Pathogen Inactivation in Thermophilic Anaerobic Digestion

Significant advances have been made in the knowledge base and practical options for improving thermophilic anaerobic digestion over the past 10 to 15 years. Today, more options exist that promise to enhance the degree of stabilization achieved and finished product quality in new and retrofitted existing processes. In parallel, the body of knowledge regarding pathogen inactivation in these systems has also been advanced, well beyond that available at the time that the 40 CFR, Part 503 regulations were promulgated.This paper summarizes recent work with a focus on pathogen destruction in thermophilic anaerobic systems. Specifically, this paper:Analyzes the body of work relative to Ascaris and poliovirus sensitivity to thermal stresses in comparison with the time and temperature equation in the 40CFR, Part 503 regulation. In particular, prior research suggests that destruction of these particular pathogens can be achieved in combinations of time and temperature that are much less conservative than defined by the equation.Discusses similar experiments that indicate that the Class-A fecal coliform standard of less than 1,000 MPN/g TS is likely the most difficult standard to achieve using thermophilic anaerobic digestion (compared to the helminths and enterovirus standards).Considers recent research into the effects of ammonia and volatile acids on fecal coliform in the context of identifying potential stressors (other than time and temperature) that could contribute to decreased fecal coliform levels in thermophilic anaerobic digesters.This paper is a literature review and comparison of recent publications and work from a number of sources. Specifically, the following work is cited:Ferran and others at Infilco Degremont, Inc. in development of the 2PAD process.Mike Aitken, Mark Sobsey and others on laboratory-scale pathogen spiking studies in the development of design data for Columbus Water Works CBFT3 process (Aitken, et. al, 2003, 2003, 2005 and 2005).R. J. Barnard's work enumerating dead and live Ascaris ova at various batch times and temperatures.E. G. Carrington performed similar experiments and observed the destruction of Ascaris in sludge pasteurization scenarios at relatively low thermophilic temperatures.Jones and Martin reference D-values (the amount of time to cause a 1 log10 reduction for a given organism) for a variety of organisms, including Ascaris, poliovirus and fecal coliform.Don Gray (Gabb) and associates at EBMUD on the antimicrobial effects of ammonia and volatile fatty acids (VFAs) at higher pH.B. Puchajda and Jan Oleszkiewicz of the University of Manitoba on the antimicrobial effects of unionized VFAs at lower pH.