Effectiveness of using Bentonite clay as a coagulant aid in conventional water treatment

Abstract

Conventional water treatment is very vital to a developing country like Uganda. Many water treatment plants use a combination of coagulation, sedimentation, filtration and disinfection to provide clean safe drinking water to the public. This study was aimed at evaluating the cost of conventional drinking water treatment using Bentonite clay as a coagulant aid. The specific objectives were to determine color and turbidity removal efficiencies while using only polymer as a coagulant on one hand, and when polymer and Bentonite clay on the other. The study also was designed to compare the treatment costs of using Bentonite clay and polymer and, polymer only in provision of safe drinking water. The Jar test method was the experimental procedure used to find out the treatment efficiencies under the two cases outlined above. Two sets of experiments were done one with polymer only and the other polymer plus Bentonite. This was used to compare the doze, what is better and compare the costs. A series of batch coagulation tests were conducted by jar test to obtain the optimum dosage, pH, ratio of coagulant aid and primary coagulant, and the efficiency time for the jar test, by evaluating the standard parameters, such as turbidity, pH, color, and chlorine. The results showed that polymer dose used in the polymer only scenario was higher compared to the polymer-Bentonite combination. This meant more costs of the chemicals used in polymer only compared to polymer-Bentonite. The residual turbidity results in the polymer treatment only was high and the flocs formed at a lower rate or speed in the jar test experiment. The chlorine demand tests showed that the more chlorine was needed to disinfect the water in the polymer dose only scenario. This makes the chlorine costs for the polymer-Bentonite combination lower and more cheap. The study recommends that the Government should encourage the mining and manufacturing of Bentonite clay locally so as to subsidize on the cost of conventional water treatment and the time taken in treating water. In so doing less chemicals are used.