Cultivation and lipid production of yeast Cryptococcus curvatus using pretreated waste active sludge supernatant.

Oleaginous yeast Cryptococcus curvatus has become some of the most promising feedstock for biodiesel production due to their high production efficiency. However, high cost of cultivation, especially substrate cost, hinders rapid commercialization of yeast-based biodiesel. In this study, waste activated sludge (WAS), which is rich in nutrients and organic matters, was examined as an economic substitute for organic substances. To be efficiently bioavailable, WAS must be pretreated. Hydrodynamic cavitation reaction time and pH were identified as experimental factors, whereas growth rate was selected as response parameter. The experimental factors were optimized employing Response Surface Methodology (RSM). Growth rate of 1.13/h was optimized at reaction time 12.5 min and pH 8.65. When sludge pretreated under these optimal conditions was used as a substitute to yeast extract, 9.84 g/L of biomass was obtained in a day and lipid was accumulated up to 23% of dry weight.