The effect of settlement time on reducing coagulant dosage in water treatment plants

Turbidity is a measure of the relative clarity of water. Its removal is one of the important steps in water treatment process and it’s generally achieved using coagulation/flocculation process. The most wildly coagulant used in water treatment plants is Aluminum sulfite (Alum). The aim of this study is to reduce the amount of Alum used in Iraqi water treatment plants as much as possible in order to reduce its side effects but yet stay within required quality of water requirements; this was done by testing different durations of slow mixing with Alum and finale settlement as well. This research showed that the percentage removal of turbidity increases when the time of slow mixing with Alum and the time of final settlement of the water samples were increased for the same dosage of Alum used, hence, decreasing the final turbidity of water. The dosage of Alum added to the water sample was reduced to the half and obtained the same percentage of final turbidity removal by increasing the time of slow mixing and final settlement. An empirical equation was obtained relating the percentage of removal with the Alum dosage, time of slow mixing, time of final settlement and final turbidity of water samples. Extra safety from the effect of Alum on human body is offered by reducing the amount of Alum used in water treatment plants and increasing the time of final settlement.