**12. Sustainability**

Environmental protection will be one of the prominent reasons foe utilization of biomass resources. Microalgal biofuels are more important because it is useful to counter Energy Security and Climate Change problem which is main issue through worldwide. The microalgal Biomass absorbs carbon dioxide during growth, and emits it during combustion. Hence it does not contribute to green house effect. There can be a substantial reduction in the overall carbon dioxide emission as the microalgal biomass is a carbon dioxide neutral fuel. Microalgal biofuels is also sustainable because away from conventional crops algae biomass can be grow on the land which is not arable land so it not affect food security to anywhere in the world. As discussed above, algae is fastest growing biomass on less land required to agriculture product so there is no any problem associated with row material required for biofuels generation.

Sustainability is the subject of much discussion at international scientific and governmental forums on biofuels. Emerging from this discussion is a consensus that sustainability is of foremost importance as an overarching principle for the development of biomass-to-energy agro-industrial enterprises. While sustainability criteria that are agreeable to all nations are still being expounded, the generally accepted principles of sustainability include that;


**11. Biodiesel production from algal oil**

long chain hydrocarbons, known as fatty acids.

compounds, and traces of water [17].

128 Biofuels - Status and Perspective

68].

**12. Sustainability**

Biodiesel is a mixture of fatty acid alkyl esters obtained by transesterification (ester exchange reaction) of vegetable oils or animal fats. These lipid feedstocks are composed by 90–98% weight) of triglycerides and small amounts of mono and diglycerides, free fatty acids (1–5%), and residual amounts of phospholipids, phosphatides, carotenes, to copherols, sulphur

Transesterification is a multiple step reaction, including three reversible steps in series, where triglycerides are converted to diglycerides, then diglycerides are converted to monoglycerides, and monoglycerides are then converted to esters (biodiesel) and glycerol (by-product). The overall transesterification reaction is described in Fig. 3 where the radicals R1, R2, R3 represent

For the transesterification reaction oil or fat and a short chain alcohol (usually methanol) are used as reagents in the presence of a catalyst (usually NaOH). Although the alcohol: oil theoretical molar ratio is 3:1, the molar ratio of 6:1 is generally used to complete the reaction accurately. The relationship between the feedstock mass input and biodiesel mass output is about 1:1, which means that theoretically, 1 kg of oil results in about 1 kg of biodiesel.

A homogeneous or heterogeneous, acid or basic catalyst can be used to enhance the transes‐ terification reaction rate; although for some processes using supercritical fluids (methanol or ethanol) it may not be necessary to use a catalyst [295]. Most common industrial processes use homogeneous alkali catalysts (e.g. NaOH or KOH) in a stirred reactor operating in batch mode.

Recently some improvements were proposed for this process, in particular to be able to operate in continuous mode with reduced reaction time, such as reactors with improved mixing, microwave assisted reaction [44,65], cavitations reactors [43, 44] and ultrasonic reactors [130,

Transesterification is process algae oil must go through to become desired product biodiesel which is required two chemicals (Methanol and Sodium hydroxide) and following steps to be done as mix Methanol and Sodium hydroxide which make sodium methoxide now this sodium methoxide mix with algae oil and allow it to settle for about 8 hours. Now filter biodiesel to 5 microns and drain glycerin. This glycerin is used to make products such as soap and others.

Environmental protection will be one of the prominent reasons foe utilization of biomass resources. Microalgal biofuels are more important because it is useful to counter Energy Security and Climate Change problem which is main issue through worldwide. The microalgal Biomass absorbs carbon dioxide during growth, and emits it during combustion. Hence it does not contribute to green house effect. There can be a substantial reduction in the overall carbon dioxide emission as the microalgal biomass is a carbon dioxide neutral fuel. Microalgal biofuels


It is self evident that where there is a natural abundance of freshwater, it is likely on arable land (that may be under agriculture and may have multiple competing uses for the water resource), or on land in its natural state with considerable biodiversity value. With few exceptions where the abundance of freshwater is the consequence of human intervention, the water has multiple competing uses.

Consequently, from the perspective of sustainability it seems obvious that algal production systems should target water resources other than freshwater. In fact, the proponents of algal biofuel claim that the production system is superior to biofuels based on terrestrial biomass because it can utilize non-arable land and waste water resources.

While the literature on the sustainability of algal biofuels is sparse, recent analyses appear to dispute the claims of superiority of algal production systems when compared to terrestrial crops.

Clarens *et al.* (2010) compared the environmental life cycle impacts of algal biomass production to corn, switch grass and canola production. The functional unit was 317 GJ of biomass derived energy or the amount of energy consumed by one American citizen in one year (i.e. the study sort to inform on the life cycle impacts associated with the production of 317 GJ of biomass based on the higher heating value of the material on a dry basis). Biomass production was modeled for three locations in the USA, and for algae was based on fresh water and municipal sewerage effluents from conventional activated sludge and biological nitrogen removal treatment plants. Algae production in raceway ponds varied from 0 g m-2 d-1(seasonal shut down) to 20 g m -2 d-1 depending on site location and climate. All four biomass production systems had net positive energy (i.e. more energy produced than consumed in the biomass production). Algae cultivation had better land use and eutrophication LCA outputs than terrestrial crops, but the terrestrial crops were found to have lower energy use, greenhouse gas emissions and water use than algae production based on fresh water or municipal sewerage effluents. When industrial grade CO2 was used in algal biomass production the system emitted more greenhouse gases (GHG) than it sequestered. Even when flue gas was used, the algal production system consumed more energy and emitted more GHG than the terrestrial plant production systems (mostly as a consequence of high mineral fertilizer use).

Lardon *et al.* (2009) compared the environmental life cycle impacts of microalgae biodiesel production to the impacts of palm, rape and soybean oil biodiesel and petroleum diesel production. The LCA was based on a cradle to combustion' boundary (i.e. all products and processes upstream of fuel combustion in a diesel engine). The functional unit was 1 MJ of fuel in a diesel engine. The study considered four algae biofuel production scenarios, viz. produc‐ tion under nitrogen fertilizer rich and starved conditions and with oil extraction from wet and dry raceway ponds varied from 19.25 g m-2 d -1 (in the nitrogen starved case) to 24.75 g m-2 d -1 (in the nitrogen rich case). Of the four algae biofuel production scenarios, only growth under starved nitrogen conditions with oil extraction from wet biomass had a positive net energy. In the three other algal biofuel scenarios, the energy consumed in the production was greater than the energy in the delivered biofuel. These balances assumed 100% recovery of energy from the algae cake residue after oil extraction. Fertilizer (nitrogen) consumption had a far greater impact on cumulative energy demand than drying biomass for extraction. Algae biofuel had better land use and eutrophication LCA outputs than biofuels from the terrestrial crops, but petroleum diesel had better land use and eutrophication impacts than all biofuels. In all other assessed metrics, one or all of the terrestrial crop biofuels had lower LCA impacts than all algal biofuel scenarios (again mostly as a consequence of high mineral fertilizer use).

It should be stressed that these LCA studies are based on hypothetical operating scenarios, not real production systems. The purpose of the studies is to highlight inefficiencies in the production systems that need to be addressed to create sustainable microalgae-to-biofuel enterprises. Nevertheless, these studies created debate in the scientific community and the exchange of comments published in subsequent editions of the journal. Principal among the criticisms form algae biofuel proponents are that the authors of LCA studies that report negative outcomes use too low growth rates and too high mineral fertilizer consumption figures.

In contrast, Christi (2008), a proponent of algal biofuels, provides an opinion in *Trends in Biotechnology* titled *Biodiesel from microalgae beats bioethanol.* The claimed superiority of algal biofuel over sugarcane ethanol is based solely on land use efficiencies. In this article, Christi claims algal biofuel can sustainably and completely replace all petroleum derived transport fuels, and quotes average annual algal biomass production in tropical regions as high as 1.535 kg m -3 d-1 in photobioreactors (a productivity/reactor volume measurement). This report has already noted that claims of extremely high growth in vertically configured photobioreactors are misleading. Vertical photobioreactors must be situated far enough from each other so as to not shade, and consequently the basic limitations on land use and productivity remains the same for both open ponds and closed photobioreactors. Christi (2007) had previously claimed very high land use efficiencies in raceway ponds (viz. 136,000 L/ha of oil for algal biomass with an oil mass fraction of 70% and 58,700 L/ha of oil for algal biomass with an oil mass fraction of 30%). Such yields are only achievable with production of greater than 340 days in a year and at a pond productivity of ca. 50 g m-2 d-1 (unrealistically high at the current state of technology). *Christi* also assumes that CO2 is available at little or no cost (presumably in these same tropical regions); this is a challengeable assumption. Despite the liberal use of the word 'sustainable', *Christi* provides no other LCA metric than land use efficiency.

Reijnders (2008) in a rejoinder notes that Christi did not consider fossil fuel inputs during the biofuel life cycle, that previous LCA studies on *Dunaliella* and Spirulina production showed little or no net energy benefit, and that by comparison terrestrial plant production systems are characterized by much lower fossil fuel inputs. The studies of *Clarens et al.* and *Lardon et al.* support Reijnders views. It would seem probable that while the assumptions imbedded in hypothetical production scenarios do have significant impacts on LCA outcomes algal biofuel production faces significant challenges to meet sustainability criteria. Limited LCA studies indicate that significant advances need to be made in reducing fossil fuel inputs associated with nutrient use, harvesting and extraction.
