Strategies to enhance the biological nitrogen removal of high-strength ammonium and low C/N landfill leachate with the SBR process.

The treatment of high ammonium-nitrogen concentration landfill leachate has become an increasing problem because of the requirements to reduce nutrient emissions. A laboratory-scale sequential batch reactor (SBR) was operated and tested in order to optimize the operational strategies of a cost-saving method to enhance the removal of ammonium-nitrogen from a real landfill leachate. Two sequence schemes were tested, one with long non-aerated/aerated sequences and another with short sequences. The air supply levels with low to intermediate dissolved oxygen (DO) and external carbon addition were altered. With both schemes a high ammonium reduction (> 99%) and a reasonable total nitrogen (TN) reduction (around 60%) could be achieved with strong carbon limitation (BOD7/N = 1.1). Chemical oxygen demand (COD) removal was lower with longer sequences. Denitrification via nitrite seemed to be an important part of TN removal, controlled with the low DO. With increasing nitrite accumulation COD/N removed decreased in both schemes indicating clearly a more efficient use of COD. The scheme with short sequences indicated advantages to save the air supply preventing nitrite oxidation under low air supply conditions and better TN and COD removal efficiencies. The results show that an applicable operational strategy can be found resulting in a reasonable pre-treatment option in landfills, requiring less carbon and aeration energy.