Marine plants come in two forms. Some marine algae are so small they can only be seen under a microscope. Others are very large called macroalgae or seaweeds, such as Macrocystis, a species of kelp belonging to the Brown Algae group, which may reach 60 meters in length.
Because of its salt content, salt water is more economical than fresh water for growing algae. The main nutrients needed for algae growth is already present in seawater.
Seawater is a solution of salts of nearly constant composition, dissolved in variable amounts of water. There are over 70 elements dissolved in seawater but only 6 make up>99% of all the dissolved salts; all occur as ions - electrically charged atoms or groups of atoms:
|
Composition of Seawater |
|
|
Sulphate(SO4) |
7.68 wt% |
|
Calcium(Ca) |
1.16 wt% |
|
Sodium(Na) |
30.61 wt% |
|
Magnesium(Mg) |
3.69 wt% |
|
Potassium(K) |
1.10 wt% |
Macro-algae are cultivated at sea mainly by simply tying them to anchored floating lines. Seaweeds do not require soil, and are already provided with all the water they need, a major advantage over land production of biofuels since water is the most limiting factor for most agricultural expansion, especially with climate change
Algae Production in Open Ocean Environments
Many countries have limited land for farming or growing oil crops, or for that matter algae, but have much larger ocean areas. So a natural question that arises is: how can algae be cultivated in ocean environments for biodiesel? Most research so far into algae-culture have concentrated on inland & controlled sites.
To get high oil yields per Acre the environment needs to be controlled to a significant extent in order to keep other species from coming in and taking over. It will be extremely difficult in open, uncontrolled environments to keep lower, undesirable strains of algae from taking over high oil algae, which aren't particularly competitive in such open environments. Also to be considered are problems such as how to harvest in an open ocean, etc. At this stage of research hence, harvesting specific strains of algae in open ocean environments appears to be a considerably difficult matter.
For more inputs on heterotrophic algea in the context of
Biodiesel see: Replacement
Diets for Live Algae – from FAO & Biofuels
Production from Microalgae after Heterotrophic Growth (PDF)
See the following sections in Cultivation of Algae in Marine environment:
- Algal Strains for Marine Cultivation
- Nutrients in Marine Environment
- Harvesting in Marine Environment
