Pilot Study
The objective of the project was to identify
the most reliable and cost-effective
treatment to meet the requirements of
Stage 2 of the D/DBPR.
Conclusions
Both air stripping and GAC
treatment are effective approaches
for reduction of TTHMs in the
distribution system. The coconut
shell-based carbon showed very
fast DOC breakthrough but
exhibited very high efficiency in
THM removal, even when DOC
breakthrough was nearly complete.
The bituminous-based carbon
showed excellent DOC removal and
Figure 4: SDS-THM data against THM hold test data at 72 hours (left graph) and 168 hours (right graph);
relatively good THM removal. Under
GAC B= coconut shell; GAC C=bituminous coal
the conditions tested, coconut shellbased GAC slightly outperformed
hours. The use of the OLC 12x40 (coconut shell)
the bituminous-based GAC. The reformation of TTHMs
resulted in a 65 percent decrease in THM formation
is of concern, and the chosen decentralized treatment
at 72 hours and a 20 percent decrease at 168 hours.
system will be designed to achieve a lower target
Likewise, FILTRASORB 400-M (bituminous) showed a
treated-water TTHM level that will provide a buffer of
70 percent decrease in THM formation at 72 hours and
a magnitude sufficient to ensure that TTHM levels do
a 45 percent decrease at 168 hours. The effectiveness
not exceed the 80-ppb limit with reformation.
of the GAC media in THM mitigation dramatically
decreased toward the end of the pilot project (12,516
The authors would like to acknowledge the
bed volumes) due to the diminished carbon adsorption
assistance of the water quality staff and O&M; crew
capacity. The two carbons showed THM reduction in
for the City of Scottsdale, as well as the equipment
the 10 to 20 percent range for both 72 and 168 hours.
manufacturers who provided the pilot units for
Figure 4 illustrates THM formation potential, at 72 and
testing.
168 hours, as a function of bed volumes.
Dr. Chandra Mysore is a national practice leader for Water at
GHD, Inc., specializing in innovative solutions for water quality and
treatment, reuse, and desalination.
Bill Roberts is a service group manager at GHD Inc. He has
been planning, designing, and building water and wastewater
improvements since 1995.
James Fletcher serves as a process controls engineer at GHD Inc.
He has specialized in water and wastewater design and modeling
for more than 12 years.
Mark Xerxis is a principal scientist for the City of Scottsdale with
20 years of experience in the field of environmental testing and
water treatment.
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