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On the composition of landfill leachate!

2021-02-05 14:04:59

  We often say that landfill leachate is a kind of high-concentration wastewater formed from the water contained in the landfill itself, the rain and snow water and other water entering the landfill, deducting the saturated water holding capacity of the garbage and the overlying soil layer, and experiencing the garbage layer and overlying soil layer. Due to the complex water quality of landfill leachate, which generally contains high concentration of organic matter, heavy metal salts, SS and ammonia nitrogen, landfill leachate not only pollutes soil and surface water, but also pollutes groundwater.

垃圾渗滤液处理工艺

  

First, the source of landfill leachate


Landfill leachate mainly comes from two sources, namely landfill site and waste incineration power plant. The corresponding generation principle is as follows:


(1) Garbage landfill: garbage itself contains water, and into the landfill rain and snow water and other water, deducting the garbage, overlying soil saturated water capacity, and through the garbage layer and overlying soil formed by a high concentration of waste water;


(2) Garbage Incineration Power Plant: the most typical characteristics of solid waste are high kitchen waste, high moisture content, high organic matter, mixed collection, and low relative calorific value. Therefore, in the design of domestic waste incineration plant, the storage capacity of garbage pit is 3-7 times of the daily disposal capacity of garbage (i.e. residence time of 3-7 days); That is, the garbage is stored in the garbage pit after 3-7 days of fermentation and maturation, and the water leached from the garbage in the process of fermentation and maturation is called leachate.


Two, landfill leachate composition


The composition of organic pollutants in landfill leachate was analyzed by GC-MS, and 63 kinds of main organic pollutants in landfill leachate were detected. There were 6 alkanes, 19 carboxylic acids, 5 esters, 10 alcohols and phenols, 10 aldehydes and ketones, 7 amides, 1 aromatics and 5 others. Among them, 1 carcinogen, 4 carcinogens, 4 cocarcinogens, and 1 mutagenic compound have been confirmed, and 6 of them have been listed in the "blacklist" of environmental priority pollutants in China. The CODCr and BOD5 in the leachate were up to 90000mg/L, 38000mg/L or even higher. With the prolongation of landfill time, the increase can be as high as 1700mg/L. The nitrogen in leachate mainly exists in the form of ammonia nitrogen, accounting for about 40%-50% of TNK. There are more than ten kinds of metal ions in the landfill leachate, among which iron and zinc are higher in the acidic fermentation stage, and the concentration of iron can reach about 2000mg/L. The concentration of zinc can reach about 130mg/L, the concentration of lead can reach 12.3mg/L, the concentration of calcium can even reach 4300mg/L1.6 in the leachate microorganism nutrient element proportion imbalance, mainly is C, N, P proportion imbalance.


Water quality fluctuation of landfill leachate


According to the age of landfills, landfill leachate can be divided into two categories: one is young leachate buried for less than 5 years, which is characterized by high concentration of CODCr and BOD5 and strong biodegradability; The other type is the old leachate buried for more than 5 years. Because the fresh waste gradually becomes stale waste, its pH value is close to neutral, the concentration of CODCr and BOD5 decreases, the BOD5/ CODCr ratio decreases, and the concentration of ammonia nitrogen increases.

 




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