Citation:

Meckes*, M C. EVALUATION OF BACTERIOLOGICAL INDICATORS OF BIOSOLIDS DISINFECTION. Presented at WEF/AWWA/CWEA Joint Residuals and Biosolids Management, Baltimore, MD, February 19 - 22, 2003.

Impact/Purpose:

To inform the public

Description:

Under the current regulations (CFR 503), Class B biosolids may be land applied with certain site restrictions. One method for achieving Class B status is to raise the pH of the sludge to >12 for a minimum of 2 hours with an alkaline material (normally lime). Alternately, a Class B biosolid is any biosolid that meets the criteria of 2 million fecal coliform/g of total solids. The regulation allows for monitoring of the solids using membrane filter or multiple tube methods.

The choice of fecal coliform as an indicator of treatment efficiency is a carry-over from evaluation of municipal wastewater discharges. Early research on the effectiveness of lime treatment to reduce the number of microbes in biosolids was done before techniques were developed to rapidly measure Escherichia coli in such samples, consequently little data has been developed regarding the comparison between the number of E.coli and fecal coliform in lime treated biosolids.

Some researchers have suggested that the anaerobic bacterium Clostridium perfringens may be a better indicator of biosolids treatment efficiency than fecal coliform, due to its ability to form resistant spores. If this is true, the same phenomenon may be true for aerobic spore forming organisms.

Class A biosolids monitoring permits measurement of Salmonella spp. instead of fecal coliform. The effectiveness of Class B treatments in reducing the number of these pathogens is not well documented.

This study was conducted to determine the relationship between some common microbial indicators and fecal coliforms in lime treated biosolids., and also to compare two common analytical techniques used for enumeration of fecal coliforms, and two techniques for
E. coli. A suite of methods were used to enumerate fecal coliforms, total culturable heterotrophs, E. coli, 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 ( =0.05). Similarly the E. coli methods were also shown to be not significantly different ( =0.05). We also found that the fecal coliform and E. coli populations are more susceptible to lime treatment than other heterotrophs. We also showed that endospore forming bacteria are poor indicators of the effectiveness of lime treatment to reduce pathogenic microorganisms. We found that the density of aerobic endospores and their resistance to lime treatment was comparable to the densities and resistance of C. perfringens.

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