Assessment of traditional biosolids disposal methods for biosolids contaminated with Bacillus globigii spores

If biosolids are contaminated with Bacillus anthracis spores, either through intentional actions or a natural outbreak, a water resource recovery facility may need to consider whether their treatment processes can sufficiently inactivate this pathogen to prevent its spread. Three methods commonly employed to treat biosolids-lime stabilization, aerobic composting, and incineration-were investigated in this study through literature review and bench-scale experimentation using Bacillus globigii as surrogate for B. anthracis. This research studied parameters of these methods of pathogen treatment in wastewater biosolids that may lead to organisms surviving treatment. The literature component of this investigation indicated that lime stabilization introduces calcium ions that can fortify spores, making it problematic, and possibly counterproductive, for spore inactivation. Therefore, the experimental component of this investigation focused on aerobic composting and incineration. Although 60°C could inactivate Bacillus globigii to below detection limits in a control experiment involving direct application of heat, aerobic composting struggled to maintain sufficient temperature for the needed time and inactivated 2 to 4 log₁₀ units of Bacillus globigii spores, which may not provide reliable inactivation. Incineration studied in a bench-scale fluidized bed incinerator designed to mimic full-scale incinerators showed that spores could survive under certain combinations of furnace temperature and biosolids moisture content. Namely, 1000°C removed ∼3 log₁₀, while 500°C removed ∼7 log₁₀. Higher moisture content achieved nearly complete inactivation of spores at 750 and 1000°C. The results from this investigation may help operators assess their facility's methods for treating biosolids contaminated with high consequence persistent pathogens.