The global impact of greenhouse gas emissions requires concerted efforts to reduce emissions and energy use, and to increase carbon capture and sequestration. Promoting the circular economy in CO₂ sequestration systems optimises resource use and reduces the emissions burden throughout the supply chain. Carbon capture from anaerobic digestion, composting and fermentation (particularly ethanol) processes offers great opportunities for climate change mitigation. The waste/by-products generated from these processes can limit the need to source nutrients from outside the system and increase the potential for circular economy. The integration of microalgae cultivation with each of anaerobic digestion, composting and ethanol fermentation processes provides a new model for climate change mitigation of biogenic CO₂ and circular economy. While this model is limited by high energy consumption and nutrient demand, seasonal variability, operational efficiency and end-user requirements, further research and policy support will go a long way in realising the associated benefits, including in CO₂ fixation, nutrient recovery, waste remediation and as an alternative source of animal feed.