Degassing N2 from the Direct Oxidation of Total Ammonia in Mariculture Using a Three-Dimensional Electrode System

Abstract

Elevated levels of total ammonia nitrogen (TAN) are recognized as a primary contributor to acute toxicity in aquatic organisms across freshwater aquaculture and mariculture environments. Existing technologies for TAN removal from wastewater are constrained by complex processes, high energy consumption, and an inability to meet discharge standards in a single step. Conventional electrochemical routes often over-oxidize TAN to nitrate, which undermines the goal of achieving truly harmless wastewater. Herein, we use a three-dimensional (3D) electrochemical system packed with particulate electrodes to realize the “TAN to N2” in one step. The design exploits a synergistic mechanism in which anodic ·OH and HClO cooperatively oxidize TAN while cathodic sites concurrently reduce nitrate nitrogen, turning NH4+ directly to N2 without nitrate accumulation. The 3D electrochemical system is particularly suitable for marine aquaculture wastewater, especially when addressing the low TAN concentration characteristic. Results show that the 3D system increased N2 selectivity from 67.90% to 92.06% while stabilizing wastewater pH within a mildly alkaline window. The system operates in situ, enabling direct recycle of culture water and offering a new technological paradigm for harmless, on-site treatment and resource recovery from mariculture wastewater.