Optimization strategy for Cr(VI) removal in coke-based modular constructed wetlands: A comprehensive analysis of...

To address Cr(VI) contamination, this study designed a modular-filled constructed wetland (MFCW) by optimizing the sequence of coke, bio-ceramic, gravel and zeolite fillers. Results demonstrated that the "coke-bio-ceramic-gravel-zeolite" configuration achieved an average Cr(VI) removal efficiency of 90 %, with effluent concentrations stabilized at 0.16 mg/L (below China's discharge limit of 0.5 mg/L). The coke module contributed 52.1 % removal via adsorption (139.86 mg/kg capacity) and chemical reduction. Microbial analysis revealed Cr-resistant Proteobacteria dominance (30.4 % contribution), while plants (Acorus calamus) enhanced rhizosphere reduction (1.5 %). The system also removed NH₄⁺-N (96.0 %), TP (63.0 %) and COD (71.0 %), with modular design reducing operational costs by 32.2 %. The study innovatively proposes a coke-dominated multi-fillers sequential synergistic mechanism, providing an efficient and low-cost ecological solution for industrial wastewater treatment.