Thadomal Shahani Engineering College
Humanity has spent years, even decades, to find answers to the question, ‘What will happen if fossil fuels run out?’. Governments, organizations and even laymen have invested copious amounts of resources, time and brain power to find the answer to this age-old question and have come up with a plethora of substitutes to fossil fuels or tried to maximize process efficiency in order to increase the lifespan of this invaluable resource before exhaustion, but there still remains uncertainty in whether it can solve this crisis.
In today’s world, majority of the energy needed is derived from burning fossil fuels. With appropriate infrastructure to replace fossil fuels with more renewable and environmentally sound energy sources still being many decades away, biofuels seem like the best alternative. Biofuel is any fuel that is derived from biomass namely plants, algae or terrestrial feedstock. In this article we are going to be focusing on the biofuels derived from algae.
Why Algae derived Biofuels?
Algae largely remains as an untapped resource considering the potential in regards to the products it can develop. Algae biofuel has been identified as much more promising than other biomass derived fuel due to many reasons:
- Algae can grow rapidly (in about 4 weeks) and over a smaller piece of land requiring almost 40 times less area of land than traditional terrestrial plants(namely soybean, palm) to generate the same amount of biofuel
- It can grow in freshwater, seawater, saltwater or even brackish water
- Algae are biodegradable and relatively harmless to the environment in case of spillage
- Lastly, the fuel can yield up to 10 to 100 times more fuel per unit area.
Biofuels emit the same amount of CO2 as regular fossil fuels, but the algae that produce biofuels consume a lot of that CO2 while growing; such that the net CO2 is often negligible or zero. Algae biofuels have been found to be Carbon positive, meaning that they consume more CO2 while growing than they emit while burning.
Technical Overview of Biodiesel Production from Algae
The production of biodiesel from microalgae consists of extracting cytosolic lipid bodies that contain a large amount of triacylglycerides which can be further refined into biodiesel using transesterification.
Algae can be cultivated in various ways like open pond system, closed system, photobioreactors. The most common and high-volume production method is an open pond system where as the name suggests algae is usually grown in an open pond or lake. Closed systems like Photobioreactors involve a closed infrastructure with manual control of the conditions which facilitate optimum growth of algae. The pitfall being the high operation and maintenance cost along with low volume of production.
After cultivation comes harvesting and dewatering of the algae biomass which is usually done by filtration of centrifugation. Sometimes flocculation can be adopted to ease the harvesting process. Post harvesting is complete, extraction of lipids from biomass is done. Lipid extraction is usually done by disrupting the algal cell walls. The ways adopted for extraction include bligh and dyer, ultrasound assisted extraction, enzymatic hydrolysis, and so on. The process is selected on the basis of the requirement and cost effectiveness.
Microalgae consists of 2 lipids namely polar (phospholipids) and non-polar lipids (mono, di, triacylglycerides). The latter is the most desirable for conversion to biodiesel. After the lipids are extracted, the next and final step in the synthesis of biodiesel is transesterification of the lipids. Biodiesel is produced by transesterification of these extracted lipids with an alcohol, such as methanol or ethanol, on an alkaline, acid or enzyme catalyst, and it is composed of a mixture with at least 96 wt% of fatty acid methyl or ethyl esters.
Cultivation of microalgae for applications such as fuel is a rapidly developing area of research and investment. Whilst microalgae promise to deliver many environmental benefits compared with existing biofuel technology, there are also issues to overcome in relation to wastewater management, emissions control and land use. In a world where natural resources are being extracted and consumed at an ever increasing rate, there is also a growing need to seek alternatives to provide nutrients, chemicals and energy for mankind. Microalgae have gained attention due to their fast growing nature, adaptability to their environment and an ability to concentrate useful chemicals and capture nutrients in an economical way. The major pitfalls include the high cost involved with algae cultivation and extraction of lipids from algae. Research is underway to reduce these prices and reach a point where algae derived biodiesel prices can compete or be lower than conventional biodiesel.