Class B alkaline stabilization to achieve pathogen inactivation

Abstract

Liming is a cost-effective treatment currently employed in many Class B biosolids production plants in the United States. A bench scale model of lime stabilization was designed to evaluate the persistence of viral, bacterial and parasitic pathogens. The survival of fecal coliforms, Salmonella, adenovirus type 5, rotavirus Wa, bacteriophage MS-2, Cryptosporidium parvum oocysts, Giardia lamblia cysts, and Ascaris lumbricoides ova was evaluated under lime stabilization conditions in a water matrix. Fecal coliforms and Salmonella were undetectable following 2 hours of lime stabilization, demonstrating a 7-log reduction. Adenovirus, MS-2 and rotavirus were below detectable levels following 2 h of liming, demonstrating a 4-log reduction. G. lamblia cysts were also inactivated. A. lumbricoides ova remained viable following 72 hours of liming as did C. parvum oocysts. While this study confirmed that Ascaris ova are resistant to liming, their scarcity in sludge and low recovery efficiencies limit their use as indicator. The persistence of C. parvum oocysts after exposure to lime, suggests that this parasite would be a better choice as indicator for evaluating biosolids intended for land application. The studies done with adenovirus Type 5, rotavirus Wa and male specific bacteriophage provided preliminary data demonstrating similar inactivation rates. Monitoring anthropogenic viruses is a time consuming, labor intensive and expensive process. If further studies could demonstrate that phage could be used as an indicator of other enteric viruses, enhanced monitoring could result in greater acceptance of land application of biosolids while demonstrating no increased public health threat.

Figure 1:

E. coli and Salmonella inactivation by liming stabilization. Results are from three replicate experiments at 28°C. Following a 0.1 h period of liming E. coli counts were reduced by 6 logs and Salmonella sp. was below detectable levels, demonstrating at least a 4-log reduction. Bacterial concentrations of 10⁰ were artificially separated for clarity. Means and standard deviations are shown. Continuous lines represent untreated controls, dashed lines treatments.

Figure 2:

Adenovirus Type 5 and MS-2 inactivation in three replicate experiments conducted in limed water at room temperature. MS-2 was below detectable levels following 2 h of liming demonstrating at least 6-log reduction. Adenovirus and rotavirus was below detectable levels following lime stabilization for 6 min, demonstrating 4-log reduction. Continuous lines show untreated controls, dashed lines treatments.

Figure 3:

Inactivation of C. parvum oocysts with lime. Dose-response curves were obtained using the cumulative method (left) and the logit method (right). The 50% cumulative infection and 0 logit used for determining the ID₅₀ values are shown with dashed horizontal lines. Note the increase in oocyst infectivity (lower ID₅₀) in response to treatment.

Figure 4:

Resistance of A. lumbricoides ova to lime stabilization. Shown are mean and standard deviation from two replicate experiments conducted in limed water at 28°C. Continuous line show untreated control, dashed line treatment.