Wastewater Biovalorization for Sustainable Renewable Energy Production: Integration of Energy Storage Technologies.

The shift to a circular bioeconomy has shifted water from waste to a resource for renewable energy and resource recovery. Biological, electrochemical, and thermochemical conversion processes can be used to produce biofuels, bioelectricity, biohydrogen, bio-products, and biogas from wastewater, all of which contain high levels of organic matter, nutrients, and microorganisms that can be used for the production. The intermittency of renewables production, however, and the variability of wastewater composition demand the need to integrate the use of advanced energy storage technologies to guarantee stable, efficient, and resilient energy systems. The wastewater biovalorization pathways are presented and coupled with advanced energy storage technologies like lithium-ion, sodium-ion and flow batteries, supercapacitors, hydrogen storage, and thermal energy storage. The thermochemical conversion technologies, such as pyrolysis, gasification, hydrothermal liquefaction, and hydrothermal carbonization, are critically discussed with the biological approaches such as anaerobic digestion, microbial fuel cells, microbial electrolysis cells, algal biorefineries, and biochar production. Moreover, the recent advances in artificial intelligence, digital twins, monitoring on the Internet of Things, and smart energy management of wastewater treatment plants have been reviewed. Techno-economic feasibility, life cycle assessment, commercialization prospects, and policy considerations are also evaluated in the review. Finally, key technological challenges and future research directions to speed up the development of integrated wastewater-to-energy systems that will boost carbon neutrality, energy security, and sustainable water management in a circular bioeconomy are identified.