Engineering design of sanitary landfill of domestic waste?

What is the engineering design of domestic waste sanitary landfill? What is the content? Please read the article edited by Zhong Da Consulting Company.

1 project overview

The management area is located at the highest point of the whole site, close to the off-site road, covering an area of about 3000m2, including the comprehensive building, machine repair workshop, power distribution room, weighbridge, car washing platform and parking lot. In addition, the main entrances and exits of the yard are divided into production vehicle entrances and management entrances, which can effectively realize the safety management of different logistics.

2. Main contents of landfill engineering design

2. 1 grassroots construction in reservoir area

The present situation of the reservoir area is a north-south gully with a bottom of about 300m m, and the site stratum structure is simple, the mechanical properties of rock and soil layers are good, and the foundation bearing capacity meets the requirements, so foundation treatment is not needed. The highest elevation in the reservoir area is 169m, and the lowest elevation is131m. The main blind ditch is set at the bottom of the reservoir with an average slope of 10%. The lowest point at the bottom of the reservoir is located in front of the garbage dam, so that the collected groundwater can be collected there and discharged from the reservoir through the garbage dam by gravity flow. In addition to the large drainage slope formed by the main blind ditch, a drainage slope of not less than 2% should be built along both sides of the valley according to the situation to ensure the smooth discharge of groundwater and leachate. Before the horizontal impervious layer is laid, the site in the landfill reservoir area should be cleaned and leveled, and impurities such as roots, rubble, stones, concrete particles, steel bar heads and glass slag that may damage the artificial impervious layer materials within the vertical depth of 10cm should be removed. Topsoil excavation is the main slope in the reservoir area, the slope is controlled to be no more than 1: 1.5, and an anchor platform with a width of 4m is set every 10 ~ 15m vertically.

2.2 garbage dam

In order to make full use of the current terrain to build the reservoir area of landfill, increase the storage capacity of landfill and prolong the service life, a garbage dam was built at the downstream valley mouth. The garbage dam adopts reinforced earth-rock mixture dam with axial length of 199.57m, the maximum construction height of the dam is 32m, the total width of the dam top is 9m, and the pavement width is 4 m. The shoulders of 3m and 2m are set on both sides, which are also used as anchoring ditches and drainage ditches. Earth and stone for dam construction shall be excavated from the reservoir area, with the maximum dry density of 20kN/m2 and the compactness of not less than 0.93. The internal and external slopes of the garbage dam are all 1∶ 1.5, and the landfill height is 1∶3 near the reservoir area. The slope outside is protected by turf.

2.3 Anti-seepage system

Anti-seepage system is the core part of domestic waste sanitary landfill project. Reservoir geology is dominated by siltstone, argillaceous siltstone and argillaceous sandstone, and the permeability coefficient is greater than the requirements of natural impervious soil. Phase 5 Environmental Sanitation Engineering Volume 22, Phase 5 20 14 Volume 22, Phase 5 20 14 14? 38? With natural seepage control conditions, artificial seepage control must be adopted. This project adopts artificial composite horizontal seepage control system, and the bottom of the reservoir adopts the seepage control structure of 2.0mm smooth HDPE geomembrane and +GCL geopolymer clay liner. The protective layer on the membrane is 600g/m2 nonwoven geotextile, and the protective layer under the membrane is 300mm compacted clay. The slope adopts a 2.0mm double-textured HDPE geomembrane without GCL, and a 6.3mm geotextile composite drainage net is laid on the membrane, which is used as the drainage layer of the slope leachate and the upper protective layer of the impermeable membrane, and the lower protective layer of the membrane is 600g/m2 nonwoven geotextile.

2.4 Groundwater Drainage System

The groundwater drainage system adopts gravel diversion layer and blind ditch. Groundwater is collected through gravel blind ditch and discharged to the collection pit under the garbage dam on the north side of the reservoir area. It is transported to the downstream water body by gravity through the drainage pipe and enters the surface water system. Diversion layer: The gravel diversion layer is covered with 300mm thick gravel with particle size of 20 ~ 40mm under 300mm thick clay protective layer, with 400g/m2 nonwoven geotextile on the upper part and 200g/m2 lightweight woven geotextile on the lower part. Blind ditch: located at the lower part of diversion layer. Because the bottom of the reservoir area of this project is long and narrow, and the slope is large, only 1 main blind ditch is set, and no branch blind ditch is set. The size of the main blind ditch is 2000mm×600mm, and De250mm perforated HDPE pipe is built in.

2.5 leachate drainage system

2.5. 1 calculation of leachate yield

Leachate in the landfill area is an internal flow formed by the infiltration of liquid produced by the decomposition of domestic garbage and external moisture (including precipitation, surface water and groundwater). Its generation is usually determined by five main factors [1-2]: water source, landfill surface condition, garbage characteristics and operation mode of landfill area. According to CJJ 150—20 10, the leachate output of this project is calculated by the permeability coefficient method, and the influence of self-sustaining water of garbage is considered. The formula is as follows: q1= q× (c/kloc-0 /× a1+C2× a2+. Where: q is the amount of leachate produced (m3); Q 1 leachate generated by rainfall (m3/d); Q2 is leachate (m3/d) produced by water-retaining degradation of garbage; Q is the average monthly rainfall for many years (mm); A 1 is the area of landfill operation area (m2); C 1 is the coefficient of transformation of precipitation into leachate in landfill operation area, which should be taken as 0.5~0.8 and 0.7 in design. A2 is the middle coverage area (m2); C2 is the coefficient of transformation from precipitation to leachate in the middle coverage area, which should be taken as 0.4~0.6 and 0.4 in design. A3 is the final coverage area (m2); C3 is the coefficient of transformation of precipitation into leachate in the final coverage area, which should be 0. 1~0.2 and 0. 1 in design. M is the daily landfill volume (t/d) of main domestic garbage; B is the ratio of leachate generated by wastewater capacity to landfill volume, which is designed as 0. 15. According to the above formula, the output of landfill leachate in this project is 89.6m3/d. ..

2.5.2 leachate drainage system

Leachate collection and discharge system consists of diversion layer, blind ditch, sump and lifting pump house. Water-conducting and drainage layer: The water-conducting and drainage layer of the leachate at the bottom of the reservoir adopts 500mm thick gravel (particle size 20~30mm, CaCO3 content ≤ 10%, and permeability coefficient ≥ 1× 10-3cm/s), and the upper part is paved with 200g/m2 light woven geotextile as the filter layer. The drainage layer of guide slope adopts 6.3mm geotechnical composite drainage network. Blind ditch and sump: 1 blind ditch with the size of 2000mm×300mm is set at the bottom of the reservoir area, with 1 HDPE porous pipe laid inside and gravel filled outside. The sump is located at the intersection of the blind ditch and the bottom of the garbage dam, with a plane size of 12m× 10m and a depth of 300mm. Lift pump house: The leachate collected in the sump is finally lifted by the leachate lift pump to the leachate regulating tank downstream of the reservoir area. There is a 1 inclined tube pump in the lifting pump room, with main parameters: Q=20m3/h, H=32m and power 3kW. De 1 10mmHDPE pipe is used as the leachate conveying pipe from the lifting pump house to the regulating tank.

2.5.3 leachate regulating tank

The volume of the regulating tank is calculated according to the empirical formula, and checked with the 3d maximum rainfall. The calculated adjustment capacity is 15860m3. Considering the unfavorable factors such as the change of moisture content of domestic waste actually entering the site, the design volume of the regulating tank is 17000m3. According to the landfill area, pond bottom and slope, the anti-seepage system is designed. The regulating tank is located at the downstream of the garbage dam, adjacent to the garbage dam and leachate treatment station, with an area of about 0.66hm2, an average effective water depth of 12.0m, a longitudinal slope at the bottom of the tank of about 2%, and a slope ratio of1:1.5. The upper part of the regulating tank is made of 2.0mmHDPE membrane, and an anchor ditch is set around the membrane along the top of the tank, and an air duct is set on the membrane to collect the gas generated by anaerobic treatment in the regulating tank and then burn and discharge it. In order to ensure the stability of the membrane cover and prevent the membrane from being damaged in windy weather, and the excess material is folded after the floating membrane rises, the method of pressing the balance tube on the covering membrane is adopted in the design. The balance pipe is made of a 4-meter-long De250mmHDPE membrane sleeve, which is filled with fine sand (or water) and then blocked at both ends, and then connected with each other by chains (or other flexible connectors) and installed at a predetermined position. Engineering Design of Domestic Waste Sanitary Landfill in Yangshan County, Fuqiang County

2.6 Leachate Treatment System

2.6. 1 water quality and quantity

According to the composition and climate of domestic garbage in Yangshan County, referring to the water quality range of leachate from several garbage landfills in Guangdong Province, and combining with the characteristics of landfill technology designed in this project, the design water quality of leachate is determined. The designed effluent quality shall meet the pollutant discharge limit in Table 2 of GB 16889—2008 Pollution Control Standard for Domestic Waste Landfills. According to the calculation of section 2.5. 1, the amount of primary landfill leachate generated by this project is 89.6m3/d, and the amount of domestic sewage and washing wastewater is about 65438+ 100m3/d, so the leachate treatment scale is determined as 100m3/d. ..

Treatment process

This project adopts pretreatment+mechanical vapor compression evaporation (MVC)+ reverse osmosis system (RO). The treatment process of MVC process is completely a physical and chemical separation process. After pretreatment, most of SS and fine fibers are removed from leachate, which enters the subsequent MVC evaporation device with high efficiency, automatic control and low energy consumption. In the evaporation device, the water in the leachate stock solution is evaporated by using the flash evaporation principle, and the steam is condensed into distilled water and discharged. The effluent is desalted distilled water, which can be used as production water and greening water. Because MVC uses the principle of heat pump evaporation to separate water from pollutants, in the process of separation, some substances with low boiling point and small molecules enter the condensed water with steam, so the effluent of MVC has high ammonia nitrogen and COD can't meet the standard, so RO process is adopted for further separation to realize the effluent discharge meeting the standard.

2.7 surface water drainage system

The surface water drainage system in the reservoir area is designed according to 50-year return precipitation and checked according to 100a return precipitation. The surface water flood intercepting ditch is arranged along the roads and anchoring ditches around the reservoir area, encircling the reservoir area in a ring shape, with two outlets for downstream discharge. The flood intercepting ditch is constructed with mortar block stones, and the section size is1.0m×1.0m. A grit chamber and an open caisson are designed at the outlet to slow down the erosion of the downstream revetment by surface water.

2.8 landfill gas guidance and exhaust system

With the increase of landfill waste, the landfill gas produced in the reservoir area is collected by vertically oriented gas wells. The vertical water-collecting well adopts the gas-conducting gabion structure, with the vertical and horizontal spacing of 40~50m and the gas-conducting gabion diameter of 800 mm. From the outside to the inside, the gabion structure is: Φ 8 steel mesh, gravel with a sieve hole of 60mm× 100mm and a particle size of 32 ~ 100mm, and the center in the circumferential direction is porous HDPE with DE150 mm. The bottom of the gas guide gabion and the gas guide pipe is 0.5m higher than the unit foundation, and they are built synchronously with the increase of the landfill height. Vertical gas wells are connected by horizontal collection branch pipes, and finally connected to landfill gas active pumping combustion device by horizontal collection main pipe. The device automatically senses the concentration of combustible gas in the collection pipe, and automatically ignites when it reaches a certain concentration, so as to remove the odor in the landfill gas and burn it in time to prevent air pollution and ensure the safety of landfill operation.

3 Conclusion

According to the principle of "adapting measures to local conditions, being economical and applicable, being environment-friendly and reliable", this project rationally arranges the functional zoning of the landfill and optimizes the engineering design to the maximum extent according to the site and regional characteristics. The anti-seepage system adopts the composite anti-seepage structure of 2.0mmHDPE geomembrane and +GCL, which can ensure good anti-seepage effect. The landfill leachate is treated by MVC+RO, and the effluent quality can reach the pollutant discharge limit of GB 16889—2008.

The above are collected and sorted by Zhong Da Consulting Company.

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