Dark fermentation of expired fruit juices for biohydrogen production followed by treatment and biotechnological exploitation of effluents towards bioplastics and microbial lipids

Abstract

The treatment and biotechnological exploitation of expired fruit juices (EFJ) towards biohydrogen, polyhydroxyalkanoates (PHAs) and lipids production was investigated. The EFJ were initially fermented via an acidogenic consortium, during which the effect of the organic loading rate (OLR, 20–40 g sugars/L.d) on the sugars uptake and the yields of metabolites i.e. hydrogen, volatile fatty acids (VFAs) and lactate, was studied. The increase of the OLR resulted to lower bioconversion of sugars and metabolic shift to lactate production, whereas the highest hydrogen yield, 10.83 ± 0.41 L H2/m3 EFJ, was obtained for the OLR 30 g sugars/L.d. The acidogenic effluents were then utilized for the production of PHAs and microbial lipids, via bacterial heterotrophic and cyanobacterial consortia, respectively. The PHAs produced were in all cases copolymers, and the highest yield, 20.69 ± 1.01 kg PHAs/m3 EFJ was achieved from the effluent with the highest VFAs content. Microbial lipids were also successfully produced from all effluents. The results revealed that low VFAs and high sugars concentration, allowed cyanobacterial growth of up to 373.5 mg /L.d and maximum lipid content of up to 11.7 % d.w. (5.47 ± 0.49 kg biolipids/m3 EFJ), as well as significant substrate degradation (dissolved oxygen demand - d-COD, total nitrogen-ΤΝ, orthophosphates-PO43-, total sugars up to about 93 %, 95 %, 67 % and 96 %, respectively).