Inactivation of Cryptosporidium parvum oocysts and other microbes in water and wastewater by electrochemically generated mixed oxidants

Alternative disinfectants of water and wastewater are needed because conventional chlorination is ineffective against C. parvum oocysts. Reliable indicators of disinfection efficacy against C. parvum also are needed. Mixed oxidants (MO) electrochemically generated from brine were evaluated in batch disinfection experiments for inactivation of C. parvum oocysts and Cl. perfringens spores in both oxidant demand-free (ODF) water and treated wastewater. Coliphage MS2 and Escherichia coli B were also tested under some conditions. C. parvum oocyst infectivity was quantified by cell culture assay, and the dyes DAPI (4',6-diamidino-2-phenylindole) and propidium iodide (PI) were used to assess oocyst viability in wastewater experiments. In treated wastewater dosed with 10-13 mg/L MO, inactivation after 90 minutes was about 3 log(10) for C. parvum and about 2.5 log(10) for CI. perfringens spores; MS2 and E. coli were rapidly inactivated by > 5 log(10). In ODF water, a 4 mg/L dose of MO inactivated -3 log(10) of C. parvum oocysts and -1.5 log(10) of CI. perfringens spores. Inactivation of C. parvum oocysts and Cl. perfringens spores was less extensive at a lower MO dose of 2 mg/L. The use of DAPI and Pl to determine viability of oocysts treated with MO did not correlate with, and greatly overestimated, cell culture infectivity. At practical doses and contact times, MO disinfection of water and wastewater achieves appreciable inactivation of both C. parvum oocysts and Cl. perfringens spores. Cl. perfringens spores reliably indicated oocyst inactivation by MO, but E. coli and coliphage MS2 were inactivated much too rapidly to indicate C. parvum inactivation.