EVALUATION OF BACTERIOLOGICAL INDICATORS OF BIOSOLIDS DISINFECTION

Under the current Federal regulations 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 following treatment, meets the criterion of 2 million fecal coliform/g of total solids. 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.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 heterotrophs. We also showed that endospore forming bacteria are poor indicators of the effectiveness of lime treatment to reduce pathogenic microorganisms, and that the density of aerobic endospores and their resistance to lime treatment was comparable to the densities and resistance of C. perfringens.