leachate

Leachate is a liquid that has percolated through solid waste and has dissolved or suspended substances from it. It commonly forms in landfills but can also arise from composting facilities, mining waste piles, and other waste-handling operations. Leachate generation depends on moisture content, rainfall, waste composition, and temperature.

Young leachate often contains high levels of biodegradable organic matter and ammonia and may be acidic, while older leachate tends to be more recalcitrant, with higher inorganic salts, metals, and complex organic compounds. Typical measurements include COD, BOD, ammonium, nitrate, chloride, sulfates, pH, and various metals.

Leachate poses environmental risks if released to soil, surface water, or groundwater because it can carry pathogens, nutrients, heavy metals, salts, and organic pollutants. Contamination can affect drinking water sources, aquatic ecosystems, and soil fertility, making control and treatment essential.

Protection and management rely on containment and treatment. Landfills may use liners and leachate collection systems to contain and remove leachate via pumps to on-site treatment or off-site facilities. Treatment approaches include physical-chemical methods such as coagulation, lime precipitation, carbon adsorption, and membrane processes; biological treatments like activated sludge or anaerobic digestion; and, in some cases, constructed wetlands or advanced oxidation. The goal is to reduce contaminants to meet regulatory discharge or reuse standards.

Regulatory frameworks typically require monitoring of leachate generation, quality, and treatment performance, with requirements for reporting, receiving-water limitations, or sewer discharge permits. Ongoing research seeks to improve cost-effectiveness and environmental outcomes of leachate management.