Industrial water treatment within a wetland planted with Hemarthria compressa and subsequent effluent reuse to grow Abelmoschus esculentus

This study assesses the potential of constructed wetland systems to treat tannery effluent (TE) and mixed industry effluent (MIE). After each of the three influent cells acting as settling cells, three treatment cells in horizontal series along with a Control were applied. Each of the cells was subjected to horizontal surface flow and planted with Hemarthria compressa (L.f.) R.Br. (perennial whip grass). The percent decline in heavy metal concentrations between settling and Cell 3 over a period of 60 days varied as follows: zinc (Zn; 35.83–95.59), chromium (Cr; 30.63–95.49), copper (Cu; 24.3–97.05) and nickel (Ni; 20.3–93.2). The drop in chemical oxygen demand (COD mg L⁻¹) ranged between 3.95 and 72.14%, whilst the total dissolved solids (TDS g L⁻¹) decline was between 3.23 and 98.75%. The pH and electrical conductivity (EC) drop ranges were between 1.4 and 11.72% along with up to 92.92%, respectively. The determined decline rates of pollutants and the cumulative biomass yield of H. compressa at p = 0.05 were between 0.76 and 0.96 (20 d⁻¹). The heavy metal tolerance index for H. compressa in TE and MIE were 0.25–3.25 and 0.25–2.2, respectively. Although treated TE and MIE discharged from Cell 3 of each of the effluent treatment series on the 60th day had Zn, Ni, Cr and Cu concentrations greater than the local permissible limits (Punjab Environmental Quality Standards) of Liquid Industrial Effluents. The treated water through the constructed wetland system proved safe for cultivation of okra (Abelmoscus esculentus (L.) Moench) vegetables.