Recharging urban water bodies using nanoparticle-treated water: technical feasibility, risk potential and remediation methods

The availability of freshwater in all forms is declining at a rapid rate. Many major cities are on the verge of experiencing “day zero” due to the risk of running out of drinking water. A huge volume of wastewater is being generated daily from these cities. Therefore, there is scope for a water reuse process in which this wastewater, after treatment, is discharged into natural water bodies or artificially built water bodies for groundwater recharge. The reuse of this water for drinking and household purposes still carries a risk potential. This wastewater carries effluent from industries that might be rich in nanoparticles and other heavy metals. Water containing nanoparticles is dangerous for human consumption. This study investigates the potential effects of nanoparticle release on ecosystems and human health, as well as providing novel strategies for their mitigation and use. The literature was searched to study the removal efficiency of Ag nanoparticles using nature-based units after secondary wastewater treatment. Treated wastewater carrying Ag nanoparticles is discharged into nature-based units (constructed wetlands and soil aquifer treatments) and their removal efficiency was found to be 99.34% in the case of CW only, 99.83% in the case of CW+SAT, and 95.75% in the case of tertiary soil. The initial concentration of Ag NPs in these effluents was in the range of 0-200µg/L. The final concentrations in the water were found to be less than the regulatory permissible guidelines of 100µg/L of silver ions that is seen as being fit for consumption by humans. Limited research data were found that addressed the fact that higher levels of Ag NPs may cause an accumulation of these NPs in the biota and in sediment form on CW. Further studies for the removal of higher concentrations of Ag NPs needs to be done for the risk assessment of NP dosage on humans, the removal efficacy threshold of CW and SAT, and the effects of long-term exposure.