R&D highlights edition 2018

PROJECTS Ecosystems and environmental quality 50 I n collaboration with the University of Alberta and the Institute for Oil Sands Innovation (IOSI), Deltares is investigating whether Tubifex (endemic aquatic worms) can be used to improve the densification properties of these tailings in addition to, or as a substitute for, chemical flocculants. This innovative approach, which is inspired by the fauna-sediment interaction observed in natural lakes, introduces a nature-basedmethod for the first time in this industry to support the sustainable reclamation of tailings basins. Tubifex is a meio-benthic species of aquatic worm about 1 cm long and 0.5 mm thick. While moving through the sediment to feed, Tubifex worms create a network of channels that facilitate dewatering and also appear to change the structure of the soil, making it stronger. Densification with Tubifex was evaluated in a series of laboratory experiments that included settling columns, falling head tests and geotechnical characterisation. Settling columns measure the lowering of the mudline (in other words, the interface between the water and the bed) over time as tailings densify, providing information about how fast dewatering is taking place. Falling head tests measure the permeability of the bed directly. Finally, a number of geotechnical parameters such as Atterberg limits and density profiles were obtained. Basically, Tubifex were added to a number of columns, which were compared with columns with no Tubifex. The experiments were carried out on two types of oil-sand tailings: Fluid Fine Tailings (FFT) and Thickened Tailings (TT). The results to date have been spectacular. The initial solids content (SC) before the experiment was 29% for FFT and 43% for TT. The final SC after the experiment with Tubifex was 37% for FFT and 63% for TT, and 32%and 51% respectively without Tubifex. This means that Tubifex enhanced the densification of the tailings by 40–60 % during the three months of the experiment. These results provide the oil-sand industry with concrete nature-based technology to improve tailings densification in a sustainable, nature-based way. This knowledge and technology could be applied to other engineering solutions that rely on the densification of sediment such as nature-based land reclamation, flood defences or the remediation of sediment sites. The technology could perhaps also be used in ongoing Building with Nature pilot projects in the Netherlands such as the Marker Wadden or Clay Ripening. This study will continue with larger-scale column tests at the University of Alberta in 2018 and the programme may go forward in 2019 and beyond with an in-depth investigation of the micro-structural modification of the soil structure induced by Tubifex; coupling Tubifex with vegetation to further improve nature-based densification; and field-scale pilots to demonstrate feasibility at the operational scale. Contact: Miguel de Lucas Pardo, Miguel.deLucasPardo@deltares.nl , t +31 (0)6 1582 1880 Jill Hanssen, jill.hanssen@deltares.nl , t +31 (0)6 4691 4592 Luca Sittoni, luca.sittoni@deltares.nl , t +31 (0)6 4280 8578 Further reading: Yang et al. (2016), Addition of Tubifex accelerates dewatering of oil sands tailings, Canadian Journal of Civil Engineering Millions of cubic metres of fluid mud, a by-product of mining activities, are stored in large containing facilities or tailings (in other words, residue) basins in Northern Alberta. Mines are required to reclaim these basins and return them to nature as part of their operational life cycle. The densification (by dewatering or consolidation) of these tailings is limited and very slow. The industry uses large quantities of expensive and highly toxic chemical flocculants to speed up the process. Visual impression of bed thickness with (W) and without Tubifex augmentation at the beginning and end of the experiment p Experimental set-up of columns t Tubifex worms TUBIFEX WORMS IMPROVE DENSIFICATION RATES AND THE STRENGTHENING OF SOFT SEDIMENTS AND MINE TAILINGS