Abstract
Natural polymers have proven to be extremely interesting matrices for the immobilization of microbial biomasses, via various mechanisms, in order to bring them into a form easier to handle—the form of composites. This article aimed to study composites based on a residual microbial biomass immobilized in sodium alginate via an encapsulation technique as materials with adsorbent properties. Thus, this study focused on the residual biomass resulting from beer production (Saccharomyces pastorianus yeast, separated after the biosynthesis process by centrifugation and dried at 80 °C)—an important source of valuable compounds, used either as a raw material or for transformation into final products with added value. Thus, the biosorptive potential of this type of composite was tested—presenting in the form of spherical microcapsules 900 and 1500 μm in diameter—in a biosorption process applied to aqueous solutions containing the reactive dye Brilliant Red HE-3B (16.88–174.08 mg/L), studied in a batch system. The preparation and characterization of the obtained polymeric composites (pHPZC, SEM, EDS and FTIR spectra) and an analysis of different equilibrium isotherms (Langmuir, Freundlich and Dubinin-Radushkevich—D–R) were investigated in order to estimate the quantitative characteristic parameters of the biosorption process, its thermal effects, and its possible mechanisms of action. The modelling of the experimental data led to the conclusion that the studied biosorption process took place after reaching the Langmuir isotherm (LI), and that the main mechanism was possibly physical, being spontaneous and probably exothermic according to the values obtained for the free energy of biosorption (E = 8.45–13.608 kJ/mol, from the DR equation), as well as the negative values for the Gibbs free energy and the enthalpy of biosorption (ΔH0 = −87.795 kJ/mol). The results obtained lead to the conclusion that encapsulation of this residual microbial biomass in sodium alginate leads to an easier-to-handle form of biomass, thus being an efficient biosorbent for static or dynamic operating systems for effluents containing moderate concentrations of reactive organic dyes.
Highlights
Current technologies for water purification have limitations that require the development of new techniques
The aim of this paper is to investigate the biosorptive properties of a newly proposed polymeric composite based on a residual microbial biomass of Saccharomyces pastorianus encapsulated in sodium alginate
We approached a working protocol that aims at three stages: (1) preparation and physical–chemical characterization of a prepared polymeric composite based on a residual biomass of Saccharomyces pastorianus encapsulated in sodium alginate; (2) an investigation of the influence of certain physical parameters on the study of the biosorption process, such as the dose of the biosorbent, the size of the composite granules, the pH of the solution, the initial concentration of the dye solution, and the temperature; (3) processing of experimental data using different adsorption equilibrium isotherms in order to estimate the characteristic parameters and thermal effects of the studied bioprocess for the treatment of dye-containing watery effluents
Summary
Current technologies for water purification (chemical precipitation, membrane separation, ion exchange, evaporation and electrolysis) have limitations that require the development of new techniques. Microorganisms are, in biotechnology, important sources for a great variety of intracellular and extracellular compounds such as: organic acids, amino acids, antibiotics [1]. In these biosynthetic processes, the residual microbial biomass is an inevitable waste generated in the separation step. The residual microbial biomass is an inevitable waste generated in the separation step These by-product microorganisms (bacteria, yeast or fungi), could be used as a potential alternative to existing technologies for the recovery of pollutants from industrial waste streams, due their ability to retain, by different mechanisms, pollutants from aqueous streams through biosorption
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