The Balkfontein and Virginia plants of Sedibeng Water, situated in the Free State Province of South Africa, treat water for potable purposes. Chlorine is used as disinfectant at both plants. Low levels of free chlorine measured in the water supplied from some reservoirs, logistics and costs, related to the application of chlorination at various points in the distribution system, were the main thrusts for an investigation into the use of chloramination as an alternative means of disinfection.
The so-called contact time (CT)-approach from the United States Environmental Protection Agency was applied for the evaluation of disinfection efficiency. The distribution system was modelled by using a hydraulic computer system. Decay rates for both chlorine and monochloramine - a vital parameter for eventual determination of the amount of chlorine and ammonia to be dosed - were determined. The levels of disinfectant in the water at a specific location could be predicted by using the decay values.
The main findings of this investigation are that chloramination is an attractive and cost-effective alternative for conventional chlorination for providing quality assurance to all. It is estimated that the capital layout will be recovered within one year of operation of the ammoniation system.