Introduction: Simple Algae Home CO2 Scrubber - Part 1

I created this instructable to show how to build a simple algae based CO2 scrubber for home or apartment use. The basic design shown here will scrub its own consumption and approximately 24 pounds of carbon dioxide from the atmosphere every year. This is approximately the CO2 produced in the production of 17kW of electricity. This device may be scaled up to process larger quantities of CO2.

The carbon dioxide is consumed by the algae which release oxygen. In part I the scrubber consists of a 2 liter reactor vessel and a small aquarium air pump. The bottle contains a solution of water, algae and nutrients. Room air is passed through the bottles using a standard aquarium bubbler stone where the CO2 is absorbed by the algae and oxygen released.

In later parts this basic design will be expanded provide more flexibility and increased production.

Maintenance is simple and straightforward as any house plant. About twice a month I add a couple drops of liquid plant food. The color of your home scrubber may be kept at any desired color range by controlling the food. If the algae gets too dark for your taste simply wait until the color begins to lighten before feeding again, if its too light try adding another drop of nutrient or feeding more often to increase the population.

Once or twice a year its probably not a bad idea to clean the scrubber. Save enough medium from one of the lightest bottles to reseed them. Then empty them into your compost heap, the sink or the toilet and restart them using tap water and the reserved medium.

All that being said, let's take a quick look at the tools and materials we'll be using then we'll get started.

Step 1: Bill of Materials

Okay here's what we'll need:


Drill or drill press with 3/16" bit
Razor knife or scissors
Hot glue gun - Optional
Funnel - Optional for filling bottles

Materials and where I got them. I have no relationship with any of these stores or products. They are inexpensive and should be commonly available:

1 X 8' 1/4" aquarium airline tubing - PetSmart Top Fin brand or ACE Hardware flexible plastic tubing
1 X 3' 1/8" inch rigid plastic air hose (3/16 outer diameter) - PetSmart Top Fin brand
1 package 6 air stones - PetSmart Top Fin brand (also available individually)
1 x 2L Clear Plastic soft drink or water bottle with screw on top - Recycled
1 x 2L de-chlorinated water for breeder reactor

On the next page we'll learn more about dechlorination

Step 2: Preparing Tap Water for Use in Algae Cultivation

Most (if not all) municipal water supplies, and many holding tanks for wells in rural communities, farms, and ranches, are treated with chemicals to kill off any harmful bacteria or other pathogens which may get into the water. The most common of these chemicals are chlorine and chloramine.

Though the dosages of these chemicals in the water supply are low enough that they are not harmful to a land animal (including people, dogs, cats, hamsters, horses, etc) or house plant, they are high enough to eliminate or inhibit the growth of micro-organisms including algae

Chlorine is very volatile, so it will evaporate very quickly from your source water. If your water is only treated with chlorine, then letting it stand over night should allow the chlorine to evaporate from the water and make it safe to use. In fact, you can even speed this up by bubbling air through the water with an air stone. This will increase the surface area of the water and allow the chlorine to evaporate even faster.

However, this is one of the primary reasons for switching form chlorine to chloramine treatment of water supplies. Unlike chlorine, chloramine is non-volatile. It doesn't evaporate quickly. If your source water is treated with chloramine, it is important that you get a dechlorinator that will neutralize chloramine.

I would try letting the water stand overnight. If algae fails to grow in the medium after a couple of weeks try again with bottled or collected rainwater.

Okay, we've let the water sit out overnight and are ready to begin our adventure in algae cultivation.

First we'll need to gather some algae and nuture it until we have enough to get our scrubber going.

Step 3: Obtaining an Algae Culture

In many documents about growing algae the concept of how to get algae is arguably the most intimidating step. Practically all of the sites have recommended scientific supply houses which offer exotic algae culture specimens suitable for advanced use in the latest biotechnology project.

Fortunately we're not doing that and therefore we can take advantage of the fact that algae will grow anywhere in water unless one works actively to prevent it. Ask any aquarium owner.

So first we will obtain an algae sample.

If you know somebody who has a fish tank the simplest solution is to ask them for an algae sample before they clean it next time. Scrape the green stuff off the side of the aquarium along with a little bit of fish tank water. Trust me, that's all the algae you're going to need.

As an alternative you might check with a friend or neighbor who has a hot tub. Algae like warm temperatures so a healthy sample might easily be available before the hot tub cleaning cycle. Different folks have different tolerances for chemicals and some folks might have more or less aggressive chemical policies. The hot tub at your spa probably isn't going to yield a good sample....and if it does you might consider changing spas....also remember to be a tactful when asking that neighbor you don't know so well if they've got a hot tub full green, floating goo...

Alternatively algae cultures may be obtained by getting a little water out of a natural stream, creek, pond or lake. In this case it's been raining here lately and a nice algae culture has taken root in the birdbath. I drew out a small sample, trying to keep it clean. While we're not concerned with pure algae cultures at this time we want to reduce the number of miscellaneous micro-organisims we include.

Once we've obtained a reasonable sample we're going to breed the algae in order to produce the feedstock for the scrubber. In order to do that we're build a high volume breeder reactor in our next step.

Step 4: My First Breeder Reactor....

No, a breeder reactor is not the cornerstone of a secret WMD project. The word reactor is used in this context as shorthand for "reactor vessel". In this case the reactor vessel will hold algae, water and nutrients for the purposes of breeding the algae, hence the name "breeder reactor".

We'll start with the 2L soft drink or water bottle and the 3/16" drill bit. We're going to drill a hole in the center of the plastic cap, insert a piece of 1/8" rigid plastic tubing, glue that in place. Then we will fill the bottle with water, add the algae culture and nutrients and wait for nature to take it's course.

Fit the drill bit into the drill and drill a 3/16" hole in the center of the plastic cap. Cut off a 10" section of rigid plastic tubing with scissors. Feed that through the hole in the cap until approximately 1" projects from the top.

Cut off a 1" piece of the flexible plastic air hose and remove one of the air stones from the 6 pack. Attach the flexible tubing to the bottom of the air hose and attach one of the air stones to the other end.

Fill the bottle most of the way with dechlorinated or fresh water. Now add the algae sample we took earlier. A funnel isn't strictly required as long as most of the culture makes it into the reactor.

Fill the bottle up the rest of the way with dechlorinated water and insert the cap bubbler assembly. Your breeder reactor is now charged and ready.

Now take out the air pump. I selected the Tetra 799 based on its low capacity, inexpensive price and being in stock at PetSmart. Any air pump will suffice.

Decide where you will place your reactor, remember that this is a plant which uses photosynthesis. The more direct sunlight it recieves the better. Locate an outlet for the pump. Cut a length of flexible tubing that will reach from the air pump to the input located on the cap. Attach the pump to the reactor with the tubing. Tighten the plastic cap down and then open it 1/4 turn. This will allow the scrubbed air and generated oxygen to escape.

At this point you are actively scrubbing carbon and breeding algae for the next phase of the reactor.

Step 5: Scrubbing CO2 in the Window

Now loosen the top at least a1/4 turn and plug in the pump. Leave enough space at the top of the bottle that the water doesn't bubble out.

With a couple of days the water will begin to turn murky and then green. The intro picture shows this reactor after approximately 1 week.

Watch the water level for evaporation and top it off periodically, preferably at the same time as feeding. Mineral water is an excellent supplement for trace minerals not found in Shultz nutrients.

In Part II we'll talk more about culturing and cultivating algae and learn how to make a true algae nutrient medium.

Step 6: For More Information

For more information regarding this I used the following sources:

Carbon Dioxide Emissions from the Generation of Electric Power in
the United States available from the Department of Energy:

and "Gas Exchange of Algae" available via the National Library of Medicine ( at

or the PDF is attached.