Valorization of Reground Pasta By-Product through PHA Production with Phototrophic Purple Bacteria

Annually, the food industry generates large amounts of waste and by-products, causing serious problems in their management and final disposal. In particular, by-products are mainly recovered as livestock feed. A most appealing strategy to valorize them has herein been investigated, through polyhydroxyalkanoate (PHA) production. In this view, a stream rich in volatile fatty acids deriving from the acidogenic fermentation of reground pasta (RP), a farinaceous food-industry by-product, was used as a carbon source for PHA production with a phototrophic purple bacteria (PPB) consortium. PPB are very versatile organisms that present a unique metabolism allowing them to adapt to a variety of environmental conditions. The PPB-PHA enrichment phase was performed in a lab-scale semi-continuous photo-bioreactor under a permanent carbon feast regime, with organic loading rate (OLR) increments from 14 to 19 mmolC/Ld. The results showed that the fermented RP solution composition (with 23.4% of HV precursors on a COD basis) was suitable for the PHBHV copolymer production, with the PPB consortium being capable of reaching a very high content in the hydroxyvalerate (HV) monomer, with a maximum of 60% (gHV/gPHA). Regarding the PHA accumulation stage where the light intensity was increased up to 20.2 W/L, a further increase in the culture PHA content by 76% after 12 h was obtained. Overall, these results open the possibility of valorizing food-industry by-products through the development of a biocatalytic process for PHA production with PPB, thus making the overall approach more sustainable from a green perspective.