PhD Oral Exam - Masoumeh Javid, 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

Heavy metal pollution is an anthropogenic unavoidable issue with implications for life. Heavy metals are natural occurring elements, having both natural and anthropogenic sources. Sediment and soil contamination with toxic heavy metals, including (Cr, Ni, Cu, Zn, As, Cd and Pb), represents a major long-term remediation challenge. A surface sediment sample (<10 cm) was collected from shallow harbour on the bank of the St. Lawrence River, in Quebec, Canada in 2019 and 2021 for a sediment decontamination study. Harbour sediment from the St. Lawrence River, in Quebec is anthropogenically polluted by heavy metals. To evaluate the metal pollution in this area, the total concentrations of heavy metals in selected stations were analyzed.  A series of laboratory-based experiments under various conditions were performed using designed reactor in order to provide information for sediment remediation technology development. The concept of the resuspension method is that finer sediments have a greater tendency to adsorb the contamination. We are therefore developing a sediment-treatment process based on heavy metal removal by resuspension technique. Sequential extraction procedures were used on the sediment to determine the speciation of the heavy metals before remediation and in the suspended particle matter (SPM). The resuspension method was successful in reducing the concentration of seven selected heavy metals (Cr, Ni, Cu, Zn, As, Cd and Pb) by removing just 2.63% of the contaminated sediment (2019). Removal efficiency values on average were positive for all heavy metals (with a minimum 3.48% for Cd and a maximum of 32.4% for Cu). The results of the sequential extraction tests implied that the resuspension technique is capable of decreasing the risk of remobilization of heavy metals in the aquatic ecosystem. The effects of heavy metals on survival and growth of midge Chironomus riparius and Hyalella azteca were investigated. Both larval survival and growth did not show significantly difference between sediment samples (before remediation, after remediation and SPM) with controls. Therefore, exposure of Chironomus riparius and Hyalella azteca larvae to sediments collected in the St. Lawrence River did not have any toxic effects according to the biomarkers used in this study.

The resuspension method showed desirable results for the removal of heavy metals from bottom sediments (2019). A small amount of sediment removed from the system, and no chemical substances were employed. Consequently, the resuspension method causes less destruction in the aquatic ecosystem.