Background Research

Algae:

We decided to pick algae--autotrophic protists--over plants to use in the air purifying system because algae is small, and it has a large surface area to volume ratio. Also, algae does not require the same level of nutrition and maintenance as plants do. Algae is easily obtainable and easily grown.

As a whole category, green algae have a higher photosynthetic rate than red algae. The absorption spectrum of chlorophyll a and chlorophyll b (which are found in green algae) and carotenoids (which is found in red algae) indicates that the chlorophyll has a much higher absorption range--compared to carotenoids.

A graph of the absorption spectra can be found at http://hyperphysics.phy-astr.gsu.edu/hbase/biology/ligabs.html

According to Photosynthesis, Photorespiration, and Plant Productivity by Israel Zelitch, the green algae Chlorella has a high photosynthetic efficiency which is comparable to other efficient crops such as sugarcane. A high photosynthetic efficiency would lead to a higher rate of oxygen output, since oxygen is produced in photosynthetic reactions.

Plastic:

In previous renditions, we researched a multitude of plastics that would allow carbon dioxide that would diffuse through a membrane. Polyethylenemine is a plastic that specifically lets carbon dioxide through its membrane. However, since polyethylenemine is very weak and soft on its own, it needed a porous mount. Polysulfone provided an ideal mount for the polyethylenemine because its pores were small enough to retain water inside the container, but large enough to let carbon dioxide in and oxygen out.

Eventually, it was decided that these materials would be too expensive to create a practical model. With our present redesign--a system that contains algae growing on screens in a trough--such plastics would be unnecessary, as the flow of contents in and out of the system do not need to be controlled to such a specific degree. In the new design, a simple porous Plexiglass ceiling would allow carbon dioxide to enter and oxygen to escape without the need for a membrane. The walls of the container would also be made of Plexiglass, lined with reflective Mylar to keep in light and heat.