Sanitary landfill is the basic way of garbage disposal in most cities in China. In the future, sanitary landfill will still be the basic way to treat domestic municipal solid waste. Sanitary landfill, as the most common garbage disposal method at present, also has many pollution problems, especially a large amount of landfill leachate, which will cause serious pollution to the surrounding water and soil if it is not handled properly. Landfill leachate is the sewage percolated out by fermentation, rainwater scouring and surface water and groundwater soaking in the process of garbage stacking and landfill. There are four main sources: water contained in garbage, water produced by garbage biochemical reaction, groundwater reverse infiltration and atmospheric precipitation, among which atmospheric precipitation is centralized, short-term and repetitive, accounting for most of the total leachate. Leachate is a kind of high-concentration organic wastewater with complex components, and its properties depend on factors such as garbage composition, garbage particle size, compactness, site climate, hydrological conditions, landfill time and so on. Generally speaking, it has the following characteristics:

1. 1 The water quality is complex and harmful. The research shows that by using GC-MS technology to analyze the composition of organic pollutants in landfill leachate, 63 kinds of main organic pollutants in landfill leachate were detected, and the reliability of 34 kinds was over 60%. Among them, there are 6 kinds of alkyl olefins, 0/9 kinds of carboxylic acids/kloc, 5 kinds of esters, 0/0 kinds of alcohols and phenols, 0/0 kinds of aldehydes and ketones/kloc, 7 kinds of amides, 0/0 kinds of aromatic hydrocarbons and 5 others. Among them, 1 carcinogen, 4 carcinogens and auxiliary carcinogens, and 1 mutagen have been identified, and 6 species have been included in the "blacklist" of China Environmental priority pollutants.

The concentration of 1.2 CODcr and BOD5 is high. The highest CODcr and BOD5 in leachate can reach 90000 mg/L, 38000mg/L or even higher. The content of ammonia nitrogen in 1.3 is high, which increases with the extension of landfill time, and the highest content can reach1700 mg/L/L. The nitrogen in leachate mostly exists in the form of ammonia nitrogen, accounting for about 40%-50% of TNK.

1.4 The water quality changes greatly. According to the years of landfill, landfill leachate can be divided into two types: one is young leachate with landfill time less than 5 years, which is characterized by high concentration of CODcr and BOD5 and strong biodegradability; The other is aged leachate that has been buried for more than 5 years. With the gradual change of fresh garbage into old garbage, its pH value is close to neutral, the concentrations of CODcr and BOD5 decrease, the ratio of BOD5/CODcr decreases, and the concentration of ammonia nitrogen increases. 1.5 has high metal content. There are more than ten kinds of metal ions in landfill leachate, among which the contents of iron and zinc are relatively high in the acid fermentation stage, and the concentration of iron can reach about 2000 mg/L, zinc can reach about 130mg/L, lead can reach 12.3mg/L, and calcium can even reach 4300 mg/L [4]/kloc-. The proportion of microbial nutrients in leachate is out of balance, mainly the proportion of C, N and P. Generally, BOD5: P in landfill leachate is more than 300. In view of the problems existing in the landfill, the following improvement suggestions are put forward for the sewage treatment facilities of the landfill:

(1) In the selection of treatment process, it is necessary to change the old thinking mode, abolish the process scheme that can not meet the treatment index, and adopt the MVC pressure steam evaporation treatment process with high efficiency and energy saving.

(2) Strengthen the operation and management of oxidation pond. It is hoped that through this improvement, the treated wastewater can meet the discharge standards and effectively control the pollution of leachate to the surrounding environment. The control and treatment of landfill leachate is the key to ensure the long-term safe disposal of garbage. Therefore, it is very important to study the treatment of landfill leachate. Through the analysis and summary of the current situation of leachate treatment, the future research on leachate treatment should focus on the following aspects.

First of all, the existing leachate treatment methods are various, because the treatment process has its own characteristics, so the application can not be applied mechanically, but should be adapted to local conditions. Differences in geographical location, geographical structure, meteorological conditions and garbage composition in different regions will lead to differences in leachate quality and quantity. For example, in view of the characteristics of less rainfall and large evaporation in the north, leachate recharge method is more economical and effective; The warm and humid climate in the south is beneficial to the development and application of soil-plant method to treat leachate.

Secondly, it is necessary to study the stabilization of landfill. Promoting the stabilization of landfill waste can not only shorten the stabilization time of landfill waste and improve the gas production rate, but also shorten the generation period of landfill leachate to a certain extent and range and improve the difficulty of leachate treatment.