. Part of the system can not run low temperature, rural sewage daily variation coefficient and seasonal variation coefficient, the system a few time high load operation, if there is little sewage, it will stop running 4.(5) Wide and scattered. Scattered geographical distribution of villages caused sewage dispersion and it is difficult to collect.2.2 the main source of rural sewageRural sewage refers to the formation of sewage of the rural areas in the life and production process, including rural production wastewater and rural domestic sewage two aspects. Rural domestic sewage refers to the residents living in the process of toilet discharge of sewage, bath, laundry and kitchen sewage, etc. Rural production sewage refers to livestock and poultry breeding, aquaculture, agricultural products processing and other high concentration of organic wastewater. Because Chinas rural living is scattered, rural domestic sewage showed a small amount and wide dispersion. Lack of appropriate sewage collection, treatment facilities, domestic sewage without treatment will be free to discharge, the health of rural residents to bring greater harm. At the same time, rural sewage production also poses a greater threat to the rural ecological environment.2.3main technologies of decentralized domestic sewage treatment Beginning in 1970s, Japan, the United States, Europe and other developed countries on the use of decentralized sewage treatment of rural sewage treatment, has accumulated a lot of experience, achieved good results. The United States since the mid-20th century began the construction of rural sewage treatment facilities, in 1972 promulgated the first complete clean water, then according to the distributed processing technology in 2002 promulgated the decentralized sewage treatment system application manual 5. 1987, In Denmark promulgated a decentralized sewage treatment guidelines 6. Germany from 2003 to implement the decentralized needle infrastructure system project research, use membrane bioreactor purification to treat remote rural sewage 7. Australia proposed a sewage treatment land use system 8.While research and application of rural sewage decentralized treatment in China began in late 1980s, Compared with developed countries and regions, there are still many gaps in laws and regulations system, technical standard system and management and service system. In recent years, domestic scholars have done a lot of research on rural domestic sewage,and puts forward some mature processing technology, including aerobic biological treatment, anaerobic biological treatment technology, soil infiltration technique and physical and chemical processing technology etc. There are many scholars in the multi-soil-layer system improvement and application development of the Japanese, it has also done a lot of research, some scholars found through experiments: to earthworm soil infiltration layer can also solve the problem of blockage of MSL system, but also can guarantee the winter operation effect in winter 9-10.2.4 Multi-soil-layer system (MSL) technology2.4.1Structural characteristics of multi-media-soil layer system Multi-soil-layer treatment (MSL) system is a kind of land sewage treatment system. Mainly composed of Permeable layer (PL) and a soil mixing layer block (SMB), From top to bottom are waterproof layer, gravel layer, soil layer and mixed layer (two alternately arranged), in addition, the MSL technology has a certain terrain fall from the inlet to the outlet, mainly by the drop let water can automatically flow in the system, at the same time to purify 11.2.4.2 Purification mechanism of multi-soil-layer systemWastewater contains high concentrations of BOD, COD, ammonia nitrogen, phosphate ions and organic matter. When the wastewater into the MSL system, the organic matter in wastewater can be adsorbed on the surface of zeolite and soil through physical and chemical effects, followed by decomposition of soil layer in microorganism, and phosphorus removal is mainly through the soil layer of iron is oxidized to ferric hydroxide after the formation of insoluble iron, then adsorption in wastewater the formation of phosphate coprecipitation. Nitrogen removal is mainly through nitrification and denitrification by ammonia ion, and finally reduced to nitrogen discharge system.2.4.3 Advantages of multi-soil-layer systemMulti-media-soil layer system is used to treat wastewater from traditional soil infiltration system. It has the disadvantages of low treatment load, large ground, easy to block nitrogen and phosphorus removal and other shortcomings 12. The MSL system with soil modular as the core concept, its unique brick type internal structure can form a plurality of aerobic and anaerobic environment in order to promote the removal of pollutants, Among them, the permeable layer greatly improves the water permeability of the system to prevent clogging, adding natural materials in the soil increases the purification capacity of the system.3.ConclusionsWith the economic reform and development, Chinas environmental awareness is also improving, water pollution in rural areas have also obtained more and more attention, The MSL system applicable to the small population, scattered in rural areas, the decentralized sewage treatment system can be widely installed and used in the rural society, especially in rural areas of developing countries such as Chinese, Chinese is in need of such technology, sustainable development can protect the public health and the environment.4.Reference1 Ye Hai Ye et al. Effect of surface load on polluted river water treated by multi-soil- layer systemJ. China water supply and drainage, 2012,28 (19): 74-772 Ying Song et al.Treatment of turtle aquaculture effluent by an multi-soil-layer systemJ.Journal of Zhejiang University Science B.2015,16(2):145-1543 Zou Jun, Chen Xin et al. Effect of material selection of multi-soil-layer system on domestic wastewater treatment efficiencyJ. Journal of ecology and rural environment, 2010,26 (1): 14-184 Zhang Keqiang et al. Rural sewage treatment technologyM Beijing: China Agricultural Science and Technology Press, 2006.105 Chen Jinming et al. Policy and experience of managing decentralized wastewater treatment systems in the United States J. China water supply and drainage, 2004,20 (6): 104-1066 Hans B.Danish guidelines for small-scale constructed wetland systems for onsite treatment of domestic sewageC.Proceedings of the 9th International Conference on Wetland Systems for Water Pollution Control, Avignon, France,2004:1-87 Li Wushuang, Wang Hongyang. Status and treatment technology of rural decentralized domestic wastewater J. Tianjin Agricultural Sciences, 2008,14 (6): 75-778 Zhang Jiawei, Zhou Zhiqin. Application of decentralized treatment technology for rural domestic sewage J. environmental science and management, 2011,36 (1): 95-999 Wang Xixi, Guo Feihong, et al. A new improved capillary infiltration ditch for domestic wastewater treatment. J.environmental chemistry,2011,30(3): 721-72210 Zhang Xiaowei, Li Jianchao, et al. Experimental study on earthworm enhanced land treatment of rural wastewater J. Journal of agro environmental science,2009,28 (6): 1225-122911 Hu Hongqi, Yang Yong et al. Analysis of practical application of two efficient rural sewage treatment technologies J. Heilongjiang environmental bulletin, 2016, 40 (1): 20-2412 Xin Chen et al.An introduction of a multi-soil-layering system:a novel green technology for wastewater treatment in rural areasJ.Water and Environment Journal.2009:255-262.
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