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After several years following deposition, oil sands fine tailings settle to a solids content of 30 ~ 40% and are subsequently termed mature fine tailings (MFT).Once they have reached this state, MFT do not appreciably dewater, even after several decades. The particle size and dispersed structure of the fines (and possibly residual bitumen), negatively impacts the consolidation behavior of MFT.Several technologies currently being trialed to accelerate dewatering of MFT, such as in-line flocculation, centrifuge, and tank thickening, flocculate the tailings using a polymer. The addition of polymer results in substantial dewatering in the short term (24 hours) after in-line flocculation, and increases dewatering in tank thickening and centrifugation. This is well understood in industry. However, the polymer may also change longer term dewatering behaviour by potentially changing the consolidation characteristics and water-retention characteristics of the tailings.To assess the effect of polymer on all aspects of dewatering behaviour, column experiments simulating deposition of in-line flocculated tailings were undertaken for different times, different thicknesses, and under different environmental conditions. This allowed for the study to separate initial dewatering from selfweight consolidation, subsequent desiccation, and further consolidation of desiccated tailings when they are buried by fresh deposition. The behaviour was iv analyzed by tracking fabric changes using mercury intrusion porosimetry and scanning electron microscopy.Differences in dewatering behaviour following initial self-weight consolidation due to differences in polymer dose appeared to be minimal. Consolidation behaviour of previously desiccated tailings converged to the same properties by 80 kPa vertical effective stress. Optimizing for dose should therefore be done in terms of self-weight consolidation. It was observed that optimizing for yield stress may yield a higher optimal dose than for dewatering.

A landfill biocover system optimizes environmental conditions for biotic methane (CH4) consumption that controls the fugitive and residual emissions from landfills. Research shows that wasted compost material has more (CH4) oxidation potential than other materials. Thus, in this study, the authors investigate the engineering properties of compacted compost to test its suitability for CH4 oxidation capacity. Different laboratory and analytical approaches are employed to attain the set objectives. The biochemical tests show that the studied material indicates the presence of methanotrophs with sufficient organic contents. The compacted compost also shows adequate diffusivity potential to free air space for a wide range of water content. The data also imply that compacting compost to low hydraulic conductivity can be accomplished for a wide range of water content, according to the suggested values for a landfill hydraulic barrier. Furthermore, the low thermal properties of compost as compared to other mineral materials seem more beneficial, as specifically, during the winter season, when the atmospheric temperature is low, low thermal conductivity enables it to sustain a stable temperature for the activities of the microbial organisms, which therefore extends the CH4 oxidation process right through a long period in the winter.

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