Fermented Rice Noodle Wastewater Treatment and Ethanol Production Potential Using Entrapped Yeast Cells

Fermented rice noodle is a major source of food industry generating highly complex organic content (starch) wastewater. This study investigated the treatment of fermented rice noodle wastewater using calcium alginate entrapped yeast cells compared to the free cells. The treatment includes a two-step process: acid hydrolysis for breaking down starch to glucose and fermentation for degrading glucose to ethanol. Yeast culture, Saccharomyces cerevisiae, was used in this study. The experiment was conducted to examine optimum acid concentration and cell entrapment condition for fermentation. Sulfuric acid concentrations ranged from 0.25 to 1.00% by volume were tested while the cells entrapped in calcium alginate at cell-to-matrix (alginate) ratios (by volume) of 1:5, 1:10, and 1:20 were varied. The result showed that the optimum acid concentration of 1.00% provided 5-time higher glucose concentration compared to that in raw wastewater. After the batch fermentation, the entrapped cells reduced total chemical oxygen demand (COD) by 33-46% and glucose concentration by 88-90% while the free cells cannot obviously remove COD and reduced glucose concentration by 62%. The entrapped cells at the cell-to-matrix ratio of 1:5 achieved the best glucose biotransformation performance. The treatment reaction followed second-order kinetics. The entrapped and free cell systems gave the treatments with kinetic constants of 0.007 to 0.010 and 0.001 L/mg/hr, respectively. The entrapped and free yeast cell system potentially produced ethanol of 643 to 801 mg/L.