| Summary: | 碩士 === 國立臺灣大學 === 環境衛生研究所 === 86 === The presence of natural organic matter (NOM) in drinking water affect
s water treatment processes including coagulation and adsorption of synthetic
organic like pesticides and herbicides, it also causes disinfection byproducts
(DBPs) during disinfection process. It has been shown that treatment process
es such as coagulation with alum, filtration or softening can effectively remo
ve an average of 30% high molecular weight humic substances, predominantly hum
ic acids. In general, the TOC removal in conventional drinking water treatmen
t processes is low, between 10 and 50 percent.Advanced Oxidation Processes (AO
P) is the one that deserves more study for potential applications in drinking
water treatment. AOP can effectively mineralize many organic contaminants and
have made them attractive for control of synthetic organic compounds in waste
water treatments. The combination of the H2O2/UV process was used in this stu
dy to evaluate the suitability for control of NOM in drinking water. The resul
ts showed that the rate constant decreases as the initial NPOC concentration i
ncreases at constant H2O2 concentration. In UV/H2O2 system, it is important t
o calculate the relative concentrations (or molar ratios) between H2O2 and tar
get compounds to find optimum H2O2 concentration. In order to maintain a suit
able rate constant, the H2O2 concentration should be raised to increase the co
llision frequency When the quartz tube is used as the filter in the experiment
s, the short wavelength UV can pass through the filter and be utilized for NOM
oxidation. More than 80 percent of the NPOC was removed after three hours of
irradiation. Compared to the 30 to 60 percent oxidation with PYREX filter, t
his demonstrates the great oxidation power of the short wavelength UV light.
It is important to look at the correlation between the H2O2 addition and the q
uantity of NPOC removed (or the rate constants). The optimum H2O2 concentrati
on is between 0.1% and 0.3%, and the increase in the H2O2 concentration reduce
the treatment efficiency. The optimum H2O2 concentration in a UV/H2O2 system
depends on the intensity of the UV light and the target compounds to be remov
ed. In general, the increase of the H2O2 concentration will increase the conc
entration of hydroxyl radicals and increase the reaction rates. However, the
increase in H2O2 concentration will reduce the depth that light can penetrate
in water and thus inhibit the oxidation reaction for NOM.Bicarbonate ion is a
hydroxyl radical trap, and will affect the AOP treatment process. The results
showed that the presence of the alkalinity will reduce the rate constant in t
he UV oxidation of the NOM in drinking water. However, the efficiency of AOP
in this study was not affected by the presence of hardness and sulfates.As a c
onclusion, this study shows that catalytic photochemical oxidation provides an
effective method for the control of NOM. The NOM oxidation process followed
simple first-order kinetics in the batch system used in this study. With suit
able H2O2 addition, UV light can effectively oxidize the NOM in aqueous phase.
Increasing the H2O2 concentration above the optimum dose (0.1 - 0.3% H2O2 in
this study) has minor or no improvement on NOM destruction. Alkalinity has m
inor effects on NOM oxidation when PYREX filter is used. However, the NOM red
uction greatly affected by alkalinity when quartz tube is used to allowed the
transparency of short wavelength UV.
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