Ammonium Removal by the Oxygen-Limited Autotrophic Nitrification-Denitrification System

The present lab-scale research reveals the potential of implementation of an oxygen-limited autotrophic nitrification-denitrification (OLAND) system with normal nitrifying sludge as the biocatalyst for the removal of nitrogen from nitrogen-rich wastewater in one step. In a sequential batch reactor, synthetic wastewater containing 1 g of NH(4)(+)-N liter(−1) and minerals was treated. Oxygen supply to the reactor was double-controlled with a pH controller and a timer. At a volumetric loading rate (B(v)) of 0.13 g of NH(4)(+)-N liter(−1) day(−1), about 22% of the fed NH(4)(+)-N was converted to NO(2)(−)-N or NO(3)(−)-N, 38% remained as NH(4)(+)-N, and the other 40% was removed mainly as N(2). The specific removal rate of nitrogen was on the order of 50 mg of N liter(−1) day(−1), corresponding to 16 mg of N g of volatile suspended solids(−1) day(−1). The microorganisms which catalyzed the OLAND process are assumed to be normal nitrifiers dominated by ammonium oxidizers. The loss of nitrogen in the OLAND system is presumed to occur via the oxidation of NH(4)(+) to N(2) with NO(2)(−) as the electron acceptor. Hydroxylamine stimulated the removal of NH(4)(+) and NO(2)(−). Hydroxylamine oxidoreductase (HAO) or an HAO-related enzyme might be responsible for the loss of nitrogen.