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

Naphthenic acids (NAs) are considered the biggest contributor to the acute toxicity in the oil sands waste produced from bitumen extraction processes. To reclaim and remediate the tailings and oil sands process-affected water, oil sands end pit lakes (EPL) have been proposed and constructed. NA removal is inevitably a challenge for the EPL, a water-capped tailings reclamation method. Chlorella kessleriand Botryococcus brauniiwere tested for their tolerance to and biodegradation ability of three model NAs (cyclohexanecarboxylic acid, cyclohexaneacetic acid and, cyclohexanebutyric acid). BML cap water was also used as inoculum alone or co-cultured with C. kesslerito biodegrade cyclohexanecarboxylic acid and cyclohexanebutyric acid. All tested cultures metabolized the model compounds via β-oxidation. The co-culture of C. kessleriand BML cap water inoculum achieved a more effective and rapid degradation: the generated cyclohexaneacetic acid from cyclohexanebutyric acid could be further completely degraded by the co-culture, while the generated cyclohexaneacetic acid could not be consumed by pure algal cultures or BML cap water inoculum alone. C. kessleriaddition greatly made the microbial community in the BML cap water more diverse: many known hydrocarbon and NA degraders were identified from the 16S rRNA gene sequencing. This more diverse microbial community can also have more potential for remediation in an EPL context.