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Phytoremediation of LNAPLs and residual oils in the vadose zone and capillary fringe

Oniosun, Sunday 2019. Phytoremediation of LNAPLs and residual oils in the vadose zone and capillary fringe. PhD Thesis, Cardiff University.
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The success of phytoremediation is dependent on the exposure of plants to contaminants, which is controlled by root distribution, physicochemical characteristics, and contaminant behaviour in the soil environment. Whilst phytoremediation has been successful in remediating hydrocarbons and other organic contaminants; there is little understanding of the impact of non-aqueous phase liquids (NAPLs) on plant behaviour, root architecture and the resulting impact of this on phytoremediation. The ability of plants to phytoremediate dissolved-phase contamination is well known, but the impact of Light NAPLs (LNAPLs) contaminants on plant growth and subsequent contaminant behaviour is largely unknown. A review of current literature available on phytoremediation was conducted. Across the studies considered, sandy loam, loam, and silt loam appear to have a better organic contaminant removal than other soil types because of nutrient availability and water supply for plant growth and root development. The review shows that the NAPLs, in particular, have an effect, which suggests that there is a physical effect of NAPLs on plants rather than the chemical impact. In this thesis, experimental works with ryegrass (Lolium perenne) grown under both hydroponic conditions and planted in artificial soils are presented, exploring the impact of the physical presence of an LNAPL (mineral oil) on plant growth, root distribution and oil removal. In the presence of LNAPL, a significant increase in root biomass yields and distribution, a decrease in shoot biomass and significant LNAPL removal were observed. Roots close to LNAPL sources were able to remove dissolved-phase contamination, and root growth through LNAPL sources suggest that direct uptake/degradation is possible, but any contribution from physical and direct interaction between root and NAPL has not been conclusively demonstrated here. Evidence of root redistribution in the case of LNAPL contamination across multiple adjacent pores is also presented. Although some impediment to root growth was seen at low oil contamination levels in general increased root biomass and also deeper root structures were observed as the coverage of the oil layer increased. The presence of plants corresponded to significant removal of the LNAPL in both hydroponic conditions and planted soil, whereas without plants only minimal oil loss was observed. The research has demonstrated the potential for plants to tackle NAPL contamination and shows that the phytoremediation of organic contamination is not limited to tackling only the dissolved phase, but that roots interacted with the NAPL which resulted in a significant indirect reduction in the presence of the LNAPL.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Phytoremediation; Remediation; Mineral Oil; Ryegrass; Non-Aqueous Phase Liquids; Organic Contaminants.
Date of First Compliant Deposit: 23 May 2019
Last Modified: 23 May 2019 09:32

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