Suraphong Wattanachira, Charongpun Musikavong, Orathai Permsuk, and Prasert Pavasant

pp. 25 - 35

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 THMs
in 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.