Optimisation of Cost Effectiveness of Water Treatment Works: Coagulation Processes

The process of coagulation and flocculation is one of the most important operations among the water purification process, but its effectiveness is determined by cost. The purpose of this study was to evaluate optimum conditions, effects of varying velocity gradients, times during coagulation and flocculation in water treatment to make the process cost effective. Optimum conditions include optimum pH and optimum coagulant dosage. Test water was obtained from Chiromo River during a dry season. The turbidity of raw water was found to be 46 NTU.
Coagulation and flocculation tests using jar test procedures were performed using aluminium sulphate (alum) to determine optimum pH, optimum dosage and mixing regime that would yield optimum removal of turbidity. Turbidity, colour, alkalinity and pH were measured before and after tests. The optimum pH was found by adjusting pH of jars using lime and same coagulant dose of 10 mg/l. Optimum pH was found to be 6.5. The optimum aluminium sulphate dose was found to be 39 mg/l. Tests to demonstrate effects of varying velocity gradients (for both flash and slow mixing speeds) and mixing time (for both flash and slow mixing times) were performed. Among the analytical parameters, turbidity gave the most reliable results as to the determination of efficient velocity gradients and mixing times. Tests indicated that results were successful in reducing colour and turbidity to suitable concentrations using relatively low levels of aluminium sulphate. The study enables cost reduction of coagulation process.


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