1. Anti-seepage at the bottom of the landfill site
In order to prevent landfill leachate from contaminating groundwater, effective anti-seepage measures must be taken at the bottom of the landfill site. In the past, a layer of anti-seepage material was laid at the bottom of the landfill, mainly including clay, asphalt, plastic film and other synthetic rubber.
In recent years, foreign countries have begun to use synthetic anti-seepage layers, and some use double anti-seepage layers, and the effect is significantly better than the former. Vertical anti-seepage can use curtain grouting, impermeable cloth, etc. Each landfill can take corresponding anti-seepage measures based on specific projects and hydrogeological conditions.
2. Collection and treatment of leachate
Due to its complex composition and high pollution, leachate must be treated before discharge. However, there is currently no perfect treatment technology at home and abroad that can adapt to various landfill leachates. Generally speaking, leachate can be treated by the method of "cleaning diversion - leachate recirculation - pretreatment - combined treatment in urban sewage treatment plants".
Cleaning and diversion. In order to prevent landfill leachate from contaminating surface water and groundwater, and at the same time reduce the amount of leachate, the landfill should be equipped with cleanup and diversion facilities; flood interception ditches and drainage channels should be set up outside the garbage dump to intercept and divert the surface upstream of the landfill area. Runoff and partial diving.
Due to the limited depth of the flood interception ditch, part of the underground water from upstream of the landfill will enter the landfill, which may increase the amount of leachate. To this end, rainwater diversion can be set up at appropriate locations in the landfill. Ditches and drainage pipes are used to reduce the amount of rainwater and phreatic water entering the landfill.
For groundwater, it is necessary to set up a groundwater diversion system, lay a diversion layer on the bottom of the site, lay a drainage blind ditch at the bottom of the diversion layer, place a porous diversion pipe in the blind ditch, and collect the leachate. deal with.
Leachate recharge. Leachate recirculation is to re-inject the leachate collected at the bottom of the landfill into the landfill from the surface of the covering layer or the lower part of the covering layer, and use the "biological filter bed" of the landfill garbage layer to purify the leachate.
Reinjection shortens the time required for garbage degradation, increases the compaction density of garbage, thereby increasing the amount of landfill, and at the same time increases the residence time of leachate in the landfill, allowing the leachate pollutants to be fully degraded and The concentration is greatly reduced. The recharge method is mainly suitable for situations where the climate is dry and the amount of leachate produced is small.
Preprocessing. Leachate is high-concentration wastewater and must undergo necessary on-site pretreatment before it can be collected into urban sewage treatment plants for combined treatment. On-site pretreatment can usually adopt biochemical treatment and physicochemical treatment. Biochemical treatment can use aerobic treatment, anaerobic treatment or a combination of the two. Physicochemical methods mainly include: activated carbon adsorption, precipitation, redox, ion exchange and wet oxidation methods.
The treatment of landfill leachate has always been a difficult problem, and various localities can choose appropriate methods according to actual conditions. The second phase of the Shijiazhuang Xiashigou Sanitary Landfill in 2001 has been completed. The sewage treatment station pipelines of the garbage dump have been connected to the urban sewage system. The activated sludge turntable aeration treatment process is now being used to pretreat the leachate on site. Afterwards, it is collected into the urban sewage system through pipelines for treatment.
3. Recycling of landfill gas
Landfill gas (also called biogas) is a recyclable energy source with a calorific value similar to that of city gas. . However, due to the complexity of landfill gas recovery equipment, high investment and low efficiency, most of the landfills currently operating in my country do not have gas recovery systems. A large amount of toxic and harmful gases are put into the air, which not only causes pollution, but is also a waste of resources.
Generally speaking, biogas recycling can be carried out through the method of "collection-purification-utilization".
Collection of landfill gas. Since most of the biogas is already formed during the landfill process, biogas collection should start during the landfill process. In the Netherlands, vertical or horizontal collection technologies are mainly used for the garbage dumps in use.
The vertical gas extraction system is gradually built during the landfill process of the garbage dump. The method is to erect large-diameter steel pipes evenly distributed in the landfill and build shafts outside each steel pipe. When the landfill thickness reaches 2 to 5 meters, pull up part of the steel pipe and continue to build it until the landfill reaches the design height, and then remove the steel pipe.
By connecting each shaft horizontally with exhaust pipes, landfilling and biogas recovery can be carried out simultaneously. For landfills stacked in layers, a horizontal gas extraction system can be used, but care should be taken that the laying of gas extraction pipelines does not affect the landfill of garbage. For closed landfills, surface collection or shaft collection technology can be used.
Purification of landfill gas. The solvent absorption method is currently a relatively mature biogas purification method. For example, the double-tower solvent absorption method is used to purify garbage biogas. It has simple equipment, low cost, easy operation, and good purification effect.
Using MDEA as the CO2 absorbent can separate CH in garbage biogas and supply it as vehicle fuel, or as high-thermal gas to be incorporated into the natural gas pipeline network for use in industrial boilers, civil gas or power generation. The composition of biogas before and after purification is as follows.
The CO2 removal rate of the above process is greater than 90%, the methane recovery rate is 90-95%, and the methane content in the purified gas is higher than 90%. According to reports, Beijing Kelinman Environmental Engineering Technology Co., Ltd. has conducted this type of Development of purification technology. Its purification technology is the absorption method, which has low operating costs, low investment and high purification degree; all equipment is domestically produced, simple to operate, no secondary pollution, and the process is in line with China's national conditions.
Utilization of landfill gas. Biogas is an economically viable energy source, and its application mainly has the following three forms: directly supplied to industry and greenhouses or greenhouses for heating or industrial production. In this way, biogas has the highest thermal efficiency; biogas is dehydrated and used in gas engines. It drives a generator to generate electricity; after processing and upgrading, the biogas reaches the quality of natural gas and has a wider range of uses.
4. Prevention and Control of Soil Pollution
Control the source of garbage well. Waste reduction and harmlessness are the keys to solving the problem of urban domestic waste. We must vigorously promote cleaner production, control excessive packaging, and strictly limit the production of disposable goods. Advocate green consumption, call on people to pick up vegetable baskets, rice bags, and rice boxes again, and use less or no plastic packaging.
We should promote the use of degradable lunch boxes and packaging materials, encourage the reasonable reuse of packaging materials, and eliminate "white pollution" through the method of "use less, recycle more, degrade some, and replace more".
Implement garbage classification and recycling. Urban garbage contains a large number of pollutants and also contains a large amount of recyclable resources. Implementing garbage classification and recycling can not only solve the problem of garbage pollution, but also create considerable economic benefits. Waste products such as waste paper, glass, and waste plastics must be sorted, recycled, and reused.
According to calculations: for every ton of waste paper recycled, 800 kilograms of paper can be remade, which is equivalent to the paper production of 10 large trees. Used batteries and used electrical appliances that have a greater impact on the environment must be recycled and sent to designated locations for processing to ensure that they do not cause harm to the environment. The garbage that has been sorted and recycled is then sent to the landfill for landfill treatment.
Promote vegetation coverage in landfill areas. Ideal vegetation cover is an important factor in the successful promotion of sanitary landfill methods and is also the key to the redevelopment and utilization of closed landfills. During the landfill process, greening should be done while filling to reduce pollution as much as possible. For landfills that have been closed after completion, great efforts should be made to cover them with vegetation to create good conditions for the redevelopment and utilization of the landfill areas.
5. Strengthen monitoring and eliminate hidden dangers
It is necessary to set up observation wells around the site, configure harmful gas detectors, and regularly monitor groundwater quality and atmospheric environment to eliminate hidden dangers of pollution.
To avoid secondary pollution caused by landfills and pollution of water, soil, and air, corresponding waste management measures have been taken to improve the impact on ecological environment pollution.