Impact of concentration, temperature, and pH on inactivation of Salmonella spp. by volatile fatty acids in anaerobic digestion

Abstract

It is known that the presence of volatile fatty acids may play a role in the inactivation of pathogens for systems that employ an acid phase reactor. This study was conducted to investigate the influence of volatile fatty acids on the inactivation of Salmonella spp. over a range of digestion temperatures. In this study, digesters that were treating municipal wastewater treatment plant sludges were operated at temperatures that ranged from 35 to 49 degrees C and had a solids residence time of 15 days. Samples collected from the effluent of the digesters were dosed with solutions containing acetic, propionic, and butyric acids alone and in mixtures, and the dosed effluents were analyzed for Salmonella spp. over time. In the first round of testing, the digester effluents were dosed with individual organic acids and also a mixture containing all three volatile fatty acids over a range of concentrations from 750 to 6000 mg/L, and the pH of the samples was fixed at a value of 5.5. In the second round of testing, the sample sludges were spiked with a fixed amount of organic acid mixture, and the pH was varied from 4.5 to 7.5. The reduction of Salmonella spp. in digester effluents, when dosed with volatile organic acids, was found to depend on pH, temperature, the chain length of the acids, and the concentration and composition of the acids present. Increases in temperature appeared to increase the inhibitory effects of the volatile organic acids. At mesophilic temperatures, acidic pHs resulted in a greater inhibition of Salmonella spp.; whereas at higher temperatures neutral pHs were found to be more inhibitory. The results suggest that acid phase digesters that operate at elevated temperatures and low pH can achieve substantial reduction of Salmonella spp.

Enhanced stabilisation of municipal solid waste in bioreactor landfills

“…Dispersion due to constant recirculation as suggested by Smith et al (2005) could be considered as an environmental condition to increase the die-off process of pathogens. Factors affecting the die-off of pathogens during this experiment could be initial inactivation caused by low pH and high VFA as suggested by Salsali et al (2006), followed by the detrimental effect of high carbonate and ammonia concentrations similar as those reported by Park and Diez-Gonzalez (2003). In addition, the retention time was considerably longer than those reported by Jepsen et al (1997).…”

Alternative treatment for septic tank sludge: Co-digestion with municipal solid waste in bioreactor landfill simulators

“…Dispersion due to constant recirculation as suggested by Smith et al (2005) could be considered as an environmental condition to increase the die-off process of pathogens. Factors affecting the die-off of pathogens during this experiment could be initial inactivation caused by low pH and high VFA as suggested by Salsali et al (2006), followed by the detrimental effect of high carbonate and ammonia concentrations similar as those reported by Park and Diez-Gonzalez (2003). In addition, the retention time is considerably longer than those reported by Jepsen et al (1997).…”

The effect of volatile fatty acids on the inactivation of Clostridium perfringens in anaerobic digestion

“…Both batch acid-phase digesters and semi-continuous staged acid-digestion systems were demonstrated to achieve a Class A level of fecal coliforms at both temperatures. Salsali et al (2006) investigated the influence of organic acids on the inactivation of Salmonella spp. over a range of digestion temperatures, organic acids concentrations, and pH.…”