Carbon dioxide (CO2) emissions are one of the global threats that have an impact on environmental issues. CO2 is a source of greenhouse gas (GHG) emissions from human activities such as cement manufacturing, deforestation, and open burning. Managing GHGs sustainably while not endangering the environment is perfect for achieving the objective of sustainable development. Potential studies have suggested that the reduction of CO2 is achievable through the bioconversion process. The bioconversion process may provide promising close-loop solutions for food security, energy, resource scarcity, and reduction of GHG emissions. GHG emissions can be controlled by waste upcycling, where CO2 emissions are managed by using biological means to convert the waste into biodiesel and feed. Recognizing the potential issue, this has envisioned a review chapter addressing the unconventional way of upcycling CO2 into valuable products. This chapter reviews the opportunity and challenges in the bioconversion of carbon sources. © 2022 Elsevier B.V. All rights reserved.