Carbon Sequestration through Sustainably Sourced Algal Fertilizer: Deep Ocean Water
Abstract ID: 12622
Final Paper Number: V23A-4783
By Martin T. Sherman
1. The draw-down of carbon dioxide from the atmosphere
happens in the oceans when marine plants are growing. This
is due to the use of CO2 during photosynthetic biological
processes that raise the pH of the water. Macro- and microscopic marine photosynthesizers are limited in their growth
by the availability of light and nutrients (nitrogen, phosphorous, iron, etc.) Deep ocean water (DOW), from below about
1000m, is a natural medium for marine algae, which contains
all (except in rare circumstances) necessary components for
algal growth, except sunlight. DOW represents ~90% of the
volume of the ocean. The introduction of DOW to a tropical or summer sea can increase chlorophyll from near zero
to 60 mg per M3 or more. Oceanic thermal energy conversion (OTEC) can utilize DOW to produce electricity and high
value drinking water. DOW, with its access to a sustainable
source of nutrients and concomitant products, represents the
logical long-term solution for algal feedstocks for biofuels.
Importantly, the large-scale growth of marine plants has the
added benefit of reducing oceanic acidification, effectively
adding to the ocean’s ability to absorb carbon before biological calcificating processes are interrupted.
2. The form of the utilization infrastructure for DOW can
roughly be divided into two types; the unconstrained release, and the open pond system (There is a third type: DOW
pumped into bio-reactors made of transparent materials, but
as they are energy-intensive due to pumping, suffer from biofilm clogging and have limited economies of scale, this class
is discounted). Unconstrained release has the advantage of
having low infrastructure investment and is available to any
area of the ocean. However, there are many questions about
ecologic impact. The open pond system has high infrastructure costs but enables intensive use of DOW for harvesting
macro- and microalgae and sustainable mariculture. It also
enables greater concomitant production of DOW’s other potential products, such as electricity. Unlike an unconstrained
release, the open pond system can capture much of the biomaterial from the water, which limits the impact to the surrounding ecosystem.
3. The Tidal Irrigation and Electrical System (TIESystem),
is an open pond that is to be constructed on a continental shelf. It harnesses the tidal flux to pump DOW into the
pond on the rising tide and then uses the falling tide to pump
biologically rich material out of the pond. This biomaterial
represents fixed CO2 and can be used for biofuel or fertilizers. The TIESystem benefits from an economy of scale that
increases at a rate that is roughly equal to the relationship of
the circumference of a circle (the barrier that creates the open
pond) to the area of the pond multiplied by the tidal flux on
that particular area of the continental shelf. Despite the large
construction costs of artificial islands and structures robust
enough to withstand the conditions of the continental shelf,
1
2
1)Palm Island, Dubai. Courtesy Wikepedia 2) TIESystem, top down view lagoon/
tidal pump/open pond bioreactor. 3) TIESytem with grid connection and ship for
export. 4) TIESystem on a continental shelf
3
4
the system will become economic as it grows in size. However,
extensive research will be required to maximize the output of
each subsystem, minimize interference between these subsystems, and minimize the risk of anoxic events or bio-toxin releases.
Current Use
Soaring anthropogenic concentrations of carbon dioxide in
the atmosphere have lowered oceanic pH in the temperate
oceans by 30%. In the process, about a quarter of the CO2
has been transferred1. The growing of marine plants absorbs
carbon dioxide in the building of their bodies and in their
respiration. Wageningen biologist Ronald Osinga theorized
that growing 180,000 square kilometers of sea-lettuce (ulva
lactuca) would be enough to reverse ocean acidification. Sealettuce is one of many fast-growing edible species of marine
plants. Macroscopic algae like kelp grows 20 times as fast as
their terrestrial counterparts, and microscopic organisms, 30
times as fast.
The limiting factor in marine plant growth is the availability of fertilizers like nitrates, phosphates, carbon dioxide and
micronutrients like magnesium and iron. Experiments to in-
(Left panels) simulated latitude-depth distribution of changes in pH(relative
to pre-industrial values) in year 2100. (Right panels): simulated horizontal mean pH as a function of year and depth(refer to Table 1 for simulation
setup). It is shown here that ocean iron fertilization accelerates deep ocean
acidification. Courtesy Cao · Caldeira 2010
Terrestrial-based approaches to growing algae for utilization
consume large water resources and have low efficiencies due
to energy inputs for pumping and fertilizers. For instance, a
gram of nitrogen takes at least 30 kJ to produce and a typical
kg of algae has 60g of nitrogen and 6g of phosphates. Despite
cultivation rates reaching 5-50g per day, relative to photovoltaics and wind, this approach is land intensive. A middle ground
estimate of algal biomass cost is $1.25 per kg to produce and
has an energy density of 25MJ per kg (wet). This leads to a
best-case scenario of ~$0.68 kWh output for the consumer6.
However, most of this cost is created by the expense of generating the biomass. For instance in a Hydrothermal Liquefaction process (1 kg wet algae generates ~5 kWh), 98.5% of the
expenses are incurred in growth of the algae.
Fertilization with Utilization
A tidal pump is created by the mechanism of an artificial
atoll where its lagoon’s only access to the incoming tide is
via a conduit that descends off the edge of the (tropical or
subtropical continental) shelf, drawing up DOW. The lagoon
pumps in concert with the natural tidal flux. DOW is a near
ideal medium for algal growth and represents ~90% of the
world network of ~200 TIESystems each 20 km in radius
placed in tidal ranges of 0.7 m or more could grow enough
algae to meet world energy demand ~150,000 tWh (2014).
Tropical locations such as Pacific Central America or northwest Australia enable OTEC co-generation of ~15,000 tWh,
with tidal flow adding a further ~ 750 tWh. This network
would absorb ~2.16 bn tons of CO2. Each TIESystem would
repay its investment within 7 years. The large energy value of
algae make it economically viable to build TIESystems in temperate continental shelves forgoing the OTEC component, due
to their higher tidal fluxes. A rough estimate suggests that utilizing less than 5% of world continental shelf under TIESystems could sustainably replace all fossil fuels.
Summary
DOW fertilization with utilization is a strong CO2 offsetter
and ocean acidification reducer. To find best practice of the
TIESystem and move toward implementation, further research is called for from the fields of biology, hydrology, sedimentology, engineering, naval architecture, plant design, and
logistics. Impact assessment, engagement with NGOs and regulatory bodies are all called for due to the scope of the project.
RADIUS of TIESystem in km:
Circumference (in km)
Area of water at surface (in square km)
Volume exchange of Deep Ocean Water (DOW) per flux (cubic m)
Non-OTEC production per flux (MWH)
OTEC production per flux (MWH)
Biomass production kg per flux (Wet)
1
6.283185307
3.141592654
942477.7961
0.48747046
78.53981634
138544.236
10
62.83185307
314.1592654
94247779.61
48.74704601
7853.981634
13854423.6
20
125.6637061
1256.637061
376991118.4
194.988184
31415.92654
55417694.41
CO2 uptake per flux (kg)
10159.91064
1015991.064
4063964.257
Value of Carbon Credits per flux
406.3964257
40639.64257
162558.5703
Value of non-Biomass MWh output (total per flux)
3951.36434
395136.434
1580545.736
CE-CERT biomass conversion biodiesel (gallons per flux)
1282.838566
128283.8566
513135.4264
CE-CERT biomass conversion MWH approx per flux
39.94186012
3994.186012
15976.74405
Grand Total value per flux ($US)
8920.530904
892053.0904
3568212.361
Approx building cost ($US)
942477796.1
9424777961
18849555922
Time to recover approx building cost (years)
153.3420283
15.33420283
7.667101413
This chart shows a suboptimal location for a TIESystem such as the continental shelf
Average Tidal Flux in m .3
on the Florida Gulfcoast. Small tidal fluxes & low temperature gradient are overcome
Head in m 0.1
so that the system becomes ecconomic as it grows in size.
Number of Fluxes per year 689
***Important Notes 1) Delta is a function of the area of the lagoon unlike a normal
Turbine Efficiency coefficient (0-1) 0.95
hydro-electric dam which is based on height 2) Cost is based on the assumption of
OTEC turbine efficiency coefficient (0-1) 0.3
$150,000 per meter of atoll wall with plant costs of $5000 meter of atoll wall (because
Temperature difference (for OTEC) 20
plant costs decrease rapidly as they are scaled up and $10000 per meter of atoll wall
Biomass growth7 (g per m3) 147
for the cold water intake pipe 3) Biomass figures are based on previous studies of
Value per kWh ($US) 0.05
DOW, they include bacterial growth 4) CE-CERT figures are based on usage of muValue of 1 Carbon Credit ($US) 4
nicipal waste and it is anticipated that biomass produced by a TIESystem will contain
Value of 1 gallon of diesel ($US) 2
more energy.
COST per linear m of wall ($US) 150000
crease carbon sequestration through use of open ocean fertilization via iron in the South Atlantic (as iron availability is
the limiting factor on phytoplankton growth there) have resulted in primary growth, but this does not result in carbon
rich deposits forming on the seafloor. Instead, 99% transfers
and accelerates acidification of the deep oceans and only
delays acidification of the surface by a few years2. This has
important implications for any other system that fertilizes
the ocean such as those that create an artificial up-welling of
DOW or OTEC. The biomass created by DOW exposed to
sunlight initially raises pH by the growth of marine plants
and then it lowers the pH as animals who have consumed that
biomass respirate. This is mimicked by the seasonal pH variation in the artic ocean3.
Many projects are examining growing and harvesting kelp as
food and fodder and as source material for fertilizer, fuel and
pharmaceuticals. For instance, a kelp farm using an array of
specially planted ropes in South Korea reported CO2 capture
in the form of algal growth at ~10 t CO2eq per ha per year4
or ~10% of (wet) volume5. It's important to note that most of
this biomass increase occurred in the spring. In summer and
autumn kelps die back to their holdfasts due to lack of nutrients, releasing the CO2. The lack of nutrients is caused by surface water warming, creating thermocline layers that prevent
the mixing of deep, cold, nutrient rich water with sunlight.
ocean’s volume. DOW can also be used to generate electricity
in the megawatt range through OTEC via a thermodynamic
exchange with warm surface waters.
OTEC mixes two-thirds warm surface water and one-third
DOW. A TIESystem’s DOW moves under tidal forces, which
increases OTEC efficiency by a third. The lagoon then concomitantly acts as an open pond bioreactor, exposing pure
DOW to sunlight to create nearly ideal conditions for algal
growth. The tide flowing out of the lagoon is then harnessed
to aid biomass collection, increasing the utilization efficiency
of this resource.
The construction of artificial islands robust enough to withstand the conditions on the continental shelf is expensive.
This technology is typified by the Palm and World Island developments in Dubai. However, as a result of an exponential
increase in outputs as the TIESystem grows in size, the large
investment costs of the system will, in most locations, become
economic if constructed large enough. (See table above)
By enclosing a section of the continental shelf in this way,
biomass generated is collected for utilization and the carbon
dioxide is absorbed and removed from the water before it returns to the ocean. This discharge from the lagoon mitigates
ocean acidification by its slight alkalinity. Also, carbon offsetting is made possible by creating replacements for fossil fuels.
Based on algal growth of 147g per cubic meter of DOW7, a
Ocean Thermal Energy Conversion.
Courtesy Wikepedia
Time of Investment recoup
2πrVwD+P+C
(πr2HfS-M)F
r= Radius of the artificial atoll
Hf= Height of average tidal flux
Vw= Volume of average wall segment
S= Sale value of all products
M= Maintenance and labour cost
D= Average costs of wall per m3
P= Plant construction costs
C= Additional construction costs
F= Number of tidal fluxes per day
Biography
Martin T. Sherman is the inventor of the Tidal Irrigation and
Electrical System (USPTO 6,863,028). He is CEO of Seavac
Ltd, and a regular contributor to debate and discussion on renewable energy developments. He works as an actor, and resides in London, UK. Contact via seavac.org
Climatological distributions of pH, pCO2, total CO2, alkalinity, and CaCO3
saturation in the global surface ocean, and temporal changes at selected locations. Taro Takahashi, S.C. Sutherland, D.W. Chipman, J.G. Goddard,
Cheng Ho, Timothy Newberger, Colm Sweeney, D.R. Munro. LamontDoherty. Earth Observatory of Columbia University, Palisades, NY 10964,
United States Cooperative Institute in Environmental Sciences, University
of Colorado, Boulder, CO 80309, United States
2
Climatic Change- DOI 10.1007/s10584-010-9799-4 LETTER: Can ocean
iron fertilization mitigate ocean acidification?A letter. Long Cao · Ken Caldeira Received: 30 October 2009 / Accepted: 2 January 2010 © Springer
Science+Business Media B.V. 2010
3
Ibid (1)
4
Installing kelp forests/seaweed beds for mitigation and adaptation against
global warming: Korean Project Overview. Ik Kyo Chung, Jung Hyun
Oak, Jin Ae Lee, Jong Ahm Shin, Jong Gyu Kim and Kwang-Seok Park.
ICES J. Mar. Sci. (2013) doi:
10.1093/icesjms/fss206
5
Do trophic cascades affect the storage and flux of atmospheric carbon?
Annalysis of sea otters and kelp forests. Christopher C Wilmers, James A
Estes, Matthew Edwards, Kristin L Laidre, and Brenda Konar Front Ecol
Environ 2012; doi:10.1890/110176
6
A comparison of algae to biofuel conversion pathways for energy storage
off-grid. Matthew S. Orosz, David Forney. May 2008 Report 2.62. M.I.T.
7
Effects of deep seawater on the growth of several species of marine microalgae, Journal of Applied Phycology, February 1994, Volume 6, Issue 1,
pp 75-77. Tsuneo Matsubayashi, Isao Maruyama, Sumiko Kido, Yotaro
Ando,Toshimitsu Nakashima, Takayoshi Toyota
1