Transforming dairy waste into hydrogen fuel using alginate-encapsulated bacterial co-cultures

Dairy waste, such as whey resulting from cheese production, is produced in massive volumes worldwide and is regarded as environmentally difficult to dispose of due to its high organic content¹. Harnessing the potential of this waste material to support the synthesis of valuable products such as hydrogen fuel or reduced graphene oxide, which may be utilized for conductive thin films and energy storage^2,3, can reduce waste and add revenue streams for dairy farmers. Here, we demonstrate a circular bioeconomy using alginate-encapsulated co-cultures of Shewanella oneidensis together with lactic-acid-producing bacteria Klebsiella pneumoniae. These co-cultures can directly metabolize unprocessed cheese-making waste as an electron source instead of costly, environmentally high-impact lactic acid^4,5. Alginate-encapsulated co-cultures fed unprocessed dairy waste showed a 2-to-3-fold higher graphene oxide reduction rate compared to S. oneidensis monocultures with no supplemental electron source. Encapsulated co-cultures were able to be recycled for more than 30 days with no measurable decrease in graphene oxide reduction efficiency, showing compatibility with future industrial scaling. Photocatalytic hydrogen generation with cadmium selenide quantum dots as the catalyst resulted in 6-fold increases in hydrogen produced by co-cultures using milk as an electron source precursor for the system in comparison to S. oneidensis monocultures without any added electron sources. Thus, dairy waste may be processed to drive the synthesis of valuable products utilizing microbial electron transfer processes, converting a significant fluvial environmental pollutant into a valuable renewable energy resource that could provide a robust alternative revenue stream for dairy farmers in a volatile industry.