Insight into the C/N Effect on Treating Domestic Wastewater by the Electrical Gradual Deammonification Reactor (EGDR): Removal Performance, Microbial Communities, and the Nitrogen Removal Mechanism

An electrical gradual deammonification reactor (EGDR), combined with electrochemical technology and a deammonification process, was developed to treat domestic wastewater with a low C/N ratio. The EGDR was initiated successfully by gradually reducing the influent C/N ratio and balancing the growth of ammonium-oxidizing bacteria (AAOB) and heterotrophic denitrifying bacteria (HDB). The dissolved oxygen content in the EGDR can be controlled by the current density without the need for aeration. The findings reveal that the EGDR with a C/N ratio of 2:1 achieved an average TN removal rate of 39.44%, exhibiting a 7.01% enhancement over the biological aeration filter (BAF), whereas microbial activity was registered at 156.38 mu g of triphenylmethyl (TF) (g center dot h)(-1). The predominant genera observed in the anode region were Nitrosomonas (8.95%) and Hydrogenophaga (4.93%), while in the cathode region, Planococcus (27.34%) and Candidatus_Kuenenia (3.66%) were the major genera, likely due to the screening effect of the electric field. The electric field facilitated nitrogen removal by providing oxygen and hydrogen, thus promoting simultaneous partial nitrification, anammox, and hydrogen autotrophic denitrification in the EGDR. It was achieved by coordinating an electrochemical-biological multipathway, which envisions a novel technology to accomplish nitrogen removal in domestic wastewater with a low C/N ratio.