Modified chemical materials for mitigating copper ion interference in nitrogen cycle wastewater treatment: mechanisms, performance, and future perspectives

Biological nitrogen removal (BNR) is a cornerstone of sustainable wastewater treatment, yet its efficiency is frequently compromised by copper ion (Cu²⁺) interference. This review provides a comprehensive analysis of the dual role of copper in the nitrogen cycle: as an essential enzymatic cofactor at trace levels and as a significant toxicant at elevated concentrations. The process-specific impacts and toxicity mechanisms of ionic and nano‑copper on anammox, nitrification, denitrification, and sulfur-autotrophic systems were systematically evaluated. The focus is on modified chemical materials, including functionalized biochar, metal-organic frameworks, and mesoporous silica, designed for the selective capture and recovery of Cu²⁺ from complex matrices, with leading adsorbents achieving capacities up to 1189 mg/g. Furthermore, integrated protection strategies, including extracellular polymeric substance (EPS) engineering, bioelectrochemical systems (BES), and protective additives, are analyzed with mechanistic depth. Unlike previous reviews focused narrowly on Cu toxicity or Cu-sorption materials, this work provides an integrated framework spanning all major BNR processes and linking emerging multi-omics and machine learning tools to material discovery. Key knowledge gaps identified include the absence of lifecycle assessments for modified materials in BNR contexts and the lack of mechanistic models coupling Cu speciation to process-scale nitrogen removal dynamics. © 2026 Elsevier B.V.