Utilization of Yeast Industry Waste Water by Aspergillus niger ATCC 16404 to Produce Citric Acid

Background and aim: Citric acid is an organic acid that is widely used in food, confectionary, drink and pharmaceutical industries. In Jordan, some industries produce wastes as a result of the manufacturing process. One of the most important wastes is the Yeast Industry Wastewater (YIW) that is produced in large quantities. In this study, YIW was employed as a fermentation medium for Aspergillus niger to produce citric acid. Materials and methods: In preliminary experiments growing A. niger in Petri-plates containing different concentrations of YIW, the results revealed that undiluted (100%) YIW was the most suitable concentration for growing A. niger. Shake cultures of YIW were prepared to optimize the process of citric acid production. Results: The results revealed that fungal growth and metabolism were achieved when the fungus was grown at 27 ˚C in a YIW medium pH of 6.0, supplied with 0.5% KH2PO4, 2% ammonium sulphate, and 10% sucrose. A batch culture bioreactor experiment was conducted using Continues stirred tank reactor at the optimum conditions mentioned above. This experiment contributed to enhance citric acid production by 19 folds recoding a concentration of 36.4 g/l after 7 days of fermentation compared to shake culture experiments. The total carbohydrates concentration kept decreasing while the citric acid concentration was elevating to record a maximum yield (YP/S) of 31%. Conclusion: In conclusion, YIW is a promising media for citric acid production with additional benefits of its use with regard to environmental and economic aspects