Degradation of Bacterial Water Quality in Drinking Water after Bottling

Fluence-based QMRA model for bacterial photorepair and regrowth in drinking water after decentralized UV disinfection

Ultraviolet disinfection is a promising solution for decentralized drinking water systems such as communal water taps. A potential health risk is enzymatic photorepair of pathogens after UV disinfection, which can result in regrowth of pathogens. Even though photorepair is a known issue, no formal risk assessments have been conducted for photorepair after UV disinfection in drinking water. The main objective was to construct a quantitative microbial risk assessment (QMRA) of photorepair after UV disinfection of drinking water in a decentralized system. UV disinfection and photorepair kinetics for E. coli were modelled using reproducible fluence-based determinations. Impacts of water collection patterns, and wavelength-dependent water container material transmittance, sunlight intensity, and photorepair enzyme absorbance were quantified. After UV disinfection by 16 or 40 mJ/cm² of < 5-log microorganisms per L, risk of infection did not exceed 1-in-10,000 under conditions permitting E. coli photorepair. Risk from photorepair was less than 1-in-10,000 for photorepair light exposure < 0.75 h throughout the day for UV fluence 16 mJ/cm² or greater. UV disinfection followed by solar disinfection surpassing photoreactivation during storage reduced risk below 1-in-10,000 for photorepair light exposure > 2.5 h between modelled times of 9 AM - 3 PM. The model can be expanded to other pathogens as UV fluence and photorepair fluence response kinetics become available, and this QMRA can be used to inform the placement of community water access points to reduce risk of photorepair and ensure adequate shelf life of UV disinfected water under safe storage conditions.

Microbiological quality assessment (including antibiogram and threat assessment) of bottled water

Water pollution is a major global problem that has been the leading cause of morbidity and mortality. This study was carried out to assess the microbiological quality of popular domestic brands of bottled water available in the Kathmandu Valley in Nepal. For the study of bottled water, a total of 50 samples each of different volumes (20 and 1 L) were selected. The samples were processed at the Microbiology laboratory at St. Xavier's College, Maitighar, Kathmandu. The microbiological assessments were performed as per the methods described in the American Public Health Association, 2005. Out of 100 samples, 48% of samples were found to be contaminated with total coliform. Escherichia coli was the predominant strain among the coliforms. Multidrug-resistant E. coli, Enterobacter aerogenes, and Pseudomonas aeruginosa were isolated from the 48 bottled water. Treat assessment test revealed that 88.23% of the isolated E. coli produced β hemolytic colonies, while 11.77% did not show hemolytic colonies, 100% E. aerogenes colonies were not able to develop hemolytic colonies and 100%, P. aeruginosa colonies gave β hemolytic colonies, respectively. Chi-square test shows that there is a significant association (p ≤ .05) between fecal coliform and volume of the vessel (i.e., 20 and 1 L), bottle type (i.e., unscratched and undented and scratched and/or dented), season (i.e., monsoon and postmonsoon), and total coliform. Chi-square test shows that there is no significant (p > .05) association between Pseudomonas spp and season (i.e., monsoon and postmonsoon). Out of 100 samples, 48% of samples were found to be contaminated with total coliform. Microorganisms survive in bottled water as they have many nutrients required for the microorganism in ionic form. Surveillance is lacking by the license-providing organizations followed by governmental organizations.