Electrochemical OCNT-PPy membrane achieving high-efficiency ammonia nitrogen removal and enhanced antifouling performance: Interface design and removal mechanism

The ammonia nitrogen (NH₄⁺-N) in the biogas liquid is exposing serious ecological risks to the environment. Electrochemical membrane processes have the advantages of high efficiency and environmental sustainability in treating NH₄⁺-N. However, precisely designing the efficient catalytic interface is difficult, and the mechanism and the path of NH₄⁺-N removal are unclear. To address this issue, this study designed a highly cross-linked structure oxidized carbon nanotube/polypyrrole (OCNT–PPy) electrical membrane by precisely controlling the polymerization time (optimization for 60 min), minimizing interfacial electron transfer resistance, and achieving excellent electrochemical performance. The prepared OCNT-PPy electrical membrane with applied 3 V achieved 99% NH₄⁺-N removal within 20 min, 3 times higher than the 0 V OCNT-PPy group. Mechanism analysis revealed that hydroxyl radicals (•OH) and active chlorine synergistically contributed to the removal of NH₄⁺-N, and most of NH₄⁺-N (about 71.35%) was oxidized into nitrogen gas (N₂). Furthermore, the OCNT-PPy electrical membrane with 3 V was used to directly treat the diluted actual fermentation biogas liquid. The permeation flux increased by 67%, and the total organic carbon (TOC) enhanced removal of 11.2%, and the fluorescent organic substances were completely removed compared with the 0 V group. This work developed a scalable and high-efficiency electrochemical membrane platform for high-efficiency NH₄⁺-N removal of biogas liquid and provided a new inspiration for the precise design of the catalytic reaction interface.