Nitrogen Removal from Landfill Leachate via the Nitrite Route

The feasibility of removing nitrogen from mature landfill leachate using the nitrite route was investigated in a two-stage SBR system – (1 first stage, short-cut nitrification; second stage, denitrification via nitrite. With a volumetric exchange rate (n) of 0.3 d and an oxygen concentration of between 1.2 and 1.3 mg/L, the nitrite accumulation ratio – (NO2-N)×100/(NOx-N)% – was between 32% and 37%. For the same hydraulic retention time, but lower oxygen concentration – between 0.8 and 0.9 mg/L – nitrite accumulation averaged 96%, indicating that ammonia was removed completely via the nitrite pathway. In the second step, an external carbon source was added to promote denitrification. Complete removal of nitrite was obtained for a carbon dose of 2.4 mg COD/mg NO2-N using acetic acid and 3.8 mg COD/mg NO2-N for butyric acid. Also, a higher denitrification rate – 14.6 mg NO2-N/g VSS·h – was observed with butyric acid as compared with acetic acid – 9.12 mg NO2-N/g VSS·h.