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Nonhalogenated
VOC's:
Acetone, Styrene, etc.
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Nonhalogenated VOC's in
Ground Water
Common treatment technologies include:
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The most commonly used technologies
to treat nonhalogenated VOC's in ground water, surface
water, and leachate are air stripping and carbon adsorption.
These are both ex situ technologies requiring ground water
extraction.
Air Stripping
Air stripping involves the mass
transfer of volatile contaminants from water to air. This
process is typically conducted in a packed tower or an
aeration tank.
The generic packed tower air stripper
includes a spray nozzle at the top of the tower to distribute
contaminated water over the packing in the column, a fan
to force air counter current to the water flow, and a
sump at the bottom of the tower to collect decontaminated
water. Auxiliary equipment that can be added to the basic
air stripper includes a feed water heater (normally not
incorporated within an operational facility because of
the high cost) and an air heater to improve removal efficiencies,
automated control systems with sump level switches and
safety features such as differential pressure monitors,
high sump level switches and explosion proof components,
and discharge air treatment systems such as activated
carbon units, catalytic oxidisers, or thermal oxidisers.
Packed tower air strippers are installed either as permanent
installations on concrete pads, or as temporary installations
on skids, or on trailers.
Carbon Adsorption
Liquid phase carbon adsorption
is a proven technology in which ground water is pumped
through a series of vessels containing activated carbon
to which dissolved contaminants are adsorbed. The carbon
medium can be changed to suit specific contamination within
the ground water.
It is also possible to regenerate the
carbon where high concentrations would reduce the effective
life of the carbon. This can be done by using steam to
effectively strip the contamination from the activated
carbon allowing further use.
Other fairly common technologies used in separating contaminants
from ground water are distillation and membrane pervaporation.
Membrane Pervaporation
Membrane pervaporation is a process
that uses permeable membranes that preferentially adsorb
volatile organic compounds (VOC's) from contaminated water.
Contaminated water first passes through a heat exchanger,
raising the water temperature.
The heated water then enters the pervaporation
module, containing membranes composed of a non-porous
organophilic polymer, similar to silicone rubber, formed
into capillary fibres. VOC's diffuse by vacuum from the
membrane-water interface through the membrane wall. Treated
water exits the pervaporation module, while the organic
vapours travel from the module to a condenser where they
return to the liquid phase. The condensed organic materials
represent only a fraction of the initial wastewater volume
and may be subsequently disposed of at a cost saving.
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