PhD Oral Exam - Mohammad Farshidy, 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.
Contamination of the sediments by organics and inorganics is a rising concern. However, remediation of contaminated sediments is complex and challenging.
As yet, the application of the enhanced desorption combined with the sorption for remediation of the contaminated solid media has not been investigated. In environmental research, few studies have focused on closed-loop remediation methods. This study was to evaluate a desorption-sorption process and the influential parameters for remediation of hydrocarbon-contaminated sediments. Also, it aimed to investigate the adsorption capacity of the sorbent (silica aerogel), adsorption isotherms and adsorption kinetics, as well as the fate of heavy metals, phosphorus and nitrogen, and regeneration of aerogels by solvents and heat in the desorption-sorption process.
A laboratory-scale system was designed and built for fast remediation of sediments. A strong turbulence vessel was used to increase the desorption of contaminants from sediments. A packed column containing hydrophobic silica aerogel granules was used to remove the contaminants from the effluent slurry.
The results showed 29.5% total petroleum hydrocarbon (TPH) removal from sediment after 45 minutes of vigorous agitation at 15900 rpm. The processed sediment and effluent water met Canadian governmental and provincial quality criteria. Higher agitation speeds (22100 rpm) increased the leaching of hydrocarbons from sediments by 31%.
In a warm environment (35oC), the desorption of TPH from sediments was 28.9% higher than at ambient temperature (22oC), but in a cold environment (10oC), it was 16.3% lower than at ambient temperature. The sorption capacity of aerogels was increased from 9.6 mg/g at 22 oC to 10.5 mg/g at 10oC but decreased to 6.7 mg/g at 35oC. pH (5, 7 and 9), salinity (3.5%), solid load (5, 10 and 15 g/l) and retention time (11.5 and 26 seconds) did not show a significant effect on the efficiency of the process. Adsorption data suggested a pseudo-second-order kinetics and a Freundlich adsorption model were the most appropriate.
The sediment quality including the content of investigated heavy metals (Cr, As, Cd, Pb, Cu, Zn, Ni, Mn, Co, Mo), nitrogen, and phosphorus did not change significantly after the desorption-sorption process. The concentration of heavy metals in the effluent water was significantly lower than the drinking and freshwater standards. Aerogels showed a low affinity towards the heavy metals but decreased the concentration of total phosphorus and total Kjeldahl nitrogen in water by 65% and more than 95%, respectively. Regeneration of the aerogels by organic solvents or heat was not feasible. This research introduces a new environmentally-friendly methodology for remediation of sediments and other solid environmental media.