Removing oil hydrocarbons from water in an underground rock cavern

In a harbour in the Nordics, a DESOTEC filter is in the process of treating 50 000 - 60 000 m³ of water from a subterranean rock cavern: enough to fill 24 Olympic-sized swimming pools.

The activated carbon filter is successfully removing a range of oil-derived pollutants so the water is safe to be discharged into the sea.


DESOTEC’s client, who specializes in the treatment of polluted water in remediation and environmental projects, needed to purify water from a huge underground fuel rock cavern, owned and operated by their end client.

The technology at the site has been based on usage of a fixed water bed, on top of which the fuel has been stored.

Before the company could safely discharge the water back into the sea, it had to remove several oil-derived pollutants.

These included: C10 to C40 hydrocarbons, volatile organic compounds (VOCs), methyl tert-butyl ether (MTBE), benzene, and some polycyclic aromatic hydrocarbons (PAHs).

If the polluted water had been discharged untreated, it would have been potentially harmful to living organisms including fish and sea birds.


The client contacted DESOTEC in early 2020 as we had already worked together on other projects.

The situation was not urgent: the water was safely contained in the reservoir. We delivered our MOBICON filter two months later, and the client began ramping up their operations immediately.

The filter is supported by two add-on technologies delivered by the client at the site: an oil-water separator and a sand filter. The separator divides the bulk of the oil and water into two layers, but leaves oily residues in the water. The sand filter prevents DESOTEC’s unit from becoming clogged up. The water is then pumped through the MOBICON filter, where the pollutants are adsorbed by the activated carbon.

Currently, 300 - 600 m³ of water are treated each day, with the process ceasing at night.

Once a filter is saturated, it is exchanged by DESOTEC technicians. The spent carbon is transported back to DESOTEC’s site in Belgium, where it is carefully sampled and analysed, then recycled in one of the reactivation furnaces so that it can be reused. The state-of-the-art flue gas treatment ensures that all contamination is completely destroyed.


The results have been excellent. The PAH levels in the treated water have been reduced to below observational levels, and the VOCs removed completely. Benzene, MTBE and hydrocarbon concentrations are now within the permitted levels.

The customer is happy with the results of the process, which is expected to continue for another few months.

The usage of the cavern continues. In cases like this, in addition to temporary needs, mobile filters can be used as a long-term solution to treat the water. This case demonstrates the versatility of DESOTEC solutions. They can be used to treat very small flows of water right up to extremely large total volumes. In this particular case, the hourly flow rate was quite typical but the aggregate amount was high.

Even DESOTEC engineers are sometimes surprised by the wide range of situations and industries where our filters can be applicable.

Our solutions can also be installed temporarily, or with a view to long-term usage, making them highly adaptable to changing circumstances and requirements.

Contact DESOTEC today

To discuss how DESOTEC’s mobile activated carbon filtration solutions could work for your company or project, contact our team of engineers today.



At DESOTEC’s facilities, all used carbon is analysed so the right measures can be taken for handling and removing the saturated carbon out of the mobile filters. Used carbon which meets DESOTEC's acception criteria can be reactivated.

This means that all molecules that were adsorbed on the activated carbon at the customers’ site are desorbed inside DESOTEC’s reactivation furnaces. These contaminants are then fully destroyed, in accordance with National and European legislationby an incineration and neutralisation setup. The entire installation and its emissions are under continuous online monitoring, which guarantees that only harmless water vapour is seen exiting the chimney.

In case the saturated carbon does not meet our acceptation criteria, it is being sent for specialized external disposal.