A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1993

Natural organic matters are ubiquitous in aqueous environment. Humic substances are naturally occuring organic macromolecules formed by a complex series of biochemical reactions among carbohydrates, proteins, lignin, and tannin of the decaying animals and vegetable matters. Humic substances are of great concern in Water treatment technology because of health, aesthetics and associated operational problems. The formation of carcinogenic trihalomethanes and other toxic halogenated molecules from reactions between organic matter and chlorine, is one of the main problems caused by organic matter. The present study has aimed to assess the impairment caused by humic and tannic acids in the conventional water treatment process of "Coagulation-Flocculation", and to evaluate the removal efficiency of these organics by Alum and Cat-FlocT2, a cationic polyelectrolyte as coagulants. Alum was found to be very effective in both organics and turbidity removal, whereas . Cat-FlocT2 was not effective for either. But the Cat-FlocT2 with alum of 20 mg/L dose, was found to be effective in very narrow pH range of about 4.75-5. The pH of the suspension was observed to be the most crucial factor that determine the coagulant dose and the removal of organics and turbidity. The optimum pH for organics and turbidity removal was found to be around 5. For both Alum and Cat-FlocT2 with alum, the optimum conditions for organics removal nearly coincide with that for turbidity removal. Humic acid was found to have more affinity towards adsorption on kaoline clay in acidic condition than tannic acid. Whereas tannic acid was observed to have more tendency to form complexes in alkaline conditions than humic acid.