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502 P. Kajitvichyanukul et al.
Water samples were ozonated at transferred doses of 0.5, 0.8, 1.1, 1.8, and 2.5 mg O 3/mg
DOC. Biological treatment alone resulted in 13–14% removal of DOC. Ozonation followed
by biological treatment yielded 20–30% DOC removals. Biological treatment alone yielded a
28% reduction in THMFP. Ozonation followed by biological treatment yielded a 40–47%
reduction in THMFP. Ozonation followed by biotreatment yielded a 75–80% reduction in
HAAFP. The reduction in THMFP with respect to ozone dose is shown in Fig.11.3. THMFP
formation after biotreatment, but without ozonation, was approximately 220 mg/L. At the
lowest transferred ozone dose of 0.8 mg O3/mg DOC, followed by biotreatment, THMFP
dropped to 160 mg/L. THMFP was not reduced appreciably at higher O3/DOC ratios of 1.1,
1.8, and 2.5. The removal behavior of HAAFP through biotreatment as a function of applied
ozone dose was similar to that observed for THMFP. These results imply that THMFP
reduction through biotreatment is sensitive to the presence or absence of ozonation, but
insensitive to the ozone dose after a minimum ozone dose ( 0.8 mg/mg) is achieved. It is
possible that the greatest reduction in PM molecular weight, and corresponding increase in
PM bioavailability occurs when ozonation is introduced, and that further increases in ozone
dose do not yield proportional decreases in PM molecular weight.
The second study examined DOC removal through ozonation and biofiltration as a
function of water type (123). The first water was raw surface water from the Ohio River
(ORW). The second was artificial water, produced using a solution of humic substances
isolated and concentrated from ground water. The humic substances were mixed with
dechlorinated tap water to the desired DOC concentration. Dechlorinated tap water was
used to provide the noncarbonaceous nutrients and mineral matrix required for the growth
of microorganisms. Humic compounds are one of the major categories of organic substances
that make up DOC and which act as PM. The bench-scale biological filter was shown in
Fig. 11.2. DOC removals reported for the artificial water are significantly higher than those
observed for any of the previously described studies that used natural waters. It is possible
Fig. 11.3. Impact of ozone dose on THMFP removal (120).