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Biological approach of chlorinated solvents

Chlorinated solvents, such as: tetrachloroethylene (Per) and trichlorethylene (Tri) were widely used in dry cleaners, metal processing and print shops. Often the use resulted in severely contaminated soil. Chloroethanes distinguish themselves from chloroethene and are not quite so biodegradable.

In a collaboration between T & K Service and Deltares, in Barneveld an in-situ chloroethanes and chloroethene decontamination is being implemented. With a cocktail of dehalococcoides spp. and Dehalobacter spp. bacteria, chloroethanes and chloroethene are broken down into the harmless components of ethylene and ethane, via reductive dechlorination. Over a 2 year period of time, the concentrations in the source zone have dropped from >100,000 ug/l to less than the detection limit in multiple monitoring wells.

Dehalococcoides ethenogenes

Dehalococcoides entheogens bacteria (DHC) degrade chlorinated solvents in a natural way. The process that we have applied since 2005 is called bioaugmentation. During the process, DHC and nutrients are applied to the contaminated soil. The application takes place by means of direct soil injections or permanent infiltration filters. Since 2005 we have applied decontamination this way in more than 200 locations.

Practical example of a small contaminated soil volume

In case of a small contaminated soil volume, for instance a few hundred square metres, direct soil injections are performed. In a fixed pattern, at pre-determined depths, small quantities of DHC and a quantity of nutrients are injected into the soil. 

The inoculation and the nutrients ensure that the DHC’s quantity will quickly increase up to a colony of bacteria in the entire contaminated soil volume. The contamination is degraded into the harmless components ethylene and ethane, by the bacteria, via reductive dechlorination.

Practical example of a large contaminated soil volume

The alternative for soil injections is the application of permanent filters to extract groundwater and infiltrate it back into the soil after inoculation with DHC and nutrients. The process of extraction and infiltration can be installed entirely underground, in order to prevent nuisance at street level.

For a project in The Hague, 1 extraction source and 5 infiltration sources were used. During this project, in 2 years’ time, the soil volume was provided with DHC and nutrients, as a result of which a colony of bacteria incorporated and the degradation process took place.

Breeder reactor

The dehalococcoides entheogens bacteria (DHC), required for the degradation process, are grown in an own developed breeder reactor through a cooperation between T&K and Bioclear Earth.

The breeder reactor, with a volume of 10,000 litres, achieves a breeding density of 3 x 108 cells/ml. The cultivation is transported in oxygen tight containers to the decontamination location and injected into the soil, with nutrients, on-site. The combination of cultivation and nutrients causes the DHC quantity to quickly increase and the biological degradation of the contamination will start.

Proven method

This method is excellently suitable for situations where previously the biological degradation in the soil was not at all demonstrable. It was proven that this approach also works under non-optimal field conditions. The huge volume of the breeder reactor allows us to quickly inoculate a significant soil volume, ensuring that the degradation process will start immediately and the entire degradation process is followed.

Substrate: carbon source

In order to support the biological degradation process, nutrients are added to the soil. The nutrients of T & K Service are composed by means of an own recipe and contain both fast, medium and slowly working carbon sources. Our nutrients contain 2 times as much carbon source (TOC) as the usual nutrients. This guarantees longer activity of the DHC and reduces the risk that soil injections must be performed for a second time, for the administering of nutrients.

Zero-valent iron

In case of severely contaminated locations, we add zero-valent iron to our recipe. Zero-valent iron initiates a chemical reaction during which the contamination is degraded immediately and also it contributes to the necessary anaerobe conditions for optimal growth of the DHC. Our nutrients speed up the degradation process of the contamination and reduce the decontamination costs.

Contact details

Postal address
Spijkerboor 56
8607 KC  Sneek

Office and workplace address
De Loads 3
8447 GP  Heerenveen

+31 515 433991

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