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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