|M.Sc Thesis||Department of Civil and Environmental Engineering|
|Supervisors:||Prof. Emeritus Kott Yehuda (Deceased)|
|Prof. Emeritus Narkis Nava|
The presence of microorganisms in natural water of every quality is primarily hazardous and causes health risk of infection. Therefore, disinfection is the most important stage in water treatment for public supply.
We investigated the influence of the disinfectants, chlorine and chlorine dioxide on indicator pathogenic bacteria in two different water qualities: a) drinking water; b) effluents from municipal sewage treatment plants.
The chlorine dioxide was more efficient in destroying E.coli B, Salmonella typhimurium and Shigella sonnie as compared to chlorine. After a contact time of 4 minutes at a dose of 0.3 mg/L as ClO2 the chlorine dioxide was sufficient for total kill of E.coli B and Salmonella typhimurium with CFU of zero per 100 ml colony. The sample that contained Shigella sonnie needed 0.5 mg/L as ClO2 to show the same result. The chlorine did not kill all colonies of Salmonella typhimurium and Shigella sonnie even at a dose of 0.5 mg/L as Cl and contact time of 4 minutes.
The chlorine dioxide was more efficient comparing to chlorine at pH=8 for total kill of E.coli B at the dose of 0.2 mg/L as ClO2 and contact time of 5 minutes.
The same parameters were examined with sewage. The ClO2 seemed more efficient comparing to chlorine at dose of 4 mg/L as ClO2 and contact time of 30 minutes, MPN zero per 100 ml of E.coli B and Salmonella typhimurium. For the same result with Shigella sonnie it took 5 mg/L as ClO2. As compared to the same dose of chlorine, in which a few microorganisms survived. The sample containing E.coli B needed 8 mg/L as Cl to destroy all bacteria.
As a result of this work, it can be recommended to disinfect drinking water and effluent, with ClO2, which was found to be more efficient in destroying the indicator pathogens.