Nitrogen and Organic Carbon Removal from Landfill Leachate under Feammox Conditions

Abstract

Wastewater with high ammonium (NH₄⁺) content and low carbon-to-nitrogen (C/N) ratios is challenging for treatment technologies. The currently applied nitrogen removal technologies, including: i) Nitrification-denitrification; and ii) Partial nitritation-anammox, are insufficient for wide application. The nitrification-denitrification technology is costly due to the high oxygen demand (for the nitrification step) and the requirement for additional organic carbon (for the denitrification step). Meanwhile, the partial nitritation-anammox technology requires a stable NH₄⁺/NO₂⁻ ratio, whereas the wastewater composition often fluctuates. Feammox is an anaerobic respiration pathway discovered at the beginning of the 21^st century and has recently been shown applicable in the removal of nitrogen and organic carbon simultaneously with the advantages of energy saving and simplicity in operation. In this study, a lab-scale Feammox procedure was performed to remove nitrogen and organic carbon from mature landfill leachate with extremely high NH₄⁺ and COD contents, and very low C/N and BOD/COD ratios. The results showed that the highest removal efficiencies for NH₄⁺ (90%) and COD (63%) were achieved at a C/N ratio of 1.8 with the initial NH₄⁺ concentration of 100 mg/L and a hydraulic retention time of 6 days. Increasing the C/N ratio of wastewater to 2.5 led to an increase in COD removal efficiency to 80%, however, it reduced the NH₄⁺ removal efficiency to 58%. The NH₄⁺ treatment efficiency was also decreased to 58% when the initial NH₄⁺ concentration was increased to 150 mg/L, even if the hydraulic retention time was extended to 8 days. These results showed that nitrogen and carbon co-removal from diluted landfill leachate could be efficiently achieved via the Feammox process.