Songklanakarin Journal of Science and Technology (SJST) (Feb 2004)
Removal of surrogates for natural organic matter and the probability of finding trihalomethanes in the produced water supply from small waterworks in Chiang Mai, Thailand
Abstract
Trihalomethanes (THMs) and surrogate parameters for natural organic matter (NOM) including ultraviolet absorption at wavelength 254 nanometer (UV-254), total organic carbon (TOC) and dissolved organic carbon (DOC) in both raw and produced water from two small rural waterworks using raw water from the Aung-Keaw and Mae-Hia reservoirs, Chiang Mai, Thailand were studied. The waterworks processes of these two plants are similar and consist of poly aluminum chloride (PACl) coagulation-flocculation, sedimentation, chlorination and filtration. The results show that the average values of TOC in raw water from the Aung-Keaw and Mae-Hia reservoirs were 3.52 and 2.59 mg/L, respectively; whereas DOC values were 0.78 and 0.42 mg/L, respectively. The average values of UV-254 of 0.1278 and 0.14471/cm were measured in Aung-Keaw and Mae-Hia raw water, respectively. THMs were not detected in raw water while the average values of 60.0 and 62.5 µg/L of THMs were found in the produced water at the Aung-Keaw and Mae-Hia waterworks, respectively. However, an acceptable quality of water in terms of pH and turbidity was produced in accordance with Thai Drinking Water Standards. The correlation of THMs and TOC in the produced water supply is THMs = 37.70 + 14.32 TOC with an R2 of 0.62. The probability of finding THMsin the produced water supply from those two plants at a level that is lower than the first stage U.S.EPA MCL of 80 µg/L is 85%; whereas that of at a level that is lower than the second stage U.S.EPA MCLG of 40 µg/L is 11%. However, the removal efficiencies of NOM surrogates are as follows: 48 % removal of TOC, 32 %removal of DOC, 47% reduction of UV-254 and 98% removal of turbidity.
