Influence of Molecular Structure on the Biodegradability of Naphthenic Acids

Abstract

Large volumes of toxic aqueous tailings containing a complex mixture of naphthenic acids (NAs; CnH2n+ZO2) are produced in northern Alberta by the oil sands industry. Because of their persistence and contribution to toxicity, there is an urgent need to understand the fate of NAs under a variety of remediation scenarios. In a previous study, we developed a highly specific HPLC-high resolution mass spectrometry method for the analysis of NAs. Here we apply this method to determine quantitative structure-persistence relationships and kinetics for commercial NAs and NAs in oil sands process water (OSPW) during aerobic microbial biodegradation. Biodegradation of commercial NAs revealed thatthe mixture contained a substantial labile fraction, which was rapidly biodegraded, and a recalcitrant fraction composed of highly branched compounds. Conversely, NAs in OSPW were predominantly recalcitrant, and degraded slowly by first-order kinetics. Carbon number (n) had little effect on the rate of biodegradation, whereas a general structure-persistence relationship was observed indicating that increased cyclization (Z) decreased the biodegradation rate for NAs in both mixtures. Time to 50% biodegradation ranged from 1 to 8 days among all NAs in the commercial mixture, whereas half-lives for OSPW NAs ranged from 44 to 240 days, likely a result of relatively high alkyl branching among OSPW NAs. It is anticipated that these data will facilitate development of strategic solutions for remediating billions of cubic meters of OSPW stored, or predicted to be generated, in Northern Alberta.

Treatment of oil sands process-affected water using moving bed biofilm reactors: With and without ozone pretreatment

“…2 shows that the removal was greatest for NAs with carbon numbers from 14 to 16 and those with ÀZ numbers from 4 to 6. This is consistent with previous study, which reported that the biodegradation rate of commercial NAs decreased with an increase in the hydrogen deficiency number (Z) and that parent NAs with lower molecular weights and fewer rings are more biodegradable than those with higher molecular weight and more extensive ring formation (Han et al, 2008). Considering the NAs removal efficiency, raw OSPW MBBR (34.8%) and ozonated OSPW MBBR (34.1%) showed no significant, which is similar to the results of AEF removal mentioned above.…”

Electrochemical oxidation of sulfide ion at a Ti/IrO2–Ta2O5 anode in the presence and absence of naphthenic acids

“…Naphthenic acids are complex mixtures of polycyclic aliphatic carboxylic acids that are ubiquitously present in sour brines [26]; they exist as their conjugate bases in solutions above about pH 5. We wished to determine whether the surfactant properties of naphthenate anions would mitigate the deposition of sulfur on the anode surface.…”

Floating Photocatalysts for Passive Solar Degradation of Naphthenic Acids in Oil Sands Process-Affected Water

“…Release of OSPW to the environment is hindered by the toxicity of the water, due primarily to dissolved naphthenic acids (NAs) and other acid extractable organics (AEO) [1,2], and thus an estimated 1 billion m 3 of OSPW to date has been retained in tailings ponds on site. NAs are not fully biodegradable [3,4], and their toxicity persists over decades [5], therefore a water treatment solution may be required to enable OSPW discharge.…”