Main sources:

(1) Precipitation infiltration, including rainfall and snowfall, is the main source of leachate generation

(2) inflow of external surface water, including surface runoff and surface irrigation

(3) Infiltration of groundwater. When the infiltration water level in the landfill is lower than the underground water level outside the site and there is no anti-seepage system, groundwater may penetrate into the landfill

(4) the moisture contained in the garbage itself, including the moisture carried by the garbage itself and the amount of adsorption in the atmosphere and rainwater

(5) Water generated in the process of garbage degradation. Water will be generated when organic components in garbage are decomposed in landfills

1. What is landfill leachate?

Landfill leachate is a kind of high-concentration wastewater formed from the water contained in the landfill itself, the rain and snow water entering the landfill and other water, deducting the saturated water holding capacity of the garbage and the overlying soil layer, and experiencing the garbage layer and overlying soil layer. The properties of landfill leachate vary with the operating time of the landfill, which is mainly determined by the stabilization process of the landfill. Landfill stabilization is usually divided into five stages, namely:

Initial Adjustment Phase,

The Transition phase,

Acid phase,

Methane Fermentation Phase

Maturation Phase

Two, the characteristics of landfill leachate

The water quality of landfill leachate is affected by many factors, such as the composition of landfill, the moisture content of landfill, the temperature of landfill site, the landfill age, the landfill technology and the precipitation, etc. The water quality is complicated and difficult to treat. Generally, it has the following characteristics:

The concentration of organic matter is high, and the concentration of COD and BOD can reach thousands to tens of thousands of mg/L.

High metal content, high salt

Influenced by precipitation and surface runoff, water quantity and quality changed greatly

The composition and properties of the leachate from the same landfill site change with the prolongation of the landfill life, and the biodegradability becomes worse and the content of ammonia nitrogen becomes higher and higher.

Geographical regions affect the composition of landfill leachate and the characteristics of water quality. The leachate properties produced by different geographical regions and landfill composition are different.

Ammonia nitrogen content is high (up to thousands of mg/L), and the range of variation is large

Nutritional factor ratio imbalance, due to the high content of ammonia nitrogen, C/N ratio often appear imbalance, and P deficiency, general BOD5/TP>300, and microbial growth required carbon phosphorus ratio (100:1) is far from

The leachate will produce a lot of foam in the biochemical treatment, which is not conducive to the normal operation of the system. Because there are many refractory substances in the leachate, the COD concentration is still in a high range after the leachate treatment.

Three, the main hazards of landfill leachate

The high ammonia nitrogen /COD content of landfill leachate leads to the eutrophication of surface water and the deterioration of water quality

Landfill leachate contains a lot of pathogenic bacteria, which is very harmful

There are more than 70 kinds of organic pollutants in landfill leachate, among which 5 kinds of carcinogens and auxiliary carcinogens have been listed in the "blacklist" of environmental priority control pollutants in China.

Landfill leachate contains more than ten kinds of metal ions, which can seriously inhibit the biological treatment process

Humic acid pollutants in landfill leachate that are difficult to biodegrade lead to black and stink water. Moreover, the combination of humic acid and halogen elements (especially chloride ions) will generate some carcinogenic and mutagenic substances, which will harm human health.