Study: Faster reuse of dredged sediment and mine tailings using worms
Oligochaete worms can substantially speed up the reuse of both dredged sediment and contaminated mine tailings. Researchers from Deltares, with the support from the University of Alberta, Queen Mary University of London and NAIT (polytechnic and applied research institute) have determined this in laboratory tests. In the Netherlands, this nature-based technology is promising for the circular reuse of dredged material, while in Canada the mining industry is interested particularly for mine sites closure.
The fact that the small worms accelerate the dewatering of sediment with their bustle and appetite was already known and tested in for example water treatment plants. But now the Dutch, Canadians and British have designed the conditions under which these worms will continue to live in (oil sands) mine tailings. At this moment we still talk about laboratory tests, but the first results have positioned this technology as a promising alternative to traditional sediment management, both technically and financially. This technology reduces the storage volume, speeds up dewatering, enhances strength development, and reduces the use of chemical water treatment.
Worms must eat also
What turned out to be the last hurdle was that the worms in the trial did not live long enough in oil sands because not all the nutrients they needed were present. Because soil compaction by worms takes at least a few months, worms needs to survive at least as long, as well as be able to reproduce. Miguel de Lucas Pardo says that survival and reproduction has now been solved; we can give them an environment where organic matter degrades, and that is all they need to be happy. Now the way is open to application outside the lab.
We have agreed with our Canadian partners to scale-up this early next year. We will do this in a facility of NAIT (Canadian Institute for Polytechnic Applied Research). The Canadians have been doing research on nature-based methods for the treatment of mine tailings for a long time. By example using plants that consolidate mine waste (i.e. tailings) with their roots. De Lucas; ‘We want to find out together if a combination of worms and vegetation might work even better. Anticipating on plants to deliver necessary snacks for the worms might be a good combination.’
The interest of the Canadians in Deltares’ research is related to the sustainable closure of their oil sands mines. What is left behind is tailings, a wet substance made up of sand, clay, residual bitumen and water, for which of course there are strict regulations for storage and processing. One of those requirements regards the time in which tailings can be made solid again. The Canadians therefore expect the worms to speed this process up with minimal artificial interventions.
Research with oligochaete worms in lab
Back to the Netherlands
In the Netherlands we are also dealing with very fluid sediment that is dredged from for example ports and waterways, also subjected to long reclamation times. To be able to reuse this material first it has to be dewatered. In a small country like the Netherlands, space is scarce. The sooner the sediment can be reused, the better. Dry and sturdy dredging material can, for example, be used for land reclamation (such as Marker Wadden) or dyke reinforcement. Using this sediment as a circular material is beneficiary. But the dewatering takes a long time and the material often does not become strong enough for other applications. The work of the worms is also promising for this. But the challenges for this are different. Dredged sediment contains a lot of organic material making it possible for the worms to stay on top instead of moving up and down. De Lucas however already knows that for some applications (like dike heightening) the range of movement of 10 cm can potentially be enough, when combined with a layered sediment deposition strategy.
Baggerspecie depot, bron Beeldenbank RWS
Saving energy and nature friendly
Using worms is also a nature-friendly solution to this problem. This method also has a positive effect on CO2 emissions because the methods that are now being used all cost energy (pumping, conveyor belts, mixing, etc). The worms do their work solely on available nutrients.
The tests with the plants and worms in Canada will take place at the beginning of 2020. The field trial needs to be agreed upon later that year.