Green synthesis of zero-valent iron nanoparticles from cape gooseberry (physalis peruviana) biomass for oil spill remediation in the Albertine Graben, Uganda

Abstract

Uganda is preparing to start production of its oil and gas resource in the Albertine Graben. Oil and gas production areas are vulnerable to oil spills from tankers, barges, pipelines, refineries, drilling rigs, storage sites, and waste management facilities. Therefore, efficient, cost-effective, and environmentally friendly remediation strategies are required. The objective of this study was to establish baseline concentrations of Total Petroleum Hydrocarbons (TPH) in the Tilenga Oil fields and to assess the potential for oil spill remediation using zero-valent iron nanoparticles (nZVI) synthesized from Cape gooseberry biomass. Water and soil samples collected from eight boreholes, three Sewerage Treatment Plants (STP), three taps, and six STP effluent discharge points were extracted using cyclohexane (water) and dichloromethane (DCM) (soil), and then analysed using Gas Chromatography-Flame Ionization Detection (GC FID). Cape gooseberry fruit, leaf, or husk extracts, and iron (III) chloride (0.5 M, 0.1 M, or 0.01 M) precursor were used in a 2:1 ratio for green synthesis under sonication. The nZVI were characterized using Ultraviolet- Visible (UV-Vis) spectroscopy, Fourier transform-infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Zetasizer, and Brunauer-Emmett-Teller (BET) analysis. Batch remediation experiments for 0.01 mL, 0.05 mL, and 0.1 mL of diesel oil in 100 mL of distilled water were performed using 0.33 g of nZVI. SimpleBox4nano was then used to simulate the fate and transport of the nZVI. The TPH detected were diesel organics (C12 to C30), ranging between 0 ppm to 1.5 X 106 ppm, and hexadecane (C16) was the most abundant. TPH in soils were below the 870-10,000 mg kg-1 US EPA limit, while those in water were above the 3.2- 20 mg kg-1 US EPA limit. The nZVI ranged between 70 nm to 100 nm, were all highly stable, had a crystalline alpha-iron core and iron oxide shell, and achieved remediation efficiencies over 94.3 %. Fruit extract and 0.5 M FeCl3 generated the highest quantity of nZVI, though agglomerated. The husk extract nZVI had the highest surface area, uniform size, and highest porosity. The simulated environmental concentrations indicated slow mobility of nZVI, and their bioaccumulation was highest in the soils as compared to water, air, and sediment compartments. The study demonstrated that Cape gooseberry biomass extracts can be used in green synthesis of nZVI that are efficient in diesel contamination cleanup. In addition to being a waste material, husks were advantageous over the fruits and leaves due to their superior uniformity and surface area. Keywords: Cape gooseberry; Petroleum hydrocarbons; Remediation; SimpleBox4nano, Simulation; Zero-valent iron nanoparticles.