Degradation of naphthenic acids by sediment micro-organisms

Abstract

Aims: Naphthenic acids (NAs) are naturally occurring, linear and cyclic carboxylic surfactants associated with the acidic fraction of petroleum. NAs account for most of the acute aquatic toxicity of oil sands process‐affected water (OSPW). The toxicity of OSPW can be reduced by microbial degradation. The aim of this research was to determine the extent of NA degradation by sediment microbial communities exposed to varying amounts of OSPW. Methods and Results: Eleven wetlands, both natural and process‐affected, and one tailings settling pond in Northern Alberta were studied. The natural wetlands and process‐affected sites fell into two distinct groups based on their water chemistry. The extent of degradation of a 14C‐labelled monocyclic NA surrogate [14C‐cyclohexane carboxylic acid (CCA)] was relatively uniform in all sediments (approximately 30%) after 14 days. In contrast, degradation of a bicyclic NA surrogate [14C‐decahydronaphthoic acid (DHNA)]was significantly lower in non process‐affected sediments. Enrichment cultures, obtained from an active tailings settling pond, using commercially available NAs as the sole carbon source, resulted in the isolation of a co‐culture containing Pseudomonas putida and Pseudomonas fluorescens. Quantitative GC–MS analysis showed that the co‐culture removed >95% of the commercial NAs, and partially degraded the process NAs from OSPW with a resulting NA profile similar to that from ‘aged wetlands’. Conclusions: Exposure to NAs induced and/or selected micro‐organisms capable of more effectively degrading bicyclic NAs. Native Pseudomonas spp. extensively degraded fresh, commercial NA. The recalcitrant NAs resembled those found in process‐affected wetlands. Significance and Impact of the Study: These results suggest that it may be possible to manipulate the existing environmental conditions to select for a microbial community exhibiting higher rates of NA degradation. This will have significant impact on the design of artificial wetlands for water treatment.

Examining the Microbial Degradation of Naphthenic Acids Using Stable Isotope Analysis of Carbon and Nitrogen

“…Using the GC-MS technique to characterize the NAs, Scott et al (2005) showed that commercial NAs, with a greater proportion of lower molecular weight NAs with shorter carbon chains and fewer rings, were more easily degraded than the oil sands derived NAs. Other studies have also documented differences in the makeup of NA (Herman et al 1993;Herman et al 1994;Lai et al 1996;Clemente et al 2004;Del Rio et al 2006). It is possible that only a limited fraction of the NAs within the oil sands derived mixture is readily degraded, whereas the commercial mix may be more broadly metabolized.…”

“…Hall et al (1999) found differences in the δ 13 C values of CO 2 depending on the chemical degraded (phenol vs. benzoate) and the species of microorganism used, but found no change in the δ 13 C values of microbial biomass. While there is information on the rate of biodegradation of various surrogate NAs (Herman et al 1993;Lai et al 1996;Del Rio et al 2006) as well as commercial and oil sands processderived NA mixtures (Herman et al 1994;Clemente et al 2004;Scott et al 2005;Del Rio et al 2006), there has been no tracking of stable isotopes during microbial degradation of NAs.…”

Ozonation of Naphthenic Acids in Water: Kinetic Study

“…The wastewater generated is known as oil sands process-affected water (OSPW). OSPW has demonstrated both acute and chronic toxicity to a number of species (Del Rio et al 2006;Wang et al 2013). The toxicity of OSPW is mainly due to the presence of a group of dissolved organic acids, known as Bnaphthenic acids^(NAs) which refer to a complex suite of alkyl-substituted acyclic and cycloaliphatic carboxylic acids (Clemente et al 2004;Ahad et al 2013).…”

Threshold Considerations and Wetland Reclamation in Alberta's Mineable Oil Sands

“…Though technology is advancing rapidly to store produced water as shallow groundwater in clay and gypsum slurries, thickened tails, and polymer enriched sludges, tailings pond reclamation is an unproven technology. Companies do not yet have a cost-effective way to remediate the volumes of water produced and they may have to store it for decades to centuries (Del Rio et al 2006).…”