Optimization of volatile fatty acid production by sugarcane vinasse dark fermentation using a response surface methodology. Links between performance and microbial community composition

The recovery of volatile fatty acids (VFA) from waste and wastewaters has recently been pointed out as a promising strategy for adding value to residues, which characterizes the carboxylate platform. The exploitation of sugarcane vinasse within the carboxylate platform is still an incipient approach and has to be further investigated to determine the conditions which optimize the process. This study aimed to optimize the production of VFA (as the sum of concentrations of acetic, butyric and propionic acids) through the dark fermentation (DF) of sugarcane vinasse. A central composite design (CCD, factorial 2(2)) and response surface methodology (RSM) regarding two independent variables, namely, temperature (33-47 degrees C) and initial pH (7.1-9.9), was performed. Experiments were conducted in batch reactors using diluted vinasse (COD = 10 g L (-1)) without nutrient supplementation. The results showed that the production of VFA reached a peak of 2,980 mg L (-1) (as the sum of VFA produced), yield of 332 mg-CODVFA g 1CODtinicial and productivity of 619 mg-COD L (-1) d (1)) at 39.6.C and initial pH of 8.8. The microbial community analysis performed by 16S rRNA gene amplicon sequencing showed that organisms from the families Clostridiaceae, Enterobacteriaceae and Lachnospiraceae, and Veillonellales-Selenomonadales order prevailed during higher VFA production, whilst the presence of Desulfotomaculales and Lactobacillaceae families could be associated with VFA consumption and lactic acid production, respectively. These results provide a basis for vinasse management within the carboxylate platform context, potentially diversifying the product portfolio of sugarcane biorefineries.