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There are two main types of photobioreactors to use, you may have seen pictures of them on the "Where
to begin" page as well as these shown below. There are open-pond and closed-system reactors [1]. The main
goal of each is to grow algae at an accelerated rate by providing nutrients and light. Both types of reactors
are described below in detail with helpful pictures.
                       
Where to Begin
Photobioreactor
Harvesting Algae
Resources
Sources

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Open Pond Photobioreactor

As the name indicates the open-pond photobioreactor is simply an open body of water exposed to the elements. This may be an attractive route if you already have a pond in your yard. Be aware that different algae strains require certain conditions to grow. With an open-pond you'll need to think about a few key factors.
First, algae grows so thick in many cases that light will only penetrate about 3 to 4 inches under the surface of the pond water [1]. To maximize the amount of algae grown, many open-pond users create some sort of agitation to stir the algae around exposing more algae to sunlight. As seen in the picture below (these pictures are large examples of an open-pond, you wouldn't have to have a pond nearly this large to cultivate algae), the pond is in a race-track shape with a stirring device mixing the water. Algae will not grow quickly at night so the agitation device would not need to run 24 hours a day.

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                                 Close up of agitation device [5]                                                        Picture of race-track style opn-pond [5]

Second, most if not all algae strains photosynthesize, which means they absorb carbon dioxide and emit oxygen. In fact, most of our oxygen supply comes not from plants but from plankton (a form of algae) in the ocean. You'll want to supply your pond with plenty of CO2 to speed the growth of your algae. Finding a cheap source of CO2 will require a bit of imagination. Most commonly either pure CO2 or air with a high concentration is bubbled through the pond using an air pump. Most likely you'll not wish to pay for pure CO2 sources to use, so try to find a source of abundant ambient CO2 such as a furnace vent, a factory exhaust vent (not typically available at home), or a fireplace [6]. Feel free to be creative, this is where algae can really help the environment. See the "Resources" page for links with more ideas.

Third, open ponds are susceptible to Mother Nature. This includes everything from weather disasters to microbial invasions. Algae do not have immune systems, they cannot fight off
invading bacterial or viral infections. Losing a whole pond of algae to such an invasion is a risk to consider before growing algae in an open pond. Preventative steps can be taken to keep the algae pure and free from microbial invasion e.g. keeping animals away from the pond, be aware if the pond has a source of intake say from rain-water run-off, and starting the pond with clean water [1]. Most strains of algae will not tolerate chlorinated water! Be sure to remove chlorine before starting a crop of algae. Chlorine may be removed using a chlorine treatment kit available at pet stores and on the internet.

Problems that may arise in using an open pond are numerous and cannot be fully discussed here. There is no way to guarantee that infected algae will still produce usable fuel. It is highly recommended that you do lots of research into your chosen strain of algae to determine if it can be safely and consistently produced in an open pond photobioreactor.


Closed-System Photobioreactor

The picture shown above may give the appearance that building and using a closed-system reactor will require expensive materials and skills. This is not the case. Again the goal of the reactor is to provide light and nurients. Closed systems have the advantage over open ponds in that they require less space and are not susceptible to mother nature. The advantages will be worth the extra materials needed. Below are some examples.

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                                                                 [7]                                                                                                                   [8]

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                                                                                                                           [9]

Closed-system photobioreactors consist of a clear container with CO2 bubbling through water containing algae. This could be as simple as a fish tank with a bubbler pumping CO2 through the water. Some designs are more complex using pressure and multiple air-pumps to optimize photosynthesis. The design may be as simple or complex as you desire.

Some issues to be aware of: algae in a small closed-system will not need direct sunlight [1]. Too much sunlight can kill algae in such a container, typical practice is to use artificial light. Algae grown in a closed-system can be exposed to light 24 hours a day, another advantage over the open pond. More information on designing a closed reactor may be found on the "Resources" page.



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