Copper sulfate-enhanced horizontal subsurface flow constructed wetlands for cleaner and safer water: A sustainable approach to pathogen removal

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The inadequate management of wastewater in rural areas poses a significant sanitary and environmental risk. Constructed wetlands, although effective in reducing organic matter and suspended solids, often show limitations in the complete removal of pathogens, thereby hindering compliance with reuse or discharge standards. To address this the current study introduces a novel approach by evaluating the efficiency of copper sulfate (CuSO₄) as a dual-purpose germicidal and complementary coagulanting agent in a domestic wastewater treatment system using a horizontal subsurface flow constructed wetland (HSSF-CW). The novelty lies in utilizing CuSO₄'s synergistic properties to enhance both physical clarification and biological safety, offering a robust alternative for decentralized sanitation. The field-scale experiment comprised a septic tank, a coagulation stage with CuSO₄, and a horizontal subsurface flow constructed wetland (HSSF-CW) planted with Canna indica (total hydraulic retention time: 4.92 days). Prior to field-scale validation, a laboratory experimental design based on jar tests was conducted using CuSO₄ concentrations between 1–5% and doses ranging from 150–400 mg/L, which identified an optimal dose of 250 mg/L (3%). This optimal dose was subsequently applied and validated under field conditions. Physicochemical parameters (pH, turbidity, BOD, COD, nitrates, and phosphates) and microbiological indicators (fecal and total coliforms) were monitored weekly over a three-month period. The application of CuSO₄ significantly improved effluent quality ( p < 0.05), reducing turbidity by ≈90%, BOD by >88%, COD by >89%, nitrates by ≈98%, and fecal coliforms by >90%, with residual copper concentrations averaging 0.05 mg/L which is well below national and international regulatory limits, thereby minimizing concerns regarding effluent toxicity. Dissolved oxygen increased by approximately 73% (from 2.68 to 4.64 mg/L) thus highlighting a substantial improvement in wetland system health and treatment performance. Although chlorine achieved complete coliform removal, it presented risks of forming halogenated disinfection by-products (THMs). In contrast, CuSO₄ does not generate such compounds, provides an additional coagulating effect, and maintains residual safety levels below regulatory toxicity limits. These findings demonstrate that CuSO₄ is a highly relevant, low-cost, and sustainable alternative for improving effluent quality in rural areas thereby effectively facilitating the safe reuse of treated water in agriculture or environmental discharge.