Selective upcycling chelated copper from wastewater to Cu2-xSe-rich product: integrating selenium bio-reduction into anaerobic granular sludge technology

The treatment of wastewater containing chelated copper (Cu), such as Cu-EDTA complexes, remains a persistent challenge owing to the high stability of the chelates and the generation of hazardous heavy metal-bearing sludge. This study proposes a selenium-enhanced anaerobic granular sludge (Se-GS) technology for selective Cu recovery as a Cu 2-x Se-rich product. Over 100 days of continuous operation in a single laboratory-scale reactor with synthetic wastewater, the Se-GS reactor achieved a Cu removal efficiency of 98.7%, with dissolved effluent Cu concentrations consistently below 0.5 mg/L, outperforming the unamended control. Sequential extraction, X-ray diffraction and elemental analysis indicated that Cu and Se in the final Se-GS sludge residue may be predominantly present as crystalline Cu 2-x Se, which was extracted to obtain a Cu 2-x Se-rich product with a Cu recovery efficiency of 62.5%. Metagenomic analysis identified Desulfovibrio as a candidate functional genus associated with selenium transformation and a genome-level pathway for Cu 2-x Se biosynthesis was reconstructed. The recovered product exhibited a higher apparent methylene blue (MB) degradation rate under the tested condition than chemically synthesized Cu 2-x Se. The process is a selective Cu-recovery unit within a broader treatment train; residual EDTA, Cd and recovery-related streams require further management. Further validation with real wastewater, replicate reactors, and scale-up systems is warranted to confirm the robustness and scalability of the Se-GS process.