Solving the challenges of soil remediation – How to decontaminate brownfields

Across the EU, there are an estimated 2 800 000 developed or previously developed sites with potentially polluting activities, with 650 000 officially registered as such.[1] They include former and current petrol stations, factories and waste sites and chemical dump sites.

To prevent environmental contamination and harm to human health, soil remediation is often necessary. This involves treating the air or water derived from the soil to remove pollutants.

Soil remediation can take place in situ or ex-situ, using a variety of techniques. The process depends on the type of soil, the pollutants detected, how accessible the contaminated area is, whether the contaminants have entered the groundwater, and the past, current and proposed usage of the site in question.

DESOTEC helps companies across Europe find solutions for the remediation of contaminated sites, developing mobile activated carbon filters for the adsorption of pollutants.

Typical pollutants

Most brownfield site pollutants that can be treated with DESOTEC filters are organic components, and include:

Mineral oils, commonly found around petrol stations as the result of old spills.

Aromatic hydrocarbons, including BTEX: benzene, toluene, ethylbenzene and xylene. They are all widely used in manufacturing and can be carcinogenic.

Halogenated hydrocarbons, organic components containing chlorine, fluorine and/or bromine. Well-known products are cleaning agents commonly used in dry cleaning and in the degreasing of machine parts.

Other contaminants often found are per-and polyfluoroalkyl substances (PFAS) such as perfluoro-octane-sulphonate (PFOS) and perfluoro-octanoic Acid (PFOA). PFOS and PFOA are both now classified as Persistent Organic Pollutants (POP).

POPs are organic compounds that do not break down naturally in the environment. If they get into water courses, they can be consumed by microorganisms and fish and enter the human food chain. Even in low concentrations, these pose a very high risk to human health.

As more evidence emerges of the harm these present, and as it becomes easier to measure them, authorities and companies are making greater efforts to remove them. POPs are now on the EU’s list of Substances of Very High Concern (SVHC)

Legislative framework

Although the scale of the problem in Europe has been documented by the EU’s Joint Research Centre in a 2018 report,[2] there is no single legislative framework governing soil contamination. Instead, different regions and countries have set their own limits and targets.

Certain countries, including the Netherlands, Austria, France and Belgium, began introducing laws around soil contamination in the 1980s. Others, such as Bulgaria, Romania and Slovenia, began addressing the issue in 2000-2010.

Pollution limits also depend on the proposed usage of a site, with areas earmarked for housing being subject to more stringent regulation than those planned for further industry.

Groundwater remediation

Groundwater usually becomes contaminated due to historic spills of organics and heavy metals. “Pump-and-treat” or hydraulic containment is the most widely used remediation technique.

Essentially, the groundwater is pumped to the surface through a series of extraction wells, treated at the surface to remove pollutants, then either returned underground or discharged in the sewage system.

Pump-and-treat also prevents the contamination from spreading by installing a hydraulic barrier around the affected zone.

DESOTEC MOBICON filters can be fitted in such remediation systems to adsorb pollutants from the pumped water.

Soil remediation: ex situ

Air remediation through vapour extraction is generally the most suitable technology to remove VOCs from the soil.

On brownfield sites, this involves digging the contaminated soil out and transporting it to an off-site facility for treatment or disposal. Remediated soil can then be returned to the site.

There are two stages at which pollutants are emitted and treatment is required.

Firstly, when the soil is excavated, vapours are released that contain low concentrations of pollutants. Until recently, such vapours were simply allowed to enter the atmosphere untreated, but nowadays public pressure has led to more stringent limits.

Therefore, the excavation site will be covered with a large tent, big enough to contain heavy digging equipment. The air in this tent must then be purified before being released.

Secondly, the treatment process at the external facility releases vapours containing high concentrations of pollutants. Again, these need to be removed before the vapours can be released harmlessly into the atmosphere.

DESOTEC can supply filters suitable for both stages.

For the excavation process, the AIRCON H filter can handle the large flow rates, which are typically between 30 000 and 200 000 m3 per hour.

It is a particularly cost-effective solution and is generally far preferable to alternatives such as burning air or treating it biologically. The AIRCON H is designed to allow for a low pressure drop, thus saving energy costs. Furthermore, as the pollution levels are low, DESOTEC is able to reactivate the spent carbon so it can be reused.

For the external treatment facility, the AIRCON HC-XL is a viable solution specially developed to handle high concentrations of pollutants.

Soil remediation: in situ

Sometimes, it’s necessary to treat historically contaminated ground at factories or petrol stations that are still in operation. In these situations, excavating the soil would be impossible without dismantling the buildings on top.

Instead, the ground is treated thermally so that the pollutants are turned into gases, then these are sucked through a filter to adsorb the contaminants. Through this process of soil vapour extraction (SVE), the purified vapours can then be safely released into the atmosphere.

This typically produces very high concentrations of pollutants, which used to be difficult to treat. DESOTEC has risen to this challenge by developing its AIRCON HC-XL filter especially for situations such as these.

Safety issues

Where there are high concentrations of pollutants, there is the potential for hotspots to form inside filters. This could potentially be dangerous if left unnoticed or untreated for a few days.

DESOTEC has therefore developed an INERTI-BOX for use alongside its AIRCON HC-XL filters. This monitors the outlet of the filters and detects and stops hotspots before they can develop into a fire risk.

DESOTEC – your problem-solving partner

DESOTEC takes pride in its innovative approach. We are always looking at ways to develop, adapting our solutions to new types of remediation work.

We work with many companies involved in remediation work, supplying filters on a rental basis that would be too costly for them to develop themselves.

We are delighted to be considered highly reliable partners and leaders in our field, valued for our problem-solving approach and the innovative solutions we provide.

Contact us today to find out more about our work in soil remediation across Europe.