Thesis

Investigating the effects of treating hydrocarbon-contaminated water with green nano zero-valent iron on hydrocarbon-degrading bacteria

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Awarding institution
  • University of Strathclyde
Date of award
  • 2026
Thesis identifier
  • T17575
Person Identifier (Local)
  • 202260031
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • This thesis investigated how green-synthesised nanoscale zero-valent iron (nZVI), produced with polyphenols extracted from green tea, influenced both the breakdown of petroleum hydrocarbons and the resident hydrocarbon-degrading bacteria in contaminated water, benchmarked against a commercially manufactured nZVI of similar nominal size. Polyphenols were extracted from dried Camellia sinensis (green tea) leaves by aqueous infusion at 80°C, followed by filtration and centrifugation to obtain a clarified extract used as both the reducing and stabilising agent during synthesis. The work addressed four objectives. First, green nZVI was prepared by reducing FeCl₃·6H₂O with optimised green-tea extract, then characterised alongside the industrial material by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD revealed broader peaks for the green particles, while SEM showed agglomerates of 50–90 nm compared with 30–45 nm for the industrial sample; EDS showed that the green nZVI were composed chiefly of iron, carbon and oxygen, with a minor chlorine signal attributable to residual FeCl₃·6H₂O used in the reduction step. The industrial nZVI displayed the same dominant Fe–C–O profile without the chlorine. Second, batch samples containing hydrocarbon-contaminated water were dosed in triplicate with three concentrations of each nZVI formulation (0.004 mg/L, 0.01 mg/L and 0.004 mg/L dosages for green nZVI and 0.004 mg/L, 0.010 mg/L and 0.0040 mg/L dosages of industrial iron nanoparticles). Chemical oxygen demand (COD) and total petroleum hydrocarbons (TPH) were measured at two hours and 24h through a HACH COD test kit and GC-FID, respectively. Third, microbial DNA was extracted, quantitatively assessed, and sequenced (16s rRNA amplicons) to determine shifts in taxonomic composition, and multivariate statistics, mainly paired-sample t-tests and bar charts, were applied to relate dose, formulation and exposure time to both chemical and ecological responses. Finally, doseresponse envelopes were derived to recommend practical application rates for pilot-scale nanobioremediation. Industrial nZVI removed TPH more rapidly within two hours (mean 67 % at the lowest dose of 0.004 mg/L) but plateaued by 24 h (maximum 73 %). Green nZVI achieved lower initial removal (45 % average) yet approached comparable 24-h efficiencies (64 % at 0.004 mg/L), with COD trends mirroring TPH reductions. Early-stage differences between formulations were statistically significant (p < 0.001), but the gap narrowed after 24 h. Microbial analysis showed that untreated controls were dominated by Proteobacteria (64 %), Bacteroidetes (18 %) and Actinobacteria (14 %). Industrial nZVI caused up to a 32 % decline in total Operational Taxonomic Units (OTUs) and temporarily suppressed Flavobacteriales. In contrast, green nZVI, particularly at 0.004 mg/L, stimulated microbial abundance by 25–38 % after 24h and selectively enriched hydrocarbonoclastic orders such as Burkholderiales, Rhizobiales and Actinomycetales. The study concluded that the organically capped green nZVI balanced abiotic reduction with biotic degradation, delivering near-industrial TPH removal while fostering a more resilient and functionally relevant microbial community. A moderate green nZVI dose of 0.004-0.01 mg/L per 100 mL and a minimum 24h contact time were recommended for field trials. These findings underscore the potential of plant-derived nZVI as a sustainable alternative to chemically synthesised particles, capable of reconciling high remediation performance with ecological stewardship and providing a template for future nano-bioremediation policies.
Advisor / supervisor
  • Switzer, Christine
  • Knapp, Charles W.
Resource Type
DOI
Date Created
  • 2025

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