New from the 1st of April onwards: cradle to cradletracking of millions of tons of dredged soil for high-quality reuse

Grondbank promotes the cradle to cradle recycling of dredged soil in Flanders

From the first of April, soil management organisation Grondbank will track all material dredged from the Flemish rivers and canals in order to ensure its high-quality reuse. Approximately 10 million tons of material is dredged in Flanders every year. Over 60% of this is used by the construction industry in new high-value applications such as the foundation of buildings and stabilisation layers. By applying Grondbank's tracking system, we will be able to further boost the circular economy in our region.

For the past 15 years, Grondbank has been using its system successfully to track the transport of excavated soil. Regulations governing excavated soil are based on the European standstill principle, which safeguards the soil's environmental quality. In this regard, rgular sampling is the key. Thanks to this system, with its clear set of standards, Flanders leads the way in Europe when it comes to transporting excavated soil quickly and safely from one place to another. As a result, the construction industry now reuses over 90% of excavated soil. This system will soon also be applicable to dredged soil, making Grondbank the leading centre of excellence in the high-quality reuse of soil and dredged material, accounting for almost 27 million tons transported in total.

Reuse on the up since 2010

Anyone wishing to reuse dredged material in Flanders is bound by the VLAREMA legislation and must therefore apply for a "raw material declaration" ('grondstofverklaring') from the Flemish public waste agency OVAM. That has been the case for some time. What is new is the vital role that Grondbank will play with its tracing and quality control system designed to streamline and further encourage high-value reuse.

Dredged soil consists of sediment dredged or cleared from navigable and non-navigable waterways. For example, there are companies that reclaim sand from the River Scheldt, a by-product of dredging which is being done in order to keep the river navigable and in order to keep the port of Antwerp accessible. The sludge is dewatered for use as alternative raw material, usually at a sludge or soil recycling centre.

According to the latest data, 10,280,828 tons of material was dredged in Flanders in 2015, of which 6,776,612 tons was used as an alternative raw material, mainly by the building industry. The rest is mostly used to fill pits, quarries, docks and wells. In 2010, 2,170,000 tons was used as alternative raw material. The big increase in the past few years has been due to a triple increase in dredging works. As a result of this trend, the use of primary raw material such as sand for base, drainage and stabilisation layers has decreased substantially. Dredged material can also be used as an alternative to clay in the construction and closure of landfill sites.

Flow diagram showing use of dredged material in Flanders in 2015

Source: MDO Annual Report 2015

Wide range of applications for dredged material

Alongside tried-and-tested applications such as its use as an alternative raw material for base and stabilisation layers, the industry is also exploring new options:

  • Sand from dredging works can be used as a building material for dyke works provided that certain environmental health criteria are met.
  • KU Leuven and VITO are currently running a pilot project to use filter cake (i.e. sludge residue) as a substitute for cement. The technology grinds the filter cake, which is then heated to a high temperature and cooled to produce a glassy substance that reacts with cement, allowing some of the cement to be replaced. This apparently reduces the amount of CO² emitted. Researchers are currently testing the durability of this new building material.
  • In the Netherlands, research is under way into how dried dredging sediment can be used to restore damaged peatlands by mixing it with other local waste materials such as manure and green waste. Trials are taking place with local dairy farmers.
  • In the UK, experts are examining how erosion in ecologically valuable saltmarshes can be stopped by reinforcing natural banks with dredged material.
  • Etc.