The ability to detect the presence of microbial pathogens and the resulting health risks in biosolids is a significant issue confronting the wastewater industry. Ideally, wastewater treatment plants should be able to monitor for specific pathogens in biosolids. Since it is almost impossible to detect and quantify the presence of all possible pathogens in waste matrices, there is a compelling need to identify a suite of indicators that can be used to predict the presence of pathogenic microorganisms in biosolids. The overall objective of this project was to identify those pathogens and surrogate indicator organisms that are at the highest density in raw (untreated) sewage sludge across the United States, and determine the time-temperature relationship under controlled laboratory conditions. The results provide information about the concentrations of an extensive selection of raw sewage-associated organisms across warm and cool seasons and from locations across the United States. Additionally, the 16S pyrosequencing (non-culture based) analysis allowed for the compilation of a list of bacterial DNA sequences that were present in the raw wastewater samples. The second part of this study compared the time-temperature relationships of a subset of commonly used wastewater indicators and pathogens. The untreated sewage sludge samples were obtained from seven different U.S. locations (Illinois, Ohio, Wisconsin, California, Texas, Georgia, and the District of Columbia). Four samples were obtained from each location. Two samples were collected during the warm season (August–September, 2009), and two samples were collected during the cool season (January–February, 2010). Overall, all locations had relatively similar levels of organisms within ± 1-2 log units. There were no seasonal differences in the levels of total coliforms, fecal coliforms, E.coli, C. perfringens spores, Salmonella spp., Aeromonas spp., or Adenovirus. However, Shigella spp., enterococci, somatic coliphages, male-specific coliphages and culturable enteric viruses were higher in the warmer season than in the cooler season. Legionella spp. were higher in the cooler season as compared to the warmer season. In terms of relative abundance, there were greater numbers of indicator organisms such as fecal coliforms (10 8 MPN/g), E. coli (106 MPN/g), and enterococci (106 MPN/g) as compared to the traditional U.S. EPA 503 target pathogens, Salmonella spp. (< 8 MPN/g), culturable enteric viruses (< 1 PFU/g), and helminth ova (< 1 ova/g) in the raw sewage samples as compared to fecal coliforms (10 8 MPN/g), E.coli (106 MPN/g), and enterococci (106 MPN/g). Known pathogens, such as Shigella spp. (25 MPN/g), Legionella spp. (108 CFU/g), Aeromonas spp. (108 CFU/g), MacConkey sorbitol-negative E. coli populations (104 MPN/g) were, however, present in larger numbers. When real-time PCR-based methods were used, the presence of genetic sequences indicative of pathogens such as Adenovirus (10 7 gene copies/g), Giardia spp. (105 gene copies/g) was also evident. Aerobic spores (1066 CFU/g), Cl. perfringens spores (106 CFU/g), somatic coliphages (105 PFU/g) and male-specific coliphages (105 PFU/g) were also present. This suggests that traditional indicators such as fecal coliforms and E.coli, along with other organisms such as coliphages and enterococci, should be included in sewage monitoring studies. The presence of Aeromonas spp. and Legionella spp. in high numbers in the
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Jul 19, 2023
Tian Ma + 8
Open Access