Vertical flow constructed wetlands with Parthenium hysterophorous biochar: A nature-based solution for dairy effluent treatment

Dairy wastewater, characterized by high organic load and nutrient concentrations, poses significant environmental risks if discharged untreated. This study evaluates the potential of vertical flow constructed wetlands (VFCWs) amended with Parthenium hysterophorous biochar and planted with Canna indica (VFCW-CI) and Phagmites australis (VFCW-PA) for the treatment of dairy effluent. Key wastewater parameters that includes biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrate (NO₃⁻), and phosphate (PO₄³⁻) were monitored after a 72-hour hydraulic retention time (HRT). Results of the present study elucidated that VFCW-PA system achieved the highest removal efficiencies regarding BOD (95%), COD (99%), NO₃⁻ (97%), and PO₄³⁻ (76%), significantly outperforming the VFCW-CI, that showed removal efficiencies of BOD (91%), COD (95%), NO₃⁻ (92%), and PO₄³⁻ (70%). Also, at 72 h, VFCW-B (PA) and VFCW-C (CI) outperformed the control in all parameters, achieving >90% removal of BOD, COD, and PO₄³⁻ removal. Biochar amended setups showed about 49–57% higher COD removal, 51–55% higher BOD removal, 48–53% higher NO₃⁻ removal, and 20–35% higher PO₄³⁻ removal compared to the control, suggesting its direct role in the improved removal mechanisms in VFCWs. Major processes involved in pollutant removal likely include nitrification-denitrification, adsorption, and sedimentation. These findings demonstrate that Parthenium hysterophorous biochar integration, especially when combined with Phagmites australis , provides a cost-effective and sustainable approach for treating high-strength dairy wastewater. Future research should explore the role of microbial populations in biochar-amended VFCWs to further elucidate treatment mechanisms. • At 72 h, Biochar amended VFCW Parthenium hysterophorous and VFCW Canna indica achieved >90% removal of BOD, COD, and PO₄³⁻, significantly outperforming the control setup • Biochar-amended VFCW Parthenium hysterophorous achieved maximum pollutant removal (BOD -95%, COD-99%, NO₃⁻ -97%, PO₄³⁻- 76%), outperforming VFCW- Canna indica system • Both VFCWs improved treatment efficiencies, showing higher removal than the control of COD, BOD, NO₃⁻, PO₄³⁻by 49–57%, 51–55%, 48–53%, 20–35%, respectively • Integration of biochar with Phragmites australis provides a sustainable and low-cost approach for treating dairy wastewater