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 content. Harnessing the potential of this waste material to support the synthesis of valuable products such as hydrogen fuel 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 to produce molecular hydrogen. These co-cultures can directly metabolize unprocessed cheese-making waste as an electron source instead of costly, environmentally high-impact lactic acid. Alginate-encapsulated co-cultures were initially optimized using graphene oxide reduction assays and could be recycled for more than 30 days with no measurable decrease in extracellular reduction efficiency, showing compatibility with future industrial scaling. Photocatalytic hydrogen generation by the optimized co-cultures using milk as an electron source precursor with cadmium selenide quantum dots as the catalyst resulted in six-fold increases in hydrogen produced in comparison to S. oneidensis monocultures without any added electron sources. Thus, by utilizing microbial electron transfer processes, a significant fluvial environmental pollutant may be converted into a valuable renewable energy resource.