Biohydrogen production from agro-industrial waste: Toward clean energy and a circular economy

The growing world need of clean and renewable energy requires formulation of sustainable strategies that are capable of effectively converting organic waste into substitutes. Agro-industrial residues which include beet pulp, used coffee grounds and whey, in this case form an enormous unused biomass with high bioenergetic potential. This paper presents a combined discussion of the main biological routes to biohydrogen generation based on agro-industrial wastes and dark fermentation, photofermentation, and coupled H2-CH 4. Dark fermentation is based on the capability of anaerobic microorganisms to quickly transform organic material to hydrogen, whereas the ratio of photofermentation improves the product by recovering organic acids of the first step with the aid of photosynthetic bacteria. Moreover, the biohydrogen generation in combination with anaerobic digestion would allow the complete valorization of organic waste to biomethane, hence, maximizing the total energy balance and reducing environmental costs. The effect of important operating parameters such as pH, temperature, substrate composition, and fermentation time are also talked about in order to streamline the process performance. All in all, combined biological methods of agro-industrial waste include the integrated valorization of waste, which is a promising concept in terms of sustainable energy generation, greenhouse gas emissions, and the concept of a circular economy.