Improvement of algal-alginate bead stability by zeolite molecular sieves 13X and its application in biosorption

• Main Author: Moghaddam, Seyed Amirebrahim Emami
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: Sewage - Purification - Phosphorus removal; Sewage - Environmental aspects
• Online Access: http://psasir.upm.edu.my/id/eprint/84377/1/FK%202019%20137%20-%20ir.pdf; http://psasir.upm.edu.my/id/eprint/84377/

The interest in utilizing algae for wastewater treatment has been increased due to many advantages. Algae-Wastewater treatment system offers a cost-efficient and environmentally friendly alternative to conventional treatment processes. However, the recovery of free suspended algae from the treated effluent is one of the challenges during the treatment process. Therefore, the application of immobilized algae is a good approach to resolve the harvesting issue. Up to now, most of the algal immobilization has been done using cell entrapment method in which alginate (a natural polymer) has been applied as a carrier. Although alginate provides advantages in terms of biocompatibility, nontoxicity, cost-effectiveness, etc., this material has low stability to the chelating agents and a similar charge with cell surface of microorganisms, hence, it easily contributes to the leakage of large molecules due to the open lattice structure. Therefore, this study aims to improve the stability of Chlorella-Alginate Beads (CABs) by zeolite molecular sieves 13X (an aluminosilicate mineral with sodium ion) and further examined the potential use of the synthesized Zeolite 13X-Algal-Alginate Beads (ZABs) for copper biosorption from aqueous solution. The immobilization was done via the entrapment of green living microalgae, Chlorella vulgaris within alginate/powdered zeolite 13X hydrogels. Cross-linking was carried out using 0.1 M CaCl2 solution. The stability of the beads was tested by immersing them in a phosphate buffer solution at pH 7 as a chelating agent. Different process variables, including ratio of zeolite/alginate, pH and volume of beads were optimized using response surface methodology (RSM) to obtain the algal beads with high stability. Dissolution time of synthesized Zeolite-Algal-Alginate Beads (ZABs) in a chelating agent revealed a significant improvement on the beads stability (78.5 ± 0.5 min) compared to the control beads (51.5 ± 0.5 min) under the optimum conditions of zeolite/alginate (1.5:1), pH 5 and 2% of beads. Monitoring cell growth during 5 days of incubation showed good biocompatibility of zeolite 13X. Scanning electron microscopy (SEM) indicated rough surface and spherical shapes of ZABs. Brunauer-Emmett-Teller (BET) analysis revealed higher surface area for ZABs than other ABs. Energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR) of ZABs confirmed the presence of zeolite 13X within the matrix. The zeta potential value of ZABs (−23.33 ± 0.29 mV) indicated that the beads were relatively stable. In addition, the potential use of ZABs for copper biosorption was evaluated and compared with Blank-Alginate Beads (BABs) and Chlorella-Alginate Beads (CABs). Different process parameters were investigated including contact time, pH and initial metallic ion concentration. It was found that the maximum biosorption capacity of ZABs was 85.88 mg/g biosorbent achieved at 180 min, pH 5 and initial metallic ion concentration of 150 mg/l whereas the maximum biosorption capacity of 70.02 and 77.32 mg/g biosorbent was obtained for BABs and CABs, respectively. ZABs showed higher stability than BABs and CABs in biosorption-desorption cycles. The kinetic and equilibrium data were analyzed via reaction/diffusion and Langmuir/Freundlich models, respectively. Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR) analyses revealed bonded metal ion to the ABs. The findings of this research confirmed that modification of algal-alginate beads by zeolite molecular sieves 13X has the potential to improve the beads stability and their biosorption capacity.