Spores of sulphite-reducing clostridia (SSRC) as surrogate for verification of the inactivation capacity of full-scale ozonation for Cryptosporidium

Abstract

The inactivation of C. parvum and spores of Cl. perfringens by ozone treatment in natural water in a lab-scale continuous-flow system was compared. In addition the inactivation of the natural occurring spores of sulphite-reducing clostridia (SSRC) in this water was monitored in one of the lab-scale systems as well as in a full-scale ozonation process. The survival ratio of C. parvum oocysts was determined using the CD-1 neonatal mouse infectivity test and for Cl. perfringens and SSRC the survival ratio was assessed with the standard anaerobic colony count on the iron-sulphite medium. The results of the lab-scale experiments revealed an inactivation rate constant k (Chick-Watson modelling) at 10°C for C. parvum of 0.14 (SD=0.014; P<0.001) and for Cl. perfringens of 0.25 (SD=0.01; P<0.001). Moreover, first results of monitoring the SSRC inactivation in full-scale ozonation processes indicated that the inactivation rate constant for these wild strains was in the same order of magnitude as determined for Cl. perfringens. Further research is needed to compare inactivation ozone kinetics for Cl. perfringens D10 and SSRC at different temperatures and in other natural waters. Results of additional lab-scale experiments with Cl. perfringens strain D10 indicated that the CT of the gas-feed chamber should be incorporated in the design of a full-scale ozonation. Moreover, setting theCT with the contact time was not as effective for the inactivation capacity as setting the CT with the ozone dosage.

Influence of DOC on the Inactivation Efficiency of Ozonation Assessed withClostridium perfringensand a Lab-Scale Continuous Flow System

“…This was concluded from the results of lab-scale study with C. perfringens and SSRC monitoring under full-scale conditions (Hijnen et al, 2000a). The susceptibility of the lab-cultured C. perfringens, C. parvum (animal infectivity; Hijnen et al (2002)), and environmental SSRC (Hijnen et al (2000a) and this study) for ozone are in the same order of magnitude. Driedger et al (2001) concluded that B. subtilis is a good surrogate for C. parvum at high temperatures, but is more readily inactivated at low temperatures.…”

“…As described before (Hijnen et al, 2002) and presented in Figure 2, the disinfection kinetics of C. perfringens spores in the WBE water can be described by the Chick model with an inactivation rate constant k of −0.25 (SD = 0.014; p<0.001; n=1).…”

“…The inactivation of spores of C. perfringens was determined in a lab-scale continuous flow ozone system (Kiwa, Nieuwegein) at a constant water temperature of 10°C. This experimental setup has been used before (Hijnen et al, 2002) for experiments in the water of Water Company Europoort (WBE) with a low DOC content (Table I).…”

“…The methods for preparing a stock solution with high spore concentrations and inoculation of the water before ozonation were described earlier (Hijnen et al, 2002). Spore concentration in the water prior to ozonation was 10 3 -10 4 CFU/mL.…”

“…Clostridium perfringens was used as a model organism to verify the disinfection performances under different conditions. This indicator bacterium and also the group of sulfite-reducing clostridia (SSRC) have been proposed as surrogate parameters to monitor the treatment efficiency for the removal of persistent pathogenic viruses and protozoa (Payment and Franco, 1993;Hijnen et al, 1997Hijnen et al, , 2000aHijnen et al, , 2002. Simultaneously, the inactivation of Escherichia coli and Bacillus subtilis was determined as microorganisms with a high and low susceptibility for ozone, respectively.…”