Dual-phase extraction is a common and effective method in soil and groundwater remediation. It extracts both contaminated groundwater and soil vapor. This method is also known as bioslurping, vacuum-enhanced extraction, and multi-phase extraction. It is an on-site (in-situ) remediation process.
It works using a high vacuum system to remove various combinations of contaminated groundwater and hydrocarbon vapor from the subsurface.
Compared to traditional methods of cleaning up contamination, such as pump-and-treat, DPE is a much faster technique. Additionally, this method is capable of removing various combinations of contaminants simultaneously. Besides, it uses less energy and creates fewer greenhouse gas emissions, making it climate-friendly, as well.
Although it is more costly upfront than traditional methods, the benefits of DPE far outweigh any disadvantages in many respects.
Dual-phase extraction (DPE), also known as multi-phase extraction, vacuum-enhanced extraction, or sometimes bioslurping, is a technology that uses a high vacuum system to remove various combinations of contaminated groundwater separate-phase petroleum product, and hydrocarbon vapor from the subsurface. Extracted liquids and vapor are treated and collected for disposal or re-injected to the subsurface (where permissible under applicable state laws).
The process can target light nonaqueous phase liquids (LNAPL) such as gasoline or diesel fuel leaked from underground storage tanks. It is frequently applied in contaminated environments where LNAPL overlies groundwater containing dissolved contaminants such as volatile organic compounds (VOCs), gasoline components, and diesel fuel components. Despite its name, DPE can also extract other hydrocarbon compounds through the soil, including raw crude oil.
DPE was invented in 1995 by Vincent A. Capitanio while he was working for Praxair Surface Technologies in Lisle, Illinois, under the direction of Dr. James J. McKone (1964-2015), who is often referred to as “the father of DPE.” This technology has quickly become the industry-standard method for remediation of petroleum sites due to its speed and effectiveness compared to more traditional methods such as pump-and-treat or static vents. In some cases, DPE can remove up to 95% or more of the hydrocarbon contamination.
The process uses a combination of several phases: vapor, liquid, and solid (aqueous). A high-vacuum system is used to transport the contaminants from the subsurface into containment vessels where they are separated and treated or disposed of. The vapor phase is captured using condensers and other vacuum equipment and either re-injected underground if it is acceptable in that area or burned for fuel. The liquid phase can be reused as clean water on-site for washing down systems and dust control or treated offsite. The final product is soil free of hydrocarbons and can be disposed of without any special precautions.
Vapor recovery units collect vapors at a low dynamic head. The vapors are then delivered through a transfer line to a separator that liquefies the hydrocarbon and separates it from any water, gas or solid particles that may be present.
The recovered vapor is then vented for flaring off excess methane at high concentrations, burning as fuel, or running through an amine system to remove organics from the vapors before being burned as fuel or vented.
If applicable at a site, the solid phase products can go straight to disposal by hauling away and landfilling just like other contaminated soils. This method used less energy than removing these contaminants by evaporating and recapturing them into another vessel as with traditional methods such as pump-and-treat.
There are multiple reasons why the DPE process is becoming more popular for petroleum hydrocarbon remediation of underground storage tanks, leaking from piping or other sources that have been seeping into the soil over time. One main reason is that it is a faster method of cleaning up contamination than traditional methods such as pump and treat, which can take years to complete once all components have been identified and mobilized through injection wells. By comparison, DPE can remove 95% or more of VOCs in a matter of days using a single well at many contaminated sites. In some cases, DPE has also turned out better than expected because there was not as much contaminant left behind (i.e., more material was removed than believed initially), meaning that the site does not need to be monitored as closely, potentially saving money.
Another reason DPE is becoming more popular at petroleum sites is that it can remove various combinations of contaminants simultaneously without identifying and mobilizing each specific contaminant before treatment. This speeds up the remediation process for contaminated sites, especially if multiple contaminants are present or contamination has spread across an entire site. Complementing this factor, DPE equipment is compact and mobile, so it can be moved around easily, making it ideal for use at challenging sites with limited access where other methods may not work well.
Compared to pump-and-treat, the advantage of using DPE at contaminated sites is that it uses less energy, does not leave the site vulnerable to collapse, and does not require cleaning up the contaminated groundwater before treatment. This process also eliminates the need for costly monitoring wells if contamination has spread across an entire site because it only needs to be pumped out of one well at a time.
Since DPE uses less energy than pump-and-treat, it creates fewer greenhouse gas emissions which could contribute to climate change. It is also more cost-efficient which saves businesses time and money when compared to pump-and-treat.
The disadvantages of using DPE instead of traditional methods such as pump-and-treat are that equipment is usually much more extensive and bulky, requiring more trucks to transport it to the site. Also, DPE is more costly upfront than traditional methods; however, the benefits of using DPE outweigh these disadvantages in many cases, which is why this method is gaining popularity for petroleum hydrocarbon remediation of underground storage tanks.
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