What have we done at Orvion to solve the problem of chlorinated solvents contamination?

In 2015 we took on a project for the bioremediation of a site in Den Haag heavily contaminated by chlorinated solvents.

At the source of the contamination there was a high concentration of tetrachloroethene, caused by a leaking sewer system. Partial degradation of tetrachloroethene into trichloroethene was found, the latter being detected in the plume downgradient. Further degradation to cis-dichloroethene was happening and this compound was found mainly in the downstream channel. Normally, Geobacter and other sulfate-reducing bacteria are able to carry out these early stages of degradation. However, further transformation to vinyl chloride and ethene is usually only performed by Dehalococcoides and Dehalogenimonas, whose activity was not found at the site in question.

We therefore decided to inject ORVIaugment Dehalococcoides culture into the groundwater at the source of contamination, together with nutrients and carbon source that could support their activity, to facilitate the completion of the degradation process. The injection was repeated several times, to avoid depletion of bacteria and nutrients due to the groundwater flow. The injection was successful, as we could see with the increase in Dehalococcoides and total organic carbon, and with the decrease in sulphate due to the activity of sulphate reducers assisted by nutrients.

As regards contaminants, over the course of a few years (2015-2021) we have witnessed a progressive decrease in per, tri and dce, while vc first and then ethene increased, demonstrating that degradation products were forming. During the project, a rebound of Tetrachlorethene (PER), occurred from underneath the building. We optimised the dosing volume to reach further underneath the building (upgradient). This lead to the complete removal of Tetrachlorethene (PER).

During this project, we assessed the presence of Dehalococcoides through the use of qPCR and this, together with chemical analysis on contaminants and water flow modelling, helped us to understand which step of degradation was missing and optimise the remediation accordingly. The project is now in its final stage and we expect to close remedial actions and monitoring soon.

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