Naphthenic Acid Degradation by Pseudomonas spp. in lab-scale Bioreactors

Abstract

Naphthenic Acid Degradation by Pseudomonas spp. in lab-scale Bioreactors

The increased exploitation of oil sands deposits has led to vast amounts of toxic oil sands process waters (OSPW) being produced which have to be stored in large tailings ponds until their toxicity is reduced. The toxicity of OSPW is partly attributed to a complex mixture of organic acids known as naphthenic acids (NAs). One cost-effective approach for NA removal in OSPW is to use microorganisms in bioreactors for NA bioremediation. Here, gas-chromatography and mass spectrometry (GC-MS) was used to determine the NA degradation capabilities of two Pseudomonas spp: Pseudomonas fluorescens Pf-5 and Pseudomonas putida F1. Individual cultures of these organisms were inoculated into serum bottles which contained 30 mL of minimal salts medium. In addition, 5 litre-scale continuous culture bioreactors were also set up. Cultures in both the bottles and bioreactors were incubated with either: cyclohexanepentanoic acid (CHPA) (10 mg L-1) or 5-bromo-3-ethyl-adamantane-1-carboxylic acid (BEA) (10 mg L-1) (a model recalcitrant diamondoid NA compound). In the bottle experiments, both Pseudomonads readily degraded CHPA, by up to 53% (± 11.2% SE) after 7 days and the production of a metabolite was observed by day 3. However, in the bioreactors, P. fluorescens Pf-5 degraded >97% of CHPA after 26 days. P. putida F1 and P. fluorescens Pf-5 were also shown to degrade the model NA compound BEA by 28.2% (± 9.4% SE) and 5.6% (± 5.08% SE) respectively after 7 days. In conclusion, Pseudomonas spp. readily degraded CHPA and NA compounds. We also showed that lab-scale bioreactors were effective in the removal of recalcitrant NAs with the potential for scale-up for high-throughput removal of NAs in OSPW. Future work will investigate the use of co-cultures in larger-scale bioreactors as an alternative approach to current technologies for the rapid removal of toxic, recalcitrant NAs in OSPW and other NA contaminated waste.