Removing AOX from groundwater at Paris Metro construction site

The world’s eyes will be on Paris when it hosts the Olympic Games in 2024, and the French capital is determined to make a great impression. It has embarked on a huge programme of infrastructure works, including expanding and modernising its Metro network. DESOTEC has supplied 16 sustainable mobile filters to remove substances including adsorbable organic halides (AOX) from groundwater at one of the construction sites, ensuring that the new Metro is fit for a cleaner future.

The problem

In 2013, the Parisian authorities launched the Grand Paris Express programme to build 200 km of extended Metro lines plus 68 new stations.

This involves extensive groundworks, some of which are at sites where former industrial or commercial activity has left the land and groundwater in need of remediation.

Chlorinated compounds from pharmaceutical, chemical, and cleaning products, measured as AOX, pose a particular risk to human health and aquatic life.

A major French remediation and sanitation specialist was commissioned to purify all groundwater before discharging it into the Seine. This company has worked regularly with DESOTEC on previous remediation projects, so knew it could rely on our help with this mammoth, high-profile task.

It contacted us with a view to treating pumped-up groundwater at the Pont de Sèvres in the heart of the city, alongside the busy D1 motorway.

The solution

DESOTEC’s mobile filtration model and agile, flexible approach allowed us to meet the significant challenge of designing and delivering so many filters within a limited time frame.

We calculated that 16 large Mobicon filters would be required due to the high flow rate of 800 m³/ h. Concentrations of AOX were relatively low, making activated carbon an ideal solution.

The first eight were sand filters to remove suspended substances from the water. The treated water was then passed over a further eight activated carbon filters to remove all AOX.

All the filters were delivered by the end of May 2019.

The results

The filters operated at full power for several months, successfully reducing AOX and other substances in groundwater to the required level. The groundwater was then safe for discharge to the Seine.

As this is a phased project, DESOTEC is likely to be called upon to supply further filters if more AOX or other compounds are discovered in the groundwater at later stages.

Mobile activated carbon filters are an excellent solution for temporary remediation projects. They are plug-and-play, making them simple to operate. They have a small footprint, so fit into crowded construction sites. We supply them on a rental basis, so they require no upfront investment from the customer.

Our full-service solution also includes safe and sustainable filtration waste handling. We remove all spent carbon in closed filter units away from customers’ sites, and take it to our facilities for analysis.

All adsorbed molecules are destroyed in DESOTEC’s furnaces, which are under continuous online monitoring to ensure that only harmless water vapour exits the chimney. Wherever possible, carbon is reactivated for reuse, keeping costs low and boosting sustainability.