Biohydrogen and polyhydroxyalkanoates (PHA) as products of a two-steps bioprocess from deproteinized dairy wastes

In this study a two-steps bioprocess approach aimed at biohydrogen production via dark-fermentation, and polyhydroxyalkanoates-PHA production by mixed microbial cultures, was proposed to valorise two dairy-waste streams coming from cheese whey deproteinization (i.e. Ricotta cheese production and ultrafiltration). During the first step, the increase of OLR was tested, resulting in higher daily H₂ volume (3.47 and 5.07 NL H₂ d^-1 for second cheese whey-SCW and concentrated cheese whey permeate-CCWP) and organic acids production (14.6 and 12.6 g L^-1 d^-1 for SCW and CCWP) for both the substrates, keeping good conversion of sugars into H₂ (1.37 and 1.93 mol H₂ mol^-1 sugars for SCW and CCWP). During the second step, the organic acids were used for PHA production reaching high conversion yields for both the fermented streams (as average 0.74 ± 0.14 mg COD_PHA mg^-1 COD_OA-in), with a maximum polymer content of 62 ± 4.5 and 55.1 ± 1.3% (g PHA g^-1 VSS) for fermented SCW and fermented CCWP respectively. For the results reported, this study could be taken into consideration for larger scale application.