Progress in biohythane production from microalgae-wastewater sludge co-digestion: An integrated biorefinery approach

Recent advances in microalgae to biohythane (bio-H₂ and bio-CH₄) conversion have achieved growing attention due to their eco-friendly and energy-efficient nature. Although microalgae are considered a potential 3rd - 4th generation biomass, their low C/N ratio and cell-wall biopolymers are challenging for biohythane production. This study emphasizes the solutions to mitigate the adverse effects of microalgae-based biohythane production using co-digestion with wastewater sludge. Wastewater sludge, an emerging environmental concern, is reviewed to be an effective co-substrate with microalgae to establish a biorefinery approach. The future trends and prospects of this biorefinery approach is critically reviewed to attain a profitable process. This study also reviewed the advantages of microalgae-wastewater co-cultivation and the application of activated sludge for bio-flocculation as a cost-effective solution for microalgae cultivation and harvesting. Microalgae-wastewater co-cultivation is also recommended to be effective for biohythane purification. The liquid digestate is suggested to be used as a culture media to enhance microalgal growth; whereas, the solid digestate could be transformed into resources through hydrothermal processes as a solution of digestate management. A practical biorefinery approach combining the synergistic benefits of microalgae-wastewater sludge and its biological conversion to biohythane would be an adjoining link to the beginning of a sustainable future.