Glucan production by Rhodotorula yeasts and phenolic content reduction in olive mill wastewaters under nitro limited conditions

Olive mill wastewaters is one of the most difficult wastewaters to treat in the agricultural industry due to its chemical composition, especially its phenolic content. In this study, Rhodotorula yeast strains were examined for their ability to reduce the phenolic content of the influent but also for their ability to produce glucans. Rhodotorula diobovatum EXF-6843, Rhodotorula kratochvilovae Hamam. 1988 EXF-3471, Rhodotorula mucilaginosa EXF-8984 and Rhodotorula toruloides NRRL Y-27012 were cultivated in sterile shake flask fermentations under nitro-limited conditions (C/N=120, glucose equivalents) in wastewater from olive mills with a phenol content of ph0= 3.2 g/L including a blank fermentation in distilled water by Rhodotorula toruloides NRRL Y-27012. The results showed the maximum total glucan production: Rhodotorula toruloides NRRL Y-27012 (blank) - 1.75 g/L at after 96 hours, Rhodotorula toruloides NRRL Y-27012 (OMW) - 0.97 g/L (44.81% phenol reduction) after 76 hours, Rhodotorula kratochvilovae Hamam. 1988 EXF-3471 - 1.19 g/L (46.71% phenol reduction) after 48 hours, Rhodotorula mucilaginosa EXF-8984 - 0.77 (66.02% phenol reduction) after 96 hours and Rhodotorula diobovatum EXF-8984 – 1. 15 g/L (62.93% phenol reduction) after 72 hours. In summary, the results suggested that glucan production by Rhodotorula yeasts, can be optimized by fermentation conditions (carbon/nitrogen source, C/N, pH, temperature, etc.), and the phenol reduction were at a very satisfactory level, making them suitable to develop potential biological recovery technologies for phenols from olive mill wastewater.