Physical and chemical laboratory: understanding fine sediment better
The physical and chemical laboratory was established more than forty years ago. During that time, a number of leading scientists from the fine sediment world have made their mark on the applied research which Deltares is doing here. We have sought, and continue to seek, answers for our clients to questions such as how sediment behaves when it is suspended in water or moves during transportation in the context of industrial activities. We supply our clients with that knowledge, and our tools, to help them address their current challenges and issues in the world of fine sediments.
They include questions such as how to process dredged material and store fines. Or how to process mining waste. And in general: how our clients can manage fine sediment so as not to harm fragile waterways, shorelines and unique coral reefs. Another challenge for clients is to prevent problems that disrupt society such as dam breaches and floods, when very fine sediment is released from the soil.
There is not enough room for the storage of dredged material
Questions of this kind are a factor in major ports in Europe such as Rotterdam, Antwerp and Hamburg, as well as elsewhere in the world. For example, deeper channels have to be dredged to accommodate ever-larger vessels. This dredging work, which can result in channels as deep as five or six metres, releases a lot of extra fine sediment. Nearly 200 million cubic metres a year, in Europe alone, has to be deposited on land. That’s like filling a medium-sized town with freshly dredged material up to a depth of two metres.
These sediments generally have a high water content: particularly after dredging, they are very watery. So, areas where dredged material is stored are effectively covered with a liquid, making them unsuitable for other activities such as building work.
Dumping this sediment in the oceans is now banned: it kills the flora and fauna in the water, for example when it bonds to the vegetation. So it must be deposited on land. Land that is scarce in the Netherlands and Europe. And where it takes as much as two to three years before - after drying in the sun and being complemented with mud - it is finally transformed into a kind of clay that we can reuse for construction projects and infrastructure.
Can you accelerate dredging processes? And save storage space?
In the physical and chemical laboratory, we help our clients, including dredging and mining companies, to establish a clearer picture of the biological properties of sediment and how those properties play a role during dredging, transport, storage and the process of being dried to produce a useful end product. For example, how many years does it take for sediment to dry? When can they use the land again? And the million-dollar question: can that process be accelerated?
Our lab and field research provides answers. We advise about the strategy needed, for instance, to dredge responsibly. One example came from a dredging company that wants to dredge near a coast where there are coral reefs. That could result in contamination which could threaten the coral, but not necessarily. In this case, we are looking at the type of sediment in the area and how fast it moves or settles. The results of that research will help the company to substantiate its claim, or to decide not to proceed.
Another typical example of applied Deltares research inside and outside the lab is the acceleration of sediment processing. Six kilogrammes of worms were added to a tank the size of a swimming pool containing twelve cubic metres of mud. In that way, we investigate on a larger scale whether sediment can be processed faster. Initial projections indicate that the process can be speeded up by a factor of five to six if you let it dry exclusively in the sun. One benefit is that the company will save on lease costs for the land. The benefit for society is that less valuable space is used.
The responsible storage of dredged material is an issue throughout the world
Mining companies around the world, as in Latin America, Australia and Canada, come up against issues similar to those that concern dredging companies. They also have to store and process mining waste safely and responsibly. The difference is that mining waste does not come from the seabed or from channels, but from mining activities. A dam breach or flooding can be disastrous and disrupt society. As in the case of a dam breach in Brazil: that failure released thousands of cubic metres of sediment into rivers, with numerous fatalities and the devastation of cities as a result.
TECHNICAL FACTS AND FIGURES
- Clients who turn to the physical and chemical laboratory include organisations with national and international operations: dredging companies, mining companies and government organisations, particularly in developing countries, who want to protect their coastlines from the effects of fine sediment. Or who actually want to know if it is possible to build, for instance, hydraulic systems on that coast.
- The physical and chemical laboratory has all the instruments required to conduct measurements, and it adapts existing instruments and adds new ones to its toolbox. The researchers use new research methods. The lab can study almost everything imaginable in the field of fine sediment and the determination of the biological characteristics of waterbed materials, soil-water mixtures, industrial slurries and ores.
- Studies conducted with the measurement instruments from this lab and the results obtained are published regularly in peer-reviewed articles.
- The physical and chemical lab and the geochemical and microbiological lab work together closely and that collaboration will be even more intensive from 2023 onwards when the latter lab moves from Utrecht to Delft. This will provide clients with an integrated view of the research needed and possible solutions.
- Deltares - working with leading universities - develops broad knowledge and offers practical solutions for industrial areas.
- Behaviour of dredging plumes and their associated impact on the environment
- Stability of freshly-deposited dredged sediment
- Storage of industrial slurries
- Land reclamation and the associated soil consolidation
- De-stabilisation of dispersed industrial waste
- Transport of industrial slurries
- Land reclamation with muddy sediments
- Mechanisms to avoid segregation and improve consolidation
- Siltation rates in ports
- Erodibility of soft soil after the execution of civil engineering projects
- Hyper-turbid systems and algal blooms
Examples of science and research in frequent collaboration with universities:
- Study of the settling cycle of sediments. Settling characteristics and rates based on a thorough understanding of sediment and environment characteristics.
- Study of sediment consolidation. Consolidation rates and final strength based on the understanding of the sediment characteristics.
- Bed strength and sediment re-suspension. Development of a conceptual framework for the shear-flow erosion of cohesive sediments.
- Stability and aggregation of colloidal suspensions, with a focus on the consequences for the physical processes to which these colloids may contribute (all those mentioned above).
The measurement facilities are available for:
- Particle size distribution of granular materials ranging from 5 nm up to 64 mm
- Zeta potential of particles (characteristic surface charge of clay particles)
- Rheological instruments to measure the viscosity and shear stress of slurries
- Sedimentation and consolidation characteristics of soil samples
- Seepage-induced consolidation
- Tensiometer for capillary suction of non-saturated granular materials
- Turbidity of water samples
- pH, Redox potential and dissolved oxygen
- oil/water interface processes, either physical or physiobiological