Electrical resistance heating
The resistance to electrical flow that exists in the soil causes the formation of heat; resulting in an increase in temperature until the boiling point of water at depth is reached.
After reaching this temperature, further energy input causes a phase change, forming steam and removing volatile contaminants.
Volatilized contaminants are captured by a subsurface vapor recovery system and conveyed to the surface along with recovered air and steam.
The design and cost of an ERH remediation system depends on a number of factors, primarily the volume of soil/groundwater to be treated, the type of contamination, and the treatment goals.
The physical and chemical properties of the target compounds are governed by laws that make heated remediations advantageous over most conventional methods.
The electrical energy usage required for heating the subsurface and volatilizing the contaminants can account for 5 to 40% of the overall remediation cost.
Henry's law describes the tendency of a compound to join air in the vapor phase or dissolve in water.
At an ERH site, the primary electrical current path is on the thin layer of water immediately adjacent to the soil or rock grains.
1,4-dioxane has a high solubility in water and a low Henry's Law constant which combine to present complex challenges associated with remediation.
At ERH sites, steam stripping was observed to effectively transfer 1,4-dioxane to the vapor phase for subsequent treatment.
ERH can be used to provide controlled low temperature heating for projects with remediation processes that do not involve steam stripping.
Examples of low temperature ERH include heat-enhanced bioremediation, heating the subsurface to temperatures above the solubility of dissolved gasses to induce VOC stripping (most notably carbon dioxide ebullition), heat enhanced in situ chemical oxidation (especially for persulfate activation), and heat-enhanced reduction (such as with iron-catalyzed reactions).
Using low temperature heating coupled with bioremediation, chemical oxidation, or dechlorination will result in increased reaction rates.
When heat is combined with multi-phase extraction, the elevated temperatures will reduce the viscosity and surface tension of the recovered fluids which makes removal faster and easier.
