Author: Enemona Greg Ademu (Mr.)
Algae are morphologically simple, chlorophyll-containing organisms that range from microscopic and unicellular, to very large and multicellular. They are typically autotrophic, deriving their food or energy from their surroundings in the form of sunlight.
Thus, microalgae are microscopic unicellular organisms capable of converting solar energy to chemical energy through the process of photosynthesis. They are found in both marine and freshwater environments and they contain a lot of bioactive compounds that can be used for commercial purposes. Due to their more efficient utilisation of sunlight energy as compared with higher plants, their potential for production of energy and other valuable compounds is widely recognised.
The first use of micro algae by humans was as far back as 2000 years ago when the Chinese used Nostoc to survive during famine. Today, apart from being used as single-cell proteins, they are also used as living-cell factories for the production of bio-fuels and various biochemical used in food, aquaculture, poultry and pharmaceutical industries.
2.0 PRODUCTION OF MICROALGAL BIOMASS
Different species of algae (being environmental friendly) are strong candidates for generation of biomass. Among renewable resources, algae have proven to be the most attractive feedstock. This is due to the fact that algae are photosynthetic microorganisms with high rate of productivity, rich in lipid content and holds no competition with food crops since it does not require arable land and can grow in any harsh condition owing to their simple organisation (Vandamme et al. 2011). An important advantage of using micro algae biomass is that there is minimal nutrient requirement so it can be grown on a range of sewage and waste water from where it derives its nitrogen and phosphorus requirement (Malik and Prajapati 2012).
2.1 CULTIVATION OF MICROALGAE
2.1.1 Internal and external factors required for growth of algal biomass
Water, containing the accurate amounts of salt and minerals, is an essential component needed for algal cultivation
Algae require very high amount of carbon for efficient growth. Foe each kg of algae grown, approximately 1.65kg of CO2 is used.
This is the key ingredient to initiate photosynthesis. As compared to higher plants, algae require relatively low intensity of light for proper development.
This plays a significant role in algal metabolism because it is the main constructing element of proteins and nucleic acids.
184.108.40.206 Additional nutrients
Other nutrients like phosphorus (used in the form of phosphates), trace amounts of vitamins and metals like sodium, calcium, iron, copper and magnesium are also required for efficient growth of algal culture.
Unlike other organisms, algae are very versatile and do not require arable land for productive growth. Hence, issue of appropriate space is usually not a concern.
2.1.2 Methods for Cultivation of Algal Biomass
220.127.116.11 Photoautotrophic Production
This form of cultivation takes place when algae utilize an energy source (light) and carbon source (inorganic carbon) to form carbohydrates. This is the most general method used for cultivating algae and results in the formation of algal cells with lipid content ranging from 5 to 68% depending on the algal specie being cultivated.
18.104.22.168 Heterotrophic Production
In this method, the algal specie is grown on a carbon substrate like glucose thus eliminating the need of light energy. Biomass produced by this method has a higher yield and cells have higher lipid content as compared to autotrophic cells.
22.214.171.124 Mixotrophic Production
This utilizes both photosynthetic and heterotrophic elements for cultivation. Here, light energy is not a primary need as cell growth can occur by digesting organic material.
126.96.36.199 Photoheterotrophic Cultivation
In this method, algae requires light energy and also obtains carbon from an organic source. Unlike mixotrophs, photoheterotrophs cannot grow without light energy.
2.1.3 Cultivation Systems
There are two main cultivation systems used for the production of algal biomass: open ponds and closed photobioreactors.
188.8.131.52 Open Ponds
These are open tanks or naturally existing water bodies such as ponds, lakes, lagoons, etc. They are easy to construct and use and are kept shallow for easy penetration of solar radiations. They are a cheaper method for algal cultivation and they require less energy for their operation. Water and nutrients are continuously circulated in the culture. Output of the pond is measured by calculating the biomass produced each day per unit area.
184.108.40.206 Closed Photobioreactors (PBR)
Closed photobioreactors are used to cultivate algae in closed environment under manageable conditions. These systems are more expensive than open ponds and present more technical problems. Efficiency of this system can be appreciated by considering the fact that it does not permit the algae to be exposed to the external environment thus eliminating contamination, losses due to evaporation, temperature vacillation and inept mixing, all of which are associated with open pond systems.
220.127.116.11 Hybrid Production System
This cultivation method comprises of two stages and uses both open ponds and PBR for different growth phases. The first stage of cultivation is completed in a photobioreactor where uninterrupted cell growth occurs in a pollution-free environment under controlled conditions. The second stage occurs in open ponds and is intended to expose the culture to ecological and nutrient stresses. This enhances the production of desired lipid product.
3.0 COMMERCIAL USES OF MICRO ALGAE
There are numerous commercial applications of micro algae such as in food and feed to enhance nutritional value; in aquaculture; and in cosmetics.
3.1 Micro algae and human food
Micro algae are a rich source of carbohydrates, protein, enzymes, fibre, and many vitamins and minerals.
Spirulina platensis, a blue green algae has been shown to be an excellent source of proteins (Colla et al. 2007), polyunsaturated fatty acids (Sajilata, 2008), vitamins and phenolics (Colla et al. 2007; Ogbonda et al. 2007).
Another algae used as food is the green algae Chlorella which is mainly sold in health food stores and as fish food. The major economic important product of Chlorella are several by-products that are used in fruit and vegetable preservatives. Microalgae are also added to pasta, snack foods or drinks either as nutritional supplements or natural food colorants (Becker, 2004).
3.2 Use in Cosmetics
Components of algae are frequently used in cosmetics as thickening agents, water-binding agents, and antioxidants. They can be found in face and skin care products such as anti-aging cream, emollient and as anti-irritant in peelers. Microalgae are also represented in sun protection and hair care products. The main microalgal species established in the skin care market are Anthrospira and Chlorella (Stolz and Obermayer, 2005). Others are Chondrus crispus, Mastocarpus stellatus, Ascophyllum nodosum, Alaria esculenta, Spirulina platensis, Nannochloropsis oculata, Chlorella vulgaris and Dunaliella salina.
More recently, a carbohydrate discovered in microscopic algae could be useful in cosmetic products. The substance was discovered by scientists at the Industrial Biotechnology Innovation Centre (IBioIC) in Scotland. Called Prasinococcus capsulatus, the ingredient has natural anti-inflammatory and anti-viral properties. It could potentially be used in products such as sunscreens and moisturizers as well as first-aid creams. The ingredient requires only seawater, light and CO2 in order to grow, making it a natural and sustainable option for cosmetic manufacturers.
3.3 Microalgae and Biofuel
Microalgae have long been recognised as good sources for biofuel production because of their high oil content and rapid biomass production. Microalgae offer many potential benefits when used as biofuel:
- They can potentially produce 1000-4000 gallon/acre/year significantly higher than soybeans and other oil crops.
- They do not compete with traditional agriculture because they can be cultivated on non-arable land.
- They can grow in a different climatic and water conditions; and can utilize and sequester CO2 from many sources.
- Finally, they can be processed into a wide range of products including biodiesel, bioethanol, methane, heat, bio-oil, and high protein animal feed.
3.4 Use as Biofertilizer
Microalgae are used in agriculture as fertilizers and soil conditioners. Majority of cyanobacteria are capable of fixing atmospheric nitrogen and are effectively used as biofertilizers. Blue green algae belonging Nostoc, Anabaena, and Tolypothrix Aulosira fix atmospheric nitrogen and are used as inoculants for paddy crop. Cyanobacteria also benefit crop plants by producing various growth-promoting substances; Cylindrospermum sp, andTolypothrix tenuis produce Vitamin B12. Nostoc muscorum and Hapalosiphon fontinalis produce Vitamin B12 and Auxin.
3.5 Use in Pharmaceuticals
Microalgae are rich source of novel and biologically active primary and secondary metabolites. These metabolites may be potential bioactive compounds of interest in the pharmaceutical industry (Rania and Hala, 2008). Microalgae have a significant attraction as natural source of bioactive molecules because they have the potential to produce bioactive compounds in culture, which are difficult to produce by chemical synthesis.
Microalgae such as Ochromonas sp, Prymnesium parvum produce toxins that may have potential pharmaceutical applications (Katircioglu et al. 2006). Also, various strains of cyanobacteria are known to produce intracellular and extracellular metabolites with diverse biological activities such as antialgal, antifungal, antibacterial and antiviral activity. Both cell extracts and extracts of the growth media of various unicellular algae (e.g Chlorella vulgaris, Chlamydomonas pyrenoidosa) have been proved to have antibacterial activity in vitro against both Gram-positive and Gram-negative bacteria. It has also been reported that a wide range of in vitro active antifungal activities are obtained from extracts of green algae, diatoms and dinoflagellates.
3.6 Use as Aquaculture Feed
The most frequently used species in aquaculture are Clorella, Tetraselmis, Isochrysis, Pavlova, Phaeodactylum, Chaetoceros, Nannochloropsis, Skeletonema and Thalasiosirra. Several companies produce aquaculture feeds using Chlorella and Spirulina, or a mixture of both.
Over the last four decades, several hundred microalgae species have been tested as food, but probably less than twenty have gained widespread use in aquaculture.
Microalgae are a diverse group of microscopic plants with a wide range of physiological and biochemical characteristics and contain up to 50-70% protein, 30% lipids, over 40% glycerol, up to 8-14% carotene and a fairly high concentration of vitamins compared with other plants or animals (Avagyan, 2008). Consequently, the cultivation of microalgae is one of the most profitable ventures in the biotechnology industry. It is a “wasteless”, ecologically pure, energy and resource saving process.
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About Author / Additional Info:
Enemona Greg Ademu is a Scientist, Academic and Sportscaster. He writes from Abuja, Nigeria.