Effect of aquatic worms and straw amendments on the geotechnical and biogeochemical properties of oil sands tailings

Aquatic Oliogochaete worms ( Lumbriculus variegatus) combined with straw led to improved geotechnical properties of fluid fine tailings (FFT) and thickened tailings (TT) in large-scale column studies. Gravity settling caused 19.9% and 20.6% consolidation of FFT and TT over 125 and 127 days, while the addition of straw and worms increased consolidation to 22.0%–24.3% for FFT and 28.1%–28.9% for TT. Solids content and yield stress were up to 1.1x and 6.6x higher in straw and worm columns, with greatest improvements seen in the top tailings layers where worm tunnels were visually observed. Surviving worms were only found in one column, suggesting the worms provide benefits extending past their depth of penetration and lifespan. The addition of straw stimulated methanogenic activity, decreasing pH, increasing alkalinity, and creating strictly anaerobic conditions (−300 mV), which may have impacted the survivability of the worms but provided another bioconsolidation pathway.