Landfill leachate, which we often refer to, refers to the water contained in the landfill, the rain, snow and water entering the landfill, and other water. It deducts the saturated water holding capacity of the garbage and overburden layer, and experiences the garbage layer and the covering soil. A high concentration wastewater formed by layers. Because the water quality of landfill leachate is quite complex, it generally contains high concentrations of organic matter, heavy metal salts, SS and ammonia nitrogen. Landfill leachate not only pollutes soil and surface water sources, but also pollutes groundwater.
Landfill leachate is a high-concentration organic wastewater with complex composition and generally has the following six characteristics.
First, the water quality is complex and harmful
According to the relevant literature, GC-MS combined technology was used to analyze the organic pollutants in landfill leachate. A total of 63 main organic pollutants in landfill leachate were detected, and 34 kinds of credibility were above 60%. Among them, there are 6 kinds of alkyl olefins, 19 kinds of carboxylic acids, 5 kinds of esters, 10 kinds of alcohols and phenols, 10 kinds of aldehydes and ketones, 7 kinds of amides, 1 kind of aromatic hydrocarbons, and 5 kinds of other kinds. Among them, there are 6 kinds of carcinogens, 4 kinds of cancer-promoting substances and auxiliary carcinogens, and 1 kind of mutagen. There are 6 kinds of "blacklists" listed in China's environmental priority pollutants.
Second, the high concentration of CODcr and BOD5
The maximum CODcr and BOD5 in the leachate can reach 90,000 mg/L, 38000 mg/L or higher, respectively.
Third, high ammonia nitrogen
The ammonia nitrogen content is high and increases with the extension of the landfill time, up to 1700 mg / L. The nitrogen in the leachate is mostly present in the form of ammonia nitrogen, which accounts for 40%-50% of TNK. According to the age of landfills, landfill leachate is divided into two categories: one is young leachate with a landfill time of less than 5 years, which is characterized by high concentration of CODcr and BOD5 and strong biodegradability; the other is landfill. The old leachate with a time of more than 5 years gradually changed to a stale waste due to fresh garbage, its pH value was close to neutral, CODcr and BOD5 concentrations decreased, BOD5/CODcr ratio decreased, and ammonia nitrogen concentration increased.
Fourth, the metal content is high.
The landfill leachate contains more than ten kinds of metal ions, among which iron and zinc are higher in the acidic fermentation stage, the iron concentration can reach 2000mg/L; the zinc concentration can reach 130mg/L, and the lead concentration can reach 12.3mg/ L, the concentration of calcium even reaches 4300mg / L
Five, C, N, P ratio imbalance
The proportion of microbial nutrients in leachate is imbalanced, mainly due to the imbalance of C, N and P ratios. The BOD5:P in the general landfill leachate is mostly greater than 300.
Leachate treatment should be treated in a comprehensive manner according to local conditions due to high investment and operating costs.
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