308 Marine Macro- and Microalgae: An Overview
report (Mekonnen and Hoekstra 2012) has compiled data on the footprint of animal production. The
authors note that animal production and consumption play a significant role in depleting (and polluting)
the world’s freshwaters. They estimate that 98% of global animal production footprint arises from the
feed the animals consume (about 2374 km
3
). From these numbers, one can estimate a global average of
26% of the fresh and rain water being used for animal feed production. As the world population increases
and the standard of living improves, it is expected that feed production (and its water footprint) will also
increase. In this section, we explore the environmental benefits of replacing animal feed with microalgal
products, especially those from marine species.
For over 60 years, studies have shown that farm animal feed can be partially replaced with microalgal
biomass (e.g., Fisher and Burlew 1953; Hintz et al. 1966; Lipinsky et al. 1970). We propose that
replacement of farm animal feed with microalgae produced in seawater would have a significant impact
on freshwater use and that this would have a positive impact on the amount of fresh water available for
direct human consumption: replacing 10% of farm animal feed with marine microalgal biomass would
save nearly 240 km
3
per year of freshwater which could be redirected to other uses.
Nutrients
Algae require the addition of inorganic nutrients to grow optimally. The most significant of these
components in algal biomass are nitrogen (N), phosphorus (P), potassium (K), and iron (Fe). These
nutrients can be provided from fertilizers, waste water (municipal or industrial), or recycled (from
digested biomass). In this section, we explore nutrient demand, possible nutrient sources, and their
relative environmental and economic impacts.
Nutrient requirements
Relative to terrestrial autotrophs, algae biomass is relatively rich in nutrients (Elser et al. 2000). Unlike
more traditional agriculture systems where nutrients may be lost or gained from the soil, in a wellrun production system, algae can be grown with little to no nutrient run off down-stream of “the algae
farm”. Additionally, unlike land plants where nutrients can come from the soil, all nutrients have to be
supplemented to the system. A nutrient replete algae culture is typically ~ 10% nitrogen (N) and ~ 1%
phosphorus (P), while an algae culture which has been induced to make lipids can be ~ 6% N. However,
this means that a well-managed pond can be run such that there is little to no excess nutrients (i.e., run
off) that are lost from the system. This is in direct contrast to land plants where eutrophication of water
sheds is often a major issue.
Eutrophication of bodies of water results in high rates of accumulation of organic matter, mainly
from aquatic plants and algae. This in turn can cause an anoxic condition, which results in fish kills and
decreased biodiversity. On small scales, this can result in decreased recreational and beneficial use of
affected waters. On large scales, eutrophication induced hypoxic events have resulted in mass mortality
in coastal and estuarine areas such as the “dead zone” in the Gulf of Mexico which has been linked
to high nutrient run off from the Mississippi river (Diaz and Rosenberg 2008). Therefore, there is a
major environmental interest in reducing anthropogenic fertilization of water sheds. Clarens et al. (2010)
estimates a 2- to 8-fold reduction in eutrophication potential (as estimated by phosphate) by using algae
for biofuel production relative to switchgrass or corn respectively.
Nutrient usage is a major issue when considering the feasibility of any biofuel feedstock. We
will focus on N and P as those are by far the most important nutrients in terms of consumption. Using
fertilizers is the easiest method of nutrient delivery and allows for the most controlled scenario, and
has been effective at small scale for high value products. On larger scales, nutrient consumption from
fertilizers becomes a major issue (Table 4). Nitrogen and phosphorus requirements to produce 10 billion
gallons/year of biofuel from algae (roughly 15% of US diesel fuel demand) without recycling nutrients
requires roughly 44 and 20% of the total US use of these nutrients respectively (Pate et al. 2011), but
this issue is not unique to microalgae. Corn grain ethanol, for example, requires even more N and P to
produce ethanol per unit energy than biodesiel from microalgal based on current estimates from Hill et al.
report (Mekonnen and Hoekstra 2012) has compiled data on the footprint of animal production. The
authors note that animal production and consumption play a significant role in depleting (and polluting)
the world’s freshwaters. They estimate that 98% of global animal production footprint arises from the
feed the animals consume (about 2374 km
3
). From these numbers, one can estimate a global average of
26% of the fresh and rain water being used for animal feed production. As the world population increases
and the standard of living improves, it is expected that feed production (and its water footprint) will also
increase. In this section, we explore the environmental benefits of replacing animal feed with microalgal
products, especially those from marine species.
For over 60 years, studies have shown that farm animal feed can be partially replaced with microalgal
biomass (e.g., Fisher and Burlew 1953; Hintz et al. 1966; Lipinsky et al. 1970). We propose that
replacement of farm animal feed with microalgae produced in seawater would have a significant impact
on freshwater use and that this would have a positive impact on the amount of fresh water available for
direct human consumption: replacing 10% of farm animal feed with marine microalgal biomass would
save nearly 240 km
3
per year of freshwater which could be redirected to other uses.
Nutrients
Algae require the addition of inorganic nutrients to grow optimally. The most significant of these
components in algal biomass are nitrogen (N), phosphorus (P), potassium (K), and iron (Fe). These
nutrients can be provided from fertilizers, waste water (municipal or industrial), or recycled (from
digested biomass). In this section, we explore nutrient demand, possible nutrient sources, and their
relative environmental and economic impacts.
Nutrient requirements
Relative to terrestrial autotrophs, algae biomass is relatively rich in nutrients (Elser et al. 2000). Unlike
more traditional agriculture systems where nutrients may be lost or gained from the soil, in a wellrun production system, algae can be grown with little to no nutrient run off down-stream of “the algae
farm”. Additionally, unlike land plants where nutrients can come from the soil, all nutrients have to be
supplemented to the system. A nutrient replete algae culture is typically ~ 10% nitrogen (N) and ~ 1%
phosphorus (P), while an algae culture which has been induced to make lipids can be ~ 6% N. However,
this means that a well-managed pond can be run such that there is little to no excess nutrients (i.e., run
off) that are lost from the system. This is in direct contrast to land plants where eutrophication of water
sheds is often a major issue.
Eutrophication of bodies of water results in high rates of accumulation of organic matter, mainly
from aquatic plants and algae. This in turn can cause an anoxic condition, which results in fish kills and
decreased biodiversity. On small scales, this can result in decreased recreational and beneficial use of
affected waters. On large scales, eutrophication induced hypoxic events have resulted in mass mortality
in coastal and estuarine areas such as the “dead zone” in the Gulf of Mexico which has been linked
to high nutrient run off from the Mississippi river (Diaz and Rosenberg 2008). Therefore, there is a
major environmental interest in reducing anthropogenic fertilization of water sheds. Clarens et al. (2010)
estimates a 2- to 8-fold reduction in eutrophication potential (as estimated by phosphate) by using algae
for biofuel production relative to switchgrass or corn respectively.
Nutrient usage is a major issue when considering the feasibility of any biofuel feedstock. We
will focus on N and P as those are by far the most important nutrients in terms of consumption. Using
fertilizers is the easiest method of nutrient delivery and allows for the most controlled scenario, and
has been effective at small scale for high value products. On larger scales, nutrient consumption from
fertilizers becomes a major issue (Table 4). Nitrogen and phosphorus requirements to produce 10 billion
gallons/year of biofuel from algae (roughly 15% of US diesel fuel demand) without recycling nutrients
requires roughly 44 and 20% of the total US use of these nutrients respectively (Pate et al. 2011), but
this issue is not unique to microalgae. Corn grain ethanol, for example, requires even more N and P to
produce ethanol per unit energy than biodesiel from microalgal based on current estimates from Hill et al.