Waste-Derived Renewable Hydrogen and Methane: Towards a Potential Energy Transition Solution

Anaerobic digestion (AD) is an environmentally friendly process for recovering low-carbon energy from the breakdown of organic substrates. In recent years, AD has undergone a major paradigm shift, and now the technology is not only considered as a “waste treatment” method and is instead viewed as a key enabler of the future “circular economy” with its potential for resource recovery (low-carbon energy, safe water, and nutrients). Currently, waste-derived biogas from AD is the most affordable and scalable source of renewable energy. Biomethane (upgraded biogas) can serve as a significant renewable and dispatchable energy source for combating the problem of global warming. Acidogenesis, an intermediate step of AD, can produce molecular hydrogen (H2) along with green chemicals/platform chemicals. The use of low-carbon hydrogen as a clean energy source is on the rise throughout the world, and is currently considered a potential alternative energy source that can contribute to the transition to a carbon-neutral future. In order to determine the future trade routes for hydrogen, nations are developing hydrogen policies, and various agreements. Hydrogen produced by biological routes has been found to be suitable due to its potential as a green energy source that is carbon neutral for the developing “Hydrogen Economy”. Recently, hydrogen blended with methane to a specific proportion and known as biohythane/hydrogen-enriched compressed natural gas (HCNG) has emerged as a promising clean fuel that can substantially contribute to an integrated net-zero energy system. This review provides an overview of the current state of fermentative hydrogen and methane production from biogenic waste/wastewater in a biorefinery approach and its utilization in the context of energy transition. The limitations and economic viability of the process, which are crucial challenges associated with biohydrogen/biomethane production, are discussed, along with its utilization.