Biohydrogen and the Circular Economy: Insertion of Biohydrogen Production in Biorefineries Aiming at Zero-Waste Processes

Renewable energy derived from alternative waste resources has the potential to gradually replace fossil fuels or at least supplement the ever-growing energy demand. Hydrogen is one such clean renewable energy source which can be produced from a wide range of substrates by both biological and physico-chemical processes. However, biological methods employing different classes of microorganisms seem to be advantageous over other methods from the economical and sustainability aspects. In this regard, producing biohydrogen from organic waste from different industrial, agricultural, and domestic sources is an interesting option. Hydrogen is an attractive tool due to its diverse application potential, choice of diverse substrate for its production, and capacity to reduce carbon emissions. Along with hydrogen production, this biological route can also be utilized for the production of valuable chemicals, food, feed, and other materials under the biorefinery concept. Moreover, integration of biohydrogen production processes with other systems such as methane production, microbial fuel cells, and algal bioprocess can boost the economic prospect of the entire system. This will not only provide cheap substrates for energy generation but will also fulfil the goals of circular economy, i.e. reduce, reuse, and recycle. The principle of circular economy is derived from the Paris climate conference and is built on the concept of carbon balance or net zero release to manage the energy and carbon flow.