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Unsurprisingly, clean air is also a topic that might benefit from bridging the gap between space and Earth. Notoriously devoid of oxygen, space is not the easiest environment for human life. From the onset it has therefore been a challenging endeavour to ensure good air quality on board space craft and space stations. Some of the earliest scientific studies on the air purifying qualities of plants were conducted by NASA. But ever since, research has made impressive progress in ensuring better life support systems, relying increasingly on new technology for microalgae cultivation and harvesting. This technology in particular, is promising and is studied intensively by ESA in framework of the MELISSA (Micro-Ecological Life Support System Alternative) program. The GreenLung project initiated by QinetiQ, together with ESA and Achilles Design, aims to explore its terrestrial potential. 

The GreenLung features column bioreactors placed in indoor spaces to purify ambient air, by increasing O2 levels and decreasing CO2 levels, thus benefitting health and concentration. It is designed as an eye catcher and invites users to think about the environment, their health, science and technology. 

How does it work? An indoor concentric column bioreactor was developed to capture CO2 and to convert it in biomass and O2. Robust microalgae are grown in the bioreactor outer compartment. A system of aeration pumps and associated ducts leads ambient air to the reactor, where gas exchange with the microalgae culture medium takes place. Ambient CO2 is captured in the culture medium, and progressively released to the microalgae and converted to O2 via photosynthesis. Treated air (poorer in CO2, richer in O2) is evacuated via the reactor inner compartment, where the LED lighting system is also located. The ascending air movement generated this way takes care of the reactor mixing. Microalgae requires also nutrients such as nitrogen which are supplied by using a fertilizer derived from processed urine. At regular times, the produced biomass is harvested to maintain the algae concentration in the reactor at a desired level. 

The prototype yielded interesting results. However, several challenges remain and require further development. First of all, it will be necessary to find a way to capture and concentrate the CO2 before directing it to the bioreactor. Why? The higher the concentration, the better CO2 is transferred to the growth medium and converted to O2. In other words, for the GreenLung to currently work and deliver, you need a very unhealthy environment. Another challenge is to ensure energy-efficient ventilation and aeration. Blowing air though the reactor medium requires a ventilator capable to deliver a high air flow at a pressure of 300 mbar. And finally, we have to decide on a useful purpose for the produced microalgae that grows by converting CO2 into biomass. Since the algae are aerated with ambient air that might be polluted, direct consumption in feed or food is not advised. However, there are plenty of other options. Useful products for feed preparation such as proteins, amino acids, fatty acids and carbohydrates can still be extracted. Also, algae contain pigments and antioxidants which can be processed in chemical products, soil enhancers and even cosmetics. And even more surprising, algae biomass is an energy carrier that can be used as an additive in biobased liquid fuels. 

At QinetiQ we strongly believe that the GreenLung concept has potential as an air purifying technology and that it can interact with traditional heating, ventilation, and air conditioning (HVAC) systems. We are currently looking for partners to further define and explore the opportunities.