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BACKGROUND The influence of pH, sludge retention time (SRT) and organic loading rate (OLR) were evaluated in the fermentation of cheese whey to produce volatile fatty acids (VFA) in a sequencing batch reactor (SBR). The reactor performance was studied at SRT of 4, 6 and 10 days and the influence of pH (5, 5.5 and 6) was determined at each SRT. The OLR effect was also studied in the range 3 to 12 g COD L‐1 d‐1, while keeping the other parameters mentioned above constant. RESULTS A more acidic pH , improved the degree of acidification at short SRT (4 and 6 days), reaching 76 and 84%, respectively, meanwhile at pH 6 the degree of acidification (DA) improved and reached 85% at longer SRT (10 d). Regarding the VFA profile, a pH shift from 5 to 6 stimulated the production of acetic and propionic acids, whereas the production of butyric and valeric acids decreased irrespective of the SRT applied. Moreover, the increase of SRT from 4 to 10 d boosted propionic and valeric acids production regardless of the pH applied. Lower OLR favoured the production of propionic and valeric acids, while higher OLR increased the production of butyric acid. Lactose degradation and VFA production followed the Michaelis–Menten model. CONCLUSION A selective VFA distribution can be reached by modifying parameters such as pH, SRT and OLR in acidogenic reactors, therefore, they could be suitable for further valorisation purposes in the production of polyhydroxyalkanoates from such VFA. © 2017 Society of Chemical Industry

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Agroindustrial by-products hold an enormous potential to be bioconverted into high-value-added products such as polyhydroxyalkanoates (PHA), a cost-effective alternative to conventional plastics. In this study, cheese whey, a highly abundant side stream of the cheese making process, was explored as a feasible substrate for the selection of a mixed culture highly enriched in PHA-storing bacteria using a sequencing batch reactor under an aerobic dynamic feeding regime. For that, the absence/presence of thiourea, magnesium and iron, as well as the application of two different organic loading rates (OLR), i.e., 60 and 80 CmM d−1, were tested. The results showed an improved culture selection when thiourea, magnesium and iron were added to the culture medium as well as when the highest OLR was applied. Under these conditions, the biomass achieved a maximum PHA storage of 54% and a PHA production rate of 4.81 Cmmol-PHA L−1 h−1. Additionally, the study of the microbial community showed that during this period of maximum productivity, the biomass was enriched in Azoarcus and Amaricoccus bacterial species. Conclusively, cheese whey can be considered a good feedstock to efficiently select a mixed culture with high potential to accumulate PHA and a good way to give this by-product added value.

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