Whey and molasses as inexpensive raw materials for parallel production of biohydrogen and polyesters via a two-stage bioprocess: new routes towards a circular bioeconomy

Consecutive dark-fermentation and photo-fermentation stages were investigated for a profitable circular bio-economy. H2 photo-production versus poly(3-hydroxybutyrate) (P3HB) accumulation is a modern biotechnological approach to use agro-food industrial byproducts as no-cost rich-nutrient medium in eco-sustainable biological processes. Whey and molasses are very important byproducts rich in nutrients that lactic acid bacteria can convert, by dark-fermentation, in dark fermented effluents of whey (DFEW) and molasses (DFEM). These effluents are proper media for culturing purple non-sulfur bacteria, which are profitable producers of P3HB and H2. The results of the present study show that Lactobacillus sp. and Rhodopseudomonas sp. S16-VOGS3 are two representative genera for mitigation of environmental impact. The highest productivity of P3HB (4.445 mg/(L·h)) was achieved culturing Rhodopseudomonas sp. S16-VOGS3, when feeding the bacterium with 20% of DFEM; the highest H2 production rate of 4.46 mL/(L·h) was achieved when feeding the bacterium with 30% of DFEM.