Cheese whey integrated valorisation: Production, concentration and exploitation of carboxylic acids for the production of polyhydroxyalkanoates by a fed-batch culture

The present work aimed to verify the feasibility of producing polyhydroxyalkanoates (PHAs) at high concentrations from an alternative and cheap carbon source such as the carboxylic acids (VFAs) obtained by the anaerobic fermentation of cheese whey (CW). An electrodialysis (ED) step was proposed for the obtainment of a concentrated acidic stream, suitable for being employed as feeding solution in the consecutive fed-batch culture system for PHAs production. Experiments conducted in duplicate shown that a packed bed anaerobic bioreactor resulted a robust and high repeatable culture system for a high performing continuous production of VFAs from CW. The acidogenic effluent contained 12.55 ± 1.10 g L⁻¹ of carboxylic acids (ca. 90% of the effluent soluble COD), including the hexanoic (4.13 ± 0.56 g L⁻¹) and octanoic (3.12 ± 0.94 g L⁻¹) acids. The application of 7 sequential batch ED processes allowed to obtain a carboxylic acids concentrated stream (ca. 63 g L⁻¹); by the achievement of high molar flow. Finally, this stream was utilized as the feeding solution in a fed-batch fermentation aimed to produce PHAs. The attained PHAs yield (ca. 0.60 g_PHAs g_VFAs⁻¹) was comparable to that obtained in a parallel test accomplished with a VFAs-water simulating solution and also to those previously reported from pure VFAs; i.e. no inhibition effects due to the employment of an actual biowaste as the feedstock were detected. As a whole, the results allow to conclude that the proposed integrated valorisation scheme fed with CW for the production of PHAs by an ED-concentrated carboxylic acids solution is technically feasible and robust.