Using yeast cultures to valorize tequila vinasse waste: An example of a circular bioeconomy approach in the agro-industrial sector

Inadequate disposal of tequila vinasses (TV) has the potential to generate severe environmental degradation. Therefore, cost-effective treatment and revalorization strategies for TV are required. In this study, a circular bioeconomy approach is presented for the simultaneous treatment and revalorization of TV as a source of animal feed through the culture of fodder yeast species (Candida utilis, Kluyveromyces marxianus and Rhodotorula mucilaginosa). Culture treatments (monocultures and mixed cultures) were evaluated for the removal of pollutants (chemical oxygen demand, total nitrogen, and total phosphorus) as well as protein production. A weighted performance index was used to evaluate the treatments and the best culture conditions were selected for benchtop-scale evaluation. Benchtop-scale cultures were monitored every 8 h for 48 h, and the following six response variables were measured: chemical oxygen demand, total nitrogen, total phosphorus, viable biomass, protein concentration and reducing sugar concentration. Kinetic parameters were determined for the cultures based on a mass balance model coupled with Monod's equation using a differential neural network and an optimization algorithm. The obtained biomass was spray-dried and analyzed to determine its amino acid composition and to evaluate its applicability as an animal feed supplement. The present study contributes to the development of new high-value yeast-based biorefinery TV treatment approaches that are aligned with circular bioeconomy principles and regional feed requirements. The results herein show that TV can be used as a substrate to produce a high-value yeast-based protein source (18.08 ± 2.73 g L−1) for livestock feed applications while reducing chemical oxygen demand (33.33 ± 3.46%), nitrogen (85.01 ± 8.66%) and phosphorus loads (54.08 ± 2.50%). Additional ‘proof of concept’ research is now warranted to implement this process at both pilot- and full-scale levels.