The current cultivation methods are still based on Asian techniques although currently programs are initiated in the EU to develop open sea based seaweed cultivation technology.
Although seaweeds are and have been known for their richness in bioactive substances like polysaccharides, proteins, lipids, vitamins and polyphenols, to have a wide range of potential cosmetic, pharmaceutical and medical applications,their economic potential is still insufficiently developed.
Due to the relatively high carbohydrate content in percentage of the dry weight brown macro algae in particular species of the Laminariaceae have come under the spotlight for mass-cultivation.
The chemistry as result of life or also called bio depends on carbo-hydrate based chemistry. Specifically in respect of carbohydrate production for fermentation purposes for ethanol and or biodegradable plastics production or other medical and food applications. Brown macro algae exploitation in Europe is currently restricted to manual and mechanised harvesting of natural stocks, although several EU projects explore mass cultivation in European waters.
The majority of Asian seaweed resources however are cultivated. The most common system in Europe to obtain seaweed biomass is by harvesting natural stocks in coastal areas with rocky shores and a tidal system. The natural population of seaweed is here still the main and most significant resource.
Depending on water temperature, some groups will dominate, like brown seaweeds in cold waters and reds in warmer waters.
In Europe the main harvesting countries are Norway and France. Between 120,000 and 130,000 tonnes of Laminaria are harvested annually in Norway. The standing stock is estimated to be 10 million tonnes (Vae and Ask, 2011).
The demand is there but prices/cost the main limiting factor.
Currently seaweeds and algae are used as raw material in the following sectors:
Food Health food products like omega 3 – EPA of DHA, Supplements/capsules Pharmaceuticals Animal feed incl. fish feed Agriculture, fertiliser Cosmetics Drinks.
Some of the others potential uses and utilisation are;
• Industrial gums
• Animal feed
• Ingredients and supplements
• Sugars/Bio fuels
• Fertiliser (agrochemical)
• Medicinal uses
• Bio filters in IMTA
• Use in climate change adaptation and coastal defence (Building with Nature)
• Seaweed used to enhance capture fisheries
• Wastewater treatments.
Algae Biomass cultivation
From harvesting in the wild, to the product specific spies and a kind of seedling of the desired spies attach on ropes or inside holder attached to robes. This technique is possible for growth of different seaweed (Macro Algae) but not micro algae because
these are very small and there is no hold fast you have to use ponds and reactors.
In France about 30,000 – 50,000 tonnes of seaweed are annually harvested, mainly Laminaria species for hydrocolloid production. The green alga Ulva is commonly encountered in estuaries and inshore coastal areas. When mass proliferation occurs they are known as 'green tides and becoming or turning into a pest.'
They tend to develop at more and more locations along European coasts, due to eutrophication, and are only used to a small extent as fertilisers but not yet in industrial applications. By harvesting them the damage causing part is removed and clean water salt based remains. Therefore or nevertheless form an interesting source and feedstock for important carbohydrates. Combined with waste water treatment (Kraan & Guiry, 2006).
Seaweed or Macro algae, the most important aspect is to bridge the gap in knowledge on large-scale cultivation of seaweeds and its use as a raw material for fermentable sugar production. Seaweed is grown near the coast but should move and done further er out and no additional land used other than possible processing.
We do know that seaweeds can grow fast to produce fermentable sugars without affecting the local sea environment and several suitable species have been identified for large-scale cultivation and harvesting systems in the ocean.
Suitable hydrolysis methods are being developed to obtain fermentable sugars, which can be further converted to fuel and value, added products.
Since the seaweeds will be grown under saline conditions, and it is expensive to wash them before processing further the hydrolysis and fermentation process must be marine based.
To grow high value seaweed with certain specific properties or quality biotic conditions are needed. Cultivation is the most efficient solution to guarantee consistent contents in bioactive compounds, whereas seaweeds harvested from wild resources undergo uncontrolled composition variations due to changes in growing environment. If highly valuables molecules such as fucoidan are aimed as products, that will not do and in addition seasonal variations have to be addressed. Only under controlled conditions interesting levels of bioactive polysaccharides tyo be use as medicine should be obtained and therefor certified.
Most of the micro algae cultivation is done in ponds and reactors and does take-up some land, preferably waste land. Optimisations of these downstream processing methodologies such as harvesting, lipid extraction, Fatty acid methyl ester (FAME) production and media recycling have been carried out with consideration of process time, quality and economics in different countries. Outdoor mass cultivation with seawater-based media has been done and tested to locate efficient strains succesfull. New raceway ponds, each with 30, 000 L capacity (42 x 2.73 x 0.35m) in a closed circular loop were successfully tested and in operateion on small scale. The open pond cultures are economically more favourable, but raise the issues of land use cost, water availability, and appropriate climatic conditions.
Further, there is the problem of contamination by fungi, bacteria and protozoa and competition by other micro algae.
The Photo bioreactors offer a closed culture environment, which is protected from direct fallout, relatively safe from invading micro organisms, where temperatures are controlled with an enhanced CO2 fixation that is bubbled through culture medium and normally used by air cleaning of energy producing plants.
This technology is relatively expensive compared to the open ponds because of the infrastructure costs.
An ideal biomass production system should use the freely available sunlight. It is reported the best annual averaged productivity of open ponds reported being about 24 g-1 dry weights m-2 d-1. Cultivation have been carried out in batch mode.
Algal proteins offer interesting possibilities. If all transport fuels were to be replaced by micro-algae bio diesel considerable quantities of proteins would become available as well. That is 40 times more than the amount of protein in the Soya that Europe imports each year. Thus, algae would allow the production of food and feed proteins as well as sufficient quantities of bio diesel and listed as the bio refinery.
To improve digestibility pre-treatment like heating or freezing might be needed. The production of micro algal bio diesel requires large quantities of algal biomass.Most of algal species are obligate phototropism and thus require light for their growth. Researchers and commercial producers have developed several cultivation technologies that are used for production micro algal biomass. The phototropic micro algae are most commonly grown in open ponds and photo bioreactors.
Use of light/requirement
A productivity of 100 g-1 dry weight m-2 d-1 was achieved in simple 300 l culture systems and this level possible or deriving from the light saturation effect. The light requirement coupled with high extinction coefficient of chlorophyll in algae has necessitated the design and development of novel system for large-scale growth.
Experiments have also elucidated that algal biomass production can be boosted by the flashing light effect, namely by better matching photon input rate to the limiting steps of photosynthesis. Indeed, the best annual averaged productivity has been achieved in closed bioreactors.
Tridici has reviewed mass production in photo bioreactors. Many different designs of photo bioreactor have been developed, but a tubular photo bioreactor seems to be most satisfactory for producing algal biomass on the scale needed for bio fuel
production. Closed, controlled, indoor algal photo bioreactors driven by artificial light are already economical for special high-value products such as pharmaceuticals, which can be combined with production of bio diesel to reduce the cost.