IMPACT OF E.COLI INITIAL MICROBIAL DENSITY ON PERACETIC ACID (PAA) AND MONOCHLORAMINE DISINFECTION EFFICIENCY

The main objective of this study was to investigate whether the disinfection efficiency of E. coli by peracetic acid and monochloramine was dependent on the initial microbial density. To track this hypothesis, complementary research works were carried out at Technical University of Bari, Italy (using peracetic acid to disinfect native E.COLI) and Drexel University, USA (using monochloroamine and E.COLI monoculture pure strains).Peracetic acid disinfection experiments were performed on effluent of secondary treatment of municipal wastewater. Samples were drawn from secondary settling tanks of the City of Taranto municipal wastewater treatment plant. In this case, the initial microbial density of the native Escherichia coli was intrinsically variable due to the daily variability of wastewater. Monochloramine disinfection experiments were conducted on laboratory water spiked with E. coli to produce initial microbial densities of 103 CFU/mL, 104 CFU/mL and 105 CFU/mL. At least three experiments at each initial microbial density were conducted for each of approximately 0.75 mg/L, 1.0 mg/L and 1.5 mg/L of monochloramine exposure.For both disinfectants and waters, results indicated a strong dependence of Escherichia coli disinfection efficiency on the Escherichia coli initial microbial density. These results indicate that future batch disinfection studies of Escherichia coli disinfection should include experiments performed with a wide range of initial microbial densities and that initial microbial density should be considered in determination of disinfectant dose at operational wastewater treatment plants.