In the 21st century, human beings are facing global warming caused by the greenhouse effect. Therefore, the 2015 United Nations Climate Change Conference has set the Paris Agreement to reduce the emission of greenhouse gas (mainly CO2) from ~32 Gt in 2016 to reach net-zero by 2050. While extensive research efforts have been focused on exploiting novel non-fossil energy sources, an alternative to reach net-zero emission of greenhouse gas is to fix atmospheric CO2, including the use of biological CO2 sequestration via biochemical CO2 fixation pathways. Taking the advantage of contemporary synthetic biological techniques, in the past decade, there are a plethora of studies reporting the modification of metabolic pathways in microorganisms for biosynthesis of value-added chemicals from CO2. Recently, the advance of cellfree synthetic biology has opened another door for atmospheric CO2 sequestration. Compared to in vivo CO2 fixation, the cell-free synthetic CO2 fixation is highly flexible and is not limited by microbial growth rates and nutrient availability. Interestingly, the liquid-liquid phase separation technology can further extend the might of cell-free synthetic biology, enabling (i) compartmentalization of chemicals, (ii) prolonged stability of enzymes, and (iii) enhanced catalytic rates. As such, phase-separated coacervates have been applied to biocatalysis since phase separated coacervates can produce compartments within aquatic environment to separate enzymatic components. Based on the concept of a circular bioeconomy to combat global warming, in this research project, I propose to develop a facile, cost-effective cell-free enzymatic system for synthetic CO2 fixation, along with energy supplied from sustainable sources independent of CO2 emission. The reductive acetyl-CoA pathway (WL pathway) is selected as the model pathway for cell-free synthetic CO2 fixation (ATP-yielding) because it is the only exergonic CO2 reduction pathway out of six natural routes, making the CO2 fixation reactions more product-favored. Lactate is selected as the targeted product for sequestration and long-term storage of CO2 since its polymeric form, polylactic acid (PLA), has been used globally in disposable packaging due to its outstanding chemical properties and biodegradability. The global demand of PLA doubles every 4 years, with an estimated market size value of 6.5 billion USD by 2028. In this proposed research, algal-derived polyphosphate is selected as the energy source for ATP regeneration and the building block of coacervate, respectively. Given that polyP can be readily obtained from microalgae biomass generated in the P-rich wastewater, this system is cost-effective and sustainable . If successful, this research project will develop a facile, rapid, and cost-effective platform to convert atmospheric CO2 into lactate, the industrial materials for making next generation plastic PLA, helping Taiwanese government to combat global warming and to reach net-zero CO2 emission. Moreover, the outcome of the proposed research would enable upcycling of P-rich microalgae sludge for synthetic CO2 fixation, bringing an additional industry to Taiwan's circular bioeconomy.