Page 520 - Water and wastewater engineering

DISINFECTION AND FLUORIDATION 13-15

Example 13-4. The data for HOCl disinfection of poliovirus at a concentration of 1.8 mg/L
is shown below (adapted from Floyd et al., 1979) . The temperature was 20 C, the pH was 6.0.
Determine the rate constant of inactivation assuming the Chick-Watson model applies with an n
value of 1.0.
Time, s Number of PFU a

0 6,152
2 3,000
4 1,200
6 710
8 300

a
PFU plaque forming units.
Solution:
a. Compute ln( N / N 0 ) and Ct for each time.

Time, s ln(N/N 0 ) Ct

0 0.0 0
2 0.718 3.6
4 1.63 7.2
6 2.16 10.8
8 3.02 14.4

b. A “trendline” fit of ln( N / N 0 ) versus Ct yields a straight line with a slope equal to k cw as
shown in Figure 13-5 .

c. From a spreadsheet, the equation of the trend line yields a slope of 0.2078 and k cw of
0.2078 L/mg · s.

0
0.5
1
ln(N/N 0 ) 1.5
2
2.5
y = 0.2078x 0.0092
3
2
R 0.9953
3.5
0 2 4 6 8 10 12 14 16
Ct, mg·s/L
FIGURE 13-5
Poliovirus decay rate.