Disinfection of water using chlorine generated on-site by the electrolysis of sodium chloride (common salt)

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This report covers a 3-month study into the USC of sodium chloride (common salt) for on-site generation of sodium hypochlorite for disinfection of potable water in comparison with Chlorine gas. Sodium chloride samples obtained from three sources in Southern Ghana were analyzed and thereafter used to generate chlorine in the form of sodium hypochlorite by electrolysis. The chlorine so generated was used to perform disinfection trials at the Weija Water Treatment Works. Simultaneously, chlorine solution prepared from chlorine gas was used for similar disinfection trials. The study revealed some differences among the salt samples in some parameters such as sodium chloride and moisture content; however, the differences did not affect the strength of sodium hypochlorite generated for all three samples. The study also revealed that, using sodium hypochlorite generated on-site at the same dose as chlorine gas, chlorine gas performed relatively better than sodium hypochlorite in coliform removal for contact times of 10 minutes and 20 minutes. However, at a contact time of 30 minutes, sodium hypochlorite was as effective as chlorine gas in coliform removal in post filtration disinfection. Based on 1999 prices of chlorine gas (imported) and common salt and electricity cost (both locally available), the study revealed that annual cost savings of about 0126 million ($51,782 as at April, 1999) could be realized if On-site Sodium Hypochlorite Generation were employed in place of Gas Chlorination. However further economic analysis involving other factors such as capital cost and design life of equipment would be required to establish the overall cost effectiveness of either chlorinating method. On the whole, the study revealed that On-site Sodium Hypochlorite Generation was technically feasible and could be a formidable alternative to Gas Chlorination.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Science in Water Supply and Environmental Sanitation, 1999