Landfill leachate treatment with a novel process: Anaerobic ammonium oxidation (Anammox) combined with soil infiltration system

A novel combined process was proposed to treat municipal landfill leachate with high concentrations of ammonium and organics. This process consisted of a partial nitritation reactor (PNR), an anaerobic ammonium oxidation (Anammox) reactor (AR) and two underground soil infiltration systems (USIS-1 and USIS-2). Based on the optimum operating conditions obtained from batch tests of individual unit, the combined process was continuously operated on a bench scale for 166 days. Partial nitritation was performed in a fixed bio-film reactor (PNR, working volume = 12 L). Ammonium nitrogen-loading rate (Nv) and DO were combined to monitor partial nitritation, and at T = 30 ± 1 °C, Nv = 0.27-1.2 kg/(m3·d), DO = 0.8-2.3 mg/L, the ratios of nitrite nitrogen (NO2−-N) to ammonium nitrogen (NH4+-N) were successfully kept close to 1.0-1.3 in the effluent. Nitrate nitrogen (NO3−-N) less than 43 mg/L was observed. The effluent of PNR was ideally suited as influent of AR. Sixty-nine percent CODcr from the raw leachate was degraded in the PNR. Anammox was carried out in a fixed bio-film reactor (AR, working volume = 36 L). At T = 30 ± 1 °C, Nv = 0.06-0.11 kg/(m3·d), about 60% NH4+-N and 64% NO2−-N in the influent of AR were simultaneously removed. Inhibition of high-strength NO2−-N (up to 1011 mg/L) should be responsible for the low removal rate of nitrogen. About 35% aquatic humic substance (AHS) was degraded in the AR. With the same working volume (200 L), USIS-1 and USIS-2 were alternately performed to treat the effluent from AR at one cycle of about 30 days. At hydraulic loading rate (HLR) = 0.02-0.04 m3/m3·d, pollutant loading rates (PLR) = NH4+-N ≤ 14 g/m3·d, TN ≤ 25 g/m3·d, and CODcr ≤ 13 g/m3·d, average removal efficiencies of 88% NH4+-N, 67% TN and 55% CODcr were obtained. Overall, raw leachate with 1430-2720 mg NH4+-N/L, 1524-2912 mg TN/L and 1165-2599 mg CODcr/L, was treated by the process and the effluent with 22-58 mg NH4+-N/L, 108-300 mg TN/L and 32-250 mg CODcr/L was obtained with average removal efficiencies of 97% NH4+-N, 87% TN and 89% CODcr. The test results indicated that the combined system could work stably over a long period under the operating conditions, and that the process was feasible for the leachate treatment. AR should be the key to the performance of the combined process.