Environmental Science

[CHARACTERIZING HYDROGEN PEROXIDE DEGRADATION BY ACTIVATED CARBON FOR
ADVANCED OXIDATION PROCESSES IN WATER TREATMENT]{.underline} [T. R.
Doom]{.underline}^1^, C. J. Corwin^2^, K. G. Linden^2^\*, R. S.
Summers^2^, Arizona State University^1^, Harrington Department of
Bioengineering, Tempe, AZ 85287, University of Colorado at Boulder^2^,
Department of Civil, Environmental and Architectural Engineering,
Boulder, CO 85309, Karl.Linden@Colorado.EDU

The objectives of this research were to investigate mechanisms and
parameters that may influence hydrogen peroxide (H~2~O~2~) degradation
by granular activated carbon (GAC). The ultimate purpose is to develop
optimal parameters for H~2~O~2~ quenching that follows UV-H~2~O~2~
advanced oxidation processes (AOPs) utilized in water treatment. The
research was comprised of three independent experiments. The first
experiment was a jar test that evaluated carbon sizes: 12X40, 60X80,
100X200 and 200X400 (U.S.A. standard sieve sizes) at 250RPM and 25RPM
mixing speeds. A second jar test evaluated carbon service ages: 0hrs,
1500hrs and 4700hrs in waters with 2.92ppm and 1.24ppm total organic
carbon (TOC). The third experiment was a pilot-scale continuous flow
column test operated for 8 days using 4700hrs service aged carbon and
water with 1.16ppm TOC. Influent H~2~O~2~ concentrations for all
experiments were in the range of 5-11ppm and all H~2~O~2~ concentrations
were determined with a spectrophotometer using the triiodide (I^3-^)
method. Carbon pulverized to various sizes was tested to allow the
dependence of internal diffusion on particle size to be analyzed.
Smaller carbon sizes exhibited faster H~2~O~2~ degradation and the sizes
where effectively scaled using a linear factor. The mixing was
controlled at two speeds to alter the thickness of the hydrodynamic
boundary layer surrounding the carbon particles allowing external mass
transfer to be analyzed. The high mix speed increased the H~2~O~2~
degradation rate. Furthermore various carbon ages were tested to assess
performance sustainability and high and low TOC waters were used to
assess competition between H~2~O~2~ and organics for the GAC. The
H~2~O~2~ degradation rate of the high and intermediate carbon service
ages declined to a common level while the high and low water TOC levels
had minimal impact. The column test was performed to analyze the surface
reaction as characterized by the mass transfer zone (MTZ). The H~2~O~2~
was contained with an empty-bed contact time (EBCT) less than four
minutes and appeared to stabilize after approximately 1000 bed volumes.
In conclusion the distinct degradation rates observed by controlling
carbon size and mix speed suggests both external and internal mass
transfer are significant mechanisms. Furthermore the data suggests that
the H~2~O~2~ degradation rate is linearly proportional to carbon size.
The common removal rate observed with the high and intermediate service
ages suggests that the carbon will sustain removal capability. The high
and low TOC waters revealed that at the measured concentrations
competition has negligible impact. Finally the steady-state of the MTZ
for the observed duration suggests that the surface reaction may be
catalytic.

T. R. Doom was supported by NSF-REU grant No. 0552895