There are several methods of PFAS treatment, and new technologies and solutions are continuously being developed to combat the global problem PFAS-contamination poses.
Treatment of PFAS contamination often focuses on the soil in which the contamination is located. From there, the contamination often spreads into groundwater and food, causing problems for the environment and our health.
Perpetuum specializes in PFAS treatment through depositing and remediating the soil, but there are also other ways of chemical and physical treatment of PFAS contaminated soil.
The different methods are suited for different scenarios and types of soil.
On this page you will find some of the most deployed methods of PFAS soil treatment, along with some pros and cons for each method.
Soil washing
Soil washing describes the process of PFAS soil treatment by applying large amounts of water, with the aim of transferring the PFAS to the water phase. This is easier achieved for coarse fragments of the soil (gravel, sand), while it is harder to achieve for the finer soil fragments (clay, silt). This can be done both in situ and ex situ. Ex situ treatment plants will normally be able to deliver better results than a mobile in situ plant.
Subsequent PFAS treatment of the water used for washing is an essential part of the process, and different methods may be used.
The finer soil fragments are separated from the coarser fragments, and are usually dewatered in a filter press, producing a filter cake. This filter cake usually has to be sent to a landfill for depositing, while the coarser fractions usually can be reused on site.
Cleaning contaminated soil by soil washing is widely used, but is still in an early/experimental phase as a PFAS treatment option.
Pros:
- The soil will be washed for other contaminants than PFAS as well.
- A large part of the soil may be reused on site, when washing is done in situ.
- When done in situ, there is no need for transporting reused soil over longer distances
- It might be possible to reuse some cleaned fractions from ex situ treatment plants as well.
Cons:
- Extensive and expensive work on site when done in situ.
- Long transport if ex situ plant is used.
- Uncertainties with regard to effectiveness/results, especially in situ.
- If the effectiveness of PFAS treatment is moderate, long term monitoring and other long term treatment measures may be necessary.
- Uncertainties with regard to the possibility to reuse cleaned fractions from ex situ plants
- Less suitable for cleaning contaminated soil with high silt and clay content, or high organic content.
- The filter cake may have to be deposited at a landfill.
Thermal treatment
PFAS substances will start to vaporize at around 350 Co, and will mineralize/be destructed at higher temperatures, typically 700 – 1400 Co, depending on the type of PFAS.
PFAS soil treatment using thermal processes can be done in situ and ex situ.
In situ thermal treatment of PFAS soil
In situ thermal treatment normally involves heating the soil to typical 350-400 Co, collecting the vapor and treating the vapor, after bringing the vapor back to a liquid phase.
Pros:
- The soil may be reused on site
- No need for transporting the soil over longer distances
Cons:
- Extensive and expensive work on site
- High energy consumption
- Uncertainties with regard to effectiveness/results
- If effectiveness is moderate, there might be a need for long term monitoring and other long term treatment measures
Ex situ thermal treatment of PFAS soil
ex situ thermal treatment normally involves incineration at high temperatures, typically >1000 Co, in order to destruct the PFAS compounds.
Pros:
- Effective destruction of PFAS, if the temperature is high enough
Cons:
- Very few incineration plants accept large quantities of soil
- Usually long transport
- Low calorific value for incineration with high energy consumption
- Most of the soil comes out as an “ash-fraction”.
- Reuse of the ash is uncertain
Incineration is probably most efficient for treating high concentrated sludge and bi products from other treatment methods.
Questions to any of the content in this article, or do you need asssistance with a PFAS-problem?
Sorption and Stabilization
Sorption and stabilization is not a method of cleaning contaminated soil, but rather stabilizing the PFAS from leaching from the soil. This can be done by adding various amendments to the contaminated soil, such as minerals or stabilization agents.
Sorption and stabilization is suited for on-site PFAS soil treatment, but it does not remove the contamination itself – it only stabilizes it from leaching and causing further contamination. The stabilization agent has to be evenly mixed in the soil on site, which is a challenging and comprehensive work if there is large amounts of contaminated soil, or the soil has physical properties that makes such mixing difficult.
An alternative to mixing the stabilization agent in the soil, is establishing barriers/trenches with such stabilization agents. However, this will then have more character of groundwater treatment, and not soil treatment.
Pros:
- The soil is reused on site after mixing in the stabilization agent.
- No need for transporting the soil over longer distances.
- Leakage of PFAS to sorrounding environment can be significantly reduced.
Cons:
- PFAS is not removed from the contaminated site.
- Extensive and expensive work on site.
- Uncertainties with regard to effectiveness/results, especially how well the stabilization will function over time.
- Since PFAS is only stabilized, and not removed, there is probably a need for long term monitoring and maybe also other treatment measures.
- When barriers/trenches are used, there are uncertainties both in connection to the long term sorption capacity, as well as to how well the barrier captures all contaminated groundwater.
Covering up
One method for reducing the leakage of PFAS to the surrounding environment is reducing the amount of water washing through the contaminated soil. If membranes or watertight soil (clay) can be placed in a manner that stops precipitation from penetrating the contaminated soil, and there is no groundwater coming in from the sides, leakage of PFAS can be significantly reduced or stopped.
This is not a PFAS treatment method, but can be quite effective in stopping PFAS from spreading from the original contaminated area. The method is often used in combination with other methods, for instance in areas with lower contamination, or to increase the long term effect of stabilization.
Pros:
- The soil is not moved, and therefore “reused on site”.
- Low cost with moderate need for digging/excavation.
- No need for transporting the soil over longer distances.
- Leakage of PFAS to sorrounding environment can be significantly reduced.
Cons:
- PFAS is not removed from the contaminated site, and is not stabilized either.
- Does not include cleaning of the contaminated soil.
- Often difficult to control the paths of water, and especially groundwater flows. Therefore combinations with other methods are often necessary.
- Groundwater conditions may change over time, due to constructions on or near the contaminated site, or due to climate change.
- Long term monitoring will be necessary, and maybe other treatment measures as well.
- The methods for covering up might not be stable over time, due future changes in use of the area/construction work, or deterioration of membranes used.
- The covered up area may be rendered useless for other purposes.
Disposal in landfill
Excavation and off-site disposal or treatment of PFAS is the only well-developed method for PFAS soil treatment. By excavating and depositing the contaminated soil in a landfill cell
the PFAS may be sealed from the environment in the long term, if the landfill is designed to do so. This has not always been the case, and most landfills are still not designed for PFAS. When putting PFAS in a landfill not designed for PFAS, you’ll only have achieved moving the environmental problem to another site.
A landfill designed for PFAS needs:
- A solid bottom liner construction, with several layers of membranes and drainage (multiple safety barriers), ensuring no leakage in or out of the landfill cell.
- Collection of all leachate from the landfill cell, and leachate treatment removing close to all PFAS from the leachate water.
- When the landfill cell is full, a solid water tight, long term, top coat construction ensures that all water supply to the landfill cell is stopped. The contaminated soil in the landfill cell will dry out, and all leakage will stop.
When the above criteria is met, PFAS is effectively and permanently removed from the ecosystems.
At Perpetuum, we deposit PFAS soil in designated PFAS-cells, where our technology also allows for remediation of PFAS from the leachate water from the landfill. This is a solution that both removes the contamination from the original contaminated site, but also removes the PFAS as a potential contaminant to the environment, by permanently removing it from all ecosystems.
Pros:
- The contaminated soil is removed from the original site, leaving no PFAS residue where excavation has been done.
- The fastest and most effective way to remove PFAS from a contaminated site
- No need for long term monitoring or other treatment measures on the original site.
- PFAS is not destructed, but is permanently and safely removed/sealed off from the ecosystems.
Cons:
- Very few landfills are designed for PFAS. As far as we know, such landfills are only found in Norway.
- Long transportation to the landfill site.
- No re-use of the soil (unless the landfill wash parts of the soil).
Want to know more about how our landfill is designed, and how PFAS treatment works at our facilites? Read more about our PFAS soil treatment technology here.
Questions to any of the content in this article, or do you need asssistance with a PFAS-problem?