Composting leachate: characterization, treatment, and future perspectives

The increasing production of waste has led to one of the major environmental challenges of today: waste management. A solution to this problem is the composting of organic wastes. While the composting process transforms organic wastes into biologically stable compost, large amounts of highly contaminated leachates that present a direct risk to the environment are also produced. First off, this review discusses the origin and nature of contaminants found in composting leachates. In a general perspective, composting leachates are characterized by the presence of high concentrations of moderately biodegradable organic matter and nutrients and contain toxic pollutants such as heavy metals and plasticizers. Treatment technologies that have been studied are subsequently reported and discussed (treatment efficiencies and operating costs). This review highlights the lack of available solutions to efficiently remove all contaminants found in these leachates, which is a major concern considering the increasing number of composting facilities. While both, membrane bioreactors and reverse osmosis, show promising results with NH4, COD and TSS removals of > 70, > 85 and > 99.9%, respectively, the resulting effluent remains hazardous for the environment. Further studies are required to assess the use of a combination of biological and advanced oxidation process for the production of a safely disposable effluent.