Evaluation of encapsulated Saccharomyces cerevisiae ATCC 9763 for methyl red degradation

Biological treatments employing immobilized microorganisms are increasingly being used for wastewater treatment bioreactors due to their many advantages. In the present work, encapsulated Saccharomyces as a potent GRAS microorganism is proposed for biodecolourization process. Methyl red, with a single azo group in its chemical formula, was chosen as a model azo dye for the biodecolourization studies. Various masses of S. cerevisiae ATCC 9763 were encapsulated in alginate beads and employed for removal of methyl red (100 mg.L-1) from the synthetic wastewater (SWW). Although increasing the cells entrapped in alginate beads caused an increase in decolourization rate, a mass ratio of cells to alginate beads greater than ≃1:10 (equivalent to ) led to a disruption of beads and release of cell content. The spectrophotomeric method showed that 2.5 g yeast cells entrapped in beads led to complete decolourization during 4±0.5h in an anaerobic mixed system, whereas the static medium was not completely decolourized during this period. Further studies on stored encapsulated cells exhibited that cell viability and decolourizing potential remained unchanged after a 50-day period of storage of encapsulated cells in saline; however, after 100 days, the color variations observed during the decolourization process changed significantly despite the retention of cell viability. Scanning electron microscopy (SEM) revealed that decolourization caused the shrinkage of cell surface. Moreover, morphological studies showed that osmotic pressure induced by the storage (> 50 days) in normal saline solution occasioned deformation of yeast cells, shrinkage and crenation of the outside envelope as well.

Keywords:

Biodecolourization , Saccharomyces cerevisiae , Encapsulation , Methyl red , Azo dye