Valorizing sugarcane vinasse and agricultural residues via ruminal acidogenesis

Sugarcane vinasse, a by-product of ethanol industries, is rich in organic matter and salts. While its environmental release as wastewater causes considerable pollution, it also represents a viable feedstock for valorization through microbial fermentation, a potential explored herein. The study evaluated the acidogenic potential of bovine ruminal microbiota on vinasse supplemented with dried domestic organic waste (DDOW) under different temperature conditions (25 and 39 °C), substrate sterility, and oxygen availability (oxic and microoxic). Changes in pH values were monitored over 28 days, and the results showed that non-sterile vinasse with DDOW at 39 °C achieved the most significant pH reduction, from an initial 4.1 to 3.8 under microoxic conditions. Response surface methodology (RSM) was applied to optimize sterile vinasse- and DDOW concentrations, and incubation time to achieve maximum volatile fatty acids (VFA) production, demonstrated by pH reduction. Statistical optimization analyses showed that the optimal vinasse- and DDOW amount, to achieve significant pH decreases (p < 0.001), was found at concentrations of 102 g L −1 and 20 g L −1 , respectively. Total VFA were measured by High Performance Liquid Chromatography (HPLC) during the incubation period, and there was an increase from 14.8 ± 2.5 g L −1 to 27.3 ± 0.9 g L −1 after 28 days of incubation. The concentration of four essential amino acids after 28 days of inoculation showed notable variation, among them tyrosine exhibited the most pronounced increase (1.47-fold) and lysine also increased considerably (1.23-fold). Isolation of microorganisms and microscopic examinations confirmed the presence of diverse morphotypes of acidogenic bacteria and yeasts. Re-inoculation experiments with isolated microorganisms highlighted that a diverse microbial community and its interactions drive acidogenic activity. Metabarcoding analysis showed the microbial shift from Bacteroidota to Bacillota in inoculated sterile vinasse. These results demonstrate that bovine rumen microbiota can efficiently convert the acidic composition of the vinasse and increase total VFA production, providing a basis for its sustainable valorization.