Plant-based adsorbents for the removal of BTEX compounds from water

Abstract: Benzene, toluene, ethylbenzene and xylene (commonly referred to as BTEX compounds) are monoaromatic hydrocarbons with a benzene core ring structure. These compounds have been reported to be present in groundwater, surface water, and even in drinking water due to various land use activities such as hydraulic fracturing and accidental events such as oil spills and leakages. Studies have estimated that the intake of BTEX by a person who drinks two litres of water a day is 10μg, 43μg, 2μg and 24μg per day for benzene, toluene, ethylbenzene and xylene respectively. These compounds have been found to be able to dissolve in water due to a low octanol partition coefficient and their relatively high solubility compared to poly-aromatic hydrocarbons (PAHs). BTEX compounds have been identified as causative agents of chemical-induced illnesses including irritation of the central nervous system, liver lesions and cancer. Past remediation efforts have utilized techniques such as bioremediation, natural attenuation and phytoremediation for the removal of BTEX from aqueous solutions. However, the limitations of these techniques, some of which include prolonged remediation time and ineffective control of the process make them unsuitable for BTEX removal. As a result, studies have focused on other techniques such as the use of membranes, ozonation and adsorption. This study focused iii particularly on adsorption as a cost-effective technique for BTEX adsorption by synthesizing adsorbents from green tea leaves for the removal of BTEX compounds from aqueous solution. Novel adsorbents, i.e. a gel adsorbent and powder adsorbent as well as iron nanoparticles (previously reported) were synthesized from dried green tea leaves. The gel was synthesized using sodium hydroxide for the extraction of reactant compounds in green tea leaves which were then cross-linked using formaldehyde, while the powder adsorbent was synthesized using distilled water for the extraction phase. Iron nanoparticles were formed through green synthesis by reacting brewed green tea with an iron precursor (FeSO4.7H2O). The three adsorbents were characterised using SEM-EDX for the surface morphology and surface elemental composition, BET for the surface area of the adsorbents, the pore volume and the pore size and FTIR analysis for the determination of surface functional groups. The adsorbents were then applied to BTEXcontaminated water in batch units (to determine their adsorption capacity and the equilibrium isotherms (Langmuir or Freundlich) that best described the data, and in a continuous packed bed column to determine the breakthrough volume (i.e. capacity) of the adsorbents in a column and to help investigate their efficiency in a continuous system...D.Phil. (Chemical Engineering