Effect of the mixing ratio during co-treatment of landfill leachate and sewage with a combined stripping and reversed A²/O process

In this study, pilot-scale tests were conducted to evaluate the effect of volumetric mixing ratio of landfill leachate to sewage on the performance of the combined ammonia stripping and reversed anaerobic/anoxic/oxic (A²/O) process for co-treatment of landfill leachate and municipal sewage. Stripping, as pre-treatment, could significantly remove ammonia nitrogen (NH₃-N) and total nitrogen (TN) by 55% and 52%, respectively. Moreover, chemical oxygen demand (COD) was slightly reduced by 6.8%, and little total phosphorus (TP) was removed. The subsequent reversed A²/O process appeared to be highly influenced by the volumetric mixing ratio of leachate to sewage. Typically, the effluent COD, NH₃-N, TN and TP increased with the increasing ratio from 1:30 to 1:15, namely, the increasing fraction of leachate. Over the all tested mixing ratio range, the effluent COD and NH₃-N were satisfied with the primary B standards of Chinese Discharge Standard of Pollutants for municipal waste water treatment plant (GB18918-2002). The standards different from the primary A standards for water reuse are used for discharge into the most surface water bodies in China. However, TN and TP would exceed the primary B standard levels at a mixing ratio of 1:15 or greater. These findings suggest that an appropriate volumetric mixing ratio should be carefully selected to ensure the performance of the reversed A²/O process.