腊明第二作者文章 AMM.260-261.1013

Research on Leachate Treatment Process Selection of GuangxiMunicipal Solid Waste PlantHao Cheng1,a, Ming La3,c, Jianhua Xiong*,2,b1.Department of Biological and Chemical Engineering, Guangxi University of Technology, Liuzhou,545006,China2.Department of the Environment of Guangxi University, Nanning,530004, China3School of Chemistry &Chemical Engineering ,Pingsingshan University, 467000, Chinaa iamchenghao@,b happybear99@ ,c laming82@ Keywords: Leachate. Refuse Disposal. Pollution-Free Disposal. Environmental Pollution.Abstract. Based on the research of municipal solid waste leachate treatment technology in China, aiming at several typical leachate treatment technologies in the Guangxi area, this paper has made analyses and studies. It has made comprehensive investigation of materials, and has obtained the final leachate treatment technology scheme applicable in the Guangxi area.IntroductionThe leachate treatment in urban landfill site is still a big problem in the process of landfill design, operation and management. The leachate is the liquid product due to gravity flow in landfill site, mainly originating from precipitation and containing water in the garbage itself. Many factors may affect the nature of leachate in the process of liquid flow, including physical factors, chemical factors, biological factors, etc., so the properties of leachate change within a substantial range [1-4].A lot of groundwater pollution incidents in landfill site shows that the leachate is the most important pollution source of groundwater. The leachate contains considerable toxic substances with high concentration, which become huge threat to the environment. The leachate in urban landfill is a kind of high-concentration organic wastewater with complex components, so non-disposal but direct discharge of leachate into the environment will cause serious environmental pollution [5-6]. For the purpose of environmental protection, it is necessary to make treatment of leachate. However, due to the complexity of refuse leachate, leachate treatment becomes one of the difficult scientific problems in the world.Current Status of Municipal Solid Waste Leachate Process SelectionRefuse leachate is sewage percolated from refuse in the process of storage and landfill due to fermentation, rain water erosion, surface water and soak of groundwater water. As a kind of special waste water with high COD, high ammonia nitrogen and complicated water composition, leachate is still the difficulty in the water treatment. Although there is no a large quantity of leachate in a waste treatment plant, its organic compounds and ammonia nitrogen concentration are dozens of even one hundred times of those of in common urban sewage. Generally speaking, the pollution load of leachate produced in a large refuse landfill site is equivalent to a medium-sized sewage treatment plant, so we must carry on the effective treatment. According to different garbage disposal processes, leachate treatments are also different. Refuse landfill includes incineration method, composting method and landfill method. In view of these three different main refuse disposal methods, correspondingly, the leachate treatment technologies are different.The selection of leachate treatment process scheme is determined by various factors. Next, several major factors will be chosen from many factors and introduced: requirements for water quality discharge, biochemical performance of raw water, local climate temperature condition in the plant, etc.Of course, there are not only three factors for process selection. And it also involves in water amount of leachate treatment. Different technological requirements for water amount are different, for example, the secondary DTRO process requirement for water treatment amount is less than 500 tons/day or so, but the MBR process demand is greater. Meanwhile, it also includes stability of process operation, covering area of plant, engineering investment condition, practical operability, etc.After 2008 new standard was enacted, the old standards, which mainly use biological method + physicochemical method, primarily cannot satisfy the standard discharge. After the publication of new standard, the main technologies of leachate treatment focus on biological method + physicochemical method, namely, MBR process, and the other one is pure physical treatment, namely, membrane treatment.Introduction of Main TechnologyTraditional Biological Treatment Process. The advantages of microorganism application include de-nitrification and phosphorous removal, the smaller output of sludge, covering less, low construction and operation cost, cheaper processing equipment, simple operation management, low cost, high equipment load, recovering a large number of resources, etc. As the disadvantages are concerned, due to the special properties of waste leachate, a single process cannot achieve the ideal treatment effect; it is influenced by the climate condition, and relies on biochemical performance of leachate seriously.MBR Process. The main pollutants, i.e. COD, BOD and ammonia nitrogen can be effectively degraded, without the secondary pollution. 100% biological cells are separated. The effluent has no bacteria and solid content. Engineering covers a small area. A little of excess sludge need no deodorizing device. The system device is simple and compact, covering less. Operation cost is low, maintenance is simple, and biochemical performance is affected by climatic conditions greatly. For the old landfill site, leachate biochemistry is gradually reduced, and the problems exist in the operation of MBR.DTRO Process. It is designed especially for the treatment of feed liquid with high concentration, to solve the problem of membrane blocking, but not to rely on special pretreatment. The advantages include over three-year service life of membrane, which improves the system stability, easy maintenance of components, low replacement cost of filtering membrane, and high concentration ratio. The disadvantages are expensive membrane and periodic cleaning of membrane; meanwhile, the intercepted concentrate treatment on the membrane side is also a big problem, which needs other process to make treatment. When replacing membrane, it is required to disassemble and install the overall tubular, which is quite troublesome.According to the contrast of the above main process, from the aspects of technical feasibility, covering area, reliability, economic analysis and long-term plans, MBR need high biochemical performance for operation, so it is difficult to operate normally in the northern Guangxi area, especially in winter. Meanwhile, most of Guangxi areas belong to karst topography, with karst geology existing, the calcium content in water quality of leachate is higher. The salt content in leachate nearby the coastal zone will be higher than that in the area relatively close to the sea. The different environmental factors will affect microbial survival and reproduction. However, DTRO process does not influenced by environmental factors, with high system stability, and blocking does not occur easily. Meanwhile, the problem of concentrate solution treatment exists, although it adopts recharge and evaporation methods, but cannot solve it. Compared with MBR process, DTRO process is more suitable for the Guangxi area, selecting a reliable, long-term, stable, and executable leachate treatment technology in accordance with economic benefit and right cost.Conclusion of Guangxi Typical Refuse Leachate Treatment TechnologySelection of refuse leachate treatment technology, which is suitable for social and economic development situation in Guangxi area, is an important task. For different ways of refuse disposal, the adopted technologies of leachate treatment are different. According to several typical refuse leachate treatment technologies in Guangxi area, make comparative analysis:Leachate Treatment for Incineration and Composting Methods.For instance, in Pingshan of Guilin, adopt the multi-stage anaerobic +aerobic treatment; after stable operation, water quality effect of effluent is good in the early stage, which can meet the national discharge standards. According to this point, the incineration and landfill technology can use biological treatment method. Of course, aiming at the severity of new standard, adopt the subsequent physicochemical treatment, i.e. increasing membrane treatment method. In the area, the cases for incineration and composting treatment of refuse are less, in most situations, landfill treatment is adopted.Aiming at Landfill Method. For example, in the Guilin Chongkou Refuse Leachate Treatment Plant, adopt “USAB + MBR (Membrane Bioreactor) + NF (Nano-filtration) + RO (Reverse Osmosis)". In Mashan County and Binyang County, it is suggested to adopt leachate treatment technology. In the normal operation, treatment effect of the process can meet the discharge standard, but along with the aging of leachate, biochemical performance becomes worse, under these circumstances, the efficiency of leachate is very low even after biochemical treatment; meanwhile, the process has a certain application range for the environmental problems such as climate factors and so on. Aiming at the above similar process, for example, a Nanning landfill site cannot be in success operation; outside the area, Beijing Asuwei Landfill Site adopts the “anaerobic + MBR + NF + RO” process, but debugging has not succeeded yet. These show us again that the debugging for biochemical method to be used for waste leachate treatment has great difficulties. Therefore, for pure physicochemical treatment, the biochemical performance, climate and other problems are not considered; for example, in the Beihai Baishuitang Refuse Disposal Plant, during the primary treatment period, use “Double-Stage Tube Reverse Osmosis (DTRO)” to make pure physical and chemical treatment. For example, In Hechi area, adopt the secondary DTRO, which can be in stable operation so far. Through the comparison of the above process in the aspects of economy and the treatment effect, adopt the secondary “DTRO” treatment, which is more suitable for the situations of Guangxi.Existing Problems and SuggestionsAt the same time, there are some problems and suggestions in the operation of the secondary DTRO: Concentrate Treatment. In most cases, the present refuse leachate treatment technology adopts the combination process of life treatment and membrane filtration; therefore, after membrane filtration, the leachate has a certain amount of concentrate incurred. Concentrate treatment is a big problem of current refuse leachate treatment. Currently, in China, mostly recharge it to the landfill site, but with the passage of time, the disadvantages of recharge gradually will reveal. In domestic landfill sites, different degrees of pollutants accumulation occur, electric conductivity of leachate increases, water productivity of membrane declines, even the increase of electric conductivity leads to the failure of membrane filtration. According to the concentrate problem, widely adopt recharge method and evaporation method at home and abroad.Membrane Pollution. Membrane pollution is an inevitable phenomenon incurred in the application process of reverse osmosis membrane, but also is the biggest constraint in the application of reverse osmosis. It not only increases operation cost, shortens service life of membrane, but also directly influences the continuous and effective operation of membrane. DTRO membrane is a kind of anti-pollution membrane. Due to its membrane material, membrane structure and unique working principle, it is determined that it is not easy to pollute membrane. But when water and solute in the leachate are separated, although take appropriate pretreatment method for basic solution, pollutants in the leachate are still gathered on the membrane surface, and membrane pollution occurs, to make the membrane separation performance and permeation rate reduced, affecting the normal use of membrane. In order to restore the performance of membrane, it is required to clean up membrane regularly.AcknowledgmentThis work was supported by the Scientific Research Foundation of GuangXi University (Grant No. XBZ110377 ).Corresponding AuthorJianhua Xiong, Email: happybear99@References[1] Wang Baozhen, Wang Lin. Urban Solid Waste Leachate Treatment and Disposal [M]. Beijing:Chemical Industry Press, 2005,P. 6-8.[2] Meng Liao, Xiong Xiangshun, Ma Jian. Recent Status and Existing Problems of Refuse LeachateTreatment in China [J]. 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