Beyond Removal Efficiency: Pollutant Speciation, Metal Fate, and Closed-Loop Strategies for Electroplating Wastewater Treatment

Electroplating wastewater treatment is governed not only by total heavy-metal concentrations but also by metal speciation, organic complexation, salinity, intermittent discharge, and increasingly stringent requirements for water reuse and metal recovery. This review reframes recent advances from a removal-efficiency-centered perspective to a speciation-driven and resource-oriented framework. Treatment technologies are evaluated according to their dominant mechanisms, including precipitation and phase transfer, ligand destruction and redox conversion, selective separation, electrochemical recovery, biological transformation, and hybrid process integration. Attention is paid to the fate of metals after treatment, the management of sludge, regenerants, and membrane concentrates, and trade-offs among removal efficiency, resource recovery, energy and chemical demand, operational stability, and engineering applicability. The analysis indicates that no single technology is likely to simultaneously address complexation, high salinity, membrane fouling, biological inhibition, and low-carbon operation. Future systems should therefore integrate source-separated collection, speciation-targeted pretreatment, selective metal recovery, water reuse, concentrate management, and digitally assisted process control. This review provides a mechanistic and decision-oriented framework for designing sustainable electroplating wastewater treatment systems beyond conventional end-of-pipe removal.