Investigation of treatment potential of horizontal subsurface flow constructed wetland for the treatment of secondary treated sewage

Present study investigated the potential of different setups of horizontal subsurface flow constructed wetland (HSSFCW) for sewage treatment in the Indian context. Total four different setups, i.e., CW1 (unplanted CW); CW2 (planted with C. Benghalensis); CW3 (planted with T. Latifolia); and CW4 (planted with C. Benghalensis and T. Latifolia; 50% each of both the plants) were used to perform the treatment experiments. To perform the treatment experiment, a HSSFCW with the surface area of 35 m2 (3.5 × 10 m) and gravel as filter medium was built. Each setup of wetland remained operational for three months during which its performance was evaluated. The CW was fed at an average flow rate of 250 L h−1 with secondary treated sewage, and the treated sewage was examined twice a week at five different hydraulic retention times (HRT), i.e., 0, 12, 24, 36 and 48 h for essential sewage quality parameters. The wetlands efficiency improved proportionally with the increase in the duration of the hydraulic retention time. However, the aquatic macrophytes enhanced the HSSFCW efficiency. The CW4, i.e., the wetland planted with combination of C. Benghalensis and T. Latifolia showed the best performance in treating the biological oxygen demand, chemical oxygen demand, nitrate, ammonia, and phosphate, i.e., 73%, 70%, 81%, 88%, and 67%, respectively. This setup also showed the best performance in treating the total coliforms, fecal coliforms, and E. coli with removal efficiency of 80%, 85%, and 83%, respectively, at 48 h HRT.