👉 In environmental science and biogeochemistry, a leachate is a liquid or gaseous substance that flows out of an activated sludge reactor, usually as a result of chemical reactions in the reactor. Leachates are often used to treat wastewater or sewage, which can contain pollutants such as bacteria, chemicals, and organic matter. The term "leachate" comes from the Latin word "leacatus," which means "to leach." In the context of activated sludge