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Modular Algae Photo Reactor V.2

This project is the second version of the basic photo bio reactor array that I started with. While it may look similar to the previous version is dramatically different overall. This design has many improvements that make it far more sustainable and practical for long-term use. I really focused on making it highly modular and insuring it was rugged for prolonged outdoor use that is easier to fill and harvest from. While the array is smaller for this project it can be scaled to any size or requirement.

The Frame :
So we will be starting this project by killing a tree for our project. Basically we will be building a fairly simple frame to hold our reactor cells and pumps. Could you use reclaimed or recycled wood products? Sure! if you have them locally or on hand… if not don’t burn off that gallon or more of gasoline driving 20 miles and back from a recycler…. just go to the home center around the block. However, if you go the home center route make sure to get some good stain to protect the wood from the weather and make it last as long as possible.

For this project we will be using some acrylic sheet that is 1/2 inch thick. This will be cut using a hole saw to make the plugs for the tube ends as well as making the holes for the plumbing. Now I realize that everything can be measured in carbon and energy required in making a product… and I realize that I will get email saying how plastics will kill the earth. Well… your likely right.

More Acrylic:
These are 3 3/4 OD 3 1/4 ID Cast acrylic tubes. There are two types of acrylic, cast and extruded. It’s important that you use a cast acrylic tube for this project. If you use extruded acrylic it will eventually crack under the pressure of the water in the tubes and you will kill an entire plankton colony. However if you use extruded lengths of 2 foot or less it will last a very long time I found.

The Pumps:
We found these WISA air pumps on eBay for 8.00 each. The cool thing about them is that they have a input and output on them so you can easily capture the air and pass it along. These are surprisingly high volume and 6 of them in parallel ran great on our 45 watt solar panel kit.

Air Tubing:
This simple component while not necessary for an algae reactor to run is really crucial in my mind. Aerating algae both agitates it so it gets uniform light exposure as well as introduces more CO2 to the mix. This air hose we picked up from a local aquarium supply store for 2.00USD and is far more than we need for this project (so we have more for future projects). It’s worth noting that this hose doesn’t react well to long term direct sunlight exposure, a simple UV resistant clear coat though makes it last much longer.

The Hose Fittings:
We found these barbed hose fittings at our local home improvement center. I really have fallen in love with these little guys. They provide a simple connection that is secure yet removable. This makes it easy to vacuumed fill the tubes from the bottom with a siphon hose. Use a plastic zip tie to secure the hose to the barbed end for long term unattended use just in case.

Plastic Dip:
This stuff was one of the major advancements for my reactors. The tubes are dipped into this stuff and allowed time to totally cure. This provides us with 2 great features; it’s totally waterproof and has tremendous shock dampening ability. So the weather and wind and even hail can blast your array and you can rest assured its safe.

Step one; just like in our version one system we install acrylic plugs into the ends of the tubes with acrylic bonding agents. But we then double dip the tubes into the plastic dip to seal them and make them shock resistant. We waited about 10 minutes between dips as per the instructions. One thing I found that was a disappointment and I sure hope your reading this; plastic dip off gasses a lot! If you do not cover the holes at the ends of the tubes with masking tape it will leak into the tubes. As it cures it will actually rupture your tubes. My array here was originally an 8 tube array… I salvaged 3 from this mistake that I masked “just in case”.

We drilled holes for the hose fittings to protrude as well as the larger holes for the tubes to seat in. this is straight forward work, however one tip to pass on is to drill / cut them in pairs just incase your measurements are off. This will maintain a consistent rig.

Here is the cut and prepared sets of ends. Each end uses both pieces. Make sure you allow space between each tube in your measurements. The inner hole is one inch to allow for a socket driver to access the pipe fitting if needed. The large hole is a 4 inch hole saw. This allows room for the plastic dip coating.

Assembly is super easy and straight forward for this build. Here we have the array upside down for ease of assembly. Make sure you predrilled each hole on the side pieces before you screw the pieces together. One tip here if you don’t like to measure or are in a hurry is to put the two bottom pieces together and install a tube to get the height of the bottom…

Here we can see the top view partly assembled. It’s important to point out here that you can see the holes for the air lines in this array now.

Test fitting the tubes in the array. The array is again upside down to make this easier to work with. You can see the bottoms of the tubes line up with the bottom of the board with the large holes in it. You really don’t want the tubes protruding in anyway. If they are correct it before proceeding.

Here we have the bottom plate installed so the tubes are now secure in the array. You can just see in this pic the hose connections protruding into the tubes. For this array I did not opt to install a bubbler because each array cell has a dedicated pump making sure it has enough volume to get the job done and keep algae agitated enough that it doesn’t stick to the inside of the pipe.

Also we added some support legs in the back to keep it upright and make it a sturdier. Now with most arrays you will want to actually place them at about 20 degrees to 35 degrees off vertical for maximum light exposure. But this little guy was designed also as a display peace to we went totally vertical.

Here is a closer view of the pump configuration. The top of each tube is connected to the input of each pump and the output travels down to the bottom of each tube. This creates a push pull scenario that makes the pumps use a little less energy to cycle the air through.

Here is our finished reactor. It’s important to point out that this type of an array can be scaled up to any number of cells. I ended up gifting this little reactor to a friend of mine that has been promoting algae tech for some time. She will put it to good use!

So how did it do? Have you ever seen a giddy geek? Well I will save you all the experience but it goes without saying… I was grinning ear to ear and giggling uncontrollably. I prefer to use the Pentium D line of processors due to their “worst case” nature and then I was even super surprised. I think that the cost effectiveness of this should spark some fun with the enthusiast markets for sure!

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  1. Avatar
    Guillaume Terrée
    July 10, 2016 at 7:43 am — Reply


    I would like to use your photo 29.jpg in my thesis manuscript.
    At one point, I want to show what a photobioreactor is — although I got no experimental setup — , and I have found that your image was so clearly illustrative. You will be cited in the legend (it is nearly mandatory, indeed).
    Is it OK for you ?

    Kind regards,

    • Inventgeek
      August 8, 2016 at 9:48 am — Reply

      Just fine, just send me a copy 😉

  2. Avatar
    September 27, 2017 at 7:02 am — Reply

    Hi I am a research science teacher and would love to build this for my class to feed the rotifers. Wheres the best place to get the acrylic?

  3. Avatar
    Umema Siddiqui
    September 27, 2017 at 10:17 am — Reply

    Hi, I was wondering how it would be possible to harvest the plankton from the tubes after they have grown significantly. I’m a student working on a research project. Is there any addtional information that you have that might be helpful? Thanks.

    • Inventgeek
      September 28, 2017 at 9:35 am — Reply

      yes absolutely. This would work fine, just watch your water temps.

  4. Avatar
    fred feraco
    September 27, 2017 at 1:20 pm — Reply

    How do you clean this out if the top and bottom is glued?

    • Inventgeek
      September 28, 2017 at 9:35 am — Reply

      just disconnect the hose and drain it.

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