310 Marine Macro- and Microalgae: An Overview
have shown near complete removal of N and P from waste water media (Picot et al. 1991; Garcia et al.
2000; Woertz et al. 2009). Although at pilot scale nutrient removal efficiencies, at least in one study, have
been less efficient (65% N removal and 2% P removal), these cultures appeared to be carbon limited,
so growth optimization is required (Craggs et al. 2012). Assuming nutrient uptake is optimized, using
microalgae to scavenge nutrients from waste water has the added advantage of allowing for recovery
of phosphate. While nitrogen can be produced from dinitrogen gas (via the Haber-Bosch process),
phosphorus is a finite resource. We are currently at peak production levels for phosphorus, and it has been
estimated that the global supply of phosphorus may be depleted in 50–100 years (Cordell et al. 2009).
Therefore, efficient recovery of phosphorus from waste waters is likely to become increasingly critical,
not only from a cost basis, but also to recycle this limiting global resource.
Some waste water sources, however, may contain high levels of heavy metals, such as cadmium,
lead, copper, nickel, and silver. Algae have been shown to be effective at removing some of these metals
(Khoshmanesh et al. 1996). This is quite advantageous from a waste water treatment standpoint, where
heavy metal removal can be expensive but may be a major issue for algae production depending on the
products produced. Heavy metals may have minimal effect on algae biofuel production, but may have
significant consequences in algae food or feed replacement stocks. Therefore, significant care must be
given with respect to waste water streams for microalgae production.
Energy
Microalgal cultivation and the production of microalgal products require energy for cultivation (e.g.,
pumps and paddlewheels), harvesting, and processing. This energy can be provided via fossil fuel
combustion (most common) but can also be resourced from renewable sources such as solar and wind.
Environmental impacts from energy use will be dependent on the type of energy used. The products of
the microalgae industry also contain energy. Of special interest, from the energy point of view, is the use
of microalgae to produce energy crops such as biofuels.
Much has been written on the use of microalgae for the production of biofuels (see Chapter 14 in this
volume for a recent review) and the environmental impact of such processes, especially since the completion
of the US Department of Energy’s Aquatic Species program (Sheehan et al. 1998). The conclusions of
that program were, essentially, that microalgae can indeed be used to produce biofuels but at a very high
cost. The concept is simple: microalgae produce oils and starches that can be converted to biodiesel and
bioalcohol, respectively, utilizing existing technologies. Companies have demonstrated the process to
completion producing liquid fuels that have actually been used in existing transportation equipment: for
example, Sapphire Energy produced jet fuel that was used in a blend in a Continental Airlines Boeing 737
jet in 2009 (http://www.sapphireenergy.com/documents/Biofuel_News_Release_1–7.pdf). However, at
the present time, most research is centered on the production of bioethanol and biodiesel.
Most bioethanol today is produced from agricultural sources such as grain and sugarcane but
microalgae heve been gaining attention (Mussatto et al. 2010). As with other products, microalgae have
the advantages that they can thrive in salt water on land not useful for agriculture thus avoiding the fuel
vs. food debate. Microalgae, however, have the disadvantage that production is expensive mainly because
of the energy required to harvest and concentrate the algae before fermentation. At least one company is
exploring selecting for microalgae that can secrete bioethanol directly (Algenol: www.Algenolbiofuels.
com) which would avoid some of these expenses (although the relatively dilute bioethanol still needs to
be concentrated at some cost).
Microalgal biodiesel has received the most attention since the result would be a drop-in fuel. Some
studies based on model predictions indicate that this activity would result in (modest) energy and GHG
emissions gains (Batan et al. 2010) while others predict that for the balance to be positive, renewable
sources of energy would be required to power the microalgal process (Sander and Murthy 2010). See also
Chapter 14 for a more extensive review.
At the present scale, it is not possible to determine whether microalgal products (fuels, feeds,
foodstuffs) will have a more favorable energy balance than the products they replace (such as petroleumderived fuels, fish meal, and other agricultural ingredients). However, there does not seem to be any
indication that they will be worse.
have shown near complete removal of N and P from waste water media (Picot et al. 1991; Garcia et al.
2000; Woertz et al. 2009). Although at pilot scale nutrient removal efficiencies, at least in one study, have
been less efficient (65% N removal and 2% P removal), these cultures appeared to be carbon limited,
so growth optimization is required (Craggs et al. 2012). Assuming nutrient uptake is optimized, using
microalgae to scavenge nutrients from waste water has the added advantage of allowing for recovery
of phosphate. While nitrogen can be produced from dinitrogen gas (via the Haber-Bosch process),
phosphorus is a finite resource. We are currently at peak production levels for phosphorus, and it has been
estimated that the global supply of phosphorus may be depleted in 50–100 years (Cordell et al. 2009).
Therefore, efficient recovery of phosphorus from waste waters is likely to become increasingly critical,
not only from a cost basis, but also to recycle this limiting global resource.
Some waste water sources, however, may contain high levels of heavy metals, such as cadmium,
lead, copper, nickel, and silver. Algae have been shown to be effective at removing some of these metals
(Khoshmanesh et al. 1996). This is quite advantageous from a waste water treatment standpoint, where
heavy metal removal can be expensive but may be a major issue for algae production depending on the
products produced. Heavy metals may have minimal effect on algae biofuel production, but may have
significant consequences in algae food or feed replacement stocks. Therefore, significant care must be
given with respect to waste water streams for microalgae production.
Energy
Microalgal cultivation and the production of microalgal products require energy for cultivation (e.g.,
pumps and paddlewheels), harvesting, and processing. This energy can be provided via fossil fuel
combustion (most common) but can also be resourced from renewable sources such as solar and wind.
Environmental impacts from energy use will be dependent on the type of energy used. The products of
the microalgae industry also contain energy. Of special interest, from the energy point of view, is the use
of microalgae to produce energy crops such as biofuels.
Much has been written on the use of microalgae for the production of biofuels (see Chapter 14 in this
volume for a recent review) and the environmental impact of such processes, especially since the completion
of the US Department of Energy’s Aquatic Species program (Sheehan et al. 1998). The conclusions of
that program were, essentially, that microalgae can indeed be used to produce biofuels but at a very high
cost. The concept is simple: microalgae produce oils and starches that can be converted to biodiesel and
bioalcohol, respectively, utilizing existing technologies. Companies have demonstrated the process to
completion producing liquid fuels that have actually been used in existing transportation equipment: for
example, Sapphire Energy produced jet fuel that was used in a blend in a Continental Airlines Boeing 737
jet in 2009 (http://www.sapphireenergy.com/documents/Biofuel_News_Release_1–7.pdf). However, at
the present time, most research is centered on the production of bioethanol and biodiesel.
Most bioethanol today is produced from agricultural sources such as grain and sugarcane but
microalgae heve been gaining attention (Mussatto et al. 2010). As with other products, microalgae have
the advantages that they can thrive in salt water on land not useful for agriculture thus avoiding the fuel
vs. food debate. Microalgae, however, have the disadvantage that production is expensive mainly because
of the energy required to harvest and concentrate the algae before fermentation. At least one company is
exploring selecting for microalgae that can secrete bioethanol directly (Algenol: www.Algenolbiofuels.
com) which would avoid some of these expenses (although the relatively dilute bioethanol still needs to
be concentrated at some cost).
Microalgal biodiesel has received the most attention since the result would be a drop-in fuel. Some
studies based on model predictions indicate that this activity would result in (modest) energy and GHG
emissions gains (Batan et al. 2010) while others predict that for the balance to be positive, renewable
sources of energy would be required to power the microalgal process (Sander and Murthy 2010). See also
Chapter 14 for a more extensive review.
At the present scale, it is not possible to determine whether microalgal products (fuels, feeds,
foodstuffs) will have a more favorable energy balance than the products they replace (such as petroleumderived fuels, fish meal, and other agricultural ingredients). However, there does not seem to be any
indication that they will be worse.