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Development of Surrogate Indicators to Monitor Pathogens in Biosolids

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Surrogate indicator organisms are needed to assess the presence of pathogenic agents in the waste matrices, to monitor the fate of potential pathogens during processing and land application and to provide a risk assessment for human health based on the presence of these indicators. Surrogate indicator organisms are indigenous to sludge, relatively inexpensive to analyze and can measured within days. These organisms have the potential to be used in place of Ascaris or poliovirus as a screening device during bench-scale or pilot-scale testing of proposed sludge disinfection processes. Additionally, they can be used for continued performance monitoring of the disinfection process prior to land application. In several studies, a variety of surrogate indicators have been assessed with various sludge disinfection processes. These disinfection processes include the Bioset Advanced Alkaline Stabilization Process, J-Vap® Heat Drying Process, Synox Process and BioChem Resources Neutralizer™ Process. For the Bioset Process, the results showed that a 3-log reduction was achieved in the aerobic endospores when the Ascaris eggs were completely eliminated. The somatic bacteriophages actually appeared to be more resistant than poliovirus. Thus, aerobic endospores could be used as a surrogate indicator of the reduction of Ascaris eggs in the advanced alkaline stabilization process. In the J-Vap Process, at 55°C or greater the somatic bacteriophage and Ascaris eggs are nearly completely inactivated. The time that the temperature was equal to or greater then 50°C was significant in the log reduction of somatic bacteriophage and Helminth egg inactivation (p < 0.05 for both). However, time at or above 50°C was not significant for Enteric Virus inactivation (p = 0.266). In the Synox Process, when the density of Clostridium spores were less than 100 CFUs per gram of solids, 80 to 90 percent of the time no viable Ascaris eggs could be detected (< 1 viable egg per 25 grams of dry solids). However, the results from the acidic treatment process did not show a linear relationship between log reduction in eggs and spores. Thus, C. perfringens showed potential to be an appropriate surrogate indicator for Ascaris for acidic treatment processes, but more research is needed. For the BioChem Process, in preliminary testing, aerobic endospores were shown to be poor indicators for inactivation of Ascaris suum eggs. Results from Clostridium perfringens and somatic bacteriophage analysis will be available in March. In conclusion, it is apparent that each disinfection process has a different surrogate indicator, rather than being able to use a universal surrogate indicator organism for all sludge disinfection processes.

Document Type: Research Article


Publication date: 2005-01-01

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