Thermal Remediation

During ERH, a power control unit (PCU) is used to pass electrical current through the soil and groundwater requiring treatment. The natural resistance of the subsurface to electrical current flow creates enough heat to convert soil moisture to steam. This in situ steam generation occurs in all soil types, regardless of permeability. The heat generated by resistance to the induced electrical current also evaporates the target contaminants. The steam created by this phase change in soil moisture and groundwater then acts as a carrier gas to sweep the contaminants to the vapor recovery (VR) wells. At sites where ERH is applied in the saturated zone the entire treated portion of the aquifer will reach these phase change conditions. 

During ERH, it is the resistance to the flow of electrical current that heats the subsurface, not the electrodes. Unlike thermal conduction heater wells, the electrodes do not get significantly hotter than the surrounding subsurface. 

During ERH, the subsurface will be heated in a smooth and controlled manner. Because ERH needs soil moisture to work, it is impossible to desiccate any part of the subsurface during ERH. The technology is also intrinsically safe. If heating stops for any reason, steam generation in the subsurface stops immediately. Redundant vapor recovery systems and backup generators are not needed at ERH sites. Finally, ERH enhances intrinsic reductive dechlorination adding a “free” chlorinated hydrocarbon polishing effect throughout the process. 

The technique is very robust. Thermal remediation is the only in situ remediation technique capable of thorough removal of free phase chlorinated hydrocarbons (DNAPL).

ERH:

• In situ remediation of soil and/or groundwater
• In situ remediation of unsaturated zones
• ERH is not influenced by heterogeneity in the subsurface. It is therefore very effective in our Western-Europe soils with many sand, clay and loam layers.
• With ERH both volatile organic carbons (VOCs) as well as semi-VOCs are treated effectively. Refer to the list of contaminants treated below. 
• The technique can be used underneath structures and is designed to not interfere with underground infrastructures like cables, pipelines, etc.

Compounds treated by ERH:

• trichloroethene (TCE) 
• tetrachloroethene (PCE)
• diesel, gasoline, kerosene, oil-grease
• NAPL 
• methylene chloride (MeCl) 
• benzene, xylene, toluene, ethylbenzene
• 1,1,1-trichloroethane (TCA) 
• dichloroethene (DCE) 
• vinyl chloride (VC) 
• 1,1,2,2-tetrachloroethane (TeCA) 
• 1,2-dichloroethane (DCA) 
• ethylene dibromide (EDB) 
• 1,2, dichlorobenzene and 1,4 dioxane 
• naphthalene

Very robust
Thermal remediation with Electrical Resistance Heating is a very robust in situ remediation technique.

All other in situ remediation methods like pump & treat, biological enhancement or chemical oxidation/reduction can be described as ‘a contact sport’. With these methods we need to get the water/air flow or the chemicals to each pore space to be effective. ERH is not a “contact sport”. With ERH we warm the complete subsurface, so we automatically reach all pollutants in every pore space in the treatment volume. Therefore, you don’t need to know the “exact” location of the contaminant.

Once the temperature of the subsurface reaches the co-boiling temperature of the pollutants, the pollutants will vaporize and will be driven out of the subsurface. The vapors will be collected by a vapor recovery system. We will continue to heat the subsurface as long as necessary to meet the remedial goals.

Robust means that we can get over 99% removal rates and no rebound, even with the presence of DNAPL.

DNAPL Hotspots
Thermal Remediation with is in our opinion the only method which is able to remove, once and for all, DNAPL hotspots of chlorinated hydrocarbons. Other in situ remediation methods have a high risk of rebound and therefore can result in project delays, budget increases & client irritation.

No soil desiccation
With ERH we do not completely dry out the soil.

Heterogeneous sites
ERH is not negatively influenced by heterogeneous soils. This is contrary to the more classic in-situ remediation methods, including steam enhanced thermal remediation.

There is even a positive effect. If a clay or loam layer is present, this layer often contains the most pollutant mass. As a result of biological processes there are more chlorinated ions present around soil layers with more pollutants. This focuses the electrical energy towards where the most pollutants are present. As a result of this, soil layers where the highest concentrations are present are heated preferably.

Proven to be SAFE
Electrical Resistance Heating has proven to be safe. Over 80 projects have been carried out with this technique, with only a broken finger in over 550,000 man-hours worked. With proper design and engineering controls, the technique can also be applied in combination with all subsurface infrastructures.

In contrary to other thermal techniques we do not ‘overheat’ the subsurface. The process reacts like a pot of boiling water: once we shut off the electricity, the steaming stops almost immediately. There is no stored heat energy. This makes the process inherently very safe. Also when there is a power failure, no electrical back-up systems are required to run soil vapor recovery and treatment systems.