Valorization of industrial waste streams via yeast based bioprocesses

Industrial waste streams can be of diverse nature and many industrial waste streams have a biodegradable fraction that can be considered a sustainable source of biomass. Waste valorization via production of energy or commodity chemicals would result in decreasing the volume of waste that needs to be managed, in minimizing the environmental impact and in generating added value through the synthesis of a wide range of products. In this work we present two examples of industrial waste valorization based on the use of yeast cell factories. The first case demonstrates the possibility to valorize cotton fabric waste from an apparel textile manufacturing company. In particular, the use of the glucose-rich stream obtained upon cotton pretreatment has been used to produce lactic acid by the recombinant Saccharomyces cerevisiae CEN.PK m850 (1) with a maximum yield of 82.7% on cotton-derived glucose. The second case we present is based on the use of the glycerol-rich waste stream deriving from biodiesel production. The crude glycerol present at very high concentration has been used as substrate to produce citric acid using the yeast Yarrowia lipolytica. The produced citric acid has been used for the synthesis of Carbon Dots (CDs), that is a new type of carbon-based nanomaterials that have attracted broad research interest due to their excellent and tunable photoluminescence, high quantum yield, low toxicity, small size, appreciable biocompatibility (2). We demonstrated that CDs produced with glycerol from biodiesel waste have physico-chemical properties equal to the ones of CDs produced with pure citric acid; thus proving that glycerol-reach waste streams can be valorised via microbial cell factories for production of materials that find their application in diverse fields, such as biomedical and optoelectronics.