Treatment of low carbon-to-nitrogen wastewater using two-stage sequencing batch reactor with independent nitrification

Two-stage sequencing batch reactor (SBR) with independent nitrification was evaluated for simultaneous removal of COD, nitrogen, and phosphorus from a low carbon-to-nitrogen wastewater (C/N ratio ranged from 1.1 to 7.4). Independent nitrification proceeded by incorporating the contact period within the system and the nitrification period in the external reactor, which was an outsourcing resource dedicated to enhancing nitrification activity. The contact period enabled the fraction of organic substrate in the influent. Ammonia nitrogen was then able to be decanted to the external nitrification reactor, in which ammonia nitrogen was nitrified as much as 70%. During the nitrification period, dominate microbial group was an ammonia oxidizing bacteria such as Nitrosomonas sp. JL21, Nitrosomonas sp. JL2, and Nitrosolobus multiformis. During the react period, the nitrogen nitrified was not only denitrified, but organic matters were also biodegraded. It was revealed that the effective and preferential use of organic substrate enhanced the overall performance of the system without the supplement of any external carbon sources. Removal efficiencies of COD, nitrogen, and phosphorus were as high as 87% at the loading rate of 0.06–4.79 kg COD/m3 day, 81% at the loading rate of 0.05–0.84 kg N/m3 day, and 60% at the loading rate of 0.01–0.09 kg P/m3 day, respectively.