REMOVING PARTICLES AND THM PRECURSORS BY ENHANCED COAGULATION

The effectiveness of enhanced coagulation for removing particles nad t rihalomethane (THM) precursors at various alum dosages and coagulation pH values was assessed. Samples of both source water and filter efflu ent were examined by counting particles and measuring particle size di stribution, turbidity, total organic carbon, ultraviolet light absorba nce at 254 nm (UV254), and THM formation potential. Removal of particl es and turbidity increased substantially at alum dosages above 20 mg/L . Particle removal was not significantly different at adjusted pH (5.5 ) compared with ambient pH. Filter effluent particle counts were consi stent with residual turbidity data; however, particle counting provide d more information on the efficiency of the solid liquid separation. S ignificantly more THM precursors were removed by enhanced coagulation at pH 5.5 than at ambient pH. Higher dosages were needed to achieve ac ceptable removal of THM precursors than were needed for removal of par ticles.