​Renewable energy production through microalgal biohydrogen systems enables sustainable conversion of CO 2 waste streams into renewable energy. A critical evaluation has been conducted on current biohydrogen production advancements regarding living microalgae chemical elements and metabolic processes together with process enhancement techniques. The article investigates integrated system concepts which unite photobiological production techniques of clean hydrogen with dark fermentation technologies while processing wastewater systems and implementing thermochemical modules. By optimizing microalgal strains and cultivation conditions for enhanced CO 2 f ixation efficiency, and co-locating production facilities with industrial emission sources, the proposed system aims to create a closed-loop, carbon-neutral biorefinery. The key innovations of this approach lie in the synergistic integration of various technologies to overcome the limitations of current microalgal biohydrogen production systems, which often suffer from low productivity, high operational costs, and challenges in capture and separation. Through detailed process modeling and feasibility analyses, this study evaluates the technical and economic viability of the proposed integrated system, including sensitivity analyses on critical parameters such as CO 2 input requirements. The review also provides a comprehensive technical and economic comparison between microalgal biohydrogen and other hydrogen production technologies, highlighting the competitive advantages of the proposed integrated system. Overall, this transformative approach to CO utilization through microalgal biohydrogen production offers a sustainable solution that can simultaneously address the challenges of renewable energy generation and carbon emissions reduction. By creating a circular economy around CO 2 2 future.​​