I. Project Overview
1. Project Background
With the development of the economy, people's living and consumption level increases, the city's domestic waste generation is increasing day by day. And at present there is no engineering measures for harmless treatment of garbage in the city, basically all the garbage is handled in simple piles without harmless treatment, and its sanitary requirements are far from the sanitary standards of environmental regulations.
These improvised dumps have caused a series of environmental pollution problems. The manifestations are:
One, the garbage is piled up in the open air, emitting gusts of stench, polluting the atmosphere, which can be smelled for several square kilometers around and seriously affecting the landscape. Second, the garbage has no isolation measures, and the leachate it produces pollutes the groundwater and surrounding surface water, greatly threatening the health of the residents.
Third, it pollutes the surrounding soil, making it lose its proper function.
The city's economy continues to grow, the population is rising and the number of consumer goods is increasing. If not deal with the harmless treatment of garbage, will cause a major disaster, so the establishment of domestic waste landfill treatment works.
2. The main contents of the engineering design
The main contents of the sanitary landfill disposal engineering design of municipal waste include: general layout (site selection and overall design of the site, etc.), landfill process, prevention and control works, leachate collection and drainage works, leachate treatment works, groundwater, surface water drainage and treatment works, landfill gas collection and utilization of the design, environmental monitoring design, and the closure works, auxiliary works (e.g., the design of the landfill). Closure works, auxiliary works (such as greening, roads, etc.), equipment selection, secondary pollution prevention design, economic analysis and so on.
3. Design Scale
Based on the city's population size and per capita waste production and other factors, to determine the sanitary landfill disposal of municipal waste starting size of 600 tons per day.
4. Technical and economic indicators
Waste treatment scale: 219,900 tons/year; landfill capacity: 6,193,200 m3; service life: 21 years; leachate treatment scale: 300 tons/day; leachate treatment standard: Class III; regulating tank volume: 20,000 m3; total cost of waste treatment per unit: 2,845,800 yuan/year; payback period : 12.95 years
II. General layout
1. Selection of site
The site of the landfill has been selected after careful consideration from engineering, economics, environmental studies, policies and regulations.
1)Economically, this landfill meets a certain reservoir capacity, which can accommodate 600~1200t/d of waste disposal; there is an avenue nearby, which is only 9.87km away from the center of the city, and the site is conveniently accessible and reasonably spaced; there is a considerable amount of soil and stone material around the site, which is used for the natural impermeable layer and the clay of the cover layer, and so on.
2)From the engineering aspect, the site has appropriate natural terrain as landfill space its topography, geomorphology and soil conditions are appropriate; the permeability coefficient of the natural strata reaches below 10-7cm/s and has a certain thickness, and its geological conditions are very good; the evaporation of the site is greater than the amount of precipitation, and it is not located in the area where typhoons pass through, and its incidence of heavy rainfall is also low, and it is located in the downwind direction of the atmospheric mixing and diffusion, i.e., the meteorological conditions are appropriate. wind direction, i.e. the meteorological conditions are appropriate.
3) Environmentally, the site is located 2,000 meters away from the dedicated water recharge area, and the foundation is located at least 1 meter above the elevation of the highest abundant water level, which has less impact on surface water and groundwater, and at the same time, the site is located 2,000 meters away from the residential area, and it is located in the downwind direction of the residential area, which also has less impact on the residential area.
4)From the viewpoint of policies and regulations, the establishment of this landfill is in line with the urban development plan and meets the requirements of the local urban environmental sanitation development plan.
In summary, the site will be determined here as a landfill site.
2. Site overview
The landfill site is two valleys, basically north-south. The topography of the valleys is open, separated by a small hill in the center, and the two valleys converge at the southern end. The entire site covers an area of 40 square kilometers.
The climate of the landfill site is subtropical monsoon climate, with north winds in winter and south-east winds in summer, and annual rainfall of more than 1,000 milliliters. Site for the two-layer structure hydrogeological type, aquifer buried shallow, water-rich general, mainly clay soil, and clay thickness is more stable, natural conditions of loose layer powder and bedrock weathering shell weathering aquifer seepage, pollution prevention performance are good.
3. General layout
The landfill treatment project is mainly living area, landfill area, leachate treatment area, biogas power generation area consists of four parts. The whole plant covers a total area of about 40 square kilometers, of which the landfill covers an area of about 25.3 square kilometers, leachate treatment area of about 5 square kilometers, and the rest is 13.7 square kilometers. (See attached Figure 1.)
The arrangement of the whole plant is designed in accordance with the current requirements of the country, based on the actual topography, hydrogeology, wind direction, and the needs of the landfill process and comprehensive consideration.
Because the city is always in the southeast monsoon prevailing wind direction in summer and in the north wind direction in winter, the landfill area is located in the eastern part of the city due to the combination of the topography and seasonal change of the wind direction, and at the same time, the landfill area is surrounded by a green belt. This can avoid seasonal changes in the wind direction and the landfill area to landfill waste generated some odor pollution affecting local residents.
Living area includes administrative office building, mechanic workshop, fountain square, pavilion, green belt and so on. Leachate treatment area includes water pump house, sedimentation tank, regulating tank, etc., of course, its surrounding with a series of green decorative embellishments. Leachate treatment area and biogas power generation area are set up near the landfill area as much as possible to facilitate fluid transportation.
Three. Landfill operation process
Sanitary landfill is usually transported to the landfill every day, after the nature and measurement of judgment into the landfill. Garbage is unloaded according to the designated unit operation point, after unloading the car with a bulldozer to push the pavement, and then crushed with a compactor. After compaction in layers to the required height, the landfill is covered with clay and polyethylene film material and the process of unloading, bulldozing, compaction and covering is repeated as described above. Mulching is carried out on a daily basis in a one-layer-a-day operational unit. The compaction density of garbage is more than 0.8t/m3. The thickness of each layer of garbage is 2.5~3.0m, and the thickness of each layer of mulch miner is 15~30cm, usually four layers of thickness make up a big unit, and the top cover soil is 45~50cm.
The landfill is pushed forward from the right to the left first, and then from the front to the back. Between the left, center, right between the joint line is arc-shaped, so that the drainage on the cover flows smoothly to both sides into the drainage ditch or side ditch, etc., in order to reduce the rainwater seepage into the garbage body, before and after the upper part of the joint line is a certain slope. The outer slope is 1:4, and the top slope is not less than 2%. After the thickness of the unit reaches the design thickness, it can be temporarily sealed and covered with 45~50cm thick clay on top of it. And evenly compacted, plus 15cm thick nutrient soil, planting shallow rooted plants. The final sealing cover thickness is more than 1m.
Landfill operation is implemented in the form of sub-district unit landfill, to sub-district unit landfill as a prerequisite, and then come back to consider the layering of landfill operations. In order to prevent the spread of pollution to the maximum extent possible, during the landfill operation, the sublandfill area where the landfill operation is being carried out is exposed, and the day cover is covered with a membrane cover, while the other areas are covered with intermediate cover or temporary closure area.
The first operation is the leveling of the bottom of the landfill storage area, in the actual landfill operations in the process, to be considered and landfill operations storage area of the temporary operation of the road in conjunction with the implementation of the road. The first arrival of the landfill operation height of 2m from the absolute elevation of the leveling inquiry and then start the second layer of landfill operation unit set up.
With the increase of the landfill operation height, the effective area of landfill operation can be utilized is also increasing, which is convenient for the utilization of the gas, the landfill unit which has been temporarily closed can be connected with the surrounding mobile gas collection station through the vertical gas well in the middle of the gas-conducting gabion, and then the gas can be reused.
The sequence of operations for the entire landfill is: Zone 1, Zone 2, then Zone 3, and then Phase II begins. Landfill phase II project operations, and landfill area one to form a new horizontal area, continue upward landfill, the formation of the pile after the temporary closure, landfill phase III operations. The landfill operation process flow diagram as shown:
Landfill operation process flow diagram
Four. Seepage control engineering and leachate treatment design
1. seepage control engineering
1.1 seepage control material
At present, from the practical view of domestic and foreign practice, used for waste sanitary landfill application of the most widely used and most successful is the high-density polyethylene (HDPE) membrane, and other seepage control materials, it has the best durability. From the seepage control performance and economic and practical point of view, this project uses 1.5mm thickness of high density polyethylene (HDPE) membrane is more appropriate. Its abrasion performance considerations, than from the point of view of security, the use of hairy HDPE membrane on the slope is better, but the design of the design because there are enough clay layer, so this project seepage control of the main structure of all the use of 1.5mm thickness of glossy HDPE membrane.
1.2 seepage control structure
In the landfill site bottom, side slopes and regulating pools are installed in the tight seepage control system, so that it is dense and impermeable to prevent contamination of groundwater. The core part is a double-layer high-density polyethylene (HDPE) membrane. A collection layer is also installed.
The structure of the bottom of the field is, from top to bottom, as follows: filtration layer, primary filtrate collection layer, protection layer, primary impermeable layer, primary impermeable layer, secondary filtrate impermeable layer, secondary impermeable layer, protection layer, and constructed bottom surface. The corresponding seepage control materials are set up in the following order: lightweight geotextile soil, gravel infiltration layer with a thickness of 600mm, 500g/m2 non-woven geotextile layer, 1.5mm glossy high-density (HDPE) membrane, 500g/m2 non-woven geotextile layer, 1.5mm glossy high-density (HDPE) membrane, 500g/m2 non-woven geotextile layer, and foundation soil. See the following table and the attached Figure 2
Fill waste layer
Filtration layer
Lightweight geotextile soil
Main filtrate collection layer
Thickness of 600mm gravel infiltration layer
Protection layer
500g/m2 non-woven geotextile layer
Main seepage control layer
1.5mm smooth surface High-density (HDPE) membrane
Secondary filtrate seepage control layer
500g/m2 non-woven geotextile layer
Secondary seepage control layer
1.5mm glossy high-density (HDPE) membrane
Protective layer
500g/m2 non-woven geotextile layer
Construction of the subgrade
Foundation soil
Slope and regulating pool seepage control structure and the bottom of the field are the same, this is from the safest point of view to start to consider, can not have a little careless.
2. leachate collection and drainage system
2.1 leachate diversion layer (i.e., the main leachate collection layer and the secondary leachate collection layer)
Leachate main collection layer: in the non-woven geotextile protective layer on the laying of 600mm gravel layer, the particle size of the requirements of the 20-40mm, according to the upper coarse under the fine laying to prevent the landfill waste plugging gravel seams, thus affecting the leachate diversion effect. The effect of the leachate.
Leachate secondary collection layer: installed directly under the main impermeable layer, the purpose is to monitor the main impermeable layer leakage, if there is a leakage, it can be found in the secondary blind trench and collected.
2.2 Leachate guide blind trench
The leachate guide blind trench is responsible for the final discharge of leachate, which is discharged from the site to the leachate settling tank and regulating tank for treatment. In order to facilitate the collection and discharge of leachate, longitudinal blind trenches are set up in each area, in which the main collection layer is paved with perforated flower pipes with a diameter of DN250mm, and the blind trench section is formed by the infiltration layer and wrapped with 150g/m2 woven geotextile. The secondary blind ditch consists of permeable hose which is permeable and less affected by the settlement of garbage. When the sub-blind trench is laid then the intermediate cover is started.
3. Groundwater conduction and drainage system
The landfill process design must consider the possible existence of groundwater conduction and drainage at the bottom of the landfill storage area. Groundwater conduction and drainage ditch is located in the leachate main drainage ditch under about 2m. First in the ditch laying anti-filtration 150g/m2 geotextile, and then laying DN200 HDPE perforated flower pipe, and finally backfill grading gravel to the top of the groundwater conduit ditch.
4. leachate treatment works
4.1 garbage leachate
The garbage leachate is light tea color or dark brown, with a chromaticity of between 2000 and 4000. There is a strong odor of decay, complex composition, toxicity, organic content is more, was included in China's priority pollution control substances "black list" there are more than 5 kinds of; chlorine and nitrogen concentration is high, BOD5 and COD concentration is far more than the general sewage.
The garbage leachate comes from three sources: one is the water carried by the garbage itself; the second is the water produced by the decomposition of organic matter in the garbage; and the third is the atmospheric precipitation and groundwater that enters the landfill in various ways. Among them, the atmospheric precipitation and groundwater entering the site are the key factors determining the amount of leachate generated.
The leachate generated in the landfill in relation to time can be divided into the following phases:
1)Adjustment period: at the beginning of the landfill, the water in the garbage body is gradually accumulating and oxygen exists, anaerobic fermentation and microbial action is slow, the amount of leachate at this stage is relatively small.
2)Transitional period: microorganisms in the leachate at this stage gradually change from aerobic to parthenogenetic or anaerobic, leachate begins to form, and the presence of volatile organic acids can be measured.
3)Acid formation period: volatile organic acids account for the majority of the filtrate, the pH decreases, the COD concentration is very high, BOD5/COD is 0.4~0.6, the biochemistry is good, and the color is very dark, which belongs to the early stage of the leachate.
4)Methane formation period: organic matter in this stage is converted into CH4 and CO2 by methanogens, pH value rises, COD concentration decreases sharply, BOD5/COD is 0.1~0.01, biochemistry is poor, belongs to the late leachate.
5) maturity: at this point in the leachate available components of the large reduction in the biological stabilization of bacteria tend to stop, and stop producing gas, the system from anaerobic to aerobic state, the natural environment is restored.
4.2 Garbage leachate treatment process
From domestic and foreign leachate water quality monitoring will be analyzed, leachate BOD5/COD = 0.2 ~ 0.8. The beginning of the landfill leachate biochemical better, but with the passage of time, its biochemical will gradually decrease. The leachate of sanitary landfill of municipal domestic waste is a kind of sewage with high nitrogen content and high concentration of organic matter, and its flow rate and load are constantly changing. Therefore, this project is proposed to use biological treatment combined with physical and chemical treatment, and supplemented by depth treatment, so that their strengths and weaknesses, complement each other, complement each other, the treatment effect to the maximum.
The equipment used are EGSB reactor and microfiltration device (CMF) and so on. Its wastewater treatment project is proposed to use EGSB reactor + CASS reaction tank + microfiltration device (CMF) + biofilter + reverse osmosis (RO) of the joint process, as shown in the figure:
Figure: garbage leachate treatment process flow
4.3 process design
(1) adjusting pool: adjusting pool capacity of 20,000 m3, wastewater enters the adjusting pool through the addition of acid or alkali to adjust the pH value. Add acid or alkali to adjust the pH value, so that it is in anaerobic slightly alkaline stage, so as to provide stable conditions for its next anaerobic reaction.
(2) EGSB reactor: (see Figure 3) EGSB is expansion granular sludge bed, which is developed on the basis of UASB reactor, inheriting almost all the advantages of UASB, and is more advanced technologically. As a kind of high-efficiency anaerobic bioreactor, it has high sludge concentration and volumetric load, can adapt to certain water quality and water quantity fluctuation, and has strong anti-shock load capacity. In addition, it can decompose difficult biodegradable macromolecular organic matter into small molecules, which helps to improve the degradability of organic matter and greatly reduces the subsequent unit treatment load. The biogas produced by the EGSB reactor is transported to the biogas power generation area for power generation. Its characteristics are as follows:
1) Granular sludge as the core of the technology
2) The height of the EGSB reaches 15m, while the UASB is only 5.5m, in the case of the same volume, the area of the EGSB is smaller, the distribution of the incoming water will be more uniform, and the mass transfer effect will be better
3) As the granular sludge of the EGSB is in suspension, the contact effect with water is better, and the organic matter removal rate is higher. Organic matter removal rate is higher
4)The sludge volume of EGSB reactor can reach 50,000~60,000mg/L, while UASB has only half of its processing capacity. Therefore, EGSB can withstand higher influent concentration, higher shock resistance and higher load.
5)When treating high concentration organic wastewater, the treated water is not recycled, which can further save energy and reduce the operation cost.
(3) CASS reaction tank: that is, circulating activated sludge system. It is developed on the basis of sequential batch activated sludge method, anoxic biological selection area is set up at the front end of the reaction tank, see attached figure. Its advantages are: there is no need for a secondary sedimentation tank, saving infrastructure investment, small footprint; reaction tank by anoxic pre-reaction area and aerobic main reaction area, the removal of difficult to degrade organic matter is better, the effluent water quality is good, does not produce sludge expansion; has a good effect of nitrogen and phosphorus removal; a high degree of automation, operation and operation is simple; CASS pool influent after dilution of the concentration of the concentration is reduced, the concentration gradient of organic pollution becomes smaller The concentration of CASS pool is reduced after dilution, and the concentration gradient of organic pollution becomes smaller.
(4) biofilter: immediately after the CASS reaction pool out of the sewage is very conducive to biological treatment, so the biofilter can be very good to remove the remaining organic matter. The remaining sludge is discharged to the sludge storage tank to be treated by filter press and then backfilled.
(5) Microfiltration device: CMF is a hollow fiber microfiltration membrane as the central processing unit, and with specially designed pipelines, valves, self-cleaning unit, dosing unit and PLC self-control unit to form a closed-circuit continuous operating system. When the water to be treated under a certain pressure through the microfiltration membrane filtration, it will achieve the physical separation of the day, so that most of the residual organic matter is effectively removed, so as to achieve the combination of physical and biological treatment, make up for each other, play a greater role in removing.
CMF device mainly includes pre-filtration system, microfiltration host, water supply system, backwash system, compressed air system, chemical cleaning system and PLC automatic control system. See the following figure:
Figure: microfiltration device CMF
(6) Reverse osmosis device: leachate post-treatment usually uses reverse osmosis process to remove medium molecular weight dissolved organic matter and the vast majority of dissolved salts. Because after a series of treatment, the concentration of organic matter in the sewage is greatly reduced, suitable for removing the remaining dissolved substances. In this way the sewage is further purified. Its effluent is sent to the water supply center or reuse after adjusting the flow rate through the adjustment pool.
V. Landfill gas collection and utilization design
1. The main composition of landfill gas
The main gases in landfill gas (LFG) include methane, carbon dioxide, ammonia, carbon monoxide, hydrogen, hydrogen sulfide, nitrogen and oxygen. The most dominant of these are methane and carbon dioxide gas. Its typical characteristics are: temperature up to 43 ~ 49 ℃, relative density of about 1.02 ~ 1.06, saturated with water vapor, the high calorific value of 15630 ~ 19537kJ/m3.
That of course, landfills produce trace gases, although very little, but its composition is complex, toxicity is greater, and can not be ignored.
2. Landfill gas collection method
This project adopts LFG active control system, i.e., laying some vertical gas-guide wells (see attached Fig. 6) or horizontal blind ditches in the landfill, connecting these gas-guide wells and blind ditches to the pumping equipment by pipelines, and utilizing the pumping equipment to pump out LFG by pumping gas to the gas-guide wells and blind ditches. Due to the large area of this landfill and the large landfill volume, the use of horizontal collection blind trench is easy to make the air into the pumping system, so the project adopts vertical pumping wells to pump out the air. Considering the landfill thickness and landfill scale and other factors, choose to use the garbage unit closed after drilling down the pipe unified collection of landfill gas.
The landfill gas active control system mainly consists of pumping wells, gas collection pipes, condensate collection wells, and pumping stations, vacuum sources, gas treatment stations and gas monitoring equipment.
Usually, landfill gas active control system is divided into internal landfill gas collection system and edge landfill gas collection system. Internal landfill gas collection system: This system is commonly used to recover landfill gas, control odor and surface emissions, as shown in the attached figure Edge landfill gas active collection system: This system is mainly to recover and control the lateral surface migration of landfill gas. Perimeter pumping wells are used to pump the gas.
3. Condensate collection and discharge
Landfill gas in the transportation process, will gradually become cooler and produce a variety of organic and inorganic chemical substances and corrosive condensate. These condensate can cause pipeline vibration, restrict airflow, increase pressure difference, hindering system operation. To set up condensate collection system, generally condensate collection wells installed in the gas collection pipeline at the lowest place, to avoid increasing the pressure difference and vibration.
4. Gas conveying system
The collected gases are finally gathered to the main trunk pipe, which is conveyed to the gas power plant by the blower. The material of the pipeline is PE.
5. Utilization of landfill gas
Because the landfill project is large, the amount of waste handled is also large, and the amount of methane gas produced is considerable, and lasts for a long period of time, so this project is mainly to use the landfill gas for power generation. Its total gas treatment and utilization process flow is shown in the following figure:
Figure: Landfill gas treatment and utilization process flow
(Its biogas turbine power generation burner is shown in the attached Figure 7)
VI. Environmental monitoring design
Landfill management must be environmental monitoring, it is the evaluation of the operating conditions of the waste disposal facilities level, the monitoring content relates to the atmosphere, groundwater, surface water, leachate, landfill gas, landfill settlement, fly density, landfill waste and other aspects of the determination. The table of its monitoring items is as follows:
Monitoring Items
Execution Standards
Description
Surface Water
H, SS, BOD5, CODcr, NH3-NNO2, NO3-N, Cl-, TP, etc.
Bottom of the landfill site is monitored 3 times, and after the commissioning of the landfill site, one time in each of the dry, rich and flat water periods. 2 times in the peak month
Groundwater
H, total hardness, chloride, CODcr, ammonia nitrogen at the water level, volatile phenols, cyanide, E. coli, etc.
Life Waste Landfill Pollution Control (GB16889 - 1997)
3 days before sampling the monitoring wells Wash the wells, wash the wells to remove the amount of water is 3 to 5 times the water stored in the wells, monitoring indicators are adjusted if necessary. The monitoring points are each groundwater monitoring wells, domestic water wells. Monitoring is conducted three times a year, with samples taken in April, August, and November. (See Attachment 5)
Leachate
H, SS, BOD5, CODcr, NH3-N E. coli, etc.
Monitoring points are: leachate collection wells, leachate treatment facility discharge, monitoring 3 times a year, sampling time in April, August, and November, respectively
Atmosphere
TSP, odor intensity, ammonia, Hydrogen sulfide, methyl mercaptan, etc.
Monitoring point country upwind and downwind each one, the wind direction can be increased appropriately when the wind direction is not fixed, monitoring 2 times a year, the sampling time were in April, August.
Landfill gas
CH4, CO2, CO, N2, O2, H2, H2S, etc.
Monitoring point for the mouth of the biogas collection pipe, you can monitor a point. Monitoring once a year, required in August
Fly density
Technical Standards for Environmental Monitoring of Domestic Waste Landfills Pollution Control Standards
Landfills are monitored four times a year within 1~3 years after commissioning, preferably measured in July~September
Noise
Field Noise
Field Noise in Industrial Enterprises Measurement Methods"
VII. Auxiliary engineering
Auxiliary engineering of landfill includes civil engineering, road engineering, water supply and drainage engineering, fire-fighting engineering, power supply and distribution design, automated instrumentation design, waste metering, communication, energy saving, greening and so on.
1)Civil engineering: the living area takes the comprehensive building as the main building, which consists of the office building and the staff canteen and the dormitory for the duty staff. The architectural shape of the comprehensive building and the center square are integrated into a complete space in front of the plant, with a strong sense of dynamism, and play a role in guiding the line of sight and the flow of people.
2) road works: road design when the curve is less than 150 meters, in the curve radius of 5% to 6% of the super-high, and set the roadbed widening and easing section. Its ancillary projects mainly include road drainage ditches and culverts, slope protection, retaining piers, signage.
3) water supply and drainage project: its water consumption design includes road spraying, green water, living water, fire water, car washing water, unforeseen water and so on the sum of water consumption.
4)Fire protection project: the project fire protection design includes living area and landfill operation area. Gas detection, alarm instrument, usually pay attention to the calibration and maintenance of the instrument.
5)Power supply and distribution design: the project's installed capacity of the whole plant equipment 453.97KW, all electrical equipment are 380/220V low voltage equipment.
6)Automatic control instrumentation design: including statistical summary, status monitoring, environmental online monitoring, office automation and so on.
7)Garbage measurement: Because the project capacity is 600~1200t/d, there are about 200~400 garbage trucks entering the field every day, i.e., an average of about 30 trucks/hour enter the field, i.e., about 1 truck enters the plant every 2 minutes and passes through the weighbridge for measurement. Therefore, two weighbridges are set up for calculation.
8) communication: set up a telephone communication line, a small telephone exchange, the entire site is equipped with four live phones, respectively, located in the general manager's office, deputy manager's office, the general dispatching office and the management section, and equipped with a facsimile phone, located in the office.
9)Energy saving: the selection of low energy consumption of vehicles for landfill operations; the selection of high efficiency leachate transfer pumps, etc.
10)Greening: while the green belt using a combination of points, lines and surfaces, including plazas, lakes, fountains and trellises, etc.. Between the landfill area and the living area separated by a 10~15 meters wide green belt, collecting different tree species to blend with each other, and arranging a layered green landscape with different colors, heights and forms.
VIII. Closure project
Landfill final cover system is mainly composed of: topsoil layer, protective layer, drainage layer, barrier layer and base layer/gas collection layer and other 5 layers. The three final field cover materials used are compacted clay, geomembrane, and geosynthetic clay layer. These three are used in combination to achieve the best economic and environmental benefits.
The final cover system of this landfill is from top to bottom as follows: 15cm topsoil layer with will shallow rooted vegetation, 60cm protective layer, HDPE geomembrane, geonet drainage layer, 45cm compacted clay layer. The sealing structure is shown in Figure 4
1) 15cm topsoil layer with shallow-rooted vegetation: its role is to promote the growth of plants and protect the barrier layer, providing a certain water-holding capacity.
2)60cm protective layer: its role is to store water infiltrated into the cover layer until it is dissipated through plant transpiration; to separate litter from digging animals and plant roots; to minimize the likelihood of contact between people and litter; to protect the layers below in the cover system from excessive wet/dry intervals and freezing, which can lead to cracking and damage to the cover material; and to drain the water laterally.
3) HDPE geomembrane: 1.5mm glossy high-density (HDPE) membrane that is consistent with the impermeable material of the foundation liner system is used to form a composite impermeable structure by combining it with the upper and lower clay layers.
4) geonet drainage layer: the use of geonet with geotextile filter layer, its role is to reduce the head of the barrier layer below it, thereby minimizing the water seepage through the cover system; reduce the pressure of pore water in the cover material to improve the stability of the slope.
5)45cm compacted clay layer: compacted clay is still a certain seepage control, and HDPE geomembrane used in combination, both economic and convenient.
After the closure of the site must also be maintained, including site maintenance and pollution control continue to operate and monitor. Specifically: leachate treatment system operation and monitoring, leachate regulating pool odor treatment system operation and monitoring, landfill gas conduction and utilization system operation and monitoring, groundwater monitoring, surface water monitoring, ground settlement monitoring, site maintenance and so on.
9. Economic Assessment
1. Overview
The annual disposal capacity of this municipal landfill project is 219,000 tons/year, the total capacity of the landfill is 6,193,200 m3, and the service life is 21 years.
2. Main technical and economic indicators
The scale of garbage disposal; 219,000 tons/year, the total capacity of the landfill: 6,193,200 m3, the service life is: 21 years. Labor force: 50 people, total project investment: 94,730,600 Yuan, unit operating cost: 12.99 Yuan/ton, financial internal rate of return 6.03%, payback period: 12.95 years.
3. Financial Analysis
3.1 Cost Benefit Estimation
1) Calculation period: calculated on the basis of 21 years, including the construction period of 12 months
2) Total investment in the project: 94,730,600 yuan
3) Source of funds: apply for a state subsidy of 50 million yuan, and the rest of the city's own funds
4) Fixed assets, Formation of intangible assets and other assets: fixed assets consist of the cost of the project, all the costs of other costs of the project except for the production of employee training costs, preparatory costs, interest during the construction period, and fixed asset investment direction adjustment tax.
5) Estimation of operating costs and expenses: Estimation of costs and expenses by elements, including: purchased materials, fuel, power, wages and benefits, maintenance costs, depreciation, management fees and finance costs. So that the total cost per unit is 34.41 yuan/ton. Operating cost refers to the total cost after deducting depreciation of fixed assets, intangible and other assets and financial expenses. The average annual unit operating cost of this project is $12.99/ton.
6) Revenue estimation: based on the garbage disposal fee charged at $48 per ton, the annual revenue will be $10.508 million.
7)Taxes: this project is a social welfare project, not for profit. No sales tax.
8)Loan: No bank loan.
9)Profit estimation: the investment profit rate is 4.08% and the investment rate tax is 4.08%.
3.2 Financial evaluation:
Profitability analysis: financial internal rate of return 6.03%, payback period: 12.95 years, financial net present value of 257,900 yuan.
4. Economic analysis
Environmental benefits: after the implementation of this project, it can well improve the environmental quality of the city, make the garbage meet the requirements of harmless treatment, with great environmental benefits; the improvement of the overall environmental quality is beneficial to the physical and mental health of people, reduce the occurrence of diseases, and reduce the cost of medical care; the construction of landfill sites and investment in the increase of employment opportunities, resulting in good The improvement of the city's environmental quality will attract more investment and promote the development of the tourism industry and other tertiary industries, which will bring other socio-economic benefits is very huge.
5. Conclusion
1. The financial internal rate of return (IRR) is 6.03%, which is greater than the minimum acceptable IRR of 6%, and the financial net present value (NPV) is greater than 0, which is a certain degree of viability.
2. The project has greater direct economic benefits (economic benefits from power generation) and indirect benefits, so its economic internal rate of return will be much greater than the financial internal rate of return, and its economic internal rate of return can also meet the requirements of greater than the benchmark economic rate of return. Therefore, from the economic point of view, the project is feasible.
3. Based on the above, the project's financial cost-effectiveness and economic cost-effectiveness are good, and the project is feasible.
X. Summarize
The landfill from the site selection, design to program selection, equipment selection, economic analysis have gone through a rigorous demonstration and repeated deliberation before the final decision, the state also gave considerable support, I believe that the establishment of this sanitary landfill disposal of domestic waste project will be a great blessing to the city, the city's level of environmental hygiene will be a new step, a win-win situation for the environment and economic development, and will contribute to the cause of China's environmental protection, and will also contribute to the cause of China's environmental protection. At the same time will contribute to the cause of environmental protection in China.
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