Quantification of human enteric viruses as alternative indicators of fecal pollution to evaluate wastewater treatment processes

Virus inactivation by sequential ultraviolet-chlorine disinfection: Synergistic effect and mechanism

The COVID-19 outbreak has raised concerns about the efficacy of the disinfection process followed in water treatment plants in preventing the spread of viruses. Ultraviolet (UV) and chlorine multi-barrier disinfection processes are commonly used in water treatment plants; however, their effects on virus inactivation are still unclear. In this study, the effects of different disinfection processes (i.e., UV, free chlorine, and their combination) on waterborne viruses were analyzed using bacteriophage surrogates (i.e., MS2 and PR772) as alternative indicators. The results showed that the inactivation rates of PR772 by either UV or free chlorine disinfection were higher than those of MS2. PR772 was approximately 1.5 times more sensitive to UV disinfection and 8.4 times more sensitive to chlorine disinfection than MS2. Sequential UV-chlorine disinfection had a synergistic effect on virus inactivation, which was enhanced by an increase in the UV dose. As compared with single free chlorine disinfection, UV irradiation at 40 mJ cm^-2 enhanced MS2 and PR772 inactivation significantly with a 2.7-fold (MS2) and a 1.7-fold (PR772) increase in the inactivation rate constants on subsequent chlorination in phosphate buffered saline. The synergistic effect was also observed in real wastewater samples, in which the MS2 inactivation rate increased 1.4-fold on subsequent chlorination following UV irradiation at 40 mJ cm^-2. The mechanism of the synergistic effect of sequential UV-chlorine disinfection was determined via sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using MS2 as an indicator. The results showed that the synergistic effect was due to damage to MS2 surface proteins caused by previous UV disinfection, which enhanced the sensitivity of MS2 to chlorination. This study provides a feasible approach for the efficient inactivation of viruses in water supply and drainage.

Development and evaluation of TaqMan-based, one-step, real-time RT-PCR assays for pepper mild mottle virus detection for near source tracking and wastewater-based epidemiology validation

Emergence of novel human pathogens pose significant challenges to human health as highlighted by the SARS-CoV-2 pandemic. Wastewater based epidemiology (WBE) has previously been employed to identify viral pathogens and outbreaks by testing samples from regional wastewater treatment plants. Near source tracking (NST) allows for more targeted WBE by analysing samples from individual buildings such as schools or even individual floors such as in multi-floor office buildings. Despite the public health advantages of WBE, few strategies exist for optimising NST sampling methodologies. Therefore, we developed a protocol to evaluate virus detection in NST sampling using Pepper Mild Mottle Virus (PMMoV) as a proxy for RNA viruses. PMMoV is the most abundant enteric human associated RNA virus and is present in peppers/pepper-containing foods. Two bespoke TaqMan RT-PCR assays were developed to detect a PMMoV genomic 5' region and a capsid associated gene. To evaluate the protocol against field samples, pepper homogenates were flushed down an in-use toilet (Liverpool School of Tropical Medicine, UK) to spike wastewater with PMMoV on multiple days, and samples collected from two sewage access points to validate NST samplers. These wastewater samples were assessed for PMMoV based on Ct values and results compared to pepper and Tabasco derived PMMoV positive controls. Positive detection of PMMoV was comparable and consistent in ten independent samples across two NST samplers regardless of pepper homogenate spiking. We have developed two novel one step TaqMan assays that amplify both PMMoV targets in viral RNA extractions from peppers, Tabasco, and wastewater samples with cDNA synthesis through to RT-PCR results taking approximately 30 minutes. Pepper homogenate flushing was not required to detect PMMoV in our wastewater samples, however this strategy of flushing PMMoV containing materials outlined here could be valuable in assessing and validating NST in buildings with no previous or current sewage flow.