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Algae are type of microorganism that grows for proteins or biofuel production or co2 hungry. Algae consume co2 during the process; by-product from the process is oil, minerals, proteins and oxygen. Contaminants from the waste water are utilized by the algae as a food source.
Hydrocarbon in the form of oil and coal are used to produce heat and electricity. When burned, the carbon and hydrogen are broken: the carbon bonds with oxygen to form carbon dioxide. Microorganisms strip the carbon atom, photosynthetically convert into proteins and oil and release the oxygen. Algae microorganism consumes 4kilos of carbon dioxide to produce 1 kilo of dry algal mass.
Algaculture involves cultivation or farming of species of algae. Cultivation of algae falls in the category of microalgae (phytoplankton, microphytes or planktonic algae). Microalgae is also know as seaweeds, has commercial and industrial uses. Since due to their size and the specific requirements of the environment in which they grow, they do not lend themselves as readily to cultivation.
Growing algae is similar to growing tomato in greenhouse, which requires the warmth, light and a steady feed of carbon dioxide and nutrients to reproduce faster than any other plant on earth. The amount of algae growth can double daily, due to which both the attraction and the problem with algae as a commercial crop. But the big "green factor" associated with algae is that it needs CO2 to grow. Algae capture CO2 during the process of photosynthesis and form oxygen and water vapor, it also absorbs nitrogen oxide and sulfur dioxide, which are contributes to acid rain. About 1kg of algae consume 4kg of CO2 to produce 1 kg of dry algal mass, this means that tubes of algae could be laid out next to the power station or a food processing plant to soak up emission. Algae growing condition must be optimized in order to have maximum growth.
Algae in the class of plankton, algae photosynthesize, i.e. they convert carbon dioxide into organic compounds, especially sugars, using the energy of light. Since light is main source, light intensity and photoperiod should be considered. Light intensity plays major role which depends on the culture strength and the density of the culture; at higher depths and cell concentrations the light intensity must be higher to penetrate through the culture (e.g.1,000 Klux is suitable for small lab flask, but 5,000-10,000 Klux must required for larger volumes). Light may be natural or florescent (tube emitting blue or red light spectrum because these portion of spectrum preferred for photosynthesis); too high light intensity leads to photo -inhibition (e.g. direct sunlight, small container close to artificial light). And also overheating by artificial or natural illumination should be avoided. The duration of artificial illumination should be minimum 18 hours of light per day.
The pH range for growing cultured algae species is between 7 to 9, with the optimum range being 8.2-8.7. High density cultured algae case, addition of carbon dioxide allows to correct for increased pH, which may reach the value up to 9 during algae growth.
Aeration and mixing
Mixing is necessary to prevent sedimentation of the algae, to ensure that all the cells of the population are equally exposed to light and nutrients, to avoid thermal stratification (e.g. outer door cultures) and to improve gas exchange between the culture medium and air. Aeration of carbon dioxide is necessary for photosynthesis, for very dense cultures, the carbon dioxide originating from the air bubble (containing 0.03% CO2) is limited by algal growth and pure carbon dioxide may be supplemented to air supply (e.g. at rate of 1% of volume of air). Further CO2 addition buffers the water against pH changes as result of the CO2/HCO3-balance. Depending on the scale in the culture system mixing can be achieved daily by hand, aeration or using paddle wheel or jet pumps.
Optimal temperature for phytoplankton culture is generally between 20 and 240c, this also varies with different culture medium, the species and strain cultured. Most tolerated temperature for most common algae is between 16 and 270c. Temperature lower 160c will slow down the growth and temperatures higher than 350c are lethal for number species. If the temperature exceed then algal culture can cooled by flow of cold water over the surface of the culture vessel or by controlling the air temperature with refrigerated air-conditioning units.
Marine phytoplankton is extremely tolerant to change in salinity. The most species of algae grows to the best at the salinity level that is slightly lower than that of their native habitat, which is obtained by diluting sea water with tap water. Salinities of 20-24 g.l-1 have been found to be optimal.
An algae bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algae bloom may occur in fresh water or in marine environment. Algae bloom is often green, but they can also be other colors such has yellow-brown or red, depending on the species of algae. Of particular some species of algae like dinoflagellates of genus alexandrium and karenia are algal bloom events involving toxic and often takes on a red or brown hue are known as red tides.
We are going to discuss about Botryococcus braunii and chlorella protothecoides, both of them are green algae.
Green colonial and pyramid shaped planktonic microalgae of order chlorococcales and has its application in the field of biotechnology mostly found worldwide in freshwater and brackish lakes, reservoirs and ponds. This species is notable for production of hydrocarbons, especially huge amount lipids. These lipids can be converted into the bio-diesel, jet-fuel, gasoline and other important chemical. B.braunii has grown to the best at an optimal temperature of 230c, a light intensity of 60W/M2, with light period of 12 hours per day, and salinity of 0.15 molar NaCl. Bloom of B.braunii has been a toxic to other microorganism and fishes, the major causes is the fatty acids because the higher the alkalinity changes these fatty acids into a form which is more toxic to other species. Up to 86% of the dry weight of B.braunii can be long chain of hydrocarbon. Hydrocarbon content differs on the basis of strain and class belong to and also the cultural and physiological condition. B.braunii is classified into A, B & L on the basis of hydrocarbon produced. "Race A" produces odd numbered n-alkadinese, mono-, tri-, tetra-, and pentanes of C23-C33 these are derived from fatty acids constituting up to 61% of the dry cell mass of the colonies. "Race L" produces single tetrarepene hydrocarbons know as lycopadiene C60H78 which constitute 2-8% of biomass. "Race B" produces polyunsaturated and branched C30-C37 terpenoid hydrocarbons to as polymethylated botryococcenes which constitute 26-86% on dry weight in the algae. Another difference among the races is the colony color in the stationary phase. "Race A" & "Race B" strains are known to produce exopolysaccharides up to 250g m3 whereas "Race L" produces up to 1 kg m3. Hydrocarbons are extracted from the total lipids as the hexane-soluble component and converted into useful fuels such gasoline by cracking.
Blooms of green colonial green algae B.braunii has widely known to exert toxic effect on a variety of aquatic organisms and have been noted cause to death of aquatic organisms. It indicates that density of B.braunii increase with time, this causes decrease in oxygen level making life difficult for other aquatic species. Other type of toxic substance like polyunsaturated fatty acids, produced by algae may inhibit the growth and occurrences of other algal species. As B.braunii blooms give rise to a film of oil forming on the surface of the water, decreasing water clarity and prevent normal oxygenation of the water. Three type of fatty acid produced when the B.braunii blooms which can exhibit allelopathic effects on other phytoplankton.
Âµg.mg-1 dry weight of B.braunii cells
Linoleic acid (18:2)
Î±-Linolenic acid (18:3)
B.braunii (early stage of bloom )
B.braunii (late stage of bloom )
Influence of CO2 on growth and hydrocarbon production in B.braunii:
Culture sample were to be maintained both in agar slants and liquid cultures medium which consist of following composition,
Taken in two tier flask vessel, where lower compartment of the flask contained 100ml of a 3M mixture (KHCO3/K2CO3) at specific ratios, which generated specific CO2 partial pressure in the two-tier flask. The partial pressure was monitored using a protomap 2 portable gas analyzer. It was observed that the concentration CO2 in the flask was found to be the same throughout the experimental period. 2.0% (v/v) CO2 favored rapid growth, resulting in increased biomass accumulation and hydrocarbon production. Biomass yield increased with increase concentration of CO2 over the control culture. Hydrocarbon content in B.braunii varied in the range of 14 to 28% at different CO2 level and maximum level hydrocarbon content found at 2% CO2. Increase in hydrocarbon content from 5% in unaerated condition to 20-61% when air mixed with 1% carbon dioxide was supplied, depending on the origin of the strain.
Green and single cell algae belong to the phylum chlorophyta. Chlorella consist of the green photosynthetic pigment "chlorophyll-a" and "chlorophyll-b" in its chloroplast. Through the process of photosynthesis it multiplies rapidly requiring only carbon dioxide, water, sunlight and small amount of minerals to reproduce. Chlorella is a potential source of food and energy because of its photosynthetic efficiency is about 8% when compared to other high efficiency crop. Green cells of Chlorella can grow in environment high nitrate and phosphate level or direct sunlight in a low glucose medium.