Most Six Phase Heating (SPH) projects involve
aquifer heating in one way or another, as the technology is specifically
applicable to the remediation of dense non-aqueous phase liquids (DNAPL)
existing as free phase product below the groundwater table.
SPH , otherwise known as Electrical Resistance Heating (ERH) works by
passing electricity through the soil and groundwater. Soil moisture has an
inherent electrical resistance which causes electrical energy to be
converted to heat. Heating of the soil and groundwater enhances many
in-situ groundwater technologies, including the following:
Soil Vapor Extraction (SVE)- SVE is an integral part of the
Electrical Resistance Heating process and it is used at virtually every
ERH site to recover the steam and volatized hydrocarbons where they are
brought to the surface for treatment.
Dual Phase Vacuum Extraction (DPE or DVE)-
Electrical Resistance Heating accelerates remediation by boiling of the
interstitial pore water. This dislodges and vaporizes contaminants the
pore level. Increased temperatures also lower the viscosity of the
hydrocarbon while the increased pore pressures create fractures which
result in increased hydraulic permeability. For example, #6 fuel oil
viscosity is reduced from roughly 5000 to 50 cS by increasing the
temperature to the boiling point of water, while extraction is further
increased by the subsurface steam movement on the soil pore level. DVE is
also used for hydraulic control of the aquifer and to prevent lateral
migration of contaminants in applications where ERH is applied below the
groundwater table.
Natural Attenuation- Degradation mechanisms are often drastically
accelerated by Electrical Resistance Heating. Common degradation
mechanisms which have affected past projects are thermo-biodegradation,
hydrous pyrolysis oxidation, hydrolysis, and reductive dechlorination via
native reactive minerals such as reduced irons, sulfide and sulfite.
Air Sparging- Electrical Resistance Heating compliments air
sparging. Volatile organic contaminants are readily partitioned into vapor
phase when heated making the sparged air much more effective as a carrier
gas. Moreover, air sparging introduces oxygen into the groundwater, which
enhances thermo biodegradation and thermally accelerated oxidation
reactions such as hydrous pyrolysis oxidation.
Bioremediation-Electrical Resistance Heating has been shown in
both laboratory and field studies to accelerate bioremediaiton at
temperatures of up to 80șC for fuel hydrocarbons and as high as 111 șC for
chlorinated hydrocarbons. Healthy microbial populations have been
identified in boiling or near-boiling site groundwater in both aerobic and
anaerobic environments.
Others- Many other groundwater treatment technologies can be
augmented with Electrical Resistance Heating. For example, treatment of
subsurface contamination by persulfate requires some sort of "activation"
either by iron-EDTA or heat. ERH can effectively provide the increased
temperatures required to activate the persulfate.
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