Horizontal flow biochar amended constructed wetlands as a sustainable approach for rural wastewater treatment

Abstract

Constructed wetlands (CWs) have provided an alternative technology to conventional wastewater treatment technologies for more than fifty years. Biochar is a carbon-rich porous material made in the absence of oxygen at higher temperatures that has recently been used as a substrate in constructed wetlands. The objective of this study was to measure the efficiency of horizontal flow (HF) biochar amended constructed wetlands planted with Eclipta alba (L) in treating rural wastewater in batch mode. A total of seven experimental sets were prepared. Two controls one without plantation (C1) and one with plantation (C2) were used in the study. In five sets, various soil and biochar ratios ranging from 5% to 25% were used as substrate, with a 5% biochar interval. Physio-chemical parameters like biological oxygen demand (BOD), chemical oxygen demand (COD), nitrate (NO₃^-), total kjeldhal nitrogen (TKN), sulphate (SO₄^2-) and phosphates (PO₄^3-) were analysed at various hydraulic retention time (HRT) of 24h, 48h, and 72h to check the performance of HFCWs. The maximum removal efficiency of BOD, COD, NO₃^-, TKN and SO₄^2- were found to be 75%, 70%, 80%, 71%, and 46%, respectively at HRT 72hrs and in B25 variation. Removal efficiency increased with an increase in HRT and biochar concentration. However, the removal of phosphates was highest at B25 at HRT 48h.  The results reveal the critical role of wetland vegetation and biochar concentration as substrates. The biochar additions effectively removed organic contaminants and nitrates. Biochar-enhanced CWs can provide a long-term solution for treating rural home wastewater.