The effectiveness of using salt electrolysis for disinfection of potable water - a case study of NWSC Jinja Municipal water supply area, Uganda

Abstract

Addition of calcium hypochlorite, also referred to as High Test Hypochlorite (HTH), is one of the conventional disinfection methods used in the treatment of drinking water. The high-water production costs associated with this disinfection method in the treatment of drinking water can be traced back to its explosive nature during transportation. Furthermore, the loss of the effective disinfection strength of HTH, during storage makes it unfavourable for use in disinfection of water worldwide. It was against these challenges that National Water and Sewerage Corporation (NWSC) introduced salt electrolysis as an alternative disinfection technology in selected small towns. The challenges related with the operation and maintenance of salt electrolysers, such as constant failure of the system prompted this study, which sought to examine the efficiency of salt electrolysis disinfection and associated costs, compared to the conventional HTH Disinfection. A quantitative approach was adopted for this study. Water samples were collected from pre-selected points within the Jinja Municipal water supply area between April and July 2017, and tested for faecal and total coliforms, residual chlorine, turbidity and Tri-halomethanes (THMs), according to (APHA, 2012) and compared against the Uganda Standards and World Health Organisation (WHO) Guidelines for drinking water. Studies were undertaken to compare the performance of HTH chlorine and salt electrolysis disinfection methods over time. The effect of variation of current on the by-products of salt electrolysis was also investigated. Cost comparison between both disinfection methods was ascertained by comparing installation, operation and maintenance costs. Salt electrolysis disinfection provides some water quality benefits for the chlorination process compared to HTH due to the production of Ozone and Hydrogen Peroxide which expedites the disinfection process. This is evident in the ability of salt electrolysis to control regulated and emerging disinfection by-products (DBPs) in drinking water. Salt Electrolysis bears a higher lethal efficiency on all coliform bacteria compared to HTH Disinfection. The cost comparison results showed that the chemical consumption of HTH was UGX 21 per m3 of water, three (3) times that of salt (UGX 7.7/m3). The Energy consumption cost when disinfecting water using salt electrolysis was estimated as UGX 2.2 per m3 of water treated, 4 times that of HTH method was UGX 0.5/m3. Despite the similar overall life-cycle costs for both Disinfection technologies, Salt Electrolysis proved to be a more attractive technology due to the non-financial benefits specific to treatment of potable water in Uganda which include; reduced neighbourhood risks during transportation compared to HTH which is explosive in nature, the availability of salt as a locally sourced material and thus reduced interruptions during chlorination, among others. No significant effect on the production of chlorine was observed with the variation of current to the electrolyser, beyond 27 amps. The findings from this study indicate that salt electrolysis produces water that meets the Uganda Standards and WHO Guidelines for drinking water. It is a cheaper disinfection method, compared to the conventional method of HTH. It is also robust, safe, and a cost-effective technology, that can be used in treatment of municipal water for small towns. It is thus recommended that Salt Electrolysis be adopted as an alternative disinfection method to HTH especially in in the production of water for small towns with similar capacity of 26,000m3/day.