Removal of organics and nitrogen from municipal landfill leachate in two-stage SBR reactors

The aim of this study was to investigate efficiency of ammonium nitrogen removal from municipal landfill leachate in activated sludge in two-stage SBR reactors. Treated leachate contains low concentrations of organic substances measured as chemical oxygen demand (COD) - 757 mg O-2/dm(3) and high concentrations of ammonium - 362 mgN(NH4)/dm(3). Nitrification was studied in two parallel, aerated SBR reactors with two different hydraulic retention times (HRT), 3 and 2 days, respectively. We have found that 2 days HRT was sufficient to achieve complete nitrification. In the effluent ammonium, nitrite and nitrate nitrogen concentrations were 0.08 mgN(NH4)/dm(3), 0.04 mgN(NO2)/dm(3) and 320 mgN(NO3)/dm(3), respectively. The ammonium nitrogen removal rate was 20.2 mgN(NH4)/dm(3.)h. The effluent from aerobic reactors (HRT 2 days) was fed to the anoxic SBR reactors. An external carbon source (methanol) was added to promote denitrification. In the anoxic reactor, at a methanol dosage 3.6 mg COD/mg N-NO3 and HRT of 1 day complete denitrification was achieve with nitrate nitrogen residual concentrations of 0.9 mgN(NO3)/dm(3). The maximum denitrification rate was 48.4 mgN(NOx)/dm(3.)h. The highest values of the yield methanol coefficient Ym/N-NOx were determined for dosages 3.6 mg COD/mg N-NO3 and 5.4 mg COD/mg N-NO3, the lowest for 1.8 mg COD/mg N-NO3.