9 Algal Biofuel: A Sustainable Green Energy Laxuman Sharma1 and Akhilesh Kumar Singh2* 1Department
of Horticulture, Sikkim University, 6th Mile, Gangtok 737102, India. 2Amity Institute of Biotechnology, Amity University Uttar Pradesh Lucknow Campus 226028, India. *E-mail:
[email protected]
Abstract
Modern world is experiencing energy insecurity because of extreme population pressure and depleting energy resources. Fossil fuels though have highly applauded for contributing to today’s development, are non renewable energy and debated for not sustainable. This has posed serious challenges to the scientific fraternity for finding the suitable alternatives. A cheap, ecofriendly, sustainable or renewable type of energy is visualized for development with added advantage of mitigating green house gases. Biofuel produced from different feedstock has been researched, trialed and commercialized with many advantages and disadvantages. Biofuel production from the oil producing crops like maize, soyabean, jatropha etc. growing in arable land are not considered ideal because it is not climate neutral and pose competition for food production. Biofuel production using non-food feedstock as wood processing residues, forest residues, agricultural residues and non-edible constituents of beet, sugarcane, corn etc., which do not directly involved in competition with human food chain, are also not feasible owing to requirement of costly and sophisticated technologies. Biofuel production using algal biomass as feedstock has attracted the researchers and policy makers having several advantages of rapid growth rate, high space efficiency, high productivity, sulphur free fuel, non toxic and biodegradability. Several strains 205
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Research on Biotechnology in India: Some Initiatives and Accomplishments
of algal species like Scenedesmus sp, Scenedesmus obliquus, Chlorella vulgaris, Chlamydomonas sp, Chlorococcum littorale etc. are reported to produce high biomass with high lipid content, making them ideal candidate for biodiesel production. Bioethanol production from species like Spirogyra, Chlorococcum humicola and Chlorococcum infusionum have also been reported. In addition to the production of the oil, these species have high CO2 sequestration ability and can be used for waste water treatment. Despite constant efforts for producing biofuels from microalgae, the economic production is still questionable. The cutting edge technology for improving cultivation techniques, growing methods, species selection and bio-engineering are still to be applied holistically for cost effective production and commercialization of algal biofuel in near future, as algal fuel is only alternative to the fossil fuels. Key words: Algae, Biodiesel, Bioenergy, Bioethanol, Biofuel, Biogas Introduction
The rapid civilization and ever expanding economy have posed mammoth scale energy demand worldwide. Fossil fuels, produced from carbon reserves of millions of years has now been debated for being non renewable and its increased used has threatened closed carbon cycle. Burning of fossils fuels is tremendously contributing to increased green house gases and climate change. The sustenance of environment, economy and the pace of development can only be achieved by shifting to the renewable source of energy. An alternative energy now sought for exploitation of biological agents to transform source of energy, such as sunlight and biomass, into fuels such as biodiesel, bioethanol etc. Biomass referred to entire cellular dry weight or organic substances manufactured by an organism generally from sunlight in conjugation with carbon dioxide. Biologically synthesized fuels or solid, liquid or gaseous fuels derived from organic matter are typically termed as biofuels. Now, biofuel have received much attention as alternative green renewable energy over conventional fossil fuel owing to severe environmental concerns, increasing crude oil price, apprehension about energy security and diminishing non-renewable fossil fuels reserves (Chhetri et al. 2008). Interestingly, biofuels are categorically a green renewable energy of the choice with positive characteristics viz. biodegradability, nontoxicity and lower releases of greenhouse gases. Currently, the exploitation of liquid biofuels viz. biodiesel, bioethanol and jet fuel has been intensified enormously particularly in the transport sector (Tabatabaei et al. 2011).
Algal Biofuel: A Sustainable Green Energy
Biofuels and their categories
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Biofuels have evolved into an innovative area of research globally. These are broadly classified into three categories: (i) Natural biofuels, (ii) Primary biofuels and (iii) Secondary biofuels (Table 1). The natural biofuels are usually manufactured from organic sources, such as landfill gas, animal waste and vegetables. Primary biofuels involve fuel-woods, which are exploited primarily for heating, cooking, electricity production or brick furnace. On the other hand, the secondary biofuels composed of biodiesel and bioethanol that are manufactured by processing of biomass (Nigam and Singh 2011). Based on features viz. feedstock, processing technology and/ or development levels, the secondary biofuels are further categorized into three sub-classes, i.e. first, second and third generation biofuels (Table 1, Dragone et al. 2010). The first generation biofuels (bioethanol), which predominantly manufactured from food crops including oil seeds are restricted in their capability to attain their goals for biofuel synthesis owing to alarming socio-economic consequences (competition of biodiesel feedstock with food commodities), climate change mitigation and requirement of more arable agricultural lands (Chhetri et al. 2008; Alam et.al. 2010). These issues have intensified the attention towards manufacturing/ producing second generation biofuels by exploiting non-food feedstocks such as wood processing residues (e.g. saw dust), forest harvesting residues, agricultural residues (wood chips, straws, sheared branches, leaves etc.) and non-edible constituents of beet, sugarcane, corn etc., which do not directly involved in competition with human food chain (Alam et al. 2010). However, the productions of second generation biofuels are not feasible owing to requirement of costly and sophisticated technologies including special enzymes (Lee et al. 2014; Espinosa-Gonzalez et al. 2014). Land based higher plants are also seen as alternative biofuels, but they are debated for not being climate neutral and potentially compete with net food production (Scharfemann and Larance 2008). Overcoming the shortfalls of first and second generation, the third generation biofuels offers pronounced feasibility (Dragone et al. 2010; Nigam and Singh 2011; Brennan and Owendue 2010; Li et al. 2008). It is anticipated that the feasibility towards biodiesel synthesis by exploiting microalgae is 15 to 300 times greater compared to conventional/ traditional crops on area basis (Dragone et al. 2010). Apart from this, microalgae have a very short harvesting cycle over conventional crop plants that facilitate continuous or
