The E.coli inactivation (expressed as percentage) obtained during chlorination test in a batch reactor (pH=8.5 and temperature 5C) are shown in table below.

Survival %

Free Cl, mg/L / Contact time, min	1	3	5	10	20
0.05	97	82	63	21	0.3
0.07	93	60	28	0.5	-
0.14	67	11	0.7	-	-

a) Convert the survival data to (-Ln) of inactivation and plot the results in logarithmic and arithmetic charts. Which representation of results is better and why?

b) Determine the required time for inactivation of 99% of bacteria.