Nitrogen Removal From Municipal Wastewater Using a Two-Sludge Denitrification/Nitrification Batch Reactor: Performance and Mechanisms

Biosorption is a common phenomenon, in that organics in wastewater are trapped by sludge flocs. To achieve high nitrogen removal efficiency from the treatment of low chemical oxygen demand (COD) content wastewater, a two-sludge denitrification/nitrification batch reactor (TDNBR) is successfully established based on the sorption of organic matter by anoxic activated sludge. During 123 days of operation, the TDNBR achieved high ammonia (>99%) and total nitrogen (TN) (80%) removal efficiency. A higher C/N ratio and exchange frequency have no obvious effect on nitrification but effectively enhanced denitrification. The sorption assays indicated that anoxic sludge could take up a large amount of organic matter (23.79–55.62 mg COD g⁻¹ TSS) but has a low sorption capacity of NH₄ ⁺-N. Nitrate utilization rate tests reveal that both the soluble and colloidal organics pre-sorbed on the sludge can be utilized in denitrification with few organics stored as PHA in bacterial cells. Through cyclic study analysis, it was found that, by interchanging the supernatant in oxic and anoxic tanks alternately, nitrification and denitrification processes are successfully separated and high ammonia and TN removal efficiencies are achieved.