Valorising polluted soils with minimal ecological footprint
Over the years, various industrial activities have had a huge impact on the environment. Often, after closing down operations, sites were abandoned as they were too polluted for launching new activities such as residential or commercial buildings. Today, people are increasingly drawing the card of revitalising such sites, but the problem remains: what to do with the heavily contaminated soils? Jan De Nul and its daughter companies Envisan and PSR are giving contaminated sites a second lease of life, thanks to a wide range of remediation techniques. In doing so, we always look for innovative and sustainable techniques.
A first example is the use of bio-piles on the site of the former Renault factory in Vilvoorde. The site suffered from severe contamination over a huge surface area. We carefully excavated the contaminated soil, paying great care not to spread the contamination even more. We first extracted the waste using filters and then treated the remaining soil through the action of micro-organisms in covered bio-piles. These break down harmful organic compounds into harmless components. The warm air released by the biological action of the bio-piles then passes through an air purification system. The captured heat is led back to the bio-piles to keep the temperature at an optimum level. In Vilvoorde, for instance, we remediated over 207,000 tonnes of contaminated soil, 95% of which could be reused for backfilling the site. By carrying out all this work on the site itself, we were able to minimise other negative effects, including emissions and unnecessary transports.
More recently, an even more specific contaminant emerged: PFAS, the so-called ‘forever chemicals’. We now know that PFAS affect the environment just about everywhere in the world. In some places, however, contamination is so severe that the risk to humans and nature is too great to ignore. A technique based on soil-washing is considered to be the most efficient and useful method currently available for cleaning PFAS-contaminated soils. Jan De Nul's Research & Development Department has therefore focused on optimising this technique specifically for the remediation of PFAS-containing soils. With success. The technique consists of a series of washing and separation processes. It converts on average more than 80% of the contaminated soil into coarse sand that is free of PFAS. This fraction can also be used in new civil engineering applications. The water is reused in the process, after which it is purified. Jan De Nul is constantly searching for new technologies to achieve even better results and also deploys mobile washing plants to avoid huge transport emissions.
Groundwater treatment plants filter out PFAS
PFAS-contamination does not only occur in soils, groundwater also often contains (too) high concentrations. If a dewatering operation takes place, the pumped-up groundwater must be purified. To this end, Envisan developed a purification process in which PFAS can be filtered out of the water to values below the detection limit. Currently, Envisan has more than 10 mobile water purification units to extract PFAS from groundwater.