As we all know, sewage produces a lot of pollution now, resulting in serious pollution of rivers, lakes, sewers, and the sea. At present, landfill is the main urban waste disposal method in my country, but this method also has great harm. If the landfill leachate is not properly treated, it will cause serious impact. Leachate is a high-concentration organic wastewater with complex components, and its properties depend on factors such as garbage composition, particle size, compaction degree, site climate, hydrological conditions, and landfill time. So, how to distinguish old and new landfill leachate?

Depending on the age of the landfill, landfill leachate is divided into two categories:

1. New landfill leachate, also known as "new waste water", has a landfill time of less than 5 years, and is characterized by high concentrations of COD and BOD5 and strong biodegradability.

2. The old landfill leachate, also known as "old waste water", has been landfilled for more than 5 years, the waste is gradually stale, and its pH value is close to neutral. The concentrations of COD and BOD5 decreased, the ratio of BOD5/COD decreased, and the concentration of ammonia nitrogen increased. It is manifested as high NH3-N, TN, low COD, poor biodegradability, and most of the humus degraded by COD, and the sludge proliferation is difficult. With the passage of time in the operation of the waste landfill, the amount and quality of the permeate are also changing, and the process system for treating fresh permeate is not suitable for the treatment of middle-aged and old permeate.