PhD Oral Exam - Huifang Bi, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Shoreline cleanup is the most challenging part of oil spill response, and the adhesion of oil to shoreline substrates makes the cleanup efforts low effective, labor-intensive and often environmentally disruptive. This thesis presents an integrated, multiphase framework for the sustainable engineering solutions for shoreline response, with focus on the novel preventative bio-based hydrogel coatings and the corresponding oil transport and fate behaviours, which is structured into four interconnected studies.

The first phase of this research developed a vegetable oil-based microemulsion as the washing fluid to remove stranded oil from beach sand. The microemulsion system maintained stable water-in-oil microstructures almost independent of salinity, a critical feature for marine applications. Under optimized conditions, the washing fluid achieved excellent oil removal efficiencies exceeding 85% and demonstrated significant reusability (still over 70% of its removal capacity even though it was used six times). However, washing methods have the inherent limitation that oil removal performance is greatly affected by operation and environmental conditions and removing oil after it has stranded remains operationally demanding, thus the research scope expanded to investigate preventative strategies. Moving from remediation to prevention, a bio-based hydrogel coating based on calcium alginate and cellulose nanocrystals was developed in the second study to protect shoreline substrates from spilled oil. The coating with a unique surface structure and superhydrophobic properties was developed to reduce the extent of shoreline oiling. The oil-repellent performance of the coated gravels implied that both oscillation time and oil concentration had almost no effects on the amount of adhered oil. Assessment of oiling prevention based on the laboratory shoreline tank simulator proved the coated gravel performed very well as more oil floated and less oil remained on substrates and penetrated into the subsurface. Biotoxicity analysis showed that the coating powders reduced impacts on the toxicity of the oil to algae (primary indicators: cell density, chlorophyll concentrations, and reactive oxygen species) at low doses (i.e., 10 and 100 mg/L). There is a good potential for the use of the coating technique to improve shoreline oil spill response.

Building on this, the third and fourth phases systematically investigated how the bio-based coating impacts oil transport behavior under various scenarios and oil fate within simulated coastal systems and revealed the mechanism underlying these features. The results revealed that the coated gravel achieved extremely low levels of oil residue (below 2%), reduced oil dispersion, and ensured the majority of oil floated on the water surface (up to 90%), aligning well with various expectations for shoreline cleanup. Observations regarding effects of coastal hydrodynamic characteristics indicated that even minimal wave energy simulated (0.1 W/kg) easily removed stranded oil with approximately 0.2% residue, while high energy levels promoted oil dispersion and inhibited oil flotation. When only tidal energy is available, the coated shoreline also can alleviate oil penetration into the subsurface by around 10%. For extended periods (up to 28 days), the remaining coating changed the oil fate in coastal settings through enhancing hydrocarbon biodegradation by approximately 16%. These findings provide critical insights into oil fate and transport following coating deployment.