Butyric acid dominant volatile fatty acids production: Bio-augmentation of mixed culture fermentation by Clostridium butyricum.

• Bioaugmentation of C. butyricum enhanced the symbiotic relation in the mixed culture. • Butyric acid production in the bioaugmented mixed culture was increased 11 times. • Total VFA production was increased 3.5 times by bioaugmentation. • Bioaugmentation improved also the production of acetic, propionic and valeric acids. • Dairy industry wastewater was used as substrate for bioaugmentation. The most sustainable and environmentally friendly butyric acid production method is fermentation; however, low production yield and high substrate cost limit the competition with petrol-based production. The study is aimed to enhance butyric acid production via bioaugmentated mixed culture by Clostridium butyricum. Anaerobic sequencing batch reactors (bioaugmented and control) were operated under alkali pH (pH 10) at 35 °C and fed by dairy industry wastewater as substrate. The performance of bioaugmentation was monitored in three stages: before the application, during the application (C. butyricum was injected as %10 of active reactor volume on a daily basis for seven days), after bioaugmentation. The VFA concentration and composition (by GC-FID) with the copy gene number of C. butyricum (by Q-PCR) were monitored in the bioaugmented reactor during the operation. The bioaugmentation of C. butyricum increased butyric acid production (mgCOD L^-1) from 260 ± 36 to 2889 ± 180. The total VFA production (mgCOD L^-1) was increased from 1434 ± 217 to 4642 ± 1778 in control and bioaugmented reactors, respectively. There was a positive correlation between the gene copies of C. butyricum with butyric, hexanoic, n-heptanoic, valeric acids production. Furthermore, the bioaugmented mixed culture had better performance than pure culture regarding butyric acid production. The cycle analysis showed that the similar butyric acid production efficiency would be obtained in the first 6 h in the bioaugmented reactor, in the first 14 h in the control reactor of the cycle. The study provides a fundamental solution to step forward to achieve next-generation biorefineries by using both monocultures modularity and mixed culture robustness and stability regarding. [ABSTRACT FROM AUTHOR]