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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Amarjeet Bassi

Affiliation

University of Western University

Abstract

Crude oil desalting operations produce an effluent stream which is challenging to treat due to its salt, heavy metal and hydrocarbon content. Consequently, desalter effluent (DE) is usually diluted into other effluent streams and sent to conventional wastewater treatment plants which may lead to upsets the plant operation.

In this study, a novel microbial approach was applied which investigated DE treatment using halotolerant yeast Debaryomyces hansenii (LAF-3 10 U) or the environmentally robust micro-algae Parachlorella kessleri strain CPCC 266. The effect of these two different approaches on both synthetic and actual DE was investigated in both batch and/or continuous mode.

In the first stage, the effect of phenol substrate inhibition in simulated desalter effluent (SDE) on D.hansenii was evaluated. The Edward inhibition model describes the yeast growth in SDE as follows: µmax 0.21 h-1, KS 633.9 mgL-1 and KI 1263.61 mg.L-1. Next, a response surface methodology was applied in SDE containing dodecane as a substrate under different growth conditions. A quadratic model based on central composite design was formulated and dodecane utilization by D.hansenii in various salt concentrations was confirmed to be efficient and rapid. A maximum chemical oxygen demand (COD) of 61.6% was obtained at a pH of 9, a dodecane concentration of 750 mgL-1, and a temperature of 20°C. Using dodecane as a model substrate, the continuous cultivation of D.hansenii was next investigated in a continuous stirred bioreactor (CSTR) at high salt concentration and different dilution rates to determine Monod kinetic model parameters with µmax 0.085 h−1, and Ks 1575.2 mgL-1. COD removal of 95.7% was obtained at a dilution rate of 0.007 h-1. Finally, the growth of P. kessleri was investigated for cultivation in batch mode for actual and SDE treatment containing benzene and phenol. These microalgae grew on both types of DE and reduced COD and benzene up to 82.9% and 51% respectively. In addition, it produced lipids with a maximum of 71.5% of dry weight.

Overall, this work demonstrated the feasibility of utilizing two different microorganisms to achieve high COD removal and biomass production on a challenging wastewater stream. The microalgae and yeast can both serve as a source of value stream for lipids for biofuel production or the nutraceutical industry.

Summary for Lay Audience

Effluent from the desalination unit from petroleum refinery wastewater (desalter effluent) contains different inorganic and organic impurities, such as nitrogen, phosphorus, heavy metals, and hydrocarbon, which can significantly impact the environment if they are discharged in soil, surface water or groundwater. Current approaches utilize mixed cultures of microorganisms in conventional wastewater treatment systems. However, the presence of salt makes desalter effluent very challenging to treat in a conventional way.

In this study, an alternative approach is investigated where a single yeast which is resistant in salt or a strain of biofuel producing green microalgae is utilized for desalter effluent treatment.

The halophilic yeast has been shown to degrade hydrocarbons in saline solutions. The microalgae use light, nutrients, and CO2 to grow, and their biomass is used for many applications, such as the production of chemicals, biodiesel, and bioenergy. These characteristics make both the yeast and the microalgae an excellent choice for investigating desalter effluent treatment. The studies were carried out in batch and continuous mode. Simulated solutions of desalter effluent were prepared using specific substrates such as phenol, Benzene, dodecane and actual samples of desalter effluent were also investigated. The results showed that both the yeast and the microalgae can be applied to effectively degrade the desalter effluent and provide biomass for further applications such as lipid production.

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