Acidogenic fermentation of dairy by-products for the utilization of volatile fatty acids IN PHBV production by Haloferax mediterranei†

Abstract

In this study, the acidogenic fermentation (AF) of cheese whey (CW) has been conducted to obtain streams with different volatile fatty acid (VFA) profiles for polyhydroxyalkanoate (PHA) biosynthesis. AF was carried out in single-phase reactors for parameter optimization under mesophilic and thermophilic conditions, and streams with 2718.2 mg L⁻¹ of VFA (predominantly acetic acid, 1288 mg L⁻¹, and propionic acid, 1119 mg L⁻¹) and 2270.2 mg L⁻¹ of VFA (predominantly butyric acid, 1339 mg L⁻¹), were obtained, respectively. The thermophilic conditions were scaled up in a two-phase leachate bed reactor to obtain a final stream with a VFA concentration of 7879 mg L⁻¹ composed mainly of butyric acid. Then, the technical feasibility of using the obtained streams as substrates for the production of poly(3-hydroxybutyrate-co-valerate) (PHBV) by Haloferax mediterranei was demonstrated. The PHBV production was found to be related to the butyric acid content, as the PHBV production was 1.4 vs. 0.3 g L⁻¹ when using the streams rich in butyric acid vs. propionic acid, but the monomeric composition was dependent on the presence of propionic acid. A maximum PHVB production of 2.43 g L⁻¹ and PHA accumulation of 44.3% were reached after 120 h of cultivation in bioreactor conditions. The characteristics of the produced PHBV bioplastic were compared with those of a commercial-grade PHA and found to be similar.