Nitrogen removal based on anammox-based processes applied to mature landfill leachate diluted with domestic wastewater: a review

The anammox process is considered a sustainable, low-cost, and promising alternative for the treatment of effluents with high concentrations of nitrogen (N) and low concentrations of chemical oxygen demand (COD). Mature landfill leachates are rich in nitrogen and a potential source of water and soil contamination, potentially causing eutrophication of surface water bodies. In developing countries, leachates have been treated together with municipal effluents in WWTP. However, there are few reports on nitrogen removal in these systems. This review evaluated studies using anammox-based processes, including partial nitrification and anammox (PN/A), focusing on mature leachates and their co-treatment with municipal wastewater. We aimed to identify anammox-based treatment strategies leading to high N and COD removal efficiencies. For PN/A, sequential batch reactors have been successfully used to treat different effluents such as leachates. Recirculation and leachate dilution in anammox-based processes were strategies successfully adopted to achieve high nitrogen removal. Temperatures above 30°C and pH values from 7.8–8.5 had positive effects on the performance of co-treatment processes. The best performances in the co-treatment processes using PN/A were achieved for dilution rates between 2 and 11.5 parts of municipal wastewater to 1 part of mature leachate, reaching N and COD removal efficiencies above 90% and 86%, respectively. Inhibition of nitrite-oxidizing bacteria, acclimatization of anammox bacteria for long periods, as well as extracellular polymeric substances production by anammox bacteria are important factors in the performance of PN/A systems for the co-treatment of mature leachate and domestic wastewater.