Environmental Engineering Reference
In-Depth Information
Reagent and crystalline permanganate or persulfate dissolved in water. Despite the
effectiveness of chemical oxidation, there are drawbacks to current chemox tech-
nologies. These drawbacks include the need (1) to inject very strong gases or
copious volumes of chemox liquids into the ground, (2) to reapply the oxidants
into the subsurface to fully clean sites due to side reactions occurring with natural
organic matter or plugging of the subsurface system with chemox precipitates, (3) to
prevent explosion hazards caused by the rapid reactions, and (4) to protect workers
from the health and safety hazards associated with use of these chemicals.
Oxidants encapsulated and stabilized in polymers for remediation provides a
novel technique for chemical oxidation treatments for water and soil due to the
ability to slow down the delivery of the oxidant to the contaminated area. The
development of a controlled release delivery system for oxidants from a degradable
shell has several advantages: (1) it stabilizes the solid oxidants for emplacement in
soil, sediment or subsurface applications. The placement may vary from ones that
form permeable reactive barriers, packing in a series of wells where contaminated
water will flow past the pellets for remediation, packing in a reactor for a pump
and treat system, emplacement in sediment or surface water, or augured into soil.
(2) It reduces the need for maintenance associated with the gaseous and liquid oxi-
dants. (3) It reduces the dangers associated with handling the oxidant by workers.
(4) It extends the release of an oxidant without the need to re-inject the gas or liquid
solutions. Therefore this new method has the potential to effectively extend the abil-
ity to provide chemox treatment in a fashion similar to using biodegradable medical
implants to deliver drug formulations in the body to provide controlled and extended
release of their active components.
This research focuses on the development of controlled release with the chemical
oxidant potassium permanganate. Potassium permanganate is a purple crystalline
oxidant that can be used to remediate trichloroethylene and was selected as the
initial target oxidant for prototype development [16-18]. Several researchers have
investigated the ability to encapsulate the chemical oxidant potassium permanganate
for slow release remediation using waxes and chlorine based polymers [16-18].
Kang et al. [16] encapsulated KMnO
4
(EPGs) in paraffin wax pellets 0.5-5 mm
in size. Using a melt-dispersion method, paraffin wax was melted and uncoated,
milled KMnO
4
(UMPP) was gradually mixed into the wax. The paraffin and milled
KMnO
4
were then cooled to produce the EPGs. The granules were milled for 20
minutes to form the final product called encapsulated KMnO
4
(EPP). The EPP
demonstrated a biphasic release of KMnO
4
where an initial rapid release of KMnO
4
(<10 min) was observed due to dissolution of KMnO
4
on the surface or par-
tially embedded in the wax. Following the rapid release, a sustained release for
the remaining four days was observed in reagent grade water. EPP encapsulation
resulted in 10-45% release of KMnO
4
over a 4-day period. Kang observed the
release of wax encapsulated KMnO
4
in the presence of perchloroethylene (PCE).
The solubility of paraffin wax in PCE resulted in complete dissolution of the
wax within 3 min resulting in the rapid release of oxidant from the encapsulated
matrix.
