Surpassing the current limitations of biohydrogen production systems: The case for a novel hybrid approach

•The drawbacks of different biological hydrogen production strategies are addressed.•Possible mitigations are thoroughly discussed.•A novel hybrid microbial–microalgal biohydrogen production system is presented.•Integration of wastewater treatment and metabolic by-products usage is proposed.•The novel approach could play a key role in climate change mitigation.

The steadily increase of global energy requirements has brought about a general agreement on the need for novel renewable and environmentally friendly energy sources and carriers. Among the alternatives to a fossil fuel-based economy, hydrogen gas is considered a game-changer. Certain methods of hydrogen production can utilize various low-priced industrial and agricultural wastes as substrate, thus coupling organic waste treatment with renewable energy generation. Among these approaches, different biological strategies have been investigated and successfully implemented in laboratory-scale systems. Although promising, several key aspects need further investigation in order to push these technologies towards large-scale industrial implementation. Some of the major scientific and technical bottlenecks will be discussed, along with possible solutions, including a thorough exploration of novel research combining microbial dark fermentation and algal photoheterotrophic degradation systems, integrated with wastewater treatment and metabolic by-products usage.

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