Page 290 - Industrial Wastewater Treatment, Recycling and Reuse

264 Industrial Wastewater Treatment, Recycling, and Reuse

fix CO 2 from the atmosphere as well as industrial emissions (Brennan and
Owende, 2010). In the process of fixation, CO 2 is utilized by microalgae
as an inorganic carbon source, while water acts as an electron donor for
the storage of reserve food material such as carbohydrates, which further
get transformed to lipids under certain stress conditions (Devi and Venkata
Mohan, 2012). Algae and cyanobacteria have different CO 2 concentrating
mechanisms and act as enhancers for higher growth (Ramanan et al., 2010).

6.6.3 Preparation of Algal Fuel

Selecting the appropriate inoculum and mode of cultivation are the key aspects
involved in preharvesting. Followed by preharvesting, a series of sequentially
integratedpostharvestingstepslikeharvesting,drying,celldisruption,extraction
andtransesterificationarecarriedoutforconvertingthealgaebiomasstobiodie-
sel(VenkataMohanetal.,2014).Dryingthebiomasspriortoextractionisapre-
requisitesoastoavoidtheinterferenceofmoisturewiththe solvents.After
drying, cell disruption, oil extraction, and transesterification of oil to fuel are
carried out sequentially. Transesterification facilitates a reaction of triglyceride
molecules with alcohol in the presence of a catalyst to produce glycerol and
mono-alkyl fatty acid esters (Harrison et al., 2012). Biodiesel is typically trans-
esterified usingmethanol; therefore, the fatty acid alkyl esters that are produced
are fatty acid methyl esters (FAME). In this process, glycerol is formed as a by-
product. The transesterification reaction proceeds in short span of time
(<5 min) and reduces the viscosity of the FAME compared to the parent
oil, while the fatty acid composition will not get altered. The properties of
the microalgae oil are mostly dependent on the feedstock and the conversion
method used. Key aspects to evaluate the properties of microalgae oil are acid
number, iodine number, specific gravity, density, kinematic viscosity, flash
point, pour point, heating value, and cetane number. The lower viscosity
and higher energy values recorded for the algae oil denotes its comparable fea-
tures with standard norms and conventional fuel (Demirbas, 2008). Algal lipids
contain a substantial quantity of long-chain polyunsaturated fatty acids (LC-
PUFA), including eicosapentaenoic acid and docosahexaenoic acid (Chisti,
2007).ThealgallipidshavegreaterquantitiesofLC-PUFAcomparedtotypical
feedstocksassociatedwithhigher quantities offully saturated fattyacids(C14:0,
C16:0, and C18:0), which have implications in terms of fuel properties
(Harrison et al., 2012). The most important characteristics affected by the level
ofunsaturationareoxidativestability,ignitionquality(i.e.,cetanenumber),and
cold flow properties (Graboski and McCormick, 1998; Knothe et al., 1997;
Ramos et al., 2009). Fully saturated methyl esters have high oxidative stability