Algae cultivation can be achieved in two ways: open ponds and photobioreactors (PBR). A photobioreactor is a closed equipment which provides a controlled environment and enables high productivity of algae. As it is a closed system, all growth requirements of algae are introduced into the system and controlled according to the requirements. PBRs facilitate better control of culture environment such as carbon dioxide supply, water supply, optimal temperature, efficient exposure to light, culture density, pH levels, gas supply rate, mixing regime, etc.,
Photobioreactor - How it works
1. From the feeding vessel, the flow progresses to the diaphragm pump which moderates the flow of the algae into the actual tube. Built into the pump is the CO2 inlet valve.
2. The photobioreactor itself is used to promote biological growth by controlling environmental parameters including light. The tubes are made of acrylic and are designed to have light and dark intervals to enhance the growth rate.
3. The photobioreactor has a built-in cleaning system that internally cleans the tubes without stopping the production.
4. After the algae have completed the flow through the photobioreactor, it passes back to the feeding vessel. As it progresses through the hoses, the oxygen sensors determine how much oxygen has built up in the plant and this oxygen is released in the feeding vessel itself. It is also at this stage that the optical Cell Density sensor determines the harvesting rate.
5. When the algae are ready for harvesting, they pass through the connected filtering system. This filter collects the algae that are ready for processing, while the remaining algae passes back to the feeding vessel.
6. The flow continues.
Advantages of Photobioreactors
- Cultivation of algae is in controlled circumstances, hence potential for much higher productivity
- Large surface-to-volume ratio. PBRs offer maximum efficiency in using light and therefore greatly improve productivity. Typically the culture density of algae produced is 10 to 20 times greater than bag culture in which algaeculture is done in bags - and can be even greater.
- Better control of gas transfer.
- Reduction in evaporation of growth medium.
- More uniform temperature.
- Better protection from outside contamination.
- Space saving - Can be mounted vertically, horizontally or at an angle, indoors or outdoors.
- Reduced Fouling - Recently available tube self cleaning mechanisms can dramatically reduce fouling.
Covering ponds does offer some of the benefits that are offered by photobioreactors, but enclosed systems will still provide better control of temperature, light intensity, better control of gas transfer, and larger surface area-to-volume ratio. An enclosed PBR design will enhance commercial algal biomass production by keeping algae genetics pure and reducing the possibility of parasite infestation.
Disadvantages of Photobioreactors
- Capital cost is very high. This is one of the most important bottlenecks that is hindering the progress of algae fuel industry.
- Despite higher biomass concentration and better control of culture parameters, data accumulated in the last two decades have shown that the productivity and production cost in some enclosed photobioreactor systems are not much better than those achievable in open-pond cultures.
- The technical difficulty in sterilizing these photobioreactors has hindered their application for algae culture for specific end-products such as high value pharmaceutical products.
Requirements to develop a high-performance photobioreactor for algal cultivation:
- In order to attain high productivity, the volume of the non-illuminated parts of the reactor should be minimized.
- In order to ensure a high efficiency of light use by the culture, the design must provide for the uniform illumination of the culture surface and the fast mass transfer of CO2 and O2.
- To prevent rapid fouling of light-transmitting surfaces of reactors, photobioreactors must be frequently shut down for their mechanical cleaning and sterilization
- High rates of mass transfer must be attained by means that neither damage cultured cells nor suppress their growth.
- For the industrial-scale production of biomass, the energy consumption required for mass transfer and the arrangement of the light-receiving surface of the algal suspension must be reduced to its minimum possible.
PBRs are complex systems composed of several subsystems. The key systems are:
- Light system
- Optical transmission system
- Air handling & gas exchange systems
- Mixing system
- Nutrient system
- Instrumentation system
- Electrical system
Some of the key sub-components of the above system are:
- Oxygen & CO2 sensors
- Temperature sensor
- pH sensor
- Light sensor
- Conductivity sensor
- Recirculation pump
- Harvest pump
- CO2 injection valve
- Substrate pump
- Filtrate recirculation valve
- Water inlet valve purge valve
- Connectors and hoses
- Oxygen release system
- PLC control panel
- Feeding tank
Several of the subsystems of a PBR interact. For instance, the optical transmission system and gas exchange system interact via the mixing that takes place in the reaction area.
To know more about Photobioreactors, buy our Comprehensive Oilgae report with its recent updated version. List of contents under this topic include
- Types of Bioreactors Used for Algae Cultivation
- Parts & Components
- Design Principles
- PBR Manufacturers & Suppliers
- Photobioreactors – Q&A
- Research Done on Bioreactors and Photobioreactors
- Challenges & Efforts in Photobioreactor
- Photobioreactor Updates and Factoids
- Useful Resource
Algae Photobioreactor Design Considerations for Commercial Scale Production
Related Blog Posts
- BioCentric Energy Algae to Unveil Provisional Patent Pending "Algae Pro Closed Loop Photobioreactor Solution"
- Algae Company BioCentric Energy Holdings Provides Update
- Algae Protein Market -A Driving Force for Algae Biodiesel
- Ben Gurion University, Primafuel Join on Algae Biorefinery
- Green Plain Renewable Energy Inc.(GPRE) forms algae venture
- Holcim Spanish Cement Plant Gets GreenFuel, Aurantia Algae CO2 Recycling Project
- Rapid Algae Farming Systems from AlgaeVenture Systems
- Solix claims cut the costs of growing algae by 90-95%
- Petroalgae Grows Algae in Plastic Tubes
- Algae Photobioreactor - Low Cost, High Efficiency, from Algasol Renewables
- Solix Photobioreactor Cuts Algae Cultivation Costs by 90% ?
- Algae Biodiesel Cost - What Exactly Makes Algae Fuel Costly?
- Algae-Covered Buildings Boost Biofuel Production
- Eastern Cape to Turn Algae into Power
- Shell awards prize to Scottish Bioenergy for Algae-to-biodiesel Process
- Shell Awards Prize For Scottish Bioenergy Cooperative Ventures
- Ben Gurion University, Primafuel Join on Algae Biorefinery
- Algae Commercialization, Research and and Business Networking Forum - Jan 2009
- Oregon State University develops biodiesel from algae
- Comparison of compact photobioreactors for large-scale monoculture of microalgae
- Biotechnology of algal biomass production: review of outdoor mass culture systems
- High-density algal photobioreactors using light-emitting diodes
- Elemental balancing of biomass and medium composition enhances growth capacity in high-density Chlorella vulgaris cultures
- Tubular photobioreactor design for algal cultures
- Flat inclined modular photobioreactor for outdoor mass cultivation of photoautotrophs
- Diatom cultivation and biotechnologically relevant products. Cultivation at various scales
- Algae to Ethanol?