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EVALUATION OF BACTERIOLOGICAL INDICATORS OF DISINFECTION FOR ALKALINE TREATED BIOSOLIDS
Citation:
Meckes*, M AND E R. Rhodes*. EVALUATION OF BACTERIOLOGICAL INDICATORS OF DISINFECTION FOR ALKALINE TREATED BIOSOLIDS. D.W. Smith, D.S. Mavinic (ed.), JOURNAL OF ENVIRONMENTAL ENGINEERING AND SCIENCE. National Research Press, Ottawa Ontario, Canada, 3(4):231-236, (2004).
Description:
In the United States, treated municipal sludge, also known as biosolids, may be land applied with certain site restrictions. According to U.S. regulations a Class B biosolid is any biosolid that following appropriate treatment, meets the criterion of 2 million or less fecal coliform g-1 total solids. More effective treatments can be used to produce Class A biosolids which must meet compliance requirements of less than 1000 fecal coliform g-1 or 3 Salmonella spp. 4g-1. The effectiveness of Class B treatments in reducing the number of specific pathogens and indicator organisms other than fecal coliforms is not well documented. One method to achieve Class B treatment is to raise the pH of the sludge to 12 for a minimum of 2 hours with an alkaline material (normally lime). Similarly, alkaline materials in combination with heat can be used to treat sludges to Class A requirements.
For this study, a suite of methods was used to enumerate fecal coliforms, total culturable heterotrophs, Escherichia coli(E. coli), Clostridium perfringens (C. perfringens), aerobic endospores, and Salmonella spp. in untreated municipal sludge and lime treated biosolids. Results of this work indicate that the fecal coliform methods used during this evaluation were not significantly different (α = 0.05). Similarly the E. coli methods were also shown to be not significantly different (α = 0.05). We also found that the fecal coliform and E. coli populations are more susceptible to lime treatment than other heterotrophic bacteria. Endospore forming bacteria were found to survive lime treatment while the numbers of other indicator organisms were significantly reduced. Finally, we showed that the density of indigenous aerobic endospores and their resistance to lime treatment was comparable to the densities and resistance of C. perfringens in both Class A and B alkaline treated biosolids.