Viral Risk Index, A Classification Approach for Safe Wastewater Reuse in Developing Countries During COVID-19 and Similar Epidemics

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), as the cause of Coronavirus Disease 2019 (COVID-19), may survive in sewage or wastewater treatment plant (WWTP). This condition increases the risks of reusing treated wastewater (TW), particularly in developing countries. We introduced a new index, Viral Risk Index (VRI), for risk classification based on available knowledge about SARS-CoV-2. It was calculated by six effective parameters on the decay rate of SARS-CoV-2 in wastewater. These parameters are easily quantifiable in WWTPs in developing countries and not limited to specific operational conditions. The concentrations of Fecal coliform (FC) and total suspended solids (TSS) in TW in addition to the temperature, WWTPs’ capacity, retention time (RT), and chemical oxidation demand (COD) removal are the six sub-indices. VRI classifies TW in 5 categories (low-high risks). This classification prioritizes WWTPs for monthly viral surveillance and risk mitigation. Here, 23 WWTPs were examined and prioritized in Iran (April-August 2020). The results indicated that the TW in 14 WWTPs could be safely reused, whereas 9 WWTPs required more surveillance and supplementary viral controls for TW reuse. Here, waste stabilization ponds had slightly safer TW than activated sludge units. Moreover, monitoring could improve the average VRI from 2019 to 2020.