1. About site selection
The location of garbage dump (factory) is obviously restricted by land resources, which can be illustrated by the change of protection distance requirements of domestic garbage landfill. Technical standard for sanitary landfill of municipal solid waste (CJJ 17- 1988) requires that the landfill of municipal solid waste be more than 800 meters away from residential areas. Because it is difficult for many cities to choose the site of domestic waste landfill according to the requirement of 800 meters, the revised standards, such as the Pollution Control Standard of Domestic Waste Landfill (GB 16889- 1997), require that domestic waste landfill be more than 500 meters away from residential areas. The newly revised Pollution Control Standard for Domestic Waste Landfills (GB 16889-2008) does not mention the specific "distance" requirement, but requires it to be determined through environmental assessment. Is this process changing from reality to strictness? What if there is no "distance" requirement? How to evaluate the "distance" when there is great uncertainty in the discharge of pollutants from landfill sites? From the perspective of environmental protection, in the past, the requirement of "protection distance" was to consider reducing the impact on people as much as possible without pollution prevention measures, such as building a domestic waste landfill in a ravine as much as possible. This idea is out of date. In fact, for many areas with fragile ecological environment, landfill in gullies will often produce more sewage, and pollution control is more costly and difficult. The consequence of this move can only be to rely on environmental capacity for self-purification and dilution. If we don't control the pollution of landfill (such as sewage and landfill gas), we don't care about its output, and even hope to meet the discharge requirements by producing a large amount and diluting it (for example, building in a ravine leads to a large amount of landfill leachate, but the concentration is low). Therefore, it is considered that the prevention and control of pollution by "distance" is obviously backward and cannot meet the requirements of environmental protection. Of course, when the level of economic development is low, such an approach is also a helpless choice. At present, most domestic waste landfills are selected under such circumstances. Nowadays, with the development of economy and the expansion of urban area, the remote landfill sites in the past are getting closer and closer to residential areas, and the amount of garbage treated by centralized landfill is increasing. The influence of sewage and landfill gas on the surrounding environment is undeniable, and the resulting contradictions are getting bigger and bigger. Do we follow the original idea of transporting garbage farther away (and increase the cost accordingly)? Or actively control pollution, so as to reduce the generation and emission of pollution? The answer is obvious. In short, with the development of environmental protection today, we can't just stay on the understanding of "protection distance", that is, meet the requirements of "protection distance" and can't ignore the pollution impact on the surrounding environment.
Article 5.2 of this standard requires setting up a fire isolation belt, and Article 5. 16 of this standard also requires that "a green isolation belt should be set up around the domestic waste landfill, and its width should not be less than 10m". According to these requirements, the contradiction between the shortage of landfill land and the difficulty of site selection will be further aggravated.
2. About the control of domestic waste landfill.
In fact, the revised standard allows domestic waste incineration fly ash to enter the domestic waste landfill, and also sets some conditions, such as water content less than 30%, dioxin content less than 3g/kg, pollutant concentration limit of fly ash leachate, etc. However, in practice, the operability of these requirements is questionable. For example, according to European research statistics, the dioxin content in fly ash ranges from 0. 14-5.72g/kg(IPPC, 2005), so it is impossible for us to monitor the dioxin content in fly ash in real time. In addition, the better the flue gas treatment effect, the higher the dioxin content in fly ash theoretically. Because of the huge difference between fly ash as hazardous waste and general waste treatment costs, if the dioxin content exceeds 3g/kg, it is unfair to treat fly ash as hazardous waste, and it cannot be implemented in practice, such as whether it can be diluted by adding more dregs. At present, the fly ash of fluidized bed incinerator used in China is low in dioxin, and its essence is dilution effect. Since it is stipulated that municipal solid waste incineration fly ash can directly enter the landfill, it should be given clear requirements and explanations, rather than vague methods and detailed requirements (such as solidification methods, etc. ) and landfill methods, so that these fly ash can enter the landfill. In addition, when the fly ash from domestic waste incineration enters the landfill, it is necessary to modify the relevant provisions in the current incineration standard by announcement.
Article 6.4 of the standard stipulates that "after the general industrial solid waste is treated, the concentration of harmful components in the leachate prepared according to HJ/T300 is lower than the limit specified in the standard, and it can enter the domestic waste landfill for disposal". In fact, this only limits the toxic and harmful aspects, and on the contrary, it needs to be restricted. General industrial waste residues should not enter domestic waste landfills, because the cost per unit capacity of domestic waste landfills is also quite high.
Article 6.2 of the Standard stipulates that the infectious wastes in the Classification Catalogue of Medical Wastes can enter the domestic waste landfill after disinfection, which conforms to the reality and embodies the idea of comprehensive treatment of solid wastes.
3. About the anti-seepage grade of the basement of domestic waste sanitary landfill.
At present, the level of anti-seepage construction in landfill sites in China is already higher than that in developed countries. For example, the basic requirements for basement seepage control in domestic waste sanitary landfill are close to German standards and higher than European Union and American standards. With the improvement of the anti-seepage standard of domestic waste, the corresponding investment has also increased greatly. According to current standards, the cost per square meter of anti-seepage system is close to that of 200 yuan. For arid areas with annual precipitation less than 500 mm (such as northwest China), the same anti-seepage standards are required, even for slopes with an annual precipitation of more than 30 degrees, anti-seepage systems need to be laid.
4. Talking about the treatment of leachate from domestic waste sanitary landfill.
At present, landfill leachate treatment is one of the weak links in the construction and management of landfill sites in China. Because the quality and quantity of leachate vary greatly, and the concentration of pollutants is high, the landfill leachate is treated on the spot and discharged up to the standard, which requires more complicated treatment technology, higher management level and higher cost.
In the design, in order to pursue reliability, the design scale of landfill leachate is generally too large. Compared with the treatment scale of landfills, the design scale of leachate in many small and medium-sized landfills is more than half, and some are more than three quarters. In actual operation, due to financial and technical factors, most of the landfill leachate treatment can not reach the designed treatment scale, so it can not meet the actual treatment needs of landfill. From the technical analysis, in order to meet the requirements of "Pollution Control Standard of Domestic Waste Landfill" (GB 16889-2008), it is necessary to use membrane treatment technology to treat landfill leachate, and the treatment cost of membrane treatment technology exceeds 20 yuan/ton. In addition, membrane treatment often produces a large number of concentrated solutions to be treated. At present, in order to save cost, most concentrated solution is directly reinjected into landfill, which further reduces the effluent rate of membrane treatment.
Article 9. 1. 1 of the standard stipulates that "the domestic waste landfill site shall be equipped with a sewage treatment device, and the sewage such as landfill leachate (hidden pond wastewater) can be directly discharged after being treated and meeting the pollutant discharge control requirements specified in this standard". This rule is too strict. At present, no domestic waste landfill can meet this requirement, and the best one only meets the requirement partially. In particular, the requirement for landfill leachate to be discharged into urban sewage treatment plants is too high, which is obviously stricter than the current requirement for industrial wastewater from chemical and pharmaceutical industries to enter urban sewage treatment plants. This requirement is unbalanced and difficult to implement.
5. The construction and operation of small sanitary landfill will face greater challenges.
According to the new standard, smaller sanitary landfills (less than 200 tons/day, which is the scale of most county-level landfills at present) will face great challenges in environmental protection and economy. Taking a landfill with a capacity of 100 tons/day as an example, when converted into one ton of garbage, the investment cost is more than 70 yuan/ton, and when the actual amount of garbage is less than 70% of the designed treatment scale, the investment cost is 100 yuan/ton; If the operating cost and site closure cost are added, the total cost of these smaller sanitary landfills will reach 150~250 yuan/ton (excluding land cost), which is more than 2 times higher than that of ordinary municipal solid waste treatment. Therefore, it can be said that if the construction and management of small sanitary landfills are carried out according to the current standards, the total cost has no economic advantage. Especially in the face of the fact that landfill is becoming more and more difficult, the transportation cost of domestic waste will further increase.
Limited by management, funds and personnel, it is difficult for the construction of small sanitary landfill to treat its landfill leachate on the spot and meet the existing standards. The biggest investment in landfill construction comes from site arrangement and seepage control. If we can't simplify seepage control and reduce one-time land occupation, the investment can't be satisfied. If the leachate cannot be reduced and the leachate treatment simplified, the operation cannot be guaranteed.
6. Concluding remarks
Standards need to be implemented by people, and standards need to be balanced. To borrow a phrase from the Wuhou Temple in Chengdu, "Don't judge the situation, temper leniency with severity." When I was standing next to the domestic waste landfill on the edge of Tarim desert in Xinjiang, I thought of the environment in which a corpse can be turned into a mummy. When I was standing next to the domestic waste landfill in the northwest Loess Plateau, I saw a huge tailings pond containing various heavy metals (without seepage control measures). Looking at these landfills built according to the current standards, I had a taste.
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