Enhancing Anaerobic Digestion with an UASB Reactor of the Winery Wastewater for Producing Volatile Fatty Acid Effluent Enriched in Caproic Acid

The production of Volatile Fatty Acids (VFAs) from wastewater holds significant importance in the context of biorefinery concepts due to their potential as valuable precursors for various bio-based processes. Therefore, the primary objective of this research is to investigate the fermentation of Winery Wastewater (WW) in an Upflow Anaerobic Sludge Blanket (UASB) reactor to generate VFAs, with particular emphasis on Caproic Acid (HCa) production and the dynamics of the microbiota, under varying Hydraulic Retention Time (HRT) periods (8, 5, and 2.5 h). The change from an 8 h to a 5 h HRT period resulted in an approximately 20% increase in total VFA production. However, when the HRT was further reduced to 2.5 h, total VFA production decreased by approximately 50%. Concerning the specific production of HCa, expressed in grams of Chemical Oxygen Demand (gCOD), the maximum yield was observed at around 0.9 gCOD/L for a 5-h HRT. Microbial population analysis revealed that Eubacteria outnumbered Archaea across all HRTs. Population dynamics analysis indicated that the Firmicutes Phylum was predominant in all cases. Within this phylum, bacteria such as Clostridium kluyveri and Clostridium sp., known for their ability to produce HCa, were identified. Based on the results obtained, the application of the UASB reactor for WW treatment, within the biorefinery framework, has the potential to provide a practical alternative for HCa production when operated with a 5 h HRT.

Automated summary

The fermentation of winery wastewater in an Upflow Anaerobic Sludge Blanket (UASB) reactor was investigated for the production of Volatile Fatty Acids (VFAs) and specifically Caproic Acid (HCa). The study focused on the dynamics of microbiota and the impact of varying Hydraulic Retention Time (HRT) periods (8, 5, and 2.5 h). Results showed that reducing HRT from 8 to 5 hours increased total VFA production by approximately 20%, while further reducing HRT to 2.5 hours decreased total VFA production by approximately 50%. Maximum HCa production was observed at a 5-h HRT. Microbial population analysis revealed the dominance of Eubacteria over Archaea, with the Firmicutes Phylum being predominant. Bacteria such as Clostridium kluyveri and Clostridium sp., known for their ability to produce HCa, were identified. The findings suggest that the UASB reactor has practical potential for HCa production when operated with a 5-h HRT, within the biorefinery framework.