Algae Farm (Bio Reactor)

It seems my curious mind got the better of me once again.  Out of boredom a couple of weeks ago, I decided to put together a simple algae "bio reactor."  The term "bio reactor" has never really sat well with me, since it makes the whole thing sound much more impressive than it really is.  Put simply, it's nothing more than pop bottles filled with water with a small air pump to aerate and encourage algae growth.  Here's my version, with a materials list, instructions, and observations:

Finished product, after a few days of growth

Materials:

- 1 liter pop bottle (x2)
- small aquarium air pump.
- small aquarium air stone (x2)
- 1 meter of air hose (silicon or PVC)
- T fitting for air hose
- small pieces of foam
- 2 liters chlorine free water
- liquid plant food (any brand)
- algae water (a few mL, from a pond or store bought)

Process:

1. Gather all necessary supplies. The air pump, air stones, hose and T fitting can all be inexpensively purchased at your local pet store.
2. Peel the plastic off the bottles and clean them up as much as possible
3. Cut two lengths of hose approximately 30 to 35 cm in length (long enough to reach the bottom of the bottles) and attach them, with an air stone on the end of each, to the top ends of the T fitting. Attach the remainder of the tubing to the bottom of the T and to the air pump.
4. Fill the bottles most of the way full with clean chlorine free water. If you are going to use tap water, make sure your local area doesn't use chloramine to make it potable.  If not, you can leave tap water sitting in an open container for a day so the chlorine can evaporate away before using it.
5. Add the algae water and a few drops of plant food to each bottle
6. Insert the air stone ends of the hose into the bottles, stuff the ends up with the foam, and turn on the air pump.
7. Make sure the bottles are in an area where they will get a lot of sunlight. Wait a few days, and the water will begin to turn more and more green as algae growth proliferates. In fact, it might go crazy, like mine did:

Crazy growth, after about 2 weeks

Observations:

I had to wait about 6 days before it began to show signs of algae growth.  It began to get a darker and darker shade of green as each day went on.  Interestingly, if I turn off the pump and let it sit over night, the algae seems to settle into 3 distinct layers.  I'm not sure what the significance of this is, but perhaps it has something to do with there being different types of algae growing at the same time, with different densities.  This picture gives you a decent idea of what I mean, although it doesn't show up all that well:

Algae layers after sitting overnight

I'm still not entirely sure what to do with this now, and I probably should have considered that beforehand. Its only real use to me is to look neat, and perhaps scrub away a bit of CO2 in my basement. I could simply use it as a fertilizer (although I should look into this first before I try).  Or maybe I could also separate the algae with a centrifuge and then squeeze the oil out of it to use as a bio fuel, but I have a feeling I would need a lot of it.  Let me know if you have any ideas.

Relevant Links:

- NASA's Offshore Membrane Enclosures for Growing Algae (OMEGA) project: NASA
- Instructable similar to my project: Instructables
- Wikipedia article on Algaculture: Wikipedia
- 7 tips for growing algae: Wikihow

Thanks again for reading!