Microwave-activated spent biomass, Saccharomyces cerevisiae for efficient methylene blue removal: mechanistic insights and regeneration potential

The purpose of this study is to examine the influence of microwave-assisted thermal treatment of spent biomass, Saccharomyces cerevisiae from invertase production, on the removal of methylene blue from wastewater. Functional group, surface morphology, and textural properties, of thermally treated yeast cells (TSAC) and untreated yeast cells (NSAC) were evaluated using FTIR and SEM. The effect of microwave power and irradiation time on the treatment of yeast cells was assessed in terms of biosorption (%). The maximum biosorption capacities of NSAC and TSAC were 7.19 and 11.17 mg/g, respectively. TSAC demonstrated superior regeneration potential over multiple biosorption cycles, retaining more than 80% of its initial biosorption efficiency after three consecutive runs, indicating its suitability for repeated wastewater treatment. Mechanistic insights suggest that microwave-induced surface restructuring and enhanced exposure of functional groups contribute to the improved biosorption capacity of TSAC. SEM analysis revealed the increased surface roughness, formation of cavities and pores as well as micro-cracks that can potentially facilitate the approach of MB molecules to their binding sites on the biosorbent surfaces. This valorisation of spent yeast biomass supports circular economy principles by converting enzyme production waste into an effective biosorbent for toxic pollutant removal.