Detection of pepper mild mottle virus as an indicator for drinking water quality in Hanoi, Vietnam, in large volume of water after household treatment

Pepper Mild Mottle Virus as Indicator of Pollution: Assessment of Prevalence and Concentration in Different Water Environments in Italy

Pepper mild mottle virus (PMMoV), a plant pathogenic virus belonging to the family Virgoviridae, has been proposed as a potential viral indicator for human faecal pollution in aquatic environments. The present study investigated the occurrence, amount and diversity of PMMoV in water environments in Italy. A total of 254 water samples, collected between 2017 and 2019 from different types of water, were analysed. In detail, 92 raw sewage, 32 treated sewage, 16 river samples, 9 estuarine waters, 20 bathing waters, 67 groundwater samples and 18 drinking waters were tested. PMMoV was detected in 79% and 75% of untreated and treated sewage samples, respectively, 75% of river samples, 67% and 25% of estuarine and bathing waters and 13% of groundwater samples. No positive was detected in drinking water. The geometric mean of viral concentrations (genome copies/L) was ranked as follows: raw sewage (2.2 × 10⁶) > treated sewage (2.9 × 10⁵) > river waters (6.1 × 10²) > estuarine waters (4.8 × 10²) > bathing waters (8.5 × 10¹) > groundwater (5.9 × 10¹). A statistically significant variation of viral loads could be observed between raw and treated sewage and between these and all the other water matrices. PMMoV occurrence and viral loads did not display seasonal variation in raw sewage nor correlation with faecal indicator bacteria in marine waters and groundwater. This study represents the first report on the occurrence and quantification PMMoV in different water environments in Italy. Further studies are required to evaluate the suitability of PMMoV as a viral indicator for human faecal pollution and for viral pathogens in waters.

Repeated pressurization as a potential cause of deterioration in virus removal by aged reverse osmosis membrane used in households

Reverse osmosis (RO) membrane is widely used for household water treatment in areas with limited access to safe drinking water; however, some studies documented deterioration in the quality of RO permeate. Repeated pressurization from intermittent operation in households is suspected to have an adverse effect on RO. This study aimed to evaluate virus removal by RO used in actual households as well as the water quality of permeate, and to elucidate the main cause of RO deterioration. We conducted a survey in households in Hanoi, Vietnam, to collect 27 membranes along with their usage history, where virus removal was investigated in laboratory. Of the used RO membranes, 22% did not show the protective level, >3 log₁₀ (99.9%) virus removal, recommended by World Health Organization. The differences in virus removal among Aichi virus, MS2 and φX-174 were <0.5 log₁₀. All membranes with estimated pressurization times of <4000 showed >3 log₁₀ virus removal, while 17% of membranes used for <3years, the manufacturers' warranty period, did not achieve the criterion. Therefore, virus removal performance may not be assured even if the users replace the membrane following the warranty period. Furthermore, more pressurized membranes exhibited significantly lower virus removal than less pressurized ones, suggesting a major role of repeated pressurization in the deterioration of RO. Coliforms were detected from 44% of the permeate of the point-of-use devices applying RO (RO-POU), raising concerns on the extrinsic contamination and regrowth of bacteria. Consequently, RO in households may deteriorate more rapidly than the manufactures' expectation due to repeated pressurization. RO in households should be replaced based on not only membrane age but also total pressurized times (i.e., 4000 times) to keep the protective level of virus removal. The deteriorated bacterial quality in RO permeate suggested the need for installing post-treatment, such as UV irradiation.

Pepper mild mottle virus: A plant pathogen with a greater purpose in (waste)water treatment development and public health management

An enteric virus surrogate and reliable domestic wastewater tracer is needed to manage microbial quality of food and water as (waste)water reuse becomes more prevalent in response to population growth, urbanization, and climate change. Pepper mild mottle virus (PMMoV), a plant pathogen found at high concentrations in domestic wastewater, is a promising surrogate for enteric viruses that has been incorporated into over 29 water- and food-related microbial quality and technology investigations around the world. This review consolidates the available literature from across disciplines to provide guidance on the utility of PMMoV as either an enteric virus surrogate and/or domestic wastewater marker in various situations. Synthesis of the available research supports PMMoV as a useful enteric virus process indicator since its high concentrations in source water allow for identifying the extent of virus log-reductions in field, pilot, and full-scale (waste)water treatment systems. PMMoV reduction levels during many forms of wastewater treatment were less than or equal to the reduction of other viruses, suggesting this virus can serve as an enteric virus surrogate when evaluating new treatment technologies. PMMoV excels as an index virus for enteric viruses in environmental waters exposed to untreated domestic wastewater because it was detected more frequently and in higher concentrations than other human viruses in groundwater (72.2%) and surface waters (freshwater, 94.5% and coastal, 72.2%), with pathogen co-detection rates as high as 72.3%. Additionally, PMMoV is an important microbial source tracking marker, most appropriately associated with untreated domestic wastewater, where its pooled-specificity is 90% and pooled-sensitivity is 100%, as opposed to human feces where its pooled-sensitivity is only 11.3%. A limited number of studies have also suggested that PMMoV may be a useful index virus for enteric viruses in monitoring the microbial quality of fresh produce and shellfish, but further research is needed on these topics. Finally, future work is needed to fill in knowledge gaps regarding PMMoV's global specificity and sensitivity.