REMOVAL OF PERFLUOROALKYL SUBSTANCES (PFAS) FROM WATER USING MODIFIED BIOCHAR ADSORBENTS PRODUCED FROM CANOLA STRAW
Date
2024-03-27
Authors
Journal Title
Journal ISSN
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ORCID
Type
Thesis
Degree Level
Masters
Abstract
Perfluorooctanoic acid (PFOA) is a persistent organic pollutant commonly found in water sources, causing severe health and environmental concerns. In this research, microwave-activated biochar adsorbents derived from canola straw were modified by chemical activators (H3PO4 and ZnCl2) to improve the PFOA removal from water. In order to obtain optimal microwave-assisted pyrolysis (MWP) conditions, different biochar adsorbents were synthesized by altering the activator molarity, microwave heating time, and microwave power. This was done utilizing a central composite design (CCD) coupled with a response surface methodology (RSM). Based on the analysis of H3PO4-treated biochar (PBC) and ZnCl2-treated biochar (ZnBC), it was found that chemical treatment of biochar under optimum MWP conditions (irradiation time of 6 min and microwave power of 600 W) enhanced the chemical functional groups, porosity, and surface area of canola-based biochar. In this condition, removal efficiencies of PFOA by PBC and ZnBC reached 368 µg/g (92%) and 336 µg/g (84%) at equilibrium and 25 °C, respectively. These amounts were significantly higher than untreated biochar (UBC), with a low removal efficiency of only 25 µg/g (5%), and raw canola straw (RCS), which exhibited a very low removal efficiency of 5 µg/g (1%).
Chemical treatment increased the PFOA adsorption by improving the interactions between PFOA and the modified biochar. Chemical analyses were conducted to identify the elemental composition of PBC and ZnBC. Furthermore, FT-IR and XPS results confirmed the addition of new chemical functional groups to the biochar surface during chemical treatment and pyrolysis. The results of a kinetic study showed that PBC and ZnBC are involved in chemisorption to remove PFOA. A Freundlich isotherm model best fitted the data for PFOA adsorption on modified adsorbents, suggesting heterogeneous multilayer adsorption is more likely to occur. Various background salts were examined, and the results demonstrated that salting-out and divalent bridges can enhance PFOA adsorption. Further investigation explored that the modified biochar adsorbents showed excellent performances over a pH range of 3 to 9. This study strongly suggests that the modified biochar adsorbents, produced through a straightforward method from readily available agricultural waste, present a sustainable and eco-friendly adsorbent for PFOA removal from water.
Description
Keywords
Modified biochar, Perfluorooctanoate (PFOA), Microwave pyrolysis, Chemical activators, Electrostatic interaction
Citation
Degree
Master of Science (M.Sc.)
Department
Chemical and Biological Engineering
Program
Chemical Engineering