Potentials for microalgae sequestration of carbon dioxide (CO2) from composting off-gas; a review

Food and other bio-waste management is an integral part of urban development and living. Composting is a common practice in most developed countries, while open burning and landfilling is widely used in waste management in low and middle income countries. The outputs of composting include compost, heat, leachate, and off -gas. The off -gas consists of carbon dioxide (CO2), methane, nitrous oxide, water vapor, ammonia and volatile organic compounds. The CO 2 , although biogenic could contribute to climate change mitigation if the emissions are controlled. CO 2 sequestration using microalgae has been widely reported has been widely reported as a viable alternative to geological storage. CO 2 sources in microalgal cultivation include ambient air, composting off -gas, combustion flue gas, wastewater aeration gas, syngas, and biogas. Carbon dioxide from composting can be used in controlled environment agriculture instead of commercially produced alternative, or from ambient air. This review examines the available information on composting off -gas dynamics, particularly CO 2 evolution, and the challenges and prospects of CO 2 use in microalgal cultivation, ensuring circularity in the composting process. This review recommends the utilization of CO 2 from composting as alternative to direct air extraction. However, achieving higher CO 2 concentration relative to oxygen is challenging. While efforts are made towards reduction in greenhouse gas emissions during composting, near zero oxygen concentration in the off -gas is essential to enhancing CO 2 utilization in microalgae cultivation. This should be achieved without compromising compost quality such as germination index and chemical oxygen demand/heavy metals reduction efficiency.