Nidhi Ahlawat, Vishal Panghal, Pooja Choudhary, Vishwajit Hooda, Sunder Singh Arya and Sunil Kumar
Abstract
Constructed wetlands (CWs) have gained prominence as a sustainable treatment technology due to their low operational costs and environmental compatibility. The incorporation of biochar, a high-surface-area carbon-rich material generated under restricted oxygen conditions, offers new opportunities to improve pollutant removal in CWs. This study evaluated the performance of vertical flow constructed wetlands (VFCWs) planted with Canna indica and amended with varying proportions of biochar (10-30%) for the treatment of dairy wastewater under continuous flow. Five experimental setups were established, comprising two controls (C1: unplanted and C2: planted) and three biochar-amended wetlands (B10, B20, B30) containing 10%, 20%, and 30% biochar, respectively. Key physico-chemical parameters-biochemical oxygen demand (BOD), Chemical oxygen demand (COD), nitrate (NO3-), phosphate (PO4³-), sulphate (SO4²â), and oil & grease (O&G)-were monitored at hydraulic retention times (HRTs) ranging from 12 to 120 hours at a 12- hour interval. Results showed that pollutant removal efficiency improved with both increased HRT and higher biochar concentration. Maximum removal efficiencies at 120 hr. were recorded in B30, reaching 81% for BOD, 77.4% for COD, 58.9% for NO3-, 57.7% for PO4³â, 64.4% for SO4²â, and 80.8% for O&G. While organic contaminants and O&G were removed rapidly between 48-72 hr., nutrient removal was slower, becoming significant after 84 hr., reflecting the time needed for microbial community establishment. The findings highlight the synergistic role of biochar and vegetation in enhancing CW performance and confirm that biochar-amended VFCWs provide an efficient, economical, and scalable solution for dairy wastewater treatment.