Study of disinfection efficiency of peracetic acid (PAA) on Escherichia coli by rapid colorimetric assay based on enzymatic substrates after eliminating hydrogen peroxide from the commercial PAA mixture

Disinfection of combined sewer overflows (CSO) is a quick approach to reduce the indicator bacteria (E. coli and Enterococcus spp) to maintain the bathing water quality on the receiving waters when CSO are discharged. Peracetic acid (PAA) has been used to disinfect combined sewer overflows. This study was conducted to investigate the disinfection efficiency of PAA against E. coli when hydrogen peroxide was removed from the commercial PAA mixture. Furthermore, disinfection efficiency of PAA, commercial PAA and hydrogen peroxide against E. coli was compared. Disinfection efficiency of PAA against E. coli was studied by using rapid colorimetric assay using enzymatic substrates 6-Chloro-3-indolyl-β-D-galactopyranoside (Red-Gal) which develops dark red when it reacts to the β- galactosidase enzyme of E. coli. The resulting color intensity from the enzymatic substrate interaction was correlated to the bacterial concentration by using plate count method. Median inhibition concentration (IC50) of PAA without hydrogen peroxide, commercial PAA and hydrogen peroxide on E. coli was determined by using the area under curve (Ct). IC50 of PAA alone on E. coli was 32 mg·min/L whilst IC50 of commercial PAA was 23 mg·min/L.