Total Chromium Removal and Mass Balance in a Hybrid Constructed Wetland Using Scirpus americanus and Hydrocotyle bonariensis for Tannery Wastewater Treatment

Tannery effluents contain high concentrations of total and hexavalent chromium, posing severe environmental risks, particularly in developing regions where inadequate treatment persists. Conventional remediation methods are often costly and complex, generating secondary pollutants and underscoring the need for sustainable alternatives. The present research evaluates the effectiveness of a hybrid constructed wetland at pilot scale for removing total chromium from final tannery effluents, applying a mass balance approach. The system comprised two levels: Scirpus americanus Pers. in the upper level and Hydrocotyle bonariensis Lam. in the lower level, each operated with a seven-day hydraulic retention time. Results showed significant total chromium removal, with the upper level retaining 47.82% in the substrate, 31.85% in roots, and 10.57% in aerial parts of Scirpus americanus. The lower level retained 53.53% in roots and 43.31% in aerial parts of Hydrocotyle bonariensis. Physicochemical parameters (pH, temperature, TSS, BOD, COD, and total hexavalent chromium) were measured before and after treatment. Tolerance indices decreased in Scirpus and increased in Hydrocotyle, while both species’ bioconcentration and translocation factors rose. Overall, the findings demonstrate this hybrid system’s effectiveness and ecological feasibility for chromium removal, underscoring its promise as a cost-efficient alternative for treating industrial effluents.