Trametes versicolor pellets production: Low-cost medium and scale-up

A cost analysis of a decolourization process using the ligninolytic fungus Trametes versicolor in pellet form was carried out. It established that the key to making the process cost-efficient was to reduce the cost of the culture medium for pellet production, which accounts for over 95% of the total cost of the process, due to the high price of malt extract. A cheaper defined medium was formulated in order to obtain spherical pellets approximately 3 mm in diameter. The pH of the medium played an important role in pellet production. Experiments were therefore conducted to allow the control of the pH. A stirred-tank bioreactor (1 L) was ruled out, since problems related to oxygen transfer and types of agitation have been shown to exert a great influence on pellet formation. Use of air-pulsed bioreactors solved these problems, allowing both pellet production and scale-up of the process in a 10 L air-pulsed bioreactor. The new pellet production process reduced the total cost by up to 94.4% per unit volume of wastewater treated. In a decolourization test the pellets obtained from the new process showed an outstanding performance.