Page 519 - Water and wastewater engineering

13-14 WATER AND WASTEWATER ENGINEERING

0 0

1 1
Log 10 PFU survival ratio 2 Log 10 PFU survival ratio 2

3 3

4 4
0 4 8 12 16 20 0 2 4 6 8
(a) Treatment time, sec (b) Treatment time, sec
FIGURE 13-4
Inactivation of single poliovirus particles by HOCl ( a ) at 10 C, pH 6.0: ( ) 1.5 M, ( ) 11 M, ( ) 20 M, and ( ) 41 M; ( b ) at 20 C, pH 6.0: ( )
2.2 M, ( ) 11 M, ( ) 22 M, and ( ) 35 M. ( Source: Floyd, et al., 1979. )

Chick-Watson Law. Chick’s law does not take into account the concentration of the disin-
fectant. From Figure 13-4 , it is obvious that the disinfectant concentration has a marked effect.
Recognizing this, Watson (1908) proposed an alternative expression to describe a given level of
inactivation:

n
Ct constant (13-21)

where C disinfectant concentration, mg/L
n coefficient of dilution
t time
Chick’s law and Watson’s equation are combined by relating the rate constant of inactivation to
the disinfectant concentration:

k c k C n (13-22)
cw

1
where k cw rate constant of inactivation independent of concentration, time
The Chick-Watson law in integrated form is then

⎛ N ⎞
n
ln ⎜ ⎝ ⎟ ⎠ kC t (13-23)
cw
N 0