Assessing the bioremediation potential of algal species indigenous to oil sands process-affected waters on mixtures of oil sands acid extractable organics

Phytoplankton ecology in the early years of a boreal oil sands end pit lake

BACKGROUND

Base Mine Lake (BML) is the first full-scale end pit lake for the oil sands mining industry in Canada. BML sequesters oil sands tailings under a freshwater cap and is intended to develop into a functional ecosystem that can be integrated into the local watershed. The first stage of successful reclamation requires the development of a phytoplankton community supporting a typical boreal lake food web. To assess the diversity and dynamics of the phytoplankton community in BML at this reclamation stage and to set a baseline for future monitoring, we examined the phytoplankton community in BML from 2016 through 2021 using molecular methods (targeting the 23S, 18S, and 16S rRNA genes) and microscopic methods. Nearby water bodies were used as controls for a freshwater environment and an active tailings pond.

RESULTS

The phytoplankton community was made up of diverse bacteria and eukaryotes typical of a boreal lake. Microscopy and molecular data both identified a phytoplankton community comparable at the phylum level to that of natural boreal lakes, dominated by Chlorophyta, Cryptophyta, and Cyanophyta, with some Bacillariophyta, Ochrophyta, and Euglenophyta. Although many of the same genera were prominent in both BML and the control freshwater reservoir, there were differences at the species or ASV level. Total diversity in BML was also consistently lower than the control freshwater site, but consistently higher than the control tailings pond. The phytoplankton community composition in BML changed over the 5-year study period. Some taxa present in 2016-2019 (e.g., Choricystis) were no longer detected in 2021, while some dinophytes and haptophytes became detectable in small quantities starting in 2019-2021. Different quantification methods (qPCR analysis of 23S rRNA genes, and microscopic estimates of populations and total biomass) did not show a consistent directional trend in total phytoplankton over the 5-year study, nor was there any consistent increase in phytoplankton species diversity. The 5-year period was likely an insufficient time frame for detecting community trends, as phytoplankton communities are highly variable at the genus and species level.

CONCLUSIONS

BML supports a phytoplankton community composition somewhat unique from control sites (active tailings and freshwater lake) and is still changing over time. However, the most abundant genera are typical of natural boreal lakes and have the potential to support a complex aquatic food web, with many of its identified major phytoplankton constituents known to be primary producers in boreal lake environments.

Abiotic and biotic constituents of oil sands process-affected waters

The oil sands in Northern Alberta are the largest oil sands in the world, providing an important economic resource for the Canadian energy industry. The extraction of petroleum in the oil sands begins with the addition of hot water to the bituminous sediment, generating oil sands process-affected water (OSPW), which is acutely toxic to organisms. Trillions of litres of OSPW are stored on oil sands mining leased sites in man-made reservoirs called tailings ponds. As the volume of OSPW increases, concerns arise regarding the reclamation and eventual release of this water back into the environment. OSPW is composed of a complex and heterogeneous mix of components that vary based on factors such as company extraction techniques, age of the water, location, and bitumen ore quality. Therefore, the effective remediation of OSPW requires the consideration of abiotic and biotic constituents within it to understand short and long term effects of treatments used. This review summarizes selected chemicals and organisms in these waters and their interactions to provide a holistic perspective on the physiochemical and microbial dynamics underpinning OSPW .

Model naphthenic acids removal by microalgae and Base Mine Lake cap water microbial inoculum

Naphthenic acids (NAs) originate from bitumen and are considered a major contributor to acute toxicity in oil sands process-affected water (OSPW) produced from bitumen extraction processes. To reclaim oil sands tailings and remediate OSPW, in-pit fluid fine tailings can be water-capped as end pit lakes (EPL). Addressing NAs present in OSPW, either through removal, dilution or degradation, is an objective for oil sands reclamation. EPLs can remediate NAs through degradation or dilution or both. To assess and understand degradation potential, Chlorella kessleri and Botryococcus braunii were tested for their tolerance to, and ability to biodegrade, three model NAs (cyclohexanecarboxylic acid, cyclohexaneacetic acid, and cyclohexanebutyric acid). Water sourced from the industry's first EPL, the Base Mine Lake (BML), was used alone as an inoculum or co-cultured with C. kessleri to biodegrade cyclohexanecarboxylic acid and cyclohexanebutyric acid. All cultures metabolized the model compounds via β-oxidation. Biodegradation by the co-culture of C. kessleri and BML inoculum was most effective and rapid: the cyclohexaneacetic acid generated from cyclohexanebutyric acid could be further degraded by the co-culture, while the cyclohexaneacetic acid generated could not be consumed by pure algal cultures or BML inoculum alone. Adding C. kessleri greatly increased the diversity of the microbial community in the BML inoculum; many known hydrocarbon and NA degraders were identified from the 16S rRNA gene sequencing from this co-culture. This more diverse microbial community could have potential for EPL remediation.

Method for routine "naphthenic acids fraction compounds" determination in oil sands process-affected water by liquid-liquid extraction in dichloromethane and Fourier-Transform Infrared Spectroscopy

Formerly classified as naphthenic acids, "naphthenic acids fraction compounds" (NAFC) have become the subject of increasing research, in particular in view of their ubiquitous presence in the Canadian oil sands of Northern Alberta and oil sands process-affected waters (OSPW). NAFC, defined herein as the polar acid-extractable organics fraction of OSPW extractable in dichloromethane, are released into OSPW during the aqueous extraction of oil sands. A method for determining total NAFC concentration based on acidification, liquid-liquid extraction, and Fourier-Transform Infrared Spectroscopy (FT-IR) was developed by Jivraj et al. in 1995. It has become widely used in the oil sands industry for routine monitoring of NAFC. Since then, multiple variations of the method are practiced by different laboratories using different calibration materials and different extraction solvents, differences which were found to affect the results by as much as 38 and 64 percent respectively. The goal of this study was to establish a robust method for routinely quantifying NAFC that does not require complex and expensive laboratory equipment such as mass spectrometers. Described improvements include a semi-automated rolling extraction and the use of a vacuum evaporator unit to reduce the method's environmental impact. The improved FT-IR method avoids emulsions, is precise, provides good agreement with gravimetric determinations of NAFC, increases sample throughput, is inexpensive compared to MS methods, and offers a typical reporting limit of 0.1 mg kg^-1. The residue recovered by this method with minimal losses can be further analyzed by MS techniques to characterize and identify individual NAFC components if desired.

Microbial Eukaryotes in Oil Sands Environments: Heterotrophs in the Spotlight

Hydrocarbon extraction and exploitation is a global, trillion-dollar industry. However, for decades it has also been known that fossil fuel usage is environmentally detrimental; the burning of hydrocarbons results in climate change, and environmental damage during extraction and transport can also occur. Substantial global efforts into mitigating this environmental disruption are underway. The global petroleum industry is moving more and more into exploiting unconventional oil reserves, such as oil sands and shale oil. The Albertan oil sands are one example of unconventional oil reserves; this mixture of sand and heavy bitumen lying under the boreal forest of Northern Alberta represent one of the world’s largest hydrocarbon reserves, but extraction also requires the disturbance of a delicate northern ecosystem. Considerable effort is being made by various stakeholders to mitigate environmental impact and reclaim anthropogenically disturbed environments associated with oil sand extraction. In this review, we discuss the eukaryotic microbial communities associated with the boreal ecosystem and how this is affected by hydrocarbon extraction, with a particular emphasis on the reclamation of tailings ponds, where oil sands extraction waste is stored. Microbial eukaryotes, or protists, are an essential part of every global ecosystem, but our understanding of how they affect reclamation is limited due to our fledgling understanding of these organisms in anthropogenically hydrocarbon-associated environments and the difficulties of studying them. We advocate for an environmental DNA sequencing-based approach to determine the microbial communities of oil sands associated environments, and the importance of studying the heterotrophic components of these environments to gain a full understanding of how these environments operate and thus how they can be integrated with the natural watersheds of the region.

Bioreactors for oil sands process-affected water (OSPW) treatment: A critical review

Canada has the world's largest oil sands reservoirs. Surface mining and subsequent caustic hot water extraction of bitumen lead to an enormous quantity of tailings (volumetric ratio bitumen:water=9:1). Due to the zero-discharge approach and the persistency of the complex matrix, oil producers are storing oil sands tailings in vast ponds in Northern Alberta. Oil sands tailings are comprised of sand, clay and process-affected water (OSPW). OSPW contains an extremely complex matrix of organic contaminants (e.g., naphthenic acids (NAs), residual bitumen, and polycyclic aromatic hydrocarbons (PAHs)), which has proven to be toxic to a variety of aquatic species. Biodegradation, among a variety of examined methods, is believed to be one of the most cost effective and practical to treat OSPW. A number of studies have been published on the removal of oil sands related contaminants using biodegradation-based practices. This review focuses on the treatment of OSPW using various bioreactors, comparing bioreactor configurations, operating conditions, performance evaluation and microbial community dynamics. Effort is made to identify the governing biotic and abiotic factors in engineered biological systems receiving OSPW. Generally, biofilms and elevated suspended biomass are beneficial to the resilience and degradation performance of a bioreactor. The review therefore suggests that a hybridization of biofilms and membrane technology (to ensure higher suspended microbial biomass) is a more promising option to remove OSPW organic constituents.

Biological filters and their use in potable water filtration systems in spaceflight conditions

Providing drinking water to space missions such as the International Space Station (ISS) is a costly requirement for human habitation. To limit the costs of water transport, wastewater is collected and purified using a variety of physical and chemical means. To date, sand-based biofilters have been designed to function against gravity, and biofilms have been shown to form in microgravity conditions. Development of a universal silver-recycling biological filter system that is able to function in both microgravity and full gravity conditions would reduce the costs incurred in removing organic contaminants from wastewater by limiting the energy and chemical inputs required. This paper aims to propose the use of a sand-substrate biofilter to replace chemical means of water purification on manned spaceflights.