Main Pollution Sources of Landfill Leachate

(1) Organic pollutants

In municipal landfills, household waste constitutes the main part. Such waste contains a high proportion of kitchen waste, which mostly consists of organic matter and is prone to oxidative decomposition. Water-quality analysis of leachate from China's operating landfills shows that its chemical oxygen demand (COD) fluctuates over a very wide range. Its constituents include low-molecular-weight (<500) volatile fatty acids (VFA), medium-molecular-weight fulvic acid (main components between 500 and 10000), and high-molecular-weight humic acid (main components between 10000 and 100000).

(2) Heavy metal pollution

Currently, China's household waste sorting and disposal system remains incomplete, so large amounts of electronic waste enter landfills together with ordinary household waste. During waste decomposition, the heavy metal ions inside these electronic products, especially batteries, are gradually released and transferred into the leachate. As a result, the leachate accumulates a variety of heavy metal ions — copper, iron, zinc, chromium, cadmium, lead, and more — at concentrations typically hundreds of times those of ordinary domestic sewage.

(3) Ammonia nitrogen pollution

Ammonia nitrogen is a key inorganic pollutant that persists long-term in leachate. The NH3-N content of leachate may exceed 5000 mg/L. When total nitrogen exceeds 40%, it inhibits microbial growth, greatly increasing the difficulty of biological degradation of the leachate.