Cascading Electrochemically Tailored NO₂^–/NH₄⁺ Ratio and Biological Anammox for Zero-Carbon and High-Standard Treatment of Nitrate-Rich Water

Abstract

In recent years, it has been difficult to remove excess N (mainly NO 3 − -N) in wastewater with a low ratio of biochemical oxygen demand/chemical oxygen demand. The present study combined the operation of electrochemical process (with a modified brass mesh electrode being used as the cathode) and anammox (anaerobic ammonium oxidation) to treat a high nitrate-simulated wastewater and investigated the overall operating parameters of the combined system. Results showed that the efficiency of the combined system for the removal of total nitrogen can be stabilized over 76.35% at an electrochemical feed of 300 mg/L NO 3 − -N, and the NO 2 − -N/NH 4 + -N (around 130 mg/L) in the effluent of the electrochemical part was kept around 1. Although specific anammox activity decreased from 142.07 to 129.23 mg/g VSS-d, the amount of secreted extracellular polymeric substances increased from an initial 152.10 to 204.12 mg/g VSS. The main functional bacteria were Candidatus Brocadia (2.80−8.84%) and Candidatus Jettenia (0.94−1.99%). Compared to traditional denitrification, the composite process lags behind but still holds a certain economic advantage over electrochemical nitrate removal counterpart. KEYWORDS: nitrate-rich wastewater, anammox, tailored ratio of NH 4 + /NO 2 − , electrochemical nitrate reduction, microbial community structure