Effect of Operational Parameters in the Continuous Anaerobic Fermentation of Cheese Whey on Titers, Yields, Productivities, and Microbial Community Structures

Volatile fatty acids (VFAs) were produced using cheese whey as feedstock. A mixed culture packed bed bioreactor was set up to digest anaerobically, under an acidogenic condition, a water solution of a cheese whey powder. Batch tests pointed out that the whole VFAs production process occurred via two sequential phases: (a) conversion of lactose into lactic acid and (b) conversion of lactic acid into a mixture of VFAs. Furthermore, the same tests showed that the ceramic material Vukopor S10 can be used as an effective support for cell immobilization in anaerobic fermentation processes. The effect of the hydraulic retention time (HRT) and organic loading rate (OLR) were then studied in a benchtop bioreactor operated continuously. By a HRT of 6 days, ORL of 4.2 g/L/d, and pH 5.8–6, 16 g·L^–1 of total VFAs were produced, with a yield higher than 75% (Cmol_VFAs·Cmol_lactose^–1). Characterization with Illumina-based sequencing suggested that high VFAs productivities were obtained when microbial community structures developed in the biofilm reactor were highly enriched in few genera