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Characterization of Roof Runoff Microbial Quality in Four U.S. Cities with Varying Climate and Land Use Characteristics
Citation:
Alja'fari, J., S. Sharvelle, N. Brinkman, M. Jahne, S. Keely, E. Wheaton, J. Garland, C. Welty, M. Sukop, AND T. Meixner. Characterization of Roof Runoff Microbial Quality in Four U.S. Cities with Varying Climate and Land Use Characteristics. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 225:119123, (2022). https://doi.org/10.1016/j.watres.2022.119123
Impact/Purpose:
To quantify pathogen loads in freshly collected roof-harvested rainwater to determine log reduction targets needed to treat this alternative water type for nonpotable end uses.
Description:
Roof runoff has the potential to serve as an important local water source in regions with growing populations and limited water supply. Given the scarcity of guidance regulating the use of roof runoff, a need exists to characterize the microbial quality of roof runoff. The objective of this 2-year research effort was to examine roof runoff microbial quality in four U.S. cities: Fort Collins, CO; Tucson, AZ; Baltimore, MD; and Miami, FL. Seven participants, i.e., homeowners and schools, were recruited in each city to collect roof runoff samples across 13 precipitation events. Sample collection was done as part of a citizen science approach. The presence and concentrations of indicator organisms and potentially human-infectious pathogens in roof runoff were determined using culture methods and digital droplet polymerase chain reaction (ddPCR), respectively. The analyzed pathogens included Salmonella spp., Campylobacter spp., Giardia duodenalis, and Cryptosporidium parvum. Several factors were evaluated to study their influence on the presence of pathogens including roof runoff physicochemical parameters, indicator organisms concentrations, presence of trees, meteorological parameters, percent of impervious cover, seasonality, and geographical location. E. coli and enterococci were detected in 73.4% and 96.2% of the analyzed samples, respectively. Concentrations of both E. coli and enterococci ranged from <0 log10 to >3.38 log10 MPN/100 mL. Salmonella spp. invA, Campylobacter spp. ceuE, and G. duodenalis β – giardin gene targets were detected in 8.9%, 2.5%, and 5.1% of the analyzed samples, respectively. Campylobacter spp. mapA and C. parvum 18S rRNA gene targets were not detected in any of the analyzed samples. The detection of Salmonella spp. invA was influenced by the geographical location of sampling (Chi-square p-value < 0.001) and antecedent dry period (p-value = 0.002, negative correlation). Campylobacter spp. ceuE occurrence also correlated negatively to the antecedent dry period (p-value = 0.07). On the other hand, the presence of G. duodenalis β–giardin in roof runoff correlated positively to rainfall depth (p-value = 0.05). While physicochemical parameters and impervious area were not found to be correlated to the presence of pathogens, significant correlations were found between meteorological parameters and pathogens’ presence. Additionally, a weak, yet significant positive correlation, was found only between the concentrations of E. coli and those of Giardia duodenalis β-giardin. This dataset represents the largest-scale study to date of enteric pathogens in U.S. roof runoff collections and will inform treatment targets for different non-potable end uses for roof runoff.
URLs/Downloads:
DOI: Characterization of Roof Runoff Microbial Quality in Four U.S. Cities with Varying Climate and Land Use Characteristics
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