Thermal and alkaline pre‐treatments of inoculum halt methanogenesis and enable cheese whey valorization by batch acidogenic fermentation

Abstract

AbstractBACKGROUNDCarboxylates such as volatile fatty acids (VFA) can be produced by acidogenic fermentation (AF) of dairy wastes including cheese whey, a massive residue produced at 160.67 million m3 of which 42% are not valorized and impact the environment. In mixed‐culture fermentations, selection pressures can favor AF and halt methanogenesis. In this study, inoculum pre‐treatment was evaluated as a selective pressure for AF demineralized cheese whey in batches. Alkaline (NaOH, pH 8.0, 6 h) and thermal (90 °C for 5 min, ice‐bath until 23 °C) pre‐treatments were tested with batch operations runs at initial pH 7.0 and 9.0, food‐to‐microorganism (F/M) ratios of 0.5 to 4.0 g COD g−1 VS, and under pressurized (P) and nonpressurized (NP) headspace, in experiments duplicated in two different research institutes.RESULTSAcetic acid was highly produced on both Unicamp and TU Delft samples (1.36 and 1.40 g CODAcOH L−1, respectively), at the expense of methanogenesis by combining a thermal pre‐treatment of inoculum with a NP batch operation started at pH 9.0. Microbial communities comprising VFA and alcohol producers, such as Clostridium, Fonticella and Intestinimonas, and fermenters such as Longilinea and Leptolinea. The lipid‐accumulating Candidatus microthrix was observed in both bulk material and foam. Despite the absence of methane production, Methanosaeta were detected within the microbial community. An F/M ratio of 0.5 g COD g−1 VS led to the best VFA production of 1769.4 mg L−1.CONCLUSIONOverall, inoculum thermal pre‐treatment, initial pH 9.0 and NP headspace acted as a selective pressure for halting methanogenesis and producing VFAs, valorizing cheese whey via batch acidogenic fermentation. © 2024 Society of Chemical Industry (SCI).