Abstract
Despite years of concerted research efforts, an industrial-scale technology has yet to emerge for production and conversion of algal biomass into biofuels and bioproducts. The objective of this review is to explore the ways of possible integration of biology, ecology and engineering for sustainable large algal cultivation and biofuel production systems. Beside the costs of nutrients, such as nitrogen and phosphorous, and fresh water, upstream technologies which are not ready for commercialization both impede economic feasibility and conflict with the ecological benefits in the sector. Focusing mainly on the engineering side of chemical conversion of algae to biodiesel has also become obstacle. However, to reduce the costs, one potential strategy has been progressing steadily to synergistically link algal aquaculture to the governmentally mandated reduction of nitrogen and phosphorous concentrations in municipal wastewater. Recent research also supports the suppositions of scalability and cost reduction. Noticeably, less is known of the economic impact of conversion of the whole algae-based biorefinery sector with additional biochemical and thermochemical processes and integration with ecological constraints. This review finds that a biorefinery approach with integrated biology, ecology, and engineering could lead to a feasible algal-based technology for variety of biofuels and bioproducts.
Highlights
The United States Energy Independence and Security Act of 2007 set targets for alternative biofuel production in the United States to be achieved by 2022; five billion gallons/ year are marked to be made by advanced biofuels-based diesel and other biofuels (Davis et al 2016; Fortier and Sturm 2012; Kheshgi and Jain 2003; Nrel 1998; Rodolfi et al 2009; US Congress 2007)
Bioprocess. (2018) 5:47 need for (i) research, development, and demonstration of algal strain selection, (ii) Energy Return on Investment (EROI) that is comparable to other transportation fuels, and (iii) the use of wastewater and recycling nutrients for cultivating algae for biofuels (National Research Council 2012a)
The report concluded that the algal biofuel production sufficient to meet at least 5% of US demand for transportation fuels would have a positive impact on energy and environment as a whole
Summary
The United States Energy Independence and Security Act of 2007 set targets for alternative biofuel production in the United States to be achieved by 2022; five billion gallons/ year are marked to be made by advanced biofuels-based diesel and other biofuels (Davis et al 2016; Fortier and Sturm 2012; Kheshgi and Jain 2003; Nrel 1998; Rodolfi et al 2009; US Congress 2007). The amounts of N and P required for algal growth can be estimated by mirroring the normal intracellular C:N:P ratio, known as the Redfield ratio (Kesaano and Sims 2014) Many factors such as N and/or P limitation, silicon limitation, control of pH, and low temperature can be used to increase oil accumulation, their effectiveness depend on the strain and other culture conditions (Hena et al 2015). A sustainable biofuel production require cultivation of microalgae with high lipid yield using nutrients recovered from wastewater and waste CO2 from such as flue gas of a coal or natural gas-fired power plant (Rodolfi et al 2009). One drawback is the risk of contamination that may require the need to keep the raceways in relatively extreme conditions, usually alkaline or salinity that may limit the type of strains (Bahadar and Bilal Khan 2013) Another drawback is the decreased lipid content (10%) compared to closed reactors (50–60%). Effective light use Little risk of contamination More controlled environment Higher productivity and cell densities High gas transfer coefficients Easy CO2 supply Lower land use Lower water loss
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