Chemical and Biological Oxidation of Naphthenic Acids - where Stoichiometry, Kinetics and Thermodynamics Meet

• Author / Creator

  Mahour,Reza

• Open-pit mining of Alberta’s oil sands deposits heavily depend on freshwater for the extraction of bitumen. It leaves 1.25 m3 oil sands process affected water (OSPW) per barrel of produced oil. In spite of years of research on treatment of OSPW, currently, there are no approved economic and environmental friendly strategies for management of OSPW. Based on Alberta’s zero discharge policy, OSPW must be kept on site in custom made tailings ponds that cover approximately 185 km2 of area. Research results in various fields indicate that naphthenic acids (NAs) are the main group of complex organics in OSPW that require remediation. NAs have been shown to be the main contributor to toxicity in OSPW, as well NAs corrode the process infrastructure. Investigations on the role of indigenous microorganisms in tailings ponds address their positive effect in removal of NAs. However, a consistent concentration of NAs in aged oil sands tailings ponds indicates that NAs are not completely biodegradable. Generally, dealing with recalcitrant compounds, coupling of chemical and biological oxidation is a method of interest. Sodium persulfate is an emerging oxidant used in OSPW treatment. Due to the challenging process of determining chemical composition, and measuring the exact concentration of NAs mixture in raw samples, for the first time in the field of NAs removal the concept of degree of reduction has been used for determining the stoichiometric amount of persulfate required for oxidation of NAs mixture. Estimated required concentrations based on proposed model show effective outcomes throughout the experiment. It also improved in optimization of the oxidation process by consuming approximately 5 times less oxidant reported in literature. To reach the application of combining chemical oxidation by sodium persulfate and biodegradation, effect of stress of sodium persulfate on Pseudomonas sp. was studied. Quantitative physiology parameters determined for the bacteria to elucidate the effect of oxidative stress on their ability to consume NAs. Growth of the bacteria in the presence of sodium persulfate significantly is affected, which is illustrated by the maximum concentration of biomass. At 1000 mg/L of sodium persulfate, the maximum concentration of biomass decreased by ~25 % respect to non-stressed controls. At the dosage of 2000 mg/L, no growth was observed. However, quantitative physiological analyses showed no significant change in ability of Pseudomonas sp. for consumption of Merichem NAs (based on DOC). The biomass specific growth rate (0.1 h-1), biomass specific substrate consumption rate (0.2 mgDOC/mgDCW/h) and yield of substrate to biomass (0.6 mgDCW/mgDOC) for each persulfate concentration series were not significantly different. Thermodynamics is a very powerful tool in understanding the limits of a system and prediction of possibilities. Some model NAs within literature have indicated to be non-biodegradable, for example dicyclohexyl acetic acid. To answer the question why dicyclohexyl acetic acid is not biodegradable, thermodynamics study applied to understand the limits and predict the possibilities for biodegradation. The University of Minnesota Biocatalysis/Biodegradation database was used for prediction of possible catabolic pathways for biodegradation of dicyclohexyl acetic acid. Interestingly, thermodynamics suggest the possibility of biodegradation under aerobic conditions. Results from bio-thermodynamics analyses predict that dicyclohexyl acetic acid can be consumed by bacteria with the maximum yield of 0.6 g organic dry weight per g of dicyclohexyl acetic acid. A 13% relative error has previously been shown with the approach used in bio-thermodynamics studies. Therefore, thermodynamics can provide a foundation for future for metabolic and genetic engineers to engineer microorganisms or microbial cultures with the objective of NAs biodegradation.

• Subjects / Keywords

  • Naphthenic acids
  • chemical oxidation
  • biological oxidation
  • oxidative stress
  • systems biology
  • thermodynamics

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R33N20N6H

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.