CEE Oct-Dec 2012

supply, water supply, optimal temperature , efficient exposure to light, culture density, pH levels, gas supply rate, mixing regime, etc. The various types of Photobioreactors available are tubular reactors {horizontal and vertical), flat panel reactors, vertical column reactors, bubble column reactors, air lift reactors, stirred tank photobioreactors and immobilized bioreactors. Tubular photobioreactors are widely used for the mass cultivation of algae. Cultivation of algae in controlled circumstances It is reported that algae yield 30 times more energy per acre than land crop such as soybeans and some estimate even higher yields up to 15000 gallons per acre. gives higher productivity. Photobioreactors greatly improve productivity through their design: the use of clear plastic tubing for efficient and volumetric distribution of light; air lift pumps to keep the algae in suspension ; mechanism for gaseous exchange; pH and growth sensors. In photobioreactors, the key systems include: light source, optical transmission system, air handling system, reactions area - the reaction mixing system, gas exchange system (C0 2 injection valve, oxygen release system), nutrient system (feeding tank), filtration system(algae collection filters to remove algal biomass), sensing system (oxygen and C02 sensors, temperature sensor, pH sensor, light sensor, conductivity sensor), electrical systems and instrumentation systems. Algae harvesting Algae are separated from the growing medium and then dried and processed to obtain biofuel. Harvesting methods depend primarily on the type of algae. The most common harvesting processes are flocculation , micro-screening and centrifugation. Selection of easy to harvest strains is important to ensure efficient and relatively inexpensive harvesting. Algal oil can be extracted using mechanical methods (expression/expeller press, ultrasonic-assisted extraction) or chemical methods (hexane solvent method, soxhlet extraction, supercritical fluid extraction). Biofuel from algae It is reported that algae yield 30 times more energy per acre than land crop such as soybeans and some estimate even higher yields up to 15000 gallons per acre. It keeps the earth clean and free from pollution as these algal biodiesel fuels help to utilize a resource that is availabie in abundance just waiting to be harnessed and exploited. Various forms of biofuel from algae are shown in Figure1 . Fig I . Showing Yariou\ form; ofbiofud\ - rl ( ·'"ri,Jttnn H l·ud ~-" 1 .-------.., H£~£-=:oH nil.<hmoal \ '-------'H lt<jU<IJ<tt<>n H 0•1 j u fhdrOt:CtUll<lO OOH._~-)jJ __ ~ I •t: 2. Showing the preparat ion of mcthvl cstcn depending upon their chemkal t ompu\ition .lltd I"J·,\ <Onlent ,- •)1\ )Jl '-I It I H • l !i O! I L . \l,th... ,..t OC!>'t !r11:h· uu! .... II{~-· I()( I ~h·t:.,f I \II nlf.tll\.1•1•1 -,-<111 ·-- -tlll L .." l ' ~ .• The procedure for the preparation of methyl esters varies from oil to oil depending upon each one's chemical composition and FFA content, shown in Figure 2. The first step is to remove water from oil by increasing its temperature to 120 °C for about 5 to 10 minutes. Then it is allowed to cool and mixed with sodium hydroxide and methanol by stirring- sodium methoxide is produced. Clean oil is heated to 60 °C for 5 minutes, mixed with the sodium methoxide and the mixture is transferred to an ultrasonic or mixer equipment for the agitation of the solution for 30 minutes after which it is cooled and separated. Microalgae produce lipids in the form of triacyglycerols (TAGs). Comparatively, algae produce more oil than any other oilseeds which are currently in use. Many micoroalgal species can be induced to accumulate substantial quantities (more than 60 per cent of their own biomass) of lipids. Micoralgae have the highest oil yield among various oil plants. It can produce up to 100,000 Its oil per hectare per year, whereas palm, coconut, castor and sunflower produce up to 5950, 2689, 1413 and 9521 per hectare per year, respectively. Algae biodiesel characteristics Algae biodiesel has many positive characteristics making it a fuel that is sustainable and great for use. It has no sulphur content and has superior lubricating properties, reducing the wear and tear of the fuel system - increasing the life of the fuel injection equi pment. Algae biodiesel has more aggressive solvent properties than petrodiesel and even dissolves varnish residue. Biodiesel has about 5 - 8 per cent less energy density than petrodiesel, but with better lubrication 34