Inactivation of faecal indicator bacteria in a roof-captured rainwater system under ambient meteorological conditions

Abstract

Aims: In this study, faecal indicator bacteria (FIB) namely Escherichia coli and Enterococcus spp. were seeded into slurries of possum faeces and placed on the roof and in the gutter of a roof-captured rainwater (RCR) system. The persistence of FIB in these circumstances was determined under ambient climatic conditions. FIB persistence was also determined under in situ conditions in tank water using diffusion chambers. Methods and Results: The numbers of surviving FIB at different time intervals were enumerated using culture-based methods. Both FIB were rapidly inactivated on the roof under sunlight conditions (T 90 = 2 h) compared with shade conditions (T 90 = 9-53 h). Significant differences were observed between sunlight and shade conditions on the roof for both T 90 values of E. coli (P < 0Á001) and Enterococcus spp. (P < 0Á001). E. coli showed biphasic inactivation patterns under both clean and unclean gutter conditions. Enterococcus spp., however, showed rapid inactivation (T 90 = 2 h for the clean gutter and T 90 = 6 h for the unclean gutter) compared with E. coli (T 90 = 22 h for the clean gutter and T 90 = 20 h for the unclean gutter). Significant differences were also observed between the T 90 values of E. coli and Enterococcus spp. for both clean (P < 0Á001) and unclean (P < 0Á001) gutters. Both E. coli and Enterococcus spp. showed nonlinear biphasic inactivation in tank water. Significant difference was observed between the T 90 value of E. coli inactivation compared with Enterococcus spp. (P < 0Á001) in the tank water. Conclusions: In this study, FIB were observed to survive longer (T 90 = 9-53 h) on the roof under shade conditions compared with sunlight conditions (T 90 = 2 h). If there is a rainfall event within two to three days after the deposition of faecal maters on the roof, it is highly likely that FIB would be transported to the tank water. When introduced into the tank, a relatively slow inactivation process may take place (T 90 = 38-72 h). Significance and Impact of the Study: The presence of FIB in water indicates faecal pollution and potential presence of enteric pathogens. Therefore, the information on the resilience of FIB, as obtained in this study, can be used for indirect assessment of health risks associated with using roof-captured rainwater for potable and nonpotable purposes.

A study of the bacteriological quality of roof-harvested rainwater and an evaluation of SODIS as a suitable treatment technology in rural Sub-Saharan Africa

“…They are always present in the faeces of warm blooded animals. Their die-off rate is slower than that of coliforms in water as well as their persistence pattern being similar to that of potential waterborne bacterial pathogens [27][28].The dominance of faecal enterococci in the harvested rainwater was in agreement with the findings of Ahmed et al [29] and others who suggested that enterococci species may be a better indicator for assessing faecal contamination in rainwater than E.…”

“…A variety of methods have been recommended to treat rainwater for drinking [29]. Treatment methods recommended in the region included boiling and the use of chlorine tablets.…”

Climate change-induced increases in precipitation are reducing the potential for solar ultraviolet radiation to inactivate pathogens in surface waters

“…2 h in sunlight vs. 9–53 h in the shade for Enterococcus spp. and Escherichia coli , two important groups of bacteria used as faecal indicators of warm-blooded animals including humans 20 . Experiments with these same bacteria in open wetlands showed 2–3 log 10 reductions from the inlet to the outlet, but only 0.5–0.6 log 10 reductions when floating-leaved plants covered the water surface and blocked sunlight 21 .…”

Zero Risk Does Not Exist: Lessons Learned from Microbial Risk Assessment Related to Use of Water and Safety of Fresh Produce

“…However, simple first‐order (single‐phase) die‐off is probably not accurate as most soil and subsurface environments are highly heterogeneous and because of the potential for long‐term survival of persistent subpopulations and/or re‐growth in the environment (Bradford and others ). As such, biphasic survival kinetics have been observed in both water (Easton and others ; Ahmed and others ) and fresh produce production environment (Petterson and others ; Seidu and others ). In biphasic decay kinetics an initial rapid decay is noted, often followed by an attenuated, slower decay.…”