ldentification of viruses, their viability and purification in drinking water

Abstract

This thesis aimed to identify viruses commonly found in water sources and assess the efficiency of water barriers in viral reduction at drinking water treatment plants (DWTPs) over time. Cell culture assays and molecular techniques were used to determine the inactivation of echovirus 30 (E30), simian rotavirus (RV SA11), and human adenovirus 2 (HAdV2) after treatment with chlorine, chlorine dioxide, and three different UV doses. All three viruses achieved a 3-4 log10 reduction after being disinfected by chlorine and chlorine dioxide. No virus was viable beyond 2 min of contact time by either chlorine or chlorine dioxide. The results suggested that the present CT (concentration x time) methods for lab-scale analysis might have an error. The UV dose of 400 J/m2 adequately inactivated E30 to 3 log10 reduction. However, 600 J/m2 was required to achieve a 3 log10 reduction of double-stranded viruses (RV SA11 and HAdV2). The viral identification in water samples from six DWTPs by next-generation sequencing (NGS) and later by qPCR revealed 147 classified viruses from 64 virus families and 6 unclassified viruses. Several viruses were identified in both raw and drinking water, although to a much lower degree, with a reduction of 1-3 log10. Virus removal by ultrafiltration increased proportionally with virus size, but other barriers such as rapid sand filtration appeared more effective at removing smaller viruses. The efficiency of some barriers was affected by factors such as temperature fluctuations, virus type, and different water sources.