Abstract
Phytoremediation is a biological treatment technology that utilizes plants to extract, stabilize, volatilize, or facilitate the degradation of pollutants in contaminated soils. The aim of this study was to compare the phytoremediation abilities of Helianthus annuus and Brassica juncea in Spent Engine Oil (SEO)and mine-spoils co-contaminated soils.This featured four experiments which investigated the effects of Spent Engine Oil and mine-spoils on germination & plant growth parameters, the potential for mixed-cropping to alleviate soil toxicity effects imposed by Spent Engine Oil, the phytoremediation abilities of the chosen species for the treatment of lead (Pb) and petroleum hydrocarbon contamination, and the potential for struvite and NPK fertilizers to deliver exogenous enhancement of the phytoremediation process.
The experiments consisted of greenhouse pollution simulations which featured a range of pollutant concentrations from 0% to 9.2% w/w for SEO single contaminant experiments, and 0.8% SEO + 10% mine-spoils and 1.6% SEO + 10% mine-spoils w/w.
Percentage germination was determined for Spent Engine Oil concentrations ranging from 0%-6% over a 21-day period, and the results showed that the studied species were adversely affected by increasing doses of Spent Engine Oil which manifested through dose-dependent decline in germination for both species as Spent Engine Oil concentrations increased. Similar patterns were also observed for the growth parameters studied in Spent Engine Oil single contaminant treatments, and in Spent Engine Oil and mine-spoils co-contaminated treatments, which manifested in significant reductions in plant height, number of leaves, and laminar leaf area with increases in contaminant doses.
Residual Total Petroleum Hydrocarbons (TPH), Polycyclic Aromatic Hydrocarbons (PAHs) and lead (Pb) concentrations in co-contaminated soils treated with Helianthus annuus and Brassica juncea were determined by Gas Chromatography with Flame Ionization Detector (GC-FID), Gas Chromatography with Mass Spectrometry (GC-MS), and Inductively Coupled Plasma with Optical Emissions Spectrometry (ICP-OES) respectively. The results showed that two species significantly reduced total PAHs, TPH and Pb, although the extent of removal decreased as contaminant doses increased in soil treatments. The highest removal for all contaminants were observed in Helianthus annuus planted soils.
Nutrient supplementation with NPK and Struvite fertilizers proved beneficial for improving the growth, total Pb uptake and dissipation of Pb, TPH and total PAHs in co-contaminated soils. However, struvite fertilizer was most promising in improving contaminant dissipation, Pb uptake and growth under contaminant stress when combined with Helianthus annuus.
Overall, a key finding from this study relating to the tolerance and phytoremediation abilities indicate that Helianthus annuus could be used for the treatment of low to medium levels of Pb and petroleum hydrocarbon co-contamination in soils. Another key finding from this study was an indication that struvite could be a promising alternative to regular fertilizers for exogenous nutrient supply for phytoremediation enhancement. This could present a tremendous opportunity for contribution to the circular economy with huge benefits for environmental sustainability, with reduced exploitation on natural nutrient reserves, and conversion of waste to resource for the resolution of other environmental challenges. However, further trials are still required with other plant species and various struvite doses and a wider range of soil contaminants to assess its potential for wider applications under a boarder spectrum of conditions, but overall, this study provided a solid launch point and a step in the right direction to further uncover struvite’s full potential.
| Date of Award | 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Steve Coupe (Supervisor), Alan Paul Newman (Supervisor), Fredrick Mbanaso (Supervisor), Augustine Ifelebuegu (Supervisor) & Anna Bogush (Supervisor) |