Biofilms for Turbidity Mitigation in Oil Sands End Pit Lakes

Abstract

End pit lakes (EPLs) have been proposed as a method of reclaiming oil sands fluid fine tailings (FFT), which consist primarily of process-affected water and clay- and silt-sized particles. Base Mine Lake (BML) is the first full-scale demonstration EPL and contains thick deposits of FFT capped with water. Because of the fine-grained nature of FFT, turbidity generation and mitigation in BML are issues that may be detrimental to the development of an aquatic ecosystem in the water cap. Laboratory mixing experiments were conducted to investigate the effect of mudline biofilms made up of microbial communities indigenous to FFT on mitigating turbidity in EPLs. Four mixing speeds were tested (80, 120, 160, and 200 rpm), all of which are above the threshold velocity required to initiate erosion of FFT in BML. These mixing speeds were selected to evaluate (i) the effectiveness of biofilms in mitigating turbidity and (ii) the mixing speed required to ‘break’ the biofilms. The impact of biofilm age (10 weeks versus 20 weeks old) on turbidity mitigation was also evaluated. Diverse microbial communities in the biofilms included photoautotrophs, namely cyanobacteria and Chlorophyta (green algae), as well as a number of heterotrophs such as Gammaproteobacteria, Desulfobulbia, and Anaerolineae. Biofilms reduced surface water turbidity by up to 99%, depending on the biofilm age and mixing speed. Lifting and layering in the older biofilms resulted in weaker attachment to the FFT; as such, younger biofilms performed better than older biofilms. However, older biofilms still reduced turbidity by 69% to 95%, depending on the mixing speed. These results indicate that biostabilization is a promising mechanism for turbidity mitigation in EPLs.

Anaerobic Microbial Activity May Affect Development and Sustainability of End-Pit Lakes: A Laboratory Study of Biogeochemical Aspects of Oil Sands Mine Tailings

“…The controlled experimental conditions permitted periodical sampling and monitoring of FFT while removing the impact of other potentially confounding in situ factors on mudline disturbance and measurements of chemical flux. Using columns sealed under dark, anaerobic conditions also (1) prevented aerobic oxidation of produced CH 4 (which has been observed and measured in situ in the water cap), thereby permitting capture and measurement of total CH 4 ebullition; (2) uncoupled the physical effects of in situ wind and wave disturbance of the mudline from microbiological effects; (3) removed any effects of photosynthesis on water cap chemistry; (4) prevented dilution of the water cap by atmospheric precipitation, thereby enabling chemical flux calculations resulting from microbial activity; and (5) introduced temperature as a factor that might influence solute flux due to microbial activities. Furthermore, introducing hydrocarbon amendment as the independent variable in otherwise duplicate columns highlighted the role of labile substrates in chemical flux.…”

“…However, several key issues with EPLs need investigation to understand their environmental implications. , The first full-scale demonstration of EPL (∼8 km 2 surface area) was commissioned in 2013 after FFT was transferred from the active Mildred Lake Settling Basin (tailings pond) into the closed West In-Pit mine site to create Base Mine Lake (BML) as a potential FFT reclamation strategy . Since then, several aspects of BML development and progression into environmentally functional aquatic ecosystem have been under investigation, particularly in the cap water zone of BML, at the laboratory and full scale including dissolved oxygen consumption in response to biogeochemical changes; alum addition , and role of biofilms and carbonate mineral dissolution in turbidity reduction; , wind action effects on physical processes (mixing, oxygenation, and turbidity); nitrogen cycling; and the effect of chemical fractions on fish reproduction . The sustainability of these ecological processes in cap water is strongly influenced by cap water chemistry which, in turn, is linked to FFT porewater chemistry via advective and diffusive chemical flux from FFT to cap water; the latter process will dominate as FFT settlement slows with time. ,, While investigating the effect of cap water chemistry on ecological processes, it is important to understand the driving forces so as to predict longevity of chemical flux/partitioning and project EPL evolution to a functional aquatic ecosystem.…”

Biofilm-Enhanced Natural Zeolite Material in Purification Performance for Slaughterhouse Wastewater

“…Comparable successes in utilizing biofilm for reducing turbidity have also been documented in existing literature. For instance, Cossey et al [52] conducted a study on the use of biofilms to reduce turbidity in end pit lakes associated with oil sands. They were able to achieve a removal efficiency of up to 95%.…”

Closing pit lakes as aquatic ecosystems: Risk, reality, and future uses

“…Base Mine Lake, a former oil sand pit lake, has been used to test the storage of fluid fine tailings (FFTs) under a 10 m-deep freshwater cap (Tedford et al, 2019). The FFT has settled despite dimixis, and the development of sediment biofilms may reduce turbidity caused by lake mixing (Cossey et al, 2021). Toxicity of the FFT is expected to decline to safe levels allowing these lakes to be permanently closed (but see Brown & Ulrich, 2015).…”