Insights Into Sustainable Environmental Remediation Approaches And The Fate And Transport Of Petroleum Hydrocarbons In Soils

In recent years, there are increasing interests in integrating sustainability as a decision-making criterion for environmental remediation. International initiatives have been established to explore sustainable remediation but there are knowledge gaps to be filled due to the specific challenges and problems in China. Improved insights into how to use the currently available frameworks to guide implementation of sustainable remediation in China are essential for improving risk assessment, remediation strategies and effective generation of previously contaminated land. This thesis explores the potential application of two remediation approaches including solvent extraction and compost amendment for petroleum hydrocarbon contaminated soils in context of China and the United Kingdom (UK).Solvent extraction is a preferred approach for sites with high levels of contamination which are not amenable for some more sustainable approaches such as bioremediation. This study provides new insights into the benefits of using integrated approaches such as solvent extraction followed by biodegradation for remediating contaminated soils with high levels of total petroleum hydrocarbons (TPH > 140 000 mg kg-1) as most of the previous studies have been only focused on low concentration contamination (< 5000 mg kg-1). The method allows > 90% of TPH to be removed within 15 min at room temperature, which is much more effective than previous reported solvent extraction method that required an extraction time ranging from 30 min to 48 h and temperature ranging from 70℃to 100℃. In addition, the issue of secondary pollution was addressed because 99% of the solvent was recycled using water. This method also shows good performance for the long-term effectiveness because the residual contaminants (mainly asphaltene) after treatment are extremely recalcitrant, non-available to ecological receptors in soil, and may be left in place without creating additional environmental risks. The complementation of solvent extraction and biodegradation promoted the strength but circumvented the drawbacks of their individual application, and therefore should be encouraged at contaminated sites for reducing remediation time, enhancing efficacy, improving sustainability and restoring previous contaminated sites especially with high concentration weathered hydrocarbons. Adding mature compost to contaminated soils is a good alternative for reusing waste and remediating the degraded land. The influence of compost addition on the degradation and bioavailability changes of polycyclic aromatic hydrocarbons (PAH) in both spiked and genuinely contaminated soils were investigated in this study. The quantified contribution of degradation and desorption/sorption to bioavailability change has implication for future studies to bring bioavailability concept into exposure assessment and to develop a more realistic and defensible remediation criteria for petroleum hydrocarbon in soils. Results of conjoint analysis reinforced the importance of incubation time and soil type (accounting for 92%) for PAH bioavailability change. The relationship between time, eleven readily accessible soil properties, and the bioavailable concentration of 16 PAHs using machine learning techniques gained insights into their high nonlinear relationship and provided a useful tool for the temporally prediction of bioavailability allowing a quick forecast of the bioremediation endpoint. Although the type and ratio of compost added were less important for bioavailability change, their interactions with other factors were significant. Results of multiple factor interactions implied that the compost addition shifted the equilibrium of soil-oil interaction (e.g. competitive sorption), however, knowledge about how to model the multi-phase partitioning of hydrocarbons in the soil-compost-oil system and the contribution of each mass transfer process (e.g. biodegradation, desorption, volatilization, diffusion, and etc.) to the overall fate and transport of hydrocarbons is still missing which warrants further investigation.