The aim of this study was to determine the efficiency of alum coagulation process for organic substances treating in raw water from U-Tapao canal, Thailand with measuring in term of dissolved organic carbon (DOC), ultraviolet absorption at wavelength 254 nm (UV-254) and Fluorescent Excitation-Emission Matrix (FEEM) reduction. Raw water samples were collected from three points of U-Tapao canal, one was existing pumping station (U-Tapao) and other two points (Sadao reservoir and Khlongla reservoir) are at upstream which may be used as an alternative pumping station. The results showed the condition of organic matter from point source and non-point source contamination in water samples. The results of FEEM showed that the water sample from U-Tapao pumping station contained both fulvic-humic acid-like substances and tryptophan-like substances were whereas Sadao and Khlongla reservoirs could detect mainly fulvic and humic acid-like substances. The coagulation gave the best results of turbidity, DOC and UV-254 reduction at pH 5 and 80 mg/L of alum dose. It could reduce 80% of the organic substances in term of UV 254, but only 50% in term of DOC and FEEM. Furtherore the DOC and UV-254 reduction efficiency were slightly declined when the tryptophan-like substances presented.

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