Inactivation kinetics of a strain of Bacillus subtilis , isolated from the effluent of a wastewater treatment plant, using peracetic acid: assessment in vegetative cells and endospores

ABSTRACT Summarizing the manuscript This study carried out the biochemical characterization and disinfection kinetics of a strain of Bacillus subtilis isolated from the effluent of a wastewater treatment plant and of a certified strain of the same species, using peracetic acid (PAA). Inactivation kinetics and the fittingness to the Chick, Weibull, and Geeraerd models were evaluated not only in vegetative cells of both strains and endospores of the isolated strain at a concentration of 25 mg/L, but also in endospores of the certified strain at 50 mg/L. The results showed nonlinear inactivation behavior, associated with microbial heterogeneity and the rapid consumption of the disinfectant. Vegetative cells exhibited the largest average reduction of 3 log10 CFU/mL, after 40 min, whereas endospores achieved the largest reduction of 5 log10 CFU/mL, at 25 mg/L (isolated) and 6 log10 CFU/mL, at 50 mg/L (certified), after 40 min. The best fitting model was that of Geeraerd, while the Weibull model adequately described only the assay on endospores of the certified strain. It is concluded that PAA effectiveness depends on the concentration and the physiological state of the microorganisms, highlighting the need to apply nonlinear models for an adequate evaluation of the disinfection process.