Supercritical water gasification (SCWG) as a potential tool for the valorization of phycoremediation-derived waste algal biomass for biofuel generation

Phycoremediation is an emerging technology, where algae-based processes were used to effectively remove nutrients, organic wastes, and toxic heavy metals from the polluted environment. The waste algal biomass obtained after phycoremediation, which may contain residual hazardous materials, could still be used as feedstock to produce biofuels/bioenergy preferably through thermochemical conversion technology. This review proposes a synergistic approach by utilizing the phycoremediation-derived algal biomass (PCDA) as feedstock for efficient hazardous waste treatment and clean energy generation via supercritical water gasification (SCWG). The review provides an in-depth study of catalytic, non-catalytic, and continuous SCWG of algal biomass, aiming to lay out the foundations for future study. In addition, the concepts of heat integration as well as water, nutrient, and CO₂ recycling were introduced for a sustainable algae-to-biofuel process, which significantly enhances the overall energy and material efficiency of SCWG. The production of biofuel from algal biomass via other advanced gasification technologies, such as integration with other thermochemical conversion techniques, co-gasification, chemical looping gasification (CLG), and integrated gasification and combined cycle (IGCC) were also discussed. Furthermore, the discussion of kinetics and thermodynamics models, as well as life cycle and techno-economic assessments, appear to provide insights for future commercial applications.