Landfills are located in the suburbs of coastal areas. It used to be a wasteland, but now it has developed into an industrial development zone due to the rapid development of the local economy. The landfill is about 30 kilometers away from the urban area and 8 kilometers away from the nearest town. At present, there are factories around the landfill. The total landfill area is about 16.585hm2, of which the landfill area is 15.838hm2, and the management area and leachate treatment area are about 0.747hm2 The whole reservoir area consists of domestic waste landfill area and demolition waste landfill area. Domestic waste landfill covers an area of 14.078hm2, which is divided into the first-phase reservoir area and the second-phase reservoir area. The first-phase reservoir area is 6.328hm2, which was started from 1998 and closed in 2006, with a landfill volume of about 330,000 tons; the second-phase reservoir area is 7.75hm2, which was started in 2006 and closed at the end of 20 12, with a landfill volume of 520,000 tons. A total of 850,000 tons of domestic demolition landfill areas are located in the west of the landfill area, covering an area of about/. The total amount of landfill waste is about150,000 tons .. By the end of 20 12, all landfill areas have reached the designed storage capacity and the landfill site will be closed. At present, it has entered the management and maintenance stage after closure.
2 local industrial development and land use status
According to the positioning of the new industrial city, the local government has formulated various industrial cluster planning and industrial development planning, invested in the construction of the park's main road network and infrastructure such as water, electricity and communication, vigorously cultivated large enterprises, enhanced the regional economic competitiveness, and formed an industrial structure dominated by five characteristic industries: electromechanical, auto parts, plastic products, hardware and aquatic refrigeration. There are 8 enterprises with 100 million yuan and more than 20 enterprises with more than 10 million yuan. According to the public announcement of the right to use state-owned land by the local land and resources bureau (2065438+June 2002), the auction of local industrial land has hit record highs recently, reflecting the reality of its tight industrial land. Municipal solid waste is incinerated, and the closed landfill is located in the core area of industrial development zone, which has become a "brown plot" of industrial park, which restricts the development of industrial park. According to the national standards, if this land is to be reused, the landfill must reach a stable and safe period before the land can be used, and permanent buildings cannot be built. In order to make the site selection of sealed landfill exert more positive land benefits and social and economic benefits, reduce the maintenance cost of landfill and reduce the risk of landfill pollution to the surrounding environment, we can take advantage of the proximity of landfill to local incineration power plants. The landfill site is disposed by "transportation and incineration", and the backfilling of the relocated site reaches GB 156 18—2008 Soil Environmental Quality Standard (revised Class II Industrial Land Standard), so that the plot is restored to industrial land, and the land disposal fee is deducted from the land transfer income.
3. Conditions for programme implementation
3. 1 transportation conditions. The road network construction in the landfill block is mature and the traffic conditions are good. The landfill is 6 kilometers away from the local incineration power plant, with suitable transportation distance and convenient transportation, and has the transportation conditions required for project implementation.
3.2 Handling site conditions. The local incineration power plant covers a total area of 6 1 124 m2, with a total investment of nearly 300 million yuan, an installed capacity of 25MW and an on-grid power consumption of 65.438+0 billion kW? H/a, the first-phase treatment scale is 1 1,000 t/d, and the annual domestic waste treatment is 280,000 t. The second phase of the project is expected to be implemented in the next two years, when the treatment capacity will increase by 800 t/d, and the treatment capacity will reach1800t/d. At present, the daily treatment capacity of the incineration power plant is 800 t/d, which can provide 200t/d surplus garbage to the landfill for secondary treatment. Two years later, the implementation of the second phase of the project can provide the landfill with a maximum disposal capacity of about 600 tons/day, which can meet the secondary disposal requirements of the landfill.
4 Analysis of landfill waste
4. 1 domestic garbage. The first phase of reservoir garbage project. The first phase of the domestic waste landfill was started on 1998 and closed in 2006, with a service life of 8 years and about 330,000 tons of landfill waste. It has been 6 years since the first-phase reservoir area was closed, and some garbage has been buried in landfills for many years. The degradation of degradable substances in garbage has been completed, the composition of garbage is basically stable and the mineralization rate is high. Garbage in the second phase reservoir area. The second phase of domestic waste landfill was started in 2006, and the site was closed at 20 12, with a service life of 6 years and 520,000 tons of landfill waste. According to the relevant data of municipal solid waste output, since 2009, the average daily landfill volume is about 500 tons. According to the calculation, the 4m-thick garbage in the upper part of the second-phase reservoir area is basically filled with nearly 1 ~ 2a, and its degradation and mineralization rate is low, and it has not even entered the mineralization stage. In 2008-2009, the amount of garbage generated increased compared with the initial landfill. The landfill life is 3-4 years, the organic matter is partially or mostly degraded, and the mineralization rate is high. After degradation, the garbage layer has a certain settlement. It is estimated that the thickness of this part of the garbage layer is about 2.5m, and the bottom garbage is landfill garbage from 2005 to 2007. At that time, the amount of garbage was small. After 5-6 years of degradation, most of the organic matter had been degraded, with a high degree of mineralization, and the amount of garbage settled after mineralization was large. The thickness of this garbage layer is about1.5m.
4.2 Disassemble garbage. The dismantling garbage storage area was opened in 2006 and closed on 20 12. It has been used for 6 years, and the landfill garbage is about 150000 t ... According to the relevant information of local garbage dismantling, the main components of garbage are rubber, sand, bricks, plastics, circuit boards, iron, copper and a very small amount of paper. The sorted garbage has high calorific value.
5. Incineration technology shipped abroad
5. 1 process design
5. 1. 1 process introduction. According to the reception capacity of the incineration plant and the processing capacity of the screening machine, the garbage excavation plan is formulated. After the garbage is excavated, it is screened by the screening machine, and the screened materials are transported to the incineration plant for incineration. The undersize is used as mineralized garbage.
5. 1.2 Equipment and staffing. The design treatment scale of the first phase of the waste incineration plant is 1 1,000 t/d, and the secondary treatment capacity of the landfill is about 200t/d in recent two years. Personnel and equipment. According to the plan of incineration power plant, the second phase will be completed and put into operation in 20 14, and the total design treatment scale will reach 1800t/d, and it is estimated that the maximum acceptable landfill secondary treatment waste is about 600 t/d.
5.2 Processing cycle analysis
5.2. 1 Composition analysis of landfill waste. According to the domestic research on the screening determination of landfill waste, the screened waste in landfill is different with the different landfill years.
5.2.2 Analysis of the total amount of garbage. Combined with the types and years of landfill, the analysis results of the above-screen and below-screen materials in landfill were obtained.
5.2.3 Analysis of garbage disposal cycle. Garbage disposal cycle of landfill.
5.3 Characteristics and uses of mineralized garbage. After several years of landfill, the degradable substances in the garbage are completely or nearly completely degraded, the surface subsidence of the landfill is very small, the garbage itself has little or no leachate and landfill gas, the biodegradable content in the garbage is small, and the COD concentration in the leachate is low. When the landfill reaches a steady state, it is harmless. This part of garbage is called mineralized garbage. According to the properties of mineralized garbage, mineralized garbage contains certain organic matter and nutrient elements, which are mainly used for: ① planting green nutrient soil; ② Building materials; ③ Packing of biological reaction bed.
6 site restoration and land reuse
6. 1 purpose of site soil detection and remediation. After the landfill blocks are vacated, soil tests can be carried out on the vacated blocks, and sampling, analysis and investigation reports are given according to GB 156 18—2008 (Revised Requirements for Soil Pollutant Concentration Control of Industrial Land), and a restoration plan is formulated to restore the site, so that it can meet the requirements of industrial land in this standard and realize land reuse.
6.2 Common repair technology foundation. Technical Guide for Soil Remediation of Contaminated Sites (draft for comment), commonly used remediation technologies of contaminated sites include excavation, stabilization/solidification, chemical leaching, gas stripping, electric power, heat treatment and bioremediation.
6.3 Land reuse. After the earthwork filling of the site is completed and accepted, the plot planning and design can be carried out, and then the site leveling, road network construction, water supply and power supply and other infrastructure construction can be carried out. After the construction is completed, the land can be reused.
7 Investment income analysis
According to each process and equipment, the total investment of the project is about 97143,000 yuan (including the cost of soil remediation, in which garbage incineration is calculated according to 80 yuan /t and site investigation and remediation is calculated according to130,000 yuan, excluding the income or treatment cost of mineralized garbage. According to statistics, the current average price of industrial land is nearly 9.3 million yuan /hm2. After the completion of this project, the industrial land can be sorted out 16.58hm2. Considering that it will take 4.3a years for the project to be completed, the land price will increase by 65,438+05%, and it is estimated that the land fund can be recovered by 65,438+0,772,850 yuan. Therefore, according to this plan, after the land of this landfill is sorted and utilized, it can be
8 conclusion
(1) After the landfill is closed, the land development and utilization should be comprehensively analyzed in combination with local economic development, environmental awareness and current situation, and the most reasonable scheme should be determined.
(2) According to the actual situation of a landfill, it is feasible to carry out off-site incineration and site soil remediation through separation technology and economic cost-benefit analysis.
(3) This scheme puts forward a new scheme for the land consolidation and utilization of closed landfill in high land price areas, and also provides a new way for the stock management of landfill.
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