Abstract With the improvement of living standards and the development of environmental protection technology, the disposal of domestic waste has become a basic issue that needs to be solved for sustainable economic development. Taking Qiqihar City as an example, a domestic waste landfill was designed. After comparison, it was proposed that the sanitary landfill method is a better treatment method.

Keywords sanitary landfill; leachate treatment; biogas treatment

1. Background and design parameters

Qiqihar City is located in the Nenjiang Plain in the northwest of Heilongjiang Province. The terrain is high in the north and low in the south, with a total land area of ??42,289 square kilometers and a population of 5.611 million, of which 1.439 million are in the urban area [1].

Design parameters: Taking the main urban area with a population of 200,000 as an example, each person produces an average of 2.0kg of garbage per day. The treatment scale is 400t/d, and the total service life is 20 years. The garbage is compressed by a small garbage compression transfer station and transported to the landfill. The effluent quality requirements of the landfill leachate after treatment meet the "National Comprehensive Wastewater Discharge Standard".

2. Principles of disposal of domestic waste

Domestic waste should be processed according to the principle of organic combination of reduction → harmless → resource utilization. At the same time, the development level of regional economy should also be considered. For small and medium-sized towns, as much as possible should be considered. Reduce infrastructure investment costs and operating costs. The basic task of reduction is to reduce and reduce the quantity and volume of solid waste through appropriate means. Waste treatment requires a large amount of land. Although the land use indicators of various treatment methods are different, they all have varying degrees of volume reduction effects. The basic task of detoxification is to process solid waste through engineering so as not to harm human health or pollute the surrounding natural environment. Harmlessness is the basic requirement for garbage disposal. Regardless of the treatment method, there should be disinfection and sterilization facilities to prevent secondary pollution to the environment. The basic tasks of resource utilization are to adopt technological measures to recover useful materials and energy from solid waste, recycling of waste materials sorted from garbage, recycling of waste heat and biogas from garbage processing, fertilizers produced by composting, and composting suspension. Post-reclamation and land reclamation are all part of recycling waste into resources.

3. Project Overview

According to the different natural terrain conditions of the site, garbage landfills can be roughly divided into three types: valley landfills, plain landfills and slope landfills. Valley-type landfills generally have large landfill storage capacity and handle the largest amount of garbage per unit of land. Taking into account Qiqihar's natural terrain factors, plain-type landfills were selected. The main design and construction content consists of four parts: the access area, the landfill area, the leachate treatment area, and the biogas drainage area. The main project includes landfill site leveling and construction, flood interception trench, anti-seepage system, leachate collection and drainage system and regulating tank, leachate treatment system, biogas collection and treatment system, and supporting road systems, etc.

The landfill of domestic waste can be divided into two categories: anaerobic landfill and aerobic landfill. Ordinary anaerobic landfill and anaerobic sanitary landfill are not set up or are only set up simply. The seepage drainage and air conduction system does not meet my country's current relevant standards for sanitary landfill of municipal solid waste and is no longer used [2]. The improved anaerobic sanitary landfill can effectively prevent the leachate and harmful gases produced by garbage from polluting the surrounding environment by setting up a complete seepage drainage and gas conduction system. It has high sanitary standards and simple landfill operations. However, this type of landfill also produces The leachate concentration is low, and the leachate treatment effect is difficult to meet high standards. Aerobic landfill mainly uses machinery to blow air into the landfill garbage, so that the garbage can be quickly decomposed and achieve the effect of early stabilization of organic matter. Due to the large number of ventilation pipelines, complicated operations and high investment costs, it is currently rarely used. Semi-aerobic landfill mainly uses leachate collection pipes and landfill gas guide gabions to discharge natural wind into the garbage, so that some areas of the landfill are in an aerobic state, thereby accelerating the decomposition of organic matter and reducing the concentration of leachate. The landfill operation method is similar to that of the improved anaerobic sanitary landfill, but the stability and biodegradability of the leachate produced are greatly improved, which can reduce the difficulty of leachate treatment to a certain extent. Considering that the landfill in this design has high requirements for the effluent quality of the treated leachate, a quasi-aerobic landfill form was adopted. In the design, the following measures have been taken to achieve quasi-aerobic landfilling. When meeting the requirements for leachate drainage, appropriately increase the diameter of the leachate drainage pipe so that it is in a non-full flow state; appropriately raise the field bottom elevation, add the regulating tank to obtain the drainage pipe bottom elevation, and control it to the highest level in the regulating pond. Above the water level, set up a blind gas ditch in the garbage; appropriately increase the diameter of the gas cage and set up biogas collection facilities in advance. By taking the above measures, the air can enter the landfill layer in the reservoir area through the leachate air pipe, air gabion, and air blind ditch. As the garbage continues to be piled high and the methane is gradually collected, the air will form inside the garbage pile. Under a certain negative pressure, air continuously enters the landfill body to achieve the purpose of quasi-aerobic landfill.

5. Landfill leachate control and anti-seepage treatment

5.1 Leachate

Landfill leachate is the main pollutant produced during the operation of the landfill. The leachate contains a large number of various Organic and inorganic pollutants, heavy metals, bacteria and other toxic and harmful substances, and the concentrations of COD and BOD are high. If they are allowed to be discharged, the degree of pollution and damage to the surrounding environment will be immeasurable. Therefore, the output of landfill leachate must be strictly controlled. It is the key to the success of sanitary landfill design. Main factors affecting leachate: Leachate mainly comes from precipitation infiltration within the landfill, groundwater intrusion, moisture contained in the garbage itself, and decomposed liquid produced during the stacking process. The factors that affect leachate production are very complex, including precipitation, groundwater intrusion, garbage composition, surface water runoff during landfill, and water evaporation. Landfills are generally not built in places where pressurized groundwater may intrude. Therefore, "groundwater intrusion" refers to surface phreatic water. The amount of this part of phreatic water is closely related to precipitation. In northern areas, except for melons and fruits in summer, In addition to the fact that garbage is rich in water, there is less water-rich garbage in other seasons, so precipitation is the main source of leachate. The function of the leachate regulating tank is to store water and regulate the water quality and quantity of the incoming water to the leachate treatment station. The volume of the regulating tank mainly depends on rainfall. Its advantages are: (1) minimizing the possibility of downstream pollution of garbage leachate water during the rainy season; (2) facilitating the self-purification function of leachate water and reducing the need for sewage treatment. Water load; (3) Implementation of reverse irrigation and spraying measures that are conducive to percolating water. The designed daily processing capacity of the garbage disposal site is 400 t. Considering various factors, the volume of the regulating tank is 1800 m3.

5.2 Anti-seepage treatment of landfill leachate

Taking into account the characteristics of landfill leachate and the limitation of the total treatment capacity of urban sewage plants and other factors, in sanitary landfill Build leachate treatment facilities on site. Currently, landfill leachate treatment technologies used at home and abroad mainly include: physical and chemical treatment, biological treatment, etc. [3]. Biological treatment of leachate ① Aerobic treatment method. Aerobic treatment mainly includes: activated sludge method, aerated oxidation pond, aerobic stabilizing pond, biological turntable and trickling filter. Aerobic treatment can not only effectively remove BOD5, COD and Ammonia nitrogen can also remove part of manganese, iron and other metal elements. For example: the "activated sludge-oxidation pond" combined treatment process used in Guangzhou Datianshan landfill has good treatment effects; ② Anaerobic treatment method. Anaerobic Treatment methods include: anaerobic sludge bed, anaerobic biological filter, anaerobic contact tank, mixed reaction tank, staged anaerobic nitrification, anaerobic stabilization pond and other methods. A large number of experiments have shown that the characteristics of anaerobic biological treatment are that it can It consumes less, produces less residual sludge, and requires less nutrients. It has a good effect on the treatment of high-concentration organic wastewater. However, there are few cases where anaerobic treatment is used alone. Generally, aerobic biological treatment is used to further ensure that it Effluent water quality. ③ Combined aerobic, anaerobic, physical and chemical treatment methods. According to the test of Beijing Municipal Design and Research Institute, the anaerobic-aerobic process is used to treat landfill leachate. The treatment process is economical and reasonable, and has good effects on COD and The removal rates of BOD5 reached 86% and 97% respectively.

6. Conclusion

With the improvement of living standards and the development of environmental protection technology, the disposal of domestic waste has become a basic issue to be solved for sustainable economic development. Due to the poor economic strength of small and medium-sized towns, domestic waste contains high inorganic content, low calorific value, and few combustible components, so sanitary landfill will be the main treatment method. Among sanitary landfills, the semi-aerobic sanitary landfill method is more suitable. However, the overall design of sanitary landfill is a very complex issue with many related influencing factors. Due to economic constraints, it is impossible to design a “perfect” sanitary landfill from the outset. However, to the best of my ability, I designed such a landfill by fully considering the various influencing factors of the landfill and strengthening the safety of the landfill in a targeted manner. It is hoped that it can not only handle domestic waste well, but also save investment and achieve quick results.

References

[1] Shen Yaoliang, Yang Quanda, Wang Baozhen, Wang Xuehua, Zhang Jianping; Estimation and case analysis of pollutant dissolution load in landfills[J]; Suzhou Urban Construction Journal of the Institute of Environmental Protection; Issue 02, 1999

[2] Liu Jiangying, Zhao Youcai, Zhao Aihua, Huang Renhua; Decay law of COD in leachate from large landfills [J]; Journal of Tongji University (Natural Science Edition ); Issue 03, 2000

[3] Zheng Manying, Li Litao; Preliminary study on organic pollutants in landfill leachate[J]; Chongqing Environmental Science; Issue 04, 1996