Investigation of microalgal tolerance and growth in simulated tailings pond water containing naphthenic acids

Abstract Oil sands tailings ponds, such as those in northeastern Alberta, present environmental challenges due to slow sedimentation, water entrapment, and toxic naphthenic acids (NAs), which hinder water reclamation. This study assessed the tolerance and biodegradation potential of Chlorella vulgaris ( C. vulgaris ) and Parachlorella kessleri ( P. kessleri ) against three model NAs (Fluorene‐1‐carboxylic acid [F‐1], Trans‐4‐pentylcyclohexane carboxylic acid [T‐4], and Cyclohexane carboxylic acid [Cyclo]) under simulated tailings pond conditions. Microalgal growth was evaluated in Bold's Basal Medium at sodium chloride concentrations of 1.5, 2.2, and 4.5 g/L and NA concentrations of 40 and 130 mg/L, with biomass productivity, specific growth rate, and chemical oxygen demand (COD) measured. Both species tolerated salinity up to 4.5 g/L, though P. kessleri exhibited delayed growth at higher sodium chloride levels, while C. vulgaris maintained stable productivity. At 40 and 130 mg/L NA concentrations, C. vulgaris grew consistently across all NA types, with evidence of T‐4 biodegradation indicated by a 16% COD reduction. P. kessleri showed variable responses, with T‐4 enhancing biomass productivity by 70.3%, but it failed to grow heterotrophically on NAs without light. The increased NA concentration did not inhibit growth. C. vulgaris demonstrated greater adaptability and partial NA biodegradation potential, particularly for T‐4, while P. kessleri exhibited tolerance but limited degradation capacity. However, the persistence of natural NAs suggests that microalgae alone may not be sufficient for effective remediation, highlighting the need for integration with microbial consortia to enhance treatment efficiency.