Phytoremediation of Light Non-Aqueous Phase Liquids

Abstract

Non-aqueous phase liquids (NAPLs) are persistent sources of contamination in the ground, providing a long-term supply of dissolved phase contamination and taking significant periods to dissipate naturally. Light NAPLs (LNAPLs) take the form of a separate phase within the ground, often as individual ganglia in pore spaces within the capillary zone such that the contaminated region is diffuse and comprised of many unconnected small contaminant sources. Consequently, remedial action is challenging and success may be limited to ex-situ remediation techniques. The ability of plants to phytoremediate dissolved-phase contamination is well known, but the impact of LNAPLs on plant growth and subsequent contaminant behaviour is largely unknown. Experimental work with ryegrass (Lolium perenne) is presented, exploring the impact of the physical presence of an LNAPL (mineral oil) on plant growth, root distribution and oil removal. The presence of the oil was found to significantly impact root biomass and distribution, leading to zones of increased root growth alongside decreased shoot growth. Significant removal of the LNAPL was noted in both hydroponic conditions and planted soil.

Plant growth, root distribution and non-aqueous phase liquid phytoremediation at the pore-scale

“…It is noted that soil texture and consequent variations in pore structure are likely to affect the interaction between oil and root/rhizosphere in a real application. Such impacts have been explored in more detail in Oniosun et al (2018) and Oniosun (2019). They report an influence of the presence of a fine-grained particle fraction on the location of oil within the pore space and discuss potential changes in contaminant bioavailability and transport in the larger pores impacting how toxic compounds can migrate in the soil and inhibit water and nutrients from reaching the rhizosphere thereby reducing the supply of oxygen, moisture, and nutrients which may lead to root damage or death.…”

“…Quantitative and semiquantitative measurements for root growth, root morphology in a particular column, NAPL loss, shoot height and root length were measured over time, and root and shoot biomass determined at the end of the experimental trial. Preliminary results from a small part of this work have been reported in Oniosun et al (2018).…”