USING DIFFERENT COAGULANTS TO IMPROVE COAGULATION PROCESS AND DRINKING WATER QUALITY

Abstract

This study aims to investigate acceptable approach to enhance coagulation for TOC (DBD precursors), turbidity and aluminum minimization using aluminum and iron based coagulants in drinking water treatment, single and dual dosing with aluminum sulphate and ferric chloride coagulants. Once the condition for optimized coagulation has been determined by Jar tests, TOC was evaluated under baseline coagulation conditions and optimized coagulation. Jar tests were conducted to simulate the conventional processes of water treatment. Enhanced coagulation used the traditional alum that is already applied in water treatment in Egypt, with a comparison with ferric chloride and mixture of alum and ferric chloride, the strategy of enhanced treatment adopted mainly organic matter and THMs beside turbidity, so the doses of coagulant were increased to achieve better removal of THMs which have a health issue. Conventional treatment processes including addition of aluminum sulphate or ferric chloride to the raw water followed by coagulation, sedimentation and rapid sand filtration are important step in water purification; they reduced the organic matter to about 42% and THMs to 37 using the baseline dose (25 mg/l). The enhanced coagulation process by increasing the dose of alum reduced the total organic carbon and THMs to 57 % and 54 % respectively. Using of ferric chloride at a baseline dose reduced TOC and THMs by 40 % and 36% respectively, while enhanced coagulation by increasing the dose of ferric chloride (at a dose of 35 mg/l) raised up the removal of TOC and THMs to 47 % and 44% respectively. The dual coagulant of alum and ferric chloride achieved 47% removal of TOC and 36% for THMs at a dosage of 25 mg/l, while the enhanced coagulation by increasing the dose of duel coagulant of alum and ferric chloride (35 mg/l) raised up the removal of TOC to 61% and THMs to 50%. The advantageous of the dual coagulant is higher reduction of residual aluminum and THMs, this attributed to the enhancement of flocculation which create activated adsorption sites of flocs surfaces.