Combined Disinfection Research Articles

Disinfection of effluents by combinations of chlorine dioxide and chlorine

The behaviour of both chlorine dioxide and chlorine, either as an individual or as combined disinfectants were studied on effluents from activated sludge. The results of the disinfection efficiency, residual disinfectants and their by-products, obtained by treating the same effluents at the same day with identical dosing sequence of chlorine dioxide and chlorine, alone and in a combined dosing, were compared after periods of the same contact. In most cases, it seems that each disinfectant maintains its individual capabilities when used in a combined manner. The combination produced a relatively stable high residual of both disinfectants. The important finding is the fact that the combinations of chlorine dioxide and chlorine decreased the concentration of the undesirable chlorite ion and increased the concentration of the newly formed chlorine dioxide. A greater advantage is obtained by using chlorine dioxide prior to chlorine. Therefore, combined disinfection in this sequence is recommended.

Disinfection of effluent by combinations of equal doses of chlorine dioxide and chlorine added simultaneously over varying contact times

The aim of this research was to investigate the possibility of using a combination of chlorine dioxide and chlorine, instead of using each of them as a single disinfectant for the disinfection of effluents from municipal sewage treatment plants, in order to obtain an environmentally safe source of water which can be reused for a variety of purposes. The main task was to investigate whether the combination of the two disinfectants maintains their advantages and decrease their disadvantages. Residual chlorine dioxide, chlorine, chlorite ion and Most Probable Number (MPN) per 100 ml of survived total coliforms, fecal coliforms, fecal streptococci and E-coliphages were determined as a function of these disinfectants doses and contact times. The combination produced a relatively stable high residual of both disinfectants, reduced the concentration of the undesirable chlorite ion, while increasing the concentration of chlorine dioxide. In all doses of the combined disinfectants there was an improvement in the destruction of the indicator pathogenic microorganisms.

Removal of Salmonella Typhi, Shigella Dysenteriae, Vibrio Cholerae and Rotavirus from Water Using a Water Treatment Tablet

Chlor-floc tablets are intended for purification of small quantities of water for individual use by combined flocculation and disinfection. Removal of Escherichia coll E25, various viruses and Giardia cysts from polluted water by Chlor-floc has been previously demonstrated. This study evaluated the efficiency of removal of Salmonella typhi, Shigella dysenteriae, Vibrio cholerae and rotavirus from simulated hard water of high organic content and colour. All four pathogenic microorganisms were successfully removed within the recommended treatment time. Log removals of 7-8 log were achieved for bacterial pathogens, and a removal of 6.5 log was obtained for rotavirus.