A photobioreactor or PBR is a device that houses and cultivates algae. It provides a suitable environment for algae growth, supplying light, nutrients, air, and heat to the culture, in addition to protecting the culture from contamination.
There are several physical arrangements of a photobioreactor. These include the following:
- Arrays of glass or plastic tubing
- Aquarium-like tanks
- Plastic sleeves or bags
Plant cells use only a small fraction of the sunlight that hits them. Conversion of photons to chemical energy could range between an efficiency of 1-10%. This can be improved through providing proper growing conditions.
Some sources that can be used to provide the light energy required to sustain photosynthesis include fluorescent lighting, high-intensity discharge lighting, light-emitting diodes, natural sunlight, and directed sunlight.
For more information, see: Light Requirements
Nutrients are a major determining factor in how fast algae grows and what composition it develops.
Algae live in water from the equator to the Arctic and Antarctic. Consequently, there is no single temperature is best for all algae. One theory is that an algae species will tolerate a few degrees above the maximum summer temperature of its natural environment. Thus, the temperature range that a given algae species will tolerate may estimated by knowing its environmental range. However, to know the temperature at which an algae species grows best must be determined by experiment.
Cultivation is the actual process of growing algae, either in batches or continuously.
Algae must be kept in a sterile environment, as they do not have an immune system to destroy bacteria or zooplankton, which are heterotrophs. Heterotrophs will generally outcompete autotrophs on about a ten-to-one basis. Thus, it is very important sterile technique is followed and sterile media is used. This can, however, be expensive. In some cases, it may be economically advantageous to use other methods to control invasive species. Such methods include:
- Altering pH to make the medium more basic or acidic
- Extremely salty environments are hypertonic (too salty) to plant cells, which can cause cells to rupture (known cytolysis).
- Dunaliella, Botryococcus, and CCMP647 are tolerant to high levels of salinity.
- Dunaliella in particular grows well in areas of high salinity, such as brine or brackish water, which is normally toxic to other organisms.
Algal concentration can double between once every day to once a week.
More information is needed in this particular section. Please add information on: Doubling rates.
If a algal medium gets contaminated, this can crash the culture. Restarting from a crash can take several days to weeks, depending upon how much culture it is seeded with.
Measuring concentration determines how much algal biomass is within a given volume. This can be measured in grams per liter. Keeping track of concentration is important to know when it's appropriate to harvest.
Yield is the measure of how much algae can be harvested from culture media accompanied by a measure of time, usually in batches, days, or years.
There are cheap methods, and there are expensive methods.
More information is needed in this particular section. Please add information on: Methods of measurement for various figures pertinent to yield.
Photobioreactors can be set up to be continually harvested-- the majority of the larger cultivation systems-- or by harvesting a batch at a time, such as in polyethlyene bag cultivation. A batch photobioreactor is set up with nutrients and algal seed, and allowed to grow until the batch is harvested. A continuous photobioreactor is harvested either continually to keep concentration at an optimal rate. Drained algae is replaced with fresh medium. PBRs can also be harvested in batches as it doubles.