Development of A Microbial Electrochemical Biosensor for Detection of Oil Sands Naphthenic Acids

Abstract

With a large number of oil deposits in Canada, Alberta oil sands industries are currently conducting bitumen extraction processes using hot water. In oil sands process water (OSPW) from these oil sands operations, naphthenic acids (NAs) are identified as one of the primary sources of acute toxicity and were assessed for their endocrine-disrupting potentials. Hence, the monitoring of NAs in aqueous environmental matrices is crucial for oil sands-related industries. Commonly used analytical methods for NAs, such as Fourier transform infrared spectroscopy and high-performance liquid chromatography, are time-consuming, expensive, and samples must be sent to an analytical lab for analysis. Therefore, this study aims to develop a microbial electrochemical biosensor (MXC) for the detection of NAs in water samples. First, experiments were conducted to develop an optimal calibration method for the MXC biosensor by comparing different approaches (closed-circuit operation vs. charging-discharging operation) using a single model NA compound (cyclohexane carboxylic acid). The charging-discharging operation significantly increased the peak currents by 90-124 folds higher than that observed for closed-circuit operation. Besides, a strong linear relationship between model NA concentrations and the peak currents (R2 = 0.96) was observed. Second, experiments were conducted to evaluate the impact of different environmental parameters on biosensor performance. The results revealed that this MXC biosensor would be sensitive to salinity levels and temperature changes; however, once calibrated, it can be used for measurement of NA concentrations. The method was further validated with a complex model NA compound (mixtures of alkylated cyclopentane carboxylic acid, CNA). Interestingly, enriching the anode biofilm with salt content (1500 mg/L) significantly reduced the performance of the MXC biosensor applied for CNA detection. Furthermore, the presence of other organics, such as polycyclic aromatic hydrocarbons (e.g., 2-methylnaphalene and pyrene) in OSPW, can greatly interfere with the current output produced by CNA. However, still a linear relationship has been observed between CNA concentrations and current from the MXC biosensor. Overall, the results of this study demonstrated that with further development, MXC biosensors could be used as a simple bioanalytical tool for monitoring NA concentrations in OSPW.