Post-treatment and reuse of secondary effluents using natural ltreatment systems: the Indian practices.

Paper summarizes the results of India-wide survey of natural treatment systems (NTSs) for wastewater treatment and reuse. The quality of treated wastewater from different types of NTSs was analyzed for various physico-chemical and bacteriological parameters, and needs for post-treatment were identified. Currently, about 1838 million liters per day (MLD) of wastewater is being treated using NTSs, of which the contributions of polishing ponds, waste stabilization ponds, duckweed ponds, constructed wetlands, and Karnal technology were found to be 53.39, 45.15, 0.13, 0.55, and 0.78 %, respectively. Among the NTSs studied, constructed wetland was found most efficient in removal of pollutants including nitrogen, phosphorus, total coliform, and fecal coliform in the range of 76, 61, 99.956, and 99.923 %, respectively. Of all types of NTSs, only constructed wetland was found to meet the total coliform count requirements (<1000 per 100 ml). Of all the 108 NTSs in operation, 23 systems are producing treated effluents for irrigation; effluents from 48 systems are being discharged into river or lake, and remaining 38 systems have not found any designated use of treated effluent. The chlorination was the only post-treatment, which is being practiced at only three wastewater treatment facilities. During post-treatment, 1–2 ppm of chlorine is applied to the secondary effluent irrespective of its quality. The treated effluents from different NTSs contain fecal bacteria in the magnitude of 103 to 105, which may cause the severe health impacts through contamination of groundwater as well as surface water resources.