Employing Spent Frying Oil as a Feedstock to Produce Short-Chain Organic Acids Using Mixed Microbial Cultures

Food industry waste and wastewater have been explored in relation to acidogenic fermentation as sources of non-competing food carbohydrates and mixed microbial cultures (MMCs), respectively, with the aim of producing short-chain organic acids (SCOAs) with general applications in polyhydroxyalkanoates (PHAs) production. However, studies on acidogenic fermentation using lipidic substrates are scarce. In this work, it was hypothesized that spent frying oil (SFO) could be used as a substrate for SCOA production via MMCs. In this study, oleic acid was used as a model molecule. The characterization of SFO revealed that it is mainly composed of oleic acid (81%), with minor amounts of palmitic, linoleic, and stearic acids. Different MMCs and food-to-microorganism (F/M) ratios were tested. MMCs collected in the aerobic tank of a municipal wastewater treatment plant (AES), at a 1:1 F/M, allowed to obtain the highest SCOA concentration (1.50 g COD/L) and the most diverse profile of SCOAs, with the production of acetic, propionic, butyric, iso-butyric, and valeric acids at 48:17:9:13:13% on a molar basis, respectively. This variety of odd and even SCOAs is of upmost importance, with potential applications in producing PHAs. This work can be considered a starting point for future acidogenic fermentation studies using lipid-based substrates and for the future production of PHAs.

Automated summary

This study explores the use of food industry waste and wastewater for acidogenic fermentation to produce non-competing food carbohydrates and mixed microbial cultures (MMCs), aiming to produce short-chain organic acids (SCOAs) for polyhydroxyalkanoates (PHAs) production. The results show that spent frying oil (SFO) can be used as a substrate for SCOA production via MMCs, with the highest SCOA concentration and diverse SCOAs profile achieved using MMCs collected from an aerobic tank of a municipal wastewater treatment plant at a specific F/M ratio. The odd and even SCOAs produced have potential applications in PHAs production.