Comparative Study of Chemical Disinfection in Drinking Water Supply
Abstract:This research was conducted to compare primary disinfection of total coliform with chlorine, chlorine dioxide and ozone for drinking water treatment and distribution systems. As part of that evaluation, kinetic models were evaluated that predict disinfection efficacy as a function of disinfectant type, contact time, pH, temperature and DOC. The water samples were taken from the outlet of settling basin in a conventional surface water treatment system that is provided with the raw water drawn from the mid-stream of the Han River or from tap water at Konkuk University.
The inactivation curves obtained from a series of disinfection processes had a sharp loss of bacterial viability within 5 minutes followed by an extended phase with little loss. The order of reaction for disinfectant decay was 2.9 and 2.5 for chlorine and chlorine dioxide, respectively. The decay reaction rates during the second phase could be expressed by a first order reaction rate. Ozone decay reaction rates were described by a 2.2 reaction order.
The experimental data obtained with chlorine, chlorine dioxide and ozone were fit using the Chick-Watson, Hom, and Selleck models. The Selleck model best fit the data for total coliform survival.
The coliform inactivation rate could vary with many factors and should be dependent on the concentration of reaction compounds. The bactericidal effects of disinfectants were decreased as the pH increased in the range of pH 6-9. The influence of pH change on the killing effect of chlorine dioxide was not strong, but for ozone and free chlorine higher pH markedly reduced effectiveness.
In order to observe the effect of suspended solids carry-over on chlorine consumption and disinfection efficiency, the water samples were filtered before inoculation using membranes of 2.5 μm or 11.0 μm pore size, or using a sand filter of 1.0 mm diameter media (uniformity coefficient of 1.4). In filtered water, chlorine disinfection effectiveness is enhanced compared with non-filtered water. Less chlorine was consumed in the filtered samples, indicating that the particulate phase had a significant chlorine demand. Consequently, disinfection was dependent on the effectiveness of filtration.
Mixing intensity was influential in the effectiveness of disinfection. Total coliform inactivation by chlorine was increased as G value increased. G values above 500 sec-1 showed little difference in disinfection effectiveness.
The predominant coliform bacteria in simulated distribution systems before chlorination were enterobacter agglomerans and klebsiella pneumonia. Klebsiella pneumonia has strong tolerance to the disinfectant, and was detected on carbon steel, galvanized steel and copper pipe after chlorination.
Document Type: Research Article
Publication date: January 1, 2005
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