(116f) Fenton-Based Oxidation As a Pre-Treatment to Sugarcane Vinasse to Lower Inhibition to the Growth of Oleaginous Fungi

The utilization of sugarcane vinasse as a feasible culture medium for fungi is hindered by the presence of inhibitory compounds, such as phenols and other recalcitrant structures. Vinasse contains a rich mineral and organic composition, which could theoretically used as nutrients and support the growth of fungi of biotechnological interest. Considering the high volumetric production of vinasse, there is a significant potential of producing value-added compounds through the utilization of microorganisms that can efficiently grow in vinasse. While it has been demonstrated that the nutrients in vinasse can support the cell growth and lipid accumulation of a wild strain of the zygomycete Mucor circinelloides (Reis et al., 2019), the presence of phenolics compounds demonstrate to pose considerable inhibitory effects on both lipid and biomass productivities by M. circinelloides. In this sense, this work analyzes the effect of different homogeneous oxidation processes used to pre-treat vinasse prior to fungal culturing. Advanced oxidation processes (AOP) represent a wide array of wastewater treatment options. The principle of most AOP techniques is involved with the high reactivity of radicals generated, which promotes oxidation of all sorts of pollutants and recalcitrant components in wastewater. Multiple AOP have been described in the literature aiming to degrade molecules that present are little to no biodegradable, including those based in ultraviolet irradiation (UV), Fenton reaction, and the oxidizing power of peroxides. With this in mind, vinasse was treated using a batch system with the addition of Fe²⁺ (Fenton), in the presence of UV, and with the addition of hydrogen peroxide (H₂O₂). The experimental design followed a full factorial design, evaluating the effect of Fenton, and Fenton combined with UV and with H₂O₂, under two different pH values, i.e., 4.5 and 10. Results show that all the reaction systems were able to degrade part of the Chemical Oxygen Demand (COD), ranging from 18.4% up to 54.1% in the factorial results. All the oxidation assays were also able to degrade the phenolic compounds present in vinasse, achieving values as high as 86.2% in the system based in the combination of Fenton with H₂O₂ addition assisted by UV irradiation. The pre-treated vinasse samples were assayed for the growth performance of M. circinelloides, demonstration that the control value of 3.54 g _biomass L^-1_vinasse was increased to values as high as 4.84 g _biomass L^-1_vinasse when the vinasse pre-treated by Fenton assisted by peroxide addition was used as culture medium. In addition, the control conditions indicated a lipid productivity of 152 mg L^-1 day^-1, which was increased by about 73% (265 mg L^-1 day^-1) when the vinasse treated by UV-assisted fenton system was used. Therefore, this work demonstrates the potential of integrating efficient homogenous Fenton-based systems to the pre-treatment of vinasse in order to increase its feasibility as culture media for fungi of biotechnological interest.
Ref.: Reis, C. E. R., Carvalho, A. K. F., Bento, H. B., & de Castro, H. F. (2019). Integration of microbial biodiesel and bioethanol industries through utilization of vinasse as substrate for oleaginous fungi. Bioresource Technology Reports, 6, 46-53.