were chosen for five different levels of ozone concentration (Table 9.1 ). for both flow rates, the highest concentration was the most effective to inactivate E. coli ATCC 25922 in TSB (Fig. 9.1 ). it is evident from Figure 9.1 that there is a stepwise decrease in the efficiency of E. coli inactivation at the lower concentration levels 1 and 2 (28-70 µg/ml and 17-28 µg/ml for flow rates of 0.06 and 0.12 l/min, respectively), where inactivation was insufficient to calculate D-values (Table 9.1).