Composites Based on Natural Polymers and Microbial Biomass for Biosorption of Brilliant Red HE-3B Reactive Dye from Aqueous Solutions

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 (pH(PZC), 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 (ΔH(0) = −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.