Science Project:

Build Your Own Photobioreactor

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The goal is to give the student an opportunity to use scientific methodology to design test a photobioreactor design.

  • Can an inexpensive photobioreactor design be found to accommodate the growth needs of algae?
  • What kinds of light sources will optimize the growth of algae?
  • Can a suitable pH be maintained in the photobioreactor?
  • Can a mixing scheme be developed to stir the algae?
  • Can a suitable temperature be maintained in the reactor?
  • Can a suitable nutrient source be found for the algae?
  • Can the initial photobioreactor design be improved?

Algae require sunlight, a source of carbon, nutrients (nitrogen or silicon), and water for growth. They also benefit from stirring.

Algae require light energy in order to convert carbon dioxide into the organic compounds required for growth. If exposed to direct sunlight, their growth may be inhibited. If artificial lighting is used, fluorescent tubes emitting blue or red light are preferred. Artificial light should be available for 18 hours a day.

The pH of the water in which algae are grown should be between 7 and 9.

Stirring is desirable so that all the algae are equally exposed to light and nutrients. The algae should be stirred daily. Not all algae can tolerate vigorous mixing, however.

The temperature of the water should be between 20 and 24 deg C. Temperatures below 16 deg C will slow down growth, while temperatures above 35 deg C are lethal to algae.

A photobioreactor is a chamber that houses and cultivates algae. It maintains suitable conditions of light, nutrients, air, and temperature for the culture.

  • The materials required to complete this project are entirely up to the student. A very basic photobioreactor might make use of three one-liter bottles of purified water; sugar; brewer’s yeast; silicone sealant; drill; 6-mm aquarium airline tubing; and algae (see the Science Fair Project entitled “Carbon Dioxide and Algae” and submitted in this group.)

  1. Review the growth requirements of algae.
  2. Design an inexpensive photobioreactor that will cause the algae to grow faster. Keep in mind the following:
  • The light should not be too intense. If algae are exposed to direct sunlight or if they are too close to an artificial light, their growth may be inhibited. If you opt for artificial light, you should use a fluorescent tube that emits either blue or red light. (These are the most active parts of the light spectrum for photosynthesis.) The light will need to be on at least 18 hours each day.
  • An algae culture can completely collapse if the pH falls out of the range between 7 and 9. During algal growth, pH may climb to 9, which may be counterbalanced by addition of carbon dioxide to the reactor.
  • Mixing the algae ensures that all of the algae cells are exposed to the light and nutrients. Mixing also prevents temperature gradients from forming in outdoor bioreactors.
  • Most strains of algae prefer a temperature range between 20 and 24 deg C, although temperatures between 16 to 27 deg C are usually tolerated. Many algae die at temperatures above 35 deg C.
  • Algae require nutrients for optimal growth.
  1. Collect some algae from a natural source such as a pond, marsh, swamp, swimming pool or bird bath. If you are unable to locate a natural source, try a biological/scientific supply house.
  2. Measure the amount of algae collected.
  3. Introduce the algae into the photobioreactor.
  4. Measure the growth of the algae after two weeks. Modify the design of the photobioreactor as needed with an eye toward improving algae yield.

Terms: Photosynthesis; Algae; Carbon dioxide; Light; pH; Nutrients; Photobioreactor

References:

Author: Randall Frost, Ph.D.
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