Oxidation - Public Water Systems - page 550

or radical pathway for ozonation and AOPs. Presence of color and turbidity will impair
the effectiveness of AOPs using UV. Waters with high NOM levels impart high oxidant
demands, which may preclude use of chlorine and chlorine dioxide due to limitations
on by-products formed by these oxidants. Changing pH may alter the form and reaction
rate of the oxidant. Many of these water quality impacts may be mitigated through
pretreatment or chemical adjustment of the source water, but the cost of these added
measures may make such approaches unattractive.
• Impacts of by-product formation. The potential for the oxidation process to ulti-
mately result in unacceptably high levels of regulated by-products such as THMs,
TOX, and bromate must be carefully considered. This evaluation must consider the
synergistic effect of the oxidation process and subsequent disinfection steps. In some
cases, preoxidation may reduce formation of halogenated organics, while in others it
may increase formation. Also, for ozone and chlorine dioxide, oxidation will increase
AOC levels in the treated water unless this material is removed through subsequent
processes such as GAC, conventional filtration, or biologically active filtration.
• Cost. When considering costs, the total system cost for implementing an oxidation
must be considered, including necessary pretreatment or post-treatment steps to ensure
the effectiveness and mitigate the impacts of a particular oxidation method.
• Compatibility with operator skills. The different oxidation processes vary in terms
of operational and maintenance complexity, ranging from simple chemical feed sys-
tems to mechanically complex systems such as O 3 / UV. The chemicals employed also
vary in terms of hazard potential and safety requirements. The process choice must be
consistent with both the skill level and operational philosophy of the water purveyor.
For some applications, such as iron and manganese removal from groundwater,
oxidant selection and plant design can be based on proven removal mechanisms and
extensive operational experience. In many other applications, such as removal of re-
fractory taste and odor compounds or pesticides, pilot testing is needed to fully assess
treatment options and to optimize design criteria for full-scale application.
Table 16-2 summarizes the relative effectiveness of the different oxidants for the
various oxidation goals described in this chapter. Their comparative effectiveness for
disinfection and iron / manganese removal is described in Chapters 19 and 14, respec-
tively. It must be noted that Table 16-2 provides a generalized comparison that does
not hold for all source waters or treatment conditions.
Table 16-3 provides a brief summary of the comparative advantages and disadvan-
tages of the oxidants with respect to operational considerations, regulatory restrictions,
and other issues.
REFERENCES
1. Stumm, W., and Morgan, J. J., Aquatic Chemistry, Wiley-Interscience, New York, 1970.
2. Snoeyink, V. L., and Jenkins, D., Water Chemistry, John Wiley & Sons, New York, 1980.
3. AWWA, ''Chemical Oxidation,'' 5th ed., Water Quality and Treatment, American Water
Works Association, McGraw-Hill, 1999.
4. Glaze, W. H., ''Oxidation of Organic Substances in Drinking Water,'' Control of Organic
Substances in Drinking Water (B. Berger, ed.), Noyes Data Corporation, Park Ridge, NJ,
1987.