Treating contaminated soils and sediments

The centre is an extension of the SEDIMED research programme that started in 2009 and in which Envisan France is the leading partner. The SEDIMED programme aims to lift the administrative and regulatory barriers for allowing recycled sediments to be used in the construction works industry. As part of this programme, Envisan took the lead in the development, design, construction and operation of a treatment centre. Envisan obtained (in 2013) the concession of a site of 3.4 hectares (8.4 acres) in the Port Zone of Brégaillon (La Seyne-sur-Mer) for the next 20 years. After receiving the three necessary permits to be able to construct and to operate the centre, construction started in September 2014 and the centre will become fully operational in mid-2015.

Research and development

The CPEM, which stands for “Centre de Production d’Eco-Materiaux” (production centre of ecomaterials) being part of the SEDIMED programme, contains a surface fully equipped for research and development, including the possibility of full scale testing of several options for the reuse of sediments. Up coming tests for 2015 include reuse for anti-noise pollution barriers (eco-models) and the construction of roads based on sediments and landscaping. During the next few years, other research and development programmes considering the reuse of sediments will also take place.

The mission of the treatment centre CPEM is the valorisation of the incoming wastes, in casu dredged sediments and excavated soils into materials that can be reused after treatment. Based on already existing legislation or the outcome of the SEDIMED programme, different possibilities for reuse, including as construction material, roads, concrete structures, landscaping, anti-noise pollution barriers (eco-models), etc will be developed, some based on the results of the research and development tests, with their specific treatment programme, adapted to the specifications of the soils and sediments in the Mediterranean region.

The site, which can process up to 160.000m³ of material a year, is licenced and equipped to execute several different types of treatment for both soils and sediments, such as lagooning, mechanical dewatering, pre-treatment by granulometric separation, biological treatment and physico-chemical treatment. Added to that, the CPEM is fully covered with a total waterproof concrete floor, so that all treatment or storage can be executed in an environmentally safe way. Furthermore, the presence of a dust-preventing sprinkler system, a wheelwash and a water treatment plant, etc are some more examples of the environmentally-friendly setup of the treatment centre.

The polluted soils or sediments can be delivered to the centre in several ways. For example, polluted soils that are being excavated on a site nearby or sediments dredged from a non-navigable waterway can be loaded directly onto a truck for delivery at the CPEM. On the other hand, larger quantities of dredged sediments in nearby marine ports can be loaded onto a ship or barge for delivery at a quay in the Port Zone of Bregaillon, where it will be unloaded by crane.

Treatment of polluted soils and sediments

After acceptance and extensive control, both organoleptic and based on analysis, the different waste streams can undergo different types of treatment, depending on the properties of the incoming soils or sediments and the linked treatment possibilities. For example, sediments polluted with hydrocarbons can be treated by lagooning followed by biological treatment. On the other hand, soils polluted with heavy metals will be treated by physico-chemical treatment.

Lagooning

A lagoon can be described as a sort of basin in which dredged sediments can dewater through drainage and evaporation. Through the use of special techniques and the specific design of the lagoon, the natural dewatering can be accelerated significantly and efficiently. After reaching a sufficient level of consistency (up to 75% dry matter content), the dewatered sediments can receive further treatment or can directly be reused in one of the above mentioned possibilities

Granulometric separation

Using a hydro cyclone can be a big advantage in case the polluted dredged sediments contain a significant amount of sand particles (usually more than 30 to 40% of sand). Based on the density of the material and the centrifugal powers, the hydro cyclone allows the sand to be separated from the rest of the sediments. As a result, almost all or even all pollution will be captured in the fine sediment parts and the sand can be directly reused or reused after a consecutive small treatment.

Mechanical dewatering

Dredged sediments can be dewatered mechanically in several ways such as filter presses or centrifuges. These techniques are based on the separation of the liquid and the solid part of the sediments. In order to facilitate this separation, the sediments are conditioned with certain type of additives. A dry matter content of 60 to 65% can easily be obtained and if necessary, further treatment of the solid material can be executed in order to enable a possible reuse.

Biological treatment

The goal of biological treatment is the breakdown into CO₂ and H₂O of organic pollutants, such as hydrocarbons, by activating bacteria. The bacteria can be activated by offering them the ideal conditions when it comes to oxygen level, water content and amount of nutrients. Adding the different ingredients can be done in several ways and at different moments in the treatment process. In order to add everything needed as homogeneously as possible, specific machines such as a windrow turner can be used.

Physico-chemical treatment

Soil washing is a mechanical process that uses liquids, usually water or water with additives, to remove chemical pollutants from soils or sediments. These pollutants usually adhere to the surfaces of the silt or clay particles rather than to the sand or gravel particles. By soil washing, the fine and clay particles are separated from the sand and gravel particles and the pollution remains only in those fine parts, while the sand and gravel can be reused.

Water treatment

In order to be able to treat various types of polluted water (rain and surface water, (mechanically) dehydrated (saline) water from sediments, etc), the CPEM has a fully equipped water treatment plant, including a water reservoir, sand filters, lamella separators and active carbon filters. The water treatment plant can treat up to 50m³ an hour and has been designed to realise the treatment of a once in 20 years rain shower. Next to this, the treated water can be reused on site in place of using fresh water, such as usage in the sprinkler system for dust prevention, usage in the wheelwash, etc.

A solution to draught problems

Many ports and harbours are located in southern France, not only large industrial ports, but also a lot of smaller ports dedicated to yachting. For these ports, the CPEM can be an ideal solution for their draught problems, caused by a lack of dredging in the past and the absence of environmentally-friendly solutions for the dredged material afterwards.

Therefore, this centre will become a useful asset not only to the dredging executors but also to the public administrations in search of an economic and environmentally-friendly solution for their polluted sediments. In addition to the sediments, the CPEM can also be a solution for several types of polluted soils, eg soils that are excavated near petrol stations or derived from contaminated sites all over the region.

Going forward

Envisan already has a broad experience for many years in treating polluted soils and sediments in Belgium, but also abroad. Until now, Envisan has been operating four centres in Belgium – Ghent (mixed), Moen (sediments), Brussels (soils) and Mons (soils). A fifth Belgian centre (Liège) is in development right now and will also, as is the case with the CPEM, open in 2015.

The company has also operated a sediment treatment centre in Dunkirk in the North of France for several years and a specialised oil-sludge and soil treatment centre in Pitesti, Romania. Depending on opportunities and the evolution of legislation other treatment centres in other countries may follow.