Only the direct removal of CO2 from the air, or “direct air capture” (DAC), can actually reduce the global atmospheric CO2 concentration. The past decade has seen a steep rise in the use of chemical sorbents that are cycled through sorption and desorption cycles for CO2 removal from ultradilute gases such as air.
Microalgae consist of a group of highly diverse and fast-growing microorganisms, capable of photoautotrophy, heterotrophy, and mixotrophy. They can be cultivated on non-fertile land with unit CO2 fixation capacity 10–50 times higher than terrestrial plants.
NASA is currently planning human spaceflight missions with longer durations than ever before. Closed-loop technologies, specifically photosynthetic algal photobioreactors, can offer multiple functions such as air revitalization (CO2 absorption and O2 provision) and thermal control with less launch mass and volume for long-duration flights.
Biological CO2 fixation depends on the tolerance of selected strains to high temperatures and the amount of CO2 present in flue gas, together with SOx and NOx.
Odour control systems do not give overall success unless the entire facility is properly enclosed and maintained, especially for the densely populated area like Hong Kong.