Leachate from municipal solid waste landfills in a global perspective: Characteristics, influential factors and environmental risks

Landfilling is one of the most common measures for disposing municipal solid waste, while the environmental leakage of landfill leachate, a kind of wastewater with complex compositions and high-level pollutants, has become a crucial eco-environmental issue all over the world. Understanding the profiles of landfill leachate can be useful for promoting sustainable municipal solid waste management, however, there are very few studies at a global level because of data insufficiency. In this work, we established a global database on the physicochemical characteristics of landfill leachate from academic literature, including 1251 pieces of data from 236 provinces or cities in 51 countries. Concentrations of typical pollutants in landfill leachate were aggregated by different categories of countries, climate zones, and landfill ages. Correlations between typical leachate pollutants (chemical oxygen demand, biochemical oxygen demand after five days, ammonia nitrogen, sulfate, chloridion, potassium, cadmium, chromium, ferrum, nickel, and lead) and their influential factors (mean annual temperature, mean annual precipitation, landfill age, and the fraction of food waste) were analysed; and the environmental risks led by landfill leachate were assessed. Results showed that: (1) landfill leachate in developing countries at the dry temperature zone, as well as the moist and wet tropical zone, contained higher concentrations of chemical oxygen demand and biochemical oxygen demand after five days; (2) the percentage of food waste, as an influential factor, has a positive correlation with typical landfill leachate pollutants, with R2 varying from 0.07 to 0.18, indicating its high potential on transforming organic fraction in solid waste into leachate; (3) In regard to the environmental risk resulted from landfill leachate, the groundwater and surface water had greater risks than soil environment nearby the landfill. Besides, chemical oxygen demand, ammonia nitrogen, ferrum, chloridion and heavy metals, especially arsenic, cadmium, nickel, and manganese were dominating pollutants in groundwater and surface water. This work provides valuable data and parameters of global landfill leachate, which could be helpful to mitigate pollution from landfills and achieve the goals of sustainable municipal solid waste management.