Effects of environmental storage conditions on survival of indicator organisms in a blend of surface water and dual disinfected reclaimed water

Abstract

Aims The purpose of this study was to evaluate the effects of temperature, mixing and sunlight exposure on the 5‐day survival of Escherichia coli, Enterococcus sp., F+/male‐specific coliphages, somatic coliphages and Clostridium perfringens spores in an 80/20 blend of surface water and reclaimed water approved for potable reuse in North Carolina. Methods and Results Grab samples of tertiary treated, dual disinfected North Carolina ‘Type 2’ reclaimed water were collected and mixed with ambient surface waters to create the 80/20 mix and then spiked with naturally occurring organisms present in the blended water or organisms isolated from sewage. Organism survival over the 5‐day period was evaluated at 4 and 20°C, 0, 60 and 120 rev min−1 mixing speeds and exposure to sunlight or darkness. The log10 survival ratio was then calculated for each organism at each condition. Conclusions There were measurable differences between the log10 survival ratios at 5 days for most organisms; indicating that storage can decrease microbial concentrations. Mixing conditions were not a significant factor in microbe survival over the 5‐day storage period. Sunlight was the most effective treatment factor to decrease log10 survival during 5‐day storage. Significance and Impact of the Study No previous studies have evaluated the survival of micro‐organisms in the NC approved 80/20 blend of surface and reclaimed water over the 5‐day storage. This study provides the first results on the survival of regulated faecal indicator organisms stored for 5 days in blended water under different environmental conditions.

Viral and Bacterial Fecal Indicators in Untreated Wastewater across the Contiguous United States Exhibit Geospatial Trends

“…Finally, somatic coliphage, total coliphage (CB-390), Bacteroidetes (GenBac3), and E. coli (EC23S857) concentrations showed a significant correlation with average air temperature prior to sampling (Table 3). A recent review suggests that ambient water temperature is a key factor influencing the decay of many indicators (70), especially coliphage (71,72). In addition, meta-analyses of somatic and F ϩ coliphage decay rates confirmed the high sensitivity of these viral groups to water temperature across multiple studies (73), potentially explaining this geospatial trend in somatic coliphage assuming there is a predictable link between air and sewage temperatures in this study.…”

Quantitative microbial risk assessment of North Carolina reclaimed water for potable reuse

“…As previously discussed, these risk calculations are conservative estimates and may be higher than what can be expected from potable reuse or drinking water treatment in practice. The numbers for recreational water exposure do not consider sunlight exposure of the water and potential die-off as a result of UV exposure, a factor that is likely to play a role in microorganism survival (Bailey et al, 2019).…”

“…Further details on the quantitative ICC-PCR method for infectivity detections is described in Bailey et al, 2018. The survival of microorganisms in the 80/20 blend of sewage-impacted surface water and reclaimed water was quantified in Bailey, Casanova, & Sobsey, 2019, and the resulting log 10 survival of indicator microorganisms was used to model the survival of pathogens over a 5-day storage period for human exposure scenarios 4 and 5 of this study.…”

“…For the purposes of this risk modeling, the survival of Salmonella bacteria over the 5-day period was modeled using the log 10 reduction of naturally present bacteria. Average viral indicator reductions were approximately −0.32 at 4 C and −1.22 at 20 C. For the protozoan parasite surrogate, the average log 10 reduction was −1.89 at 4 C and −1.64 at 20 C. The statistical analysis presented in Bailey et al, 2019, indicated a statistically significant difference in survival between each of the temperatures evaluated for all test organisms except C. perfringens, but not for the three mixing speeds during 5-day storage; accordingly, storage conditions were modeled for both temperatures. The survival of organisms in reuse water was modeled as a normal distribution of the average log 10 (n t /n o ) values at each temperature.…”

“…A person ingests 2 L of blended reclaimed water after it has been combined at a 20% to 80% ratio with run‐of‐river intake raw source water, stored for 5 days, and then treated by conventional drinking water treatment. Pathogen die‐off is evaluated in the 5‐day storage condition on the basis of microbial survival data described in Bailey et al, 2019. Pathogens are assumed to be reduced by conventional drinking water treatment by (a) the USEPA‐required log 10 reductions, (b) the WHO risk‐based method of reducing pathogens in water, and (c) a worst‐case log 10 reduction scenario based on real‐world data reviewed by Medema and Hijnen (2007).…”