The marine environment is polluted by diverse contaminants among which are toxic metals, aliphatic and polycyclic aromatic hydrocarbons (PAHs) for which marine sediments very often constitute a major reservoir. At various locations, the discharge of hazardous substances over many years has resulted in high levels of pollution. Several remediation approaches have been proposed which can be classified under physico-chemical or biological remediation. Physico-chemical methods involve processing such as thermal treatment, or the use of chemical oxidation agents while bioremediation makes use of biological agents such as microorganisms and/or their metabolic products. Generally these bioremediation approaches are considered more environmentally friendly and with lower economic cost. Throughout this PhD research, a number of sustainable bioremediation approaches were investigated on sediments highly contaminated with PAHs and toxic metals with objective to propose a sustainable remediation approach for the contaminated sediments. The initial step of this research consisted of preparing an extensive literature review on patented bioremediation approaches developed in the last 20 years. Over 150 patents were reviewed and a majority consisted of bioaugmentation methods and a number of cheap and environmentally friendly biomaterials were also proposed as biostimulating agents. In the first sets of experiments, bioaugmentation and biostimulation methods were investigated for enhanced PAH degradation, specifically bioaugmentation with Aspergillus strains, biostimulation with inorganic nutrients, microbial fuel cell experiments and natural attenuation. Also, potential effects of these biotreatments on metal mobility were studied. Results indicated significant decrease of PAH concentrations especially with the biostimulation with inorganic nutrients being the most effective approach (>90%). Also, the biotreatments changed the partitioning of metals, including their solubilization, suggesting the need of parallel environmental risk assessment. The findings of the Life Cycle Assessment (LCA) study carried out suggest that ex situ biotreatments can have a lower carbon footprint than current management options of contaminated sediments (i.e., landfill disposal and/ or disposal in confined aquatic facilities). In further experiments, more sustainable organic nutrients such as activated sludge and Supercompost were investigated as biostimulating/bioaugmentation agents. The sediments were pretreated with ozone for enhanced removal of recalcitrant PAHs and to facilitate the subsequent bioremediation experiments. However no significant effect of ozone was observed, and the efficiency of the organic nutrients for PAH degradation was very low (less than 10%) The last experiment was on Electrokinetic remediation carried out to observe metal removal from an anode to a cathode end and a possible mobilization of the PAHs and approximately 50% of Pb was mobilized during this experiment.
|Titolo:||Sustainable Remediation Strategies for Contaminated Marine Sediments|
|Data di pubblicazione:||ott-2021|
|Appare nelle tipologie:||8.1 Tesi di dottorato|