Biosorption of emerging contaminants and heavy metals by magnetic chitosan/microalgae biocomposite

This thesis focuses on the development, characterization, and application of magnetic biocomposites that are intended to effectively remove different types of water contaminants. The biocomposites are composed of a combination of chitosan, microalgae biomass, and magnetite nanoparticles, which provide a sustainable and highly effective methodology for the treatment of contaminated water. The study explores the potential of these materials as biosorbents for removing different classes of pollutants, including antibiotics, heavy metals, and organic dyes, while addressing the challenges of environmental pollution. The first part of this work investigates the use of magnetic chitosan-based biocomposites, comprising Chlorella vulgaris (MCC) and Arthrospira platensis (MCA), in the removal of antibiotics like tetracycline (TC), ciprofloxacin (CIP), and amoxicillin (AMX). The synthesized biocomposites were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), which confirmed their morphological, chemical, and thermal properties. The adsorption experiments showed that MCC and MCA had excellent removal capacities of TC, CIP, and AMX removal. MCA exhibited the highest adsorption capacities: 834.0 mg/g for TC, 394.9 mg/g for CIP, and 150.8 mg/g for AMX. The Langmuir isotherm model fitted best with the adsorption data, highlighting monolayer adsorption. Among the different kinetic models used to fit the experimental data, the best fit was observed with the pseudo-second-order kinetic model. Regeneration studies demonstrated that the biocomposites could be reused for multiple cycles without significant loss in adsorption capacity and hence may be considered viable for water treatment applications. In the second part of the research, the synergistic and competitive adsorption of antibiotics and heavy metals, specifically TC, lead (Pb), chromium (Cr), and nickel (Ni), using MCA biocomposites was examined. The presence of Pb significantly enhanced TC adsorption, indicating a synergistic effect, while Cr and Ni displayed competitive inhibition, reducing TC removal efficiency. Kinetic studies using pseudo-first-order and pseudo-second-order models showed a better fit of the latter model for TC adsorption, which further supported chemisorption as the dominant mechanism of adsorption. The Langmuir isotherm model best described the adsorption behavior, with Pb showing the highest adsorption affinity. The thermodynamic analysis confirmed that the adsorption was spontaneous and endothermic. This chapter highlights the prospects of MCA biocomposites as effective adsorbents in the simultaneous removal of multiple pollutants from aqueous solutions. The third part of the thesis considers the removal of TC and crystal violet (CV), employing a novel magnetic chitosan-biomass biocomposite prepared from Chlorella vulgaris after lipid extraction. Adsorption of both pollutants was investigated under various experimental conditions, such as pH, biocomposite dosage, initial concentration of the pollutants, and contact time. Adsorption isotherm studies showed that the Langmuir model fitted well for the removal of TC and CV, with highest adsorption capacities of TC and CV of 864.382 mg/g and 305.097 mg/g, respectively. The kinetic analysis revealed that both pollutants followed the pseudo-second-order model, while the thermodynamic one showed that the adsorption process was spontaneous and endothermic. These result as a whole suggest the potential of the biocomposite for efficient and sustainable water treatment. Finally, the performance of the MCA biocomposite in the form of beads in the fixed-bed column system was evaluated for both TC and Pb removal. Breakthrough curve analysis showed that factors such as bed height, flow rate, and initial concentration of targeted pollutants significantly influence the adsorption performance. In the case of TC, increased bed height allowed the removal efficiency to increase. For Pb, the removal efficiency remained stable across different bed heights. In binary systems, the presence of Pb increased TC adsorption, which could be due to complexation between Pb and TC. The removal efficiencies of TC and Pb were 67.85% and 81.48%, respectively. Dynamic adsorption behavior was modeled using several models, including Thomas, Adams-Bohart, Yoon-Nelson, and Dose-Response models, with the Dose-Response model providing the best fit for TC adsorption. This part of the study presents helpful knowledge on optimization of fixed-bed adsorption systems regarding the simultaneous removal of multiple contaminants. The findings of this research offer fundamental information on adsorption mechanisms and provide a basis for the design and optimization of biosorbent materials for water purification applications. In addition, given the sustainability of these biocomposites, as evidenced by their ease of regeneration and multiple utilization, they have the potential to be applied at large scale for environmental remediation and wastewater treatments.