Remediation Technologies - Environmental Investigation and Remediation - page 328

medium is contained in a series of vessels connected to the extracted groundwater stream. The
groundwater passes through the vessels containing the medium, and contaminants are transferred
to the medium before the treated groundwater exits the vessel. The contaminants removed are
trapped within or form a coating on the medium's sorptive surfaces until they reach the point of
saturation, after which no additional contaminants can be removed and breakthrough occurs. The
saturation point typically varies in proportion to the applied concentration and l ow rates. As with
air stripping, sorption technologies constitute a transference of contamination from one medium to
another, and the contaminated sorptive media must be disposed of properly and/or treated. Typical
treatment and disposal options include stream regeneration for GAC, regeneration of resins, or
disposal in landi lls. Newer sorbents may have the ability to treat contaminants after capture
[e.g., Trap and Treat ® (Remediation Products, Inc., Golden, Colorado) (R. Elliott, personal com-
munication, 2007)], which extends the life of the sorptive medium until both the treatment and
sorptive capacities are exceeded. Because of the low partitioning coefi cient of 1,4-dioxane, it is
generally considered to be resistant to sorbing to GAC (a common adsorptive medium). As dis-
cussed in the following sections, research into the efi ciency of several types of sorptive media has
been performed to assess their ability to remove 1,4-dioxane from groundwater.
7.2.1 A DSORPTIVE M EDIA
A bench-scale treatability test was performed for AFP 44 to assess the removal efi ciency of several
adsorptive media that were identii ed as potentially applicable for 1,4-dioxane treatment (Earth
Tech, 2004). These included a surfactant-modii ed zeolite (SMZ) (referred to as 14-40 SMZ) and an
SMZ with zero-valent iron (ZVI), both provided by Robert Bowman, New Mexico Institute of
Mining and Technology, and activated Tri-Base Pelletized Carbon TM (Tri-Base Carbon TM ) (Hiatt
Distributors Limited, Long Beach, California). Zeolites are natural or synthetic aluminum silicates
that form a regular crystal lattice and release water at high temperature. Zeolites are polar in nature
and have been used for the i ltration of a number of organic and inorganic contaminants (Bowman
et al., 2000). The results of the partitioning phase of the study indicate that the SMZ with ZVI media
adsorbed measurable concentrations of 1,4-dioxane at media:water ratios of 1:20 through 1:2, indi-
cating that sorption is possible at low 1,4-dioxane concentrations and low media:water ratios. No
measurable sorption of the 1,4-dioxane to the standard SMZ medium took place. Tri-Base Carbon
adsorbed 1,4-dioxane measurably. However, a high media:water ratio was required in order to sig-
nii cantly reduce 1,4-dioxane concentrations. An additional potential i ltration technology using
macroporous polymer (MPP) extraction was also tested by the manufacturer (Akzo Nobel,
Incorporated), but was ineffective at removing 1,4-dioxane from the tested water. In conclusion, the
Tri-Base Carbon exhibited a measurable sorption rate for groundwater samples from the site.
However, results of the testing and calculations to scale-up the test led to the estimate that ~1500
tons of Tri-Base Carbon would be required to treat AFP 44 regional groundwater per year. This
volume of material is prohibitive from a logistical and cost standpoint.
7.2.2 A CTIVATED C ARBON
Johns et al. (1998) performed a series of laboratory studies to determine the sorption characteristics of
activated carbons derived from a variety of waste agricultural by-products. Two groups of materials
were evaluated: soft materials (made from rice straw, soybean hulls, sugarcane waste, and peanut
shells) and hard materials (made from pecan and walnut shells). Materials were commingled with
molasses as a binder and then pressed into briquettes or pellets. All materials were carbonized and
then crushed and sieved for a consistent size fraction, prior to activating with carbon dioxide or steam.
The study specii cally utilized lower carbonization temperatures (750°C) than normally used in the
industry (1000°C) to demonstrate potential reductions in energy demands and overall manufacturing
costs. The sorption effectiveness of the agricultural products was evaluated for a variety of common