Pilot-scale production of polyhydroxyalkanoates from cheese whey: Assessing the role of mixed microbial cultures

Polyhydroxyalkanoate (PHA) is a biopolymer of great commercial interest due to its similarity to conventional plastic. In this study, polyhydroxyalkanoate production from volatile fatty acids obtained from the fermentation of cheese whey was investigated in three bioreactors at the pilot scale process. The study analysed the effects of organic loading rate (OLR) and solids retention time (SRT) on volatile fatty acids and PHA yields, as well as identified the microbial communities at each stage. In the acidogenic reactor, OLR of 3.5, 4.3, and 6.0 gCOD L⁻¹ d⁻¹ were tested with varying SRT between 5 and 10 days. In the PHA enrichment reactor, three OLR (0.7, 1.1, and 1.5 gCOD L⁻¹ d⁻¹) and SRT of 6, 5, and 4 days were evaluated. In the first bioreactor, cheese whey was converted to volatile fatty acids with an acidification ranging from 69 % to 84 % gCODeffluent gCODinitial−1. In the second bioreactor, used for enriching biomass capable of accumulating PHA from volatile fatty acids, a yield of 0.27 – 0.33 mmolCPHA mmolCVFA−1 was achieved. In the final tests of polyhydroxyalkanoate accumulation in a third bioreactor, PHA levels reached 0.50 – 0.79 gPHA gDryBiomass−1. Microbial community analysis performed with genome-focused metagenomic, revealed a predominance of the novel phylum Candidatus Saccharibacteria in the acidogenic reactor and the importance of this phylum in the process of acidogenesis. In the second reactor, the dominant microbial group was from the Rhodocyclaceae family, complemented by smaller populations of genera such as Thauera and species like Plasticicumulans acidivorans.