Step 1. Cultivating Algae
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Algae can grow significantly faster than any other plant, which is one of their biggest drawing points as a biofuel feedstock. What's more, they can be grown in a number of different ways almost anywhere that temperatures are warm enough and, depending on their strain, do not require freshwater.
Open ponds and closed photobioreactors are the two most widely accepted forms of algae cultivation, currently deployed by leading algae companies.
Open (Raceway) Pond Systems:
One of the first systems of algae cultivation experimented with and still favoured by many companies these days. This simple system involves the flow of suspended algae around a large but shallow artificial pond often referred to as a raceway. CO2 is fed into the system at the bottom of the raceway. A fraction of the algal biomass is generally harvested every day and passed on to extraction processing.
Advantages:
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Cheap and easy to operate
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Low running costs
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Very efficient
Disadvantages
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Poor light utilization by algae cells
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Evaporative losses
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Large requirement of land
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High susceptibility of contamination of unwanted species
Sapphire Energy are in the process of installing a large scale open pond facility in the desert of New Mexico. To learn more please follow the link
Closed photobioreactors:
Unlike open systems, algae are enclosed in a transparent vessel or tube which provides a controlled environment. There are many diverse forms of photobioreactors favoured by differenct manufacturers.
Advantages:
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Regulated supply of nutrients, light, CO2 and temperature enables optimum conditions to be maintained resulting in higher productivity
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Lower risk of contamination from other species
Disadvantages
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High operational costs due to large amount of energy required in additional lighting and mixing
An example of closed photobioreactor used by Algenol
The verdict:
These two traditional systems have proven to be effective methods of algal cultivation and have achieved economic viability in the production of high value products for cosmetics, medicines and nutraceuticals. The economic margins for their use in large scale biofuel production are, however, significantly smaller. Optimising cultivation is therefore essential for the economic viability of biofuel production.
One downside of these current techniques is the large requirement of light, water and essential nutrients that would be needed on a commercial scale. High contamination risks of open ponds and high initial costs of photobioreactors are also significant contributing factors, limiting economic viability.
Minimising these inputs through the use of engineered algae and advanced photobioreactors have been suggested as an efficient way of reducing energy costs as well as enhancing extraction processes.
To take a look at some examples of recent developments proposed by innovative algal companies, follow the link below:
The next step
The next processing step after cultivation is separating the algae from the growing mixture. This is known as algal harvesting and presents some challenging hurdles, which must be overcome through cost-effective and energy efficient methods to make the whole production economical.
A breakdown of current methods and how improvements may be made can be found at the following page