Treatment and recovery methods for leachate concentrate from landfill and incineration: A state-of-the-art review

Leachate concentrate (LC) is enriched with refractory organics and inorganic ions from leachate, which makes LC be hardly treated by traditional methods. Thus, the effective treatment of LC is a crucial step in the sustainable development of landfills and incineration. This review discusses the operation conditions and treatment/recovery efficiencies of various treatment and recovery methods of LC based on LC's characteristics to find effective treatment and resource recovery. The existence of low biodegradability, micropollutants, and high concentrations of humic substances (HSs), chemical oxygen demand, and inorganic salts in LC considerably affect the option and efficiency of treatment methods. Among these treatment methods, the high salinity and high concentration of chorine ions in LC can remarkably support the application of electrochemical processes. However, electrochemical processes still exist several shortcomings, including halogenated by-products, active chlorine species, and the low removal efficiency of inorganic ions, among others. The feasibility of LC recovery, including HSs-based fertilizers, magnesium potassium phosphate crystallization, BiOCl (Bi-precipitate), and pyrolysis products, are investigated. However, some long-standing questions such as the purity, safety, and economy of these products remain unanswered. Individual treatment process inadequately makes LC meets the multiple goals of the minimized amount of volume and recovery of valuable components. A potentially feasible method is through the LC treatment of electrochemical processes to increase its biodegradability, then before recirculating the biological process, the residual LC is recovered as fertilizers, biomass, or salt crystals within the recovery processes.