Page 158 - Materials Chemistry, Second Edition

146 A. Singh and S. I. Olsen

disasters, and national security concerns (Brentner et al. 2011). Alga is a very
promising source of biomass for bioenergy production as it sequesters a significant
quantity of carbon from atmosphere and industrial gases and is also very efficient
in utilizing the nutrients from industrial effluents and municipal wastewater (Singh
and Olsen 2011a; Singh et al. 2011a, b).
Algae represent a vast variety of photosynthetic species populating in diverse
environments (Nigam and Singh 2011; Mata et al. 2010), and they might be
autotrophic or heterotrophic in nature (John et al. 2011). Using only sunlight and
abundant and freely available raw materials (e.g., CO 2 from atmosphere/flue gas
and nutrients from wastewater), algae can synthesize and accumulate large
quantities of lipids and carbohydrates along with other valuable co-products (e.g.,
astaxanthin, omega-3 fatty acids) (Subhadra and Edwards 2010; Singh et al. 2011c,
2012). Like other biomass, algal biomass is also a carbon-neutral source for the
production of bioenergy (Singh and Olsen 2011b). Thus, algae can play a major
role in the treatment/utilization of wastewater and reduce the environmental
impact and disposal problems. They can also be grown on saline/coastal seawater
and on non-agricultural lands (Hu et al. 2008; Melis and Happe 2001). Recent
research initiatives have proven that microalgae biomass appears to be one of the
promising sources of renewable biodiesel, which is capable of meeting the global
energy demand and displaces the fossil diesel without compromising with pro-
duction of food, fodder, and other products derived from crops (Singh et al.
2011b). Microalgae grow extremely rapidly and many are exceedingly rich in oil.
Microalgae commonly double their biomass within 24 h. Biomass doubling times
during exponential growth are commonly as short as 3.5 h (Chisti 2007). Oil
content in microalgae can exceed 80 % by weight of dry biomass (Metting 1996;
Spolaore et al. 2006).
Life cycle assessment (LCA) has in recent years been the method of choice for
environmental assessment of various kinds of new technologies for bioenergy and
carbon sequestration. LCA is a universally accepted approach of determining the
environmental consequences of a particular product over its entire production
cycle (Korres et al. 2010; Pant et al. 2011). The LCA of biofuels is the key to
observe their sustainability (Singh and Olsen 2012). Yang et al. (2011) examined
the life cycle of water and nutrients usage of microalgae-based biodiesel pro-
duction. This study quantified the water footprint and nutrient usages during
microalgae biodiesel production. The results indicated that using seawater or
wastewater can reduce the life cycle of freshwater usage by as much as 90 %. They
also reported that utilization of sea/wastewater for algal culture can reduce
nitrogen usage by 94 % and eliminate the need for potassium, magnesium, and
sulfur. An analysis of the energy life cycle for production of microalgal biomass of
Nannochloropsis sp. was performed by Jorquera et al. (2010), which included
raceway ponds, tubular and flat-plate photobioreactors (PBRs) for algal cultiva-
tion. They concluded that net energy ratio (NER) for ponds and flat-plate PBRs
could be raised significantly by selecting algal strains having higher lipid content.
Clarens et al. (2010) demonstrated the benefits of algae production coupled with
wastewater treatment and concluded that the use of wastewater effluent as pond