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Process
Safety
and
Environmental
Protection
9
0
(
2
0
1
2
)
467–474
Contents
lists
available
at
SciVerse
ScienceDirect
Process
Safety
and
Environmental
Protection
journa
l
h
o
me
p
age:
www.elsevier.com/locate/psep
Negative
carbon
via
Ocean
Afforestation
Antoine
de
Ramon
N‘Yeurta, David
P.
Chynowethb,
Mark
E.
Capronc,∗,
Jim
R.
Stewartd,
Mohammed
A.
Hasanc
aPacific
Center
for
Environment
and
Sustainable
Development,
the
University
of
the
South
Pacific,
Suva,
Fiji
bDepartment
of
Agricultural
and
Biological
Engineering,
University
of
Florida,
Gainesville,
FL
32611,
United
States
cPODenergy,
2436
E.
Thompson
Blvd.,
Ventura,
CA
93003,
United
States
dPODenergy,
1216
S.
Westlake
Ave. ,
Los
Angeles,
CA
90006,
United
States
a
b
s
t
r
a
c
t
Ocean
Afforestation,
more
precisely
Ocean
Macroalgal
Afforestation
(OMA),
has
the
potential
to
reduce
atmospheric
carbon
dioxide
concentrations
through
expanding
natural
populations
of
macroalgae,
which
absorb
carbon
diox-
ide,
then
are
harvested
to
produce
biomethane
and
biocarbon
dioxide
via
anaerobic
digestion.
The
plant
nutrients
remaining
after
digestion
are
recycled
to
expand
the
algal
forest
and
increase
fish
populations.
A
mass
balance
has
been
calculated
from
known
data
and
applied
to
produce
a
life
cycle
assessment
and
economic
analysis.
This
analysis
shows
the
potential
of
Ocean
Afforestation
to
produce
12
billion
tons
per
year
of
biomethane
while
stor-
ing
19
billion
tons
of
CO2per
year
directly
from
biogas
production,
plus
up
to
34
billion
tons
per
year
from
carbon
capture
of
the
biomethane
combustion
exhaust.
These
rates
are
based
on
macro-algae
forests
covering
9%
of
the
world’s
ocean
surface,
which
could
produce
sufficient
biomethane
to
replace
all
of
today’s
needs
in
fossil
fuel
energy,
while
removing
53
billion
tons
of
CO2per
year
from
the
atmosphere,
restoring
pre-industrial
levels.
This
amount
of
biomass
could
also
increase
sustainable
fish
production
to
potentially
provide
200
kg/yr/person
for
10
billion
people.
Additional
benefits
are
reduction
in
ocean
acidification
and
increased
ocean
primary
productivity
and
biodiversity.
©
2012
The
Institution
of
Chemical
Engineers.
Published
by
Elsevier
B.V.
All
rights
reserved.
Keywords:
Reversing
climate
change;
Marine
agronomy;
Carbon
capture
and
storage;
Negative
emissions,
Ocean
Macroalgal
Afforestation
(OMA);
Algae
biofuel
1.
Introduction
Removing
the
major
atmospheric
greenhouse
gas
carbon
dioxide
is
a
priority
in
order
to
reduce
global
warming,
ocean
acidification
and
sea
level
rise,
which
threaten
human
civiliza-
tion
as
well
as
animal
and
plant
life
on
our
planet.
Given
the
need
for
such
negative
carbon
technology
on
a
scale
at
least
equal
to
current
anthropomorphic
carbon
emissions,
the
pro-
posed
capture
technologies
must
be
sustainable
at
scale
in
every
sense
of
the
word.
1)
Environmental
sustainability
at
scale
implies
addressing
issues
beyond
carbon
air
capture
such
as:
species
biodiver-
sity,
food,
and
energy.
∗Corresponding
author.
Tel.:
+1
805
760
1967;
fax:
+1
805
639
0307.
E-mail
addresses:
nyeurt
a@usp.ac.fj
(A.d.R.
N‘Yeurt),
dpchyn@gmail.com
(D.P.
Chynoweth),
MarkCapron@PODenergy.net
(M.E.
Capron),
JimStewart@PODenergy.net (J.R.
Stewart),
MohammedHasan@PODenergy.net (M.A.
Hasan).
Received
8
May
2012;
Received
in
revised
form
13
September
2012;
Accepted
3
October
2012
2)
Climate
sustainability
with
increased
greenhouse
gas
concentrations
implies
a
robust
and
distributed
process
that
is
neither
affected
by
nor
a
cause
of
droughts,
floods,
heat,
cold,
changing
wind
patterns,
and
ocean
acidification.
3)
Political
sustainability
requires
improving
the
quality
of
life
and
opportunities
globally,
and
particularly
in
developing
countries.
4)
Social
sustainability
means
countering
the
water,
food,
jobs,
and
natural
disaster
stresses
of
climate
change,
with
no
negative
side
effects.
5)
Energy
sustainability
implies
much
more
carbon
is
perma-
nently
stored
than
is
required
to
generate
the
energy
to
pull
the
carbon
from
the
air
and
store
it.
0957-5820/$
–
see
front
matter
©
2012
The
Institution
of
Chemical
Engineers.
Published
by
Elsevier
B.V.
All
rights
reserved.
http://dx.doi.org/10.1016/j.psep.2012.10.008
Author's personal copy
468
Process
Safety
and
Environmental
Protection
9
0
(
2
0
1
2
)
467–474
6)
Economic
sustainability
with
current
low
carbon
prices
requires
multiple
products
from
the
process
so
the
overall
system
makes
a
profit.
All
of
the
above
are
possible
by
operating
a
novel
tech-
nologically
accelerated
natural
ocean
ecosystem,
which
we
have
termed
“Ocean
Afforestation”
or
more
technically
“Ocean
Macroalgal
Afforestation”
(OMA)
because
it
is
based
on
forests
of
macroalgae
(kelp
and
other
seaweeds).1In
OMA,
the
energy
inputs
and
outputs
use
the
same
pathways
as
in
nature
(pho-
tosynthesis,
digestion,
decomposition).
What
differs
in
OMA
is
that
that
digestion
products
are
captured
and
separated,
with
the
energy
(carbon
and
hydrogen)
set
apart
from
the
plant
nutrients
(nitrogen,
phosphorus,
potassium,
sulfur,
iron,
etc.).
Hence,
an
OMA
ecosystem
is
almost
a
typical
natural
macro-algae
ecosystem.
The
main
difference
is
that
the
plant
nutrients
are
captured
and
recycled
at
the
surface
to
grow
more
plants,
instead
of
dropping
below
the
light
level
for
millennia
on
the
seafloor
or
traveling
thousands
of
kilometers
in
subsurface
ocean
currents
before
surfacing.
2.
Historic
discussions
of
macroalgae
energy
Thousands
of
researchers
and
businesses
have
unknowingly
been
developing
technologies
related
to
Ocean
Afforesta-
tion
for
decades.
OMA
is
a
combination
of
concepts
and
technologies
from
marine
agronomy,
integrated
multi-trophic
aquaculture,
ocean
thermal
energy
conversion,
the
offshore
oil
industry,
marine
sanctuaries,
municipal
wastewater
treat-
ment,
seaweed
farming,
and
more.
Even
so,
thousands
of
researchers,
engineers,
and
multiple
businesses
will
be
nec-
essary
for
decades
integrating
those
existing
technologies
and
refining
new
technologies
for
Ocean
Afforestation
ecosystems.
Recently,
the
large
ocean
area
available
and
the
high
photo-
efficiency
of
marine
vegetation
have
prompted
discussions
of
algae
and
other
plankton
as
a
sink
for
anthropogenic
car-
bon
emissions
or
as
feedstock
for
biofuels.
In
“Blue
Carbon”
Nellemann
et
al.
(2009)
point
out
that
marine
primary
pro-
ducers
contribute
at
least
50%
of
the
world’s
carbon
fixation
and
may
account
for
as
much
as
71%
of
all
carbon
storage
in
oceanic
sediments.
Potential
annual
yields
per
hectare
of
many
of
the
highly
productive
macroalgal
species
are
consid-
erably
higher
than
those
of
the
terrestrial
plants
considered
useful
candidates
for
biofuel
production
(Chung
et
al.,
2011).
Many
researchers
are
looking
seriously
at
macroalgae
for
energy
production,
such
as
Stanley
and
colleagues
at
BioMara
(Day
et
al.,
2011),
Oilgae
(2011)
Roesijadi
et
al.
(2008,
2010),
Bruton
et
al.
(2009),
Lenstra
et
al.
(2011)
and
references
therein.
Chynoweth’s
review
article
(2002)
indicates
that
the
pro-
ductivity
and
digestibility
of
macroalgae
to
produce
large
quantities
of
biomethane
have
been
well
established
by
many
researchers
over
many
decades.
He
also
reports
that
Hanisak
(1981)
has
shown
the
feasibility
of
nutrient
recycling
for
sustainability.
He
recommends
generating
income
from
co-
products
and
by-products
to
reduce
the
cost
of
the
biomethane
to
be
competitive
with
U.S.
natural
gas
prices.
OMA
proposes
1Abbreviations
appearing
later:
•
OMA
is
Ocean
Macroalgal
Afforestation,
which
is
synonymous
with
“Ocean
Afforestation”
in
this
paper.
•
bio-CO2is
carbon
dioxide
when
produced
by
anaer-
obic
digestion;
and
•
combustion-CO2is
carbon
dioxide
when
produced
by
OA’s
bio-CH4(methane)
combustion.
two
additional
co-products,
fish
and
carbon
sequestration,
which
make
OMA
currently
economic
for
many
developing
nations,
especially
those
using
high-priced
diesel
fuel
to
make
electricity.
Other
by-products,
such
as
liquid
fuels,
agar,
car-
rageenans,
algin,
etc.,
have
not
been
analyzed
for
this
paper.
3. Objectives
for
Ocean
Afforestation
The
sustainable
nature
of
Ocean
Afforestation
makes
the
fol-
lowing
primary
objective
theoretically
possible:
completely
offset
anthropomorphic
CO2emissions
by
2035
and
then
restore
the
climate
by
reducing
atmospheric
CO2concen-
trations
below
350
ppm
by
about
2085.
These
ambitious
but
achievable
timelines
are
discussed
later.
There
are
three
“steps”
within
the
OMA
ecosystem
to
accomplish
this
objective:
a.
The
biologic
portion
(seaweed
and
seaweed-digesting
microbes)
of
OMA,
concentrates
carbon
from
about
0.04%
CO2in
air
to
40%
bio-CO2and
60%
bio-methane.
b.
Any
of
several
chemical
and
physical
technologies,
includ-
ing
differential
dissolution,
pressure
swing
absorption,
gas
membranes,
chemical
extraction,
metal–organic
frame-
works,
etc.
are
available
to
separate
out
(purify)
the
bio-CO2
directly
from
the
anaerobic
digestion
and
the
combustion-
CO2from
combustion
exhaust
gases;
and
c. Any
of
several
geophysical
and
geochemical
technologies
permanently
store
pure
CO2.
Some
are
being
developed
by
others,
in
addition
to
the
one
proposed
in
this
paper.
Sub-objectives
for
Ocean
Afforestation
include:
•Create
sanctuaries
with
regionally
higher
ocean
pH.
Since
the
oceans
have
absorbed
approximately
half
of
human-
caused
CO2emissions
(Sabine
et
al.,
2004)
the
oceans
are
rapidly
acidifying
and,
in
a
relatively
short
time
(2050
by
projections,
such
as
the
Monaco
Declaration,
2008),
it
will
be
inhospitable
to
many
ecologically
essential
forms
of
life
that
rely
on
calcification,
such
as
corals,
marine
mollusks
and
coralline
algae
(for
example,
Barton
et
al.
(2012)
dis-
cuss
oyster
hatchery
mortality).
Ocean
Afforestation
could
reduce
atmospheric
and
dissolved
CO2concentrations
in
the
area
of
the
macroalgal
forest;
in
much
the
same
way
that
atmospheric
CO2is
reduced
in
terrestrial
agricultural
regions
(Miles
et
al.,
2012).
•Increase
ocean
biodiversity
and
primary
productivity
start-
ing
within
the
OMA
areas.
•
Produce
higher
value
pharmaceuticals,
chemicals,
food,
and
fish/animal
feed
from
the
macro-algae
to
satisfy
human
needs.
Produce
environmentally
and
economically
sustainable
on-going
renewable
energy,
thus
preserving
fossil
fuels
to
provide
chemicals
for
future
generations,
while
providing
income
for
maintaining
the
stored
CO2.
These
objectives
are
designed
to
be
ambitious
to
match
the
urgency
of
the
situation.
If
humans
do
not
remove
CO2with
OMA
or
other
carbon
storage
technologies,
the
excess
CO2will
persist,
lowering
the
oceanic
pH
and
raising
global
temper-
atures
for
a
millennium,
even
if
the
world
shifts
rapidly
to
non-fossil
fuels,
such
as
solar,
wind
and
geothermal
energy,
or
even
nuclear
power.
Author's personal copy
Process
Safety
and
Environmental
Protection
9
0
(
2
0
1
2
)
467–474
469
4.
The
Ocean
Afforestation
ecosystem
The
flow
chart
for
the
OMA
ecosystem
has
the
major
components
labeled
to
the
numbered
sections
below.
This
manuscript
was
prepared
primarily
to
explain
the
nutri-
ent,
energy,
and
carbon
removal
mass
balance
for
Ocean
Afforestation
ecosystems.
Work
on
economic
feasibility
is
on-going
with
a
discussion
of
preliminary
results
in
this
manuscript
and
in
the
supplemental
data.
See
the
online
supplementary
information
“OMA
Process
Concepts”
for
more
details
of
the
materials
and
energy
demands
within
a
conceptual
ecosystem.
4.1.
Grow
aquatic
plants,
absorbing
CO2
Sunlight
powers
aquatic
plants
(primarily
macro-algae
or
sea-
weed)
to
grow
anywhere
in
the
top
few
meters
of
the
world’s
oceans,
as
long
as
there
are
sufficient
nutrients.
Where
there
are
insufficient
nutrients,
there
are
fewer
plants.
That
is,
much
of
the
ocean
is
a
nutrient
desert.
Presently,
seaweeds
grow
mainly
where
nutrients
are
available
from
upwelling
ocean
currents
or
terrestrial
runoff.
An
extensive
analysis
of
harvest
production
data
for
many
macroalgae
from
around
the
world
(Gao
et
al.,
1991;
Chung
et
al.,
2011;
Oilgae,
2011;
Roesijadi
et
al.,
2008,
2010;
Bruton
et
al.,
2009;
Lenstra
et
al.,
2011;
and
references
therein)
indicates
a
conservative
harvestable
projection
of
about
18
ash-free
tons
per
hectare
per
year,
pro-
viding
sufficient
nutrients
are
available.
Note
that
Table
28
of
Chynoweth
(2002)
reports
yields
of
11–50
ash-free
t/ha/yr
are
reasonable.
More
examination
of
the
validity
of
18
ash-free
t/ha/yr
is
included
in
the
online
supplementary
information,
“OMA
Discussion
of
Macroalgae
Production
and
Density.”
4.2.
Harvest
aquatic
plants
There
are
many
current
cultivation
and
harvesting
techniques
depending
on
the
type
of
macro-algae
and
climate,
as
docu-
mented
by
Pereira
and
Yarish
(2008).
OMA
can
better
achieve
its
objectives
of
sustainability
by
harvesting
small
portions
of
the
overall
forest
throughout
the
year.
This
may
involve
“mowing”
the
top
meter
of
seafloor-rooted
kelp,
or
encircling
clumps
of
free-floating
Sargassum
in
an
ocean
gyre,
or
cut-
ting
strips
of
Gracilaria
in
a
tropical
island
bay.
The
sustainable
harvest
fraction
depends
on
local
climate
conditions,
species
rate
of
growth,
added
nutrition
from
shore
runoff,
storms,
etc.
It
could
vary
from
year
to
year.
Since
the
harvest
fraction
in
any
1
year
could
range
from
40%
to
90%,
we
have
projected
a
reasonable
average
as
75%.
The
harvesting
techniques
will
be
optimized
for
low
energy
consumption.
For
example,
the
har-
vested
biomass
would
be
moved
distances
up
to
about
6
km
at
speeds
less
than
0.3
km/h
to
the
energy
conversion/nutrient
separation
digestion
location.
4.3.
Digest
the
aquatic
plants
anaerobically
The
harvested
plants
are
taken
through
processes
that
sepa-
rate
their
energy
from
their
plant
nutrients.
Our
calculations
are
based
on
microbial
anaerobic
digestion
in
submerged
geosynthetic
containers.
No
energy
is
wasted
to
lift
the
sea-
weeds
out
of
the
water
or
dry
the
algae
for
combustion
or
squeeze
out
oil.
The
calculations
are
based
on
an
average
2%
solids
input
to
the
digestion
container
although
1%
solids
may
be
economically
feasible.
The
analysis
is
based
on
energy
saving
features
that
are
not
typical
for
anaerobic
digestion
when
volume
and
time
are
expensive,
such
as
at
a
municipal
wastewater
treatment
plant.
Not
lifting
the
seaweed
out
of
the
water
is
one
such
energy
saver.
Not
removing
all
the
excess
water
surrounding
the
sea-
weed
is
another.
(Seaweed
has
about
10–15%
total
solids
when
the
external
water
is
drained
from
the
plants
(Chynoweth,
2002).)
Not
heating
or
mixing
the
digester
also
saves
energy.
The
trade-off
for
using
less
energy
is
having
more
time
and
volume
available.
We
are
projecting
nearly
complete
digestion
over
an
average
period
of
135
days.
The
online
supplementary
information
“OMA
Calculations
Supplement”
provides
more
detailed
information.
Our
calculations
are
based
on
direct
anaerobic
diges-
tion
which
produces
biogas
that
is
about
60%
CH4and
40%
CO2,
by
volume
(Chynoweth,
2002).
We
term
this
bio-CO2
to
distinguish
it
from
the
combustion-CO2that
is
produced
during
CH4combustion.
The
Ocean
Afforestation
ecosystem
could
work
with
first
doing
other
renewable
energy
processes,
such
as:
oil
squeezing,
ethanol
fermentation,
and
other
such
energy
extraction
processes,
or
product
extraction,
such
as
carrageenans,
to
improve
the
economics.
When
the
waste
from
these
other
processes
is
fed
to
anaerobic
digestion,
the
production
of
bio-CO2would
be
less,
but
the
amount
of
key
plant
nutrients
recovered
for
recycling
can
be
similar.
4.4. Recover
the
separated
bio-CO2and
bio-CH4
When
employing
a
differential
dissolution
technique,
the
tops
of
the
geosynthetic
digestion
containers
are
held
below
about
100
m
(10
bar
pressure).
Our
calculations
are
based
on
200
m
depth
where
most
of
the
carbon
dioxide
remains
dissolved
with
the
nutrients
in
the
water
inside
the
container.
But
relatively
little
methane
dissolves.
We
expect
the
gas
col-
lected
will
be
about
90%
CH4and
10%
CO2at
the
200
m
depth
when
interpolating
from
equilibrium
dissolved
gas
concentra-
tions
identified
by
(Van
der
Meer,
2005;
Duan
and
Mao,
2006)
and
adjusting
for
partial
pressure
effects.
Small
amounts
of
H2S
and
N2O
will
remain
dissolved.
Deeper
containers
would
return
higher
purity
of
CH4,
perhaps
better
than
90%,
but
limited
by
partial
pressure
effects.
Even
CH4:CO2ratios
as
low
as
1:1
may
be
combusted
as-
is
to
produce
electricity.
Higher
than
about
95%
CH4purity
gases
may
be
shipped
as
natural
gas
(depending
on
local
requirements).
Bio-CH4can
be
converted
into
many
products:
synthetic
diesel,
methanol,
jet
fuel,
plastics
to
make
more
OA
facilities,
etc.
The
differential
dissolution
separation
of
bio-CO2and
bio-
CH4is
but
one
of
several
options
for
concentrating
the
bio-CO2.
Author's personal copy
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Other
technologies
are
typically
employed
at
natural
gas
well-
heads:
membrane
separation
and
pressure
swing
adsorption,
for
example.
More
details
of
the
arrangements
preventing
inadver-
tent
CH4release
are
included
in
the
online
supplementary
information
“OMA
Process
Concepts.”
An
analysis
showing
the
likely
effect
of
potential
N2O
emissions
is
a
small
fraction
of
the
CO2e captured
is
in
the
online
supplementary
informa-
tion
“OMA
N2O
Discussion.”
4.5.
Recycle
the
plant
nutrients
Microbial
anaerobic
digestion
converts
the
biomass
to
biogas,
plant
nutrients,
and
water.
The
plant
nutrients
are
mostly
dissolved
with
some
trapped
in
undigested
solids.
(The
term
“solids”
is
applied
to
what
remains
after
anaerobic
diges-
tion
even
though
the
material
may
be
98%
water.
These
“solids”
include
water,
the
ash
component
of
the
biomass,
some
undigested
volatile
“solids,”
and
the
digesting
microbes.)
The
nitrogen
nutrients
are
mostly
in
the
form
of
dissolved
ammonia.
The
water
with
both
liquid
and
solid
nutrients
is
pumped
to
the
ocean
surface
for
distribution
back
to
the
algal
forest.
The
nutrient
distribution
must
be
carefully
managed
to
prevent
ammonia
toxicity
and
maximize
macroalgal
forest
sustainability
without
microalgae
“blooms.”
Our
model
includes
the
materials
and
energy
to
use
all
three
of
the
following
mechanisms
to
ensure
maximum
local
recycling
of
the
plant
nutrients:
a.
The
dissolved
nutrients
are
distributed
evenly
through
a
grid
of
floating
hose.
Because
this
is
mostly
ammonia
at
perhaps
800
mg/L
of
nitrogen,
it
may
have
to
be
distributed
only
during
daylight
hours
when
the
algae
are
provid-
ing
high
dissolved
oxygen
concentrations
so
that
aerobic
microbes
can
quickly
convert
the
ammonia
to
nitrate.
b. The
undigested
solids
from
digestion
float
in
“tea-bags”
through
the
forest
providing
a
slow-release
fertilizer.
When
the
aerobic
bacteria
of
the
ocean
surface
have
extracted
most
of
the
remaining
plant
nutrients,
the
remaining
solids
would
be
released
to
sink.
c.
The
nutrients
from
dying
plants
that
are
not
harvested
are
pumped
back
up
from
the
water
or
seafloor
beneath
the
forest.
Table
1
indicates
nutrient
recycling
is
the
most
energy
intensive
process
of
the
ecosystem.
OMA
covering
4%
of
the
world’s
ocean
could
be
cycling
about
sixteen
times
the
world’s
2010
synthetic
nitrogen
production.
Hanisak
(1981)
indicates
that
recycling
nutrients
from
anaerobic
digestion
will
work
well
to
sustain
and
perhaps
increase
macroalgae
growth
when
combined
with
existing
nutrients
in
the
seawater.
Recycled
digester
residues
were
shown
to
provide
62–83%
(recycling
efficiency)
of
the
required
nutrients
for
seaweed
cultivation
(Hanisak,
1981).
Given
ambient
levels
of
inorganic
nitrogen
in
Florida
coastal
waters,
a
recycling
efficiency
of
only
45%
would
be
required
to
support
maximum
Gracilaria
productivity
of
66
ash-free
dry
t/ha/yr
(Chynoweth,
2002).
(Note
our
energy
calculations
are
based
on
conservative
average
projections
of
only
18
ash-free
dry
t/ha/yr.)More
details
about
a
potential
method
for
recovering
ammonia
to
be
recirculated
to
needy
Ocean
Afforestation
ecosystems
are
presented
in
the
online
supplementary
information
“OMA
Gas
membrane
ammonia
concentration.”
4.6. Capture
and
compress
the
bio-CO2
As
the
water
with
dissolved
gas
and
nutrients
is
pumped
to
the
ocean
surface,
the
gases
are
captured
at
one
atmosphere
pressure
as
they
come
out
of
solution,
comprising
about
90%
bio-CO2and
10%
bio-CH4.
Our
LCA
presented
below
presumes
energy
is
consumed
moving
the
nutrient-laden
water
to
the
surface.
In
practice,
gas
bubbles
coming
out
of
solution
could
pump
the
nutrient
return
water
above
the
ocean
surface
with-
out
the
assumed
parasitic
energy
loss.
To
reduce
greenhouse
gas
effects,
our
calculations
include
the
materials
and
energy
for
a
biologic
removal
process
for
any
remaining
bio-CH4even
though
very
little
remains
dis-
solved
after
the
CO2capture.
The
removal
process
is
based
on
CH4digesting
microbes,
as
was
found
in
the
BP
Gulf
of
Mexico
oil
spill
(Kessler
et
al.,
2011).
This
ensures
no
CH4or
H2S
is
emitted
to
the
atmosphere.
Also,
during
the
CH4separation
process,
some
of
the
ammonia
will
be
converted
to
nitrate
and
be
recycled
with
the
rest
of
the
nutrients.
All
the
remaining
previously
dissolved
CO2,
CH4,
H2S,
N2O,
etc.
is
compressed
to
50-bar
and
cooled
as
it
is
moved
to
the
500-m
depth
in
a
pipe.
(When
in
shallower
water
the
CO2
is
either
chilled
or
compressed
until
it
liquefies.)
The
com-
pressed
bio-CO2condenses
to
a
liquid.
Other
gases
will
either
be
recovered
with
most
of
the
bio-CH4or
will
remain
dissolved
in
the
liquid
CO2.
The
(mostly)
bio-CH4will
still
be
gaseous
and
will
be
used
to
produce
more
energy.
4.7.
Store
the
bio-CO2
Ocean
Afforestation
concentrates
CO2from
air
that
can
be
then
be
stored
as
pure
gas
or
liquid
CO2with
a
variety
of
carbon
storage
technologies:
a.
Deep
geologic
storage
where
the
CO2is
either
a
gas,
a
supercritical
fluid,
or
dissolved
in
saline
aquifers
several
kilometers
below
the
surface
of
the
earth
or
the
seafloor;
b.
Shallow
sub-seafloor
storage,
proposed
by
House
et
al.
(2006)
where
the
CO2is
either
a
liquid
or
a
hydrate
perhaps
100
m
below
the
seafloor
for
a
combined
depth
in
excess
of
3
km;
c.
Solid
snow,
proposed
by
Agee
et
al.
(2012)
where
the
CO2is
a
frozen
solid
“landfill”
in
Antarctica;
d.
Artificial
geologic
seafloor
storage
where
the
CO2is
hydrate
or
denser-than-seawater
liquid
embedded
in
geosynthetic
and
other
artificial
geologic
layers;
or
e.
Other
future
technology.
The
International
Maritime
Organization
(2011)
indicates
that
sub-seabed
CO2storage
is
legal
under
recent
amendments
to
the
London
Protocol.
While
dumping
unconfined
CO2in
the
ocean
is
prohibited,
both
the
London
Protocol
and
the
OSPAR
Commission
are
silent
on
storing
CO2in
containers
on
or
in
the
seafloor.
Research
indicates
that
appropriate
undis-
turbed
geosynthetics
will
prevent
contact
with
seawater
for
millennia
(Rowe
and
Islam,
2009)
and
that,
should
the
geosyn-
thetic
be
damaged,
insignificant
CO2hydrate
dissolves
before
the
damage
could
be
detected
and
repaired.
See
the
online
supplementary
information
“OMA
Artificial
Geologic
Seafloor
Storage”
for
a
more
detailed
description
of
the
technology
and
legal
issues.
Our
economics
calculations
for
storing
the
OMA-derived
pure
CO2are
based
on
the
geosynthetic
containers
because
the
locations
ideal
for
OMA
may
lack
the
geology
for
the
above
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471
Table
1
–
LCA
calculations
including
materials
and
energy
for
OMA
component
processes.
Process
#
Process
description
kWh/Mg
of
bio-CO2stored
4.4 Energy
produced
from
recovered
CH44400
4.1,
4.2
Growing
and
harvesting
macroalgae
−60
4.3,
4.4
Digesting
macroalgae
and
recovering
CH4−150
4.5
Recycling
plant
nutrients
−340
4.6
Converting
atmospheric
CO2to
liquid
CO2
at
500
m
depth
−430
4.7
Converting
liquid
CO2to
permanently
stored
hydrate
in
artificial
geologic
seafloor
containers
−80
Total
parasitic
energy
to
operate
above
processes
−1060
Net
energy
production
(rounded)
3300
options
a,
b,
or
c.
In
addition,
the
hydrate
is
more
secure
than
gas
or
liquid
CO2as
it
is
denser
than
seawater
below
500
m
and
could
slowly
dissolve
only
if
water
with
less
than
the
equilib-
rium
dissolved
CO2is
in
direct
contact
and
heat
is
available.
4.8.
Harvest
fish
and
other
products
Additional
potential
sources
of
income
include
sustainable
harvests
of
fish,
sea
vegetables,
and
other
macroalgal
prod-
ucts.
Replacing
fossil
fuels
will
require
so
many
macroalgal
forests
that
the
production
of
fish
sufficient
to
provide
0.5
kg
of
fish
and
sea
vegetables
per
person
per
day
for
10
billion
people
could
be
almost
an
“incidental”
by-product.
In
actu-
ality,
seafood
production
is
likely
to
be
a
higher
fraction
of
OMA
products
initially
because
food
is
generally
a
higher
unit
value
than
renewable
energy.
However,
food
uses
can
remove
nutrients
from
an
OMA
ecosystem.
We
project
that
this
would
mean
less
than
2%
of
the
annual
forest
nutrient
requirement,
in
the
2050
scenario
(OMA
over
6%
of
world
oceans)
actu-
ally
leaving
the
forests
in
the
form
of
fish
and
other
edible
food
stocks
(based
on
data
from
Ramseyer,
2002).
We
have
not
included
fish
and
other
food
products
in
our
calculated
energy
balance.
Potential
other
products
include
liquid
fuels,
agar,
carrageenans,
algin,
etc.
Quast
(1968)
and
Limbaugh
(1955)
report
that
the
long-used
southern
California
practice
of
harvesting
kelp
by
“mowing”
the
top
1.3
m
three
or
four
times
a
year
had
no
effect
on
the
sport
fish
populations
or
kelp
productivity
even
though
the
harvesting
operation
was
exporting
plant
nutrients
from
the
ecosystem.
The
actual
quantities
of
increased
fish
production
need
to
be
studied
for
each
region
and
species.
As
Graham
et
al.
(2008)
and
Graham
(2004)
report,
“One
property
clearly
common
to
southern
and
central
Californian
kelp
forests
is
the
funda-
mental
importance
of
kelp
(primarily
Macrocystis
pyrifera)
as
an
overwhelming
source
of
primary
production
and
detritus
that
fuels
both
the
grazer-dependent
and
the
detritus-dependent
trophic
pathways
in
these
systems.
The
actual
diversity
of
forest-dwelling
species
involved
in
either
or
both
of
these
pathways
has
never
been
quantified,
but
clearly
constitutes
a
major
portion
of
the
great
diversity
characteristic
of
these
communities.”
(2008,
p.
7)
Another
“product”
of
the
Ocean
Afforestation
process
can
be
concentrating
fertilizer
from
ocean
dead
zones
for
appli-
cation
on
terrestrial
farms.
Normally,
the
digestate
with
its
seawater
salt
concentrations
and
500–1000
mg/L
ammo-
nia
concentrations
would
be
too
salty
for
land
application
and
too
dilute
for
transporting.
However,
gas
membrane
technology
for
concentrating
the
salty
digestate
ammonia
into
a
concentrated
freshwater
fertilizer
is
presented
in
the
online
supplementary
information
“OMA
Ammonia
Concentrating
Process.”
5. Potential
scenarios
to
accomplish
the
objectives
and
economics
Ocean
Afforestation’s
bio-CH4is
an
appropriate
fuel
for
bio-
energy
with
carbon
capture
and
storage
(BECCS).
We
leave
the
discussion
of
BECCS
technology
to
BECCS
researchers.
How-
ever,
our
scenarios
include
the
expectation
of
a
significant
amount
of
BECCS
and
carbon
capture
and
storage
from
fossil
fuel
exhaust
in
the
future.
Table
1
combines
the
materials
and
energy
input
for
the
processes
4.1–4.7.
(The
costs
and
benefits
of
Process
4.8,
fish
and
other
products,
are
not
related
to
negative
carbon
emis-
sions.)
The
materials
have
been
converted
to
their
energy
equivalent
in
kWh.
These
calculations
are
detailed
in
a
not-
yet-published
paper
with
supporting
documentation
by
Colosi
(2012).
The
online
supplementary
information
“OMA
Process
Concepts”
presents
a
conceptual
outline
of
the
process
designs
and
many
of
the
numbers
used
in
the
LCA,
which
are
summa-
rized
in
Table
1.
Table
2
presents
a
scenario
to
attain
a
2035
objective
of
net
zero
carbon
emissions.
The
U.S.
Energy
Information
Administration
presents
current
projections
as
600
quadrillion
Btu/yr
(176
million
GWh/yr)
global
fossil
fuel
use
by
2035,
pro-
ducing
43
metric
tons
of
CO2.
The
2035
OMA
scenario
would
have
OMA
displace
nearly
half
of
the
fossil
fuels,
while
half
of
OMA
combustion-CO2exhaust
and
a
third
of
remaining
fossil
CO2emissions
would
be
captured
from
power
plant
exhaust
and
stored.
In
addition,
all
8
billion
tons
from
the
OMA
bio-CO2would
be
stored,
producing
a
carbon
neutral
world.
Varying
the
proportions
of
fossil
fuel
use,
other
renew-
able
energy,
OMA
energy,
and
OMA
sequestration
would
yield
other
scenarios.
But
even
with
net
zero
emissions,
ocean
acidification,
climate
changes,
glacier
melting,
and
methane
hydrate
dis-
sociation
will
continue
to
cause
human
misery
and
mass
extinctions,
because
atmospheric
concentrations
have
run
above
350
ppm.
The
2050
scenario
involves
storing
all
the
OMA
bio-CO2,
half
of
OMA
combustion-CO2exhaust,
and
two-
thirds
of
fossil
fuel
emissions
while
producing
420
quads/yr
(123
million
GWh/yr)
of
energy.
This
removes
a
net
20
bil-
lion
metric
tons
per
year
from
the
atmosphere.
Unfortunately,
atmospheric
CO2concentrations
would
drop
at
only
half
that
rate
as
the
oceans
start
giving
up
their
dissolved
CO2.
Author's personal copy
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Table
2
–
Scenarios
for
OMA
to
remove
anthropomorphic
CO2.
Scenario
parameter
during
scenario
year
Units
2035
2050
2070
Global
energy
quantity:
EIA
(2011)
prediction
of
energy
needed
from
fossil
fuels
in
2035
(600
quads
=
176
million
GWh)
Quadrillion
Btu/yr 600 600
600
Total
OMA
renewable
energy
output,
from
CH4
(before
efficiency
losses
electricity
conversion)
280
420
620
Remaining
fossil
fuel
energy
in
scenario
year
320
180
0
Prediction
of
fossil
CO2emissions Billion
metric
tons
of
CO2/year 43
43
43
Fossil
CO2emissions
replaced
by
combustion
of
bio-CH4from
OMA
−20
−30
−43
Remaining
fossil
CO2emissions
23
13
0
Less
fossil
fuel
emissions
neutralized
by
CCS
−8
−9
0
Less
permanently
stored
bio-CO2−8
−12
−19
Less
permanent
storage
of
half
the
combustion-CO2,
BECCS
process
−8
−11
−17
Net
CO2removal
0
−20
−36
Algal
forest
area
during
scenario
year %
of
ocean
surface
4%
6%
9%
Time
to
reduce
atmospheric
CO2by
100
ppm,
with
oceans
off-gassing
half
the
removed
CO2
Years
–
50
30
If
atmospheric
CO2concentration
(currently
400
ppm)
con-
tinues
to
grow
at
its
current
business-as-usual
exponential
pace,
it
will
be
about
480
ppm
in
2035
(Climate
Interactive,
2011).
However,
perhaps
rapid
implementation
of
renewables,
efficiency,
OMA,
and
other
carbon
capture
technologies
will
keep
it
below
450
ppm.
Presuming
100
ppm
of
atmospheric
concentration
equates
to
500
billion
tons
of
CO2and
half
of
CO2removed
will
re-emerge
from
the
oceans,
it
would
take
the
removal
about
1000
billion
tons
of
CO2to
drop
the
atmo-
spheric
concentration
from
450
ppm
to
350
ppm.
This
could
be
done
in
50
years
using
the
2040
scenario
with
OMA
over
about
6%
of
ocean
surface.
Or
it
would
only
take
30
years
(and
save
much
human
misery)
in
the
2070
scenario
with
OMA
over
about
9%
of
ocean
surface.
Note
that
the
OMA
renewable
energy
output
of
176
mil-
lion
GWh/year
(600
quadrillion
Btu/yr)
is
equivalent
to
all
the
energy
projected
to
be
needed
from
fossil
fuels
in
2035.
We
assume
additional
energy
needed
in
future
years
would
come
from
other
renewables,
such
as
wind,
solar
power,
geother-
mal,
and
other
ocean
energy
technologies.
The
timeline
could
be
faster
with
more
rapid
implementation
of
other
renewables
and
efficiency
measures
than
currently
assumed
by
EIA
(2011).
The
efficiency
of
CO2removal
is
important
and
may
be
expressed
by
a
life
cycle
assessment
as
two
or
more
out-
put/input
ratios.
Table
1
suggests
the
overall
ecosystem
ratio
of
energy
output/input
(including
all
materials
properly
amor-
tized
and
expressed
as
energy
and
the
losses
from
conversion
to
electricity
at
45%
efficiency)
for
the
CO2stored
is
4.
(This
analysis
is
based
on
the
method
described
by
a
private
communication
(Colosi,
2012)
and
including
the
analytical
methods
presented
by
Clarens
et
al.
(2011).)
Another
impor-
tant
ratio
is
about
20
tons
of
CO2are
stored
for
each
ton
of
CO2emitted
from
the
energy
required
for
capture
and
storage
(processes
4.6
and
4.7).
Converting
the
above
LCA
numbers
to
costs
using
a
fore-
casted
cost
for
on-site
generated
electricity
of
$50/MWh
and
appropriate
material
costs
would
yield:
Process
4.6
–
$9/t
of
CO2to
capture,
compress,
and
con-
dense
the
CO2.
Process
4.7
– $7/t
of
CO2to
manufacture,
monitor,
and
maintain
in
perpetuity
CO2hydrate
stored
inside
a
geosyn-
thetic
container
on
the
seafloor.
Total:
$16/t
of
CO2from
air
to
permanent
storage.
6.
A
path
to
deploying
Ocean
Afforestation
Since
Ocean
Afforestation
is
an
entire
ecosystem
and
not
a
single
product,
it
is
difficult
to
do
the
entire
process
includ-
ing
storing
carbon
economically
at
a
small
scale.
On
the
other
hand,
it
is
not
necessary
to
wait
for
governments
to
impose
a
price
on
CO2emissions,
because
OMA
produces
energy.
Fiji
and
many
other
locations
have
looked
at
producing
local
bio-
fuels
(for
example,
Krishna
et
al.,
2009)
but
the
potential
of
land-based
feedstocks
is
small.
However,
recently,
one
of
the
authors
(N‘Yeurt)
and
other
researchers
at
the
University
of
the
South
Pacific
have
begun
to
see
how
Ocean
Afforestation
could
expand
to
accomplish
Fiji’s
goal
of
replacing
100%
of
their
expensive
diesel-fueled
electricity
with
bio-CH4using
about
20,000
ha
of
their
sheltered
bays.
Our
analysis
indicates
that
sheltered
water
OMA
can
com-
pete
with
Fiji’s
diesel-powered
electricity
while
providing
many
eco-benefits,
such
as
cleaning
up
excess
nutrient
runoff.
The
report
of
a
demonstration
beginning
in
Fiji
will
be
pub-
lished
in
a
couple
years.
(This
would
initially
be
without
carbon
storage.)
Beyond
sheltered
bays,
OMA
requires
research
and
demon-
strations
of
marine
agronomy
in
the
open
ocean
by
recycling
nutrients
to
grow
macroalgae
without
producing
excessive
microalgae.
New
low-energy
and
low-materials
techniques
should
be
developed
for
growing
and
harvesting
macroal-
gae.
Marine
microbiologists
may
find
methanogens
capable
of
faster
digestion
at
higher
dissolved
gas
concentrations
than
the
present
authors
interpolated
from
previous
stud-
ies
using
terrestrial
methanogens.
Techniques
may
be
needed
to
address
the
potential
loss
of
macroalgae
during
storms.
(The
submerged
digesters
and
most
other
process
equipment
would
be
below
the
depth
influenced
by
storms.
The
harvest-
ing
equipment
may
relocate
to
avoid
storms.)
Trials
should
include
liquid
biofuel
production
and
other
systems
for
separating
CO2from
CH4.
OMA
use
of
geosynthetics,
other
CH4purifying
techniques,
and
nutri-
ent
recycling
may
help
other
terrestrial
bio-waste-to-energy
and
sequestration
operations.
There
are
potential
feed-
backs
to
investigate
as
large
algal
forests
may
change
ocean
albedo
and
thereby
alter
local
temperatures.
Increas-
ing
ocean
temperatures
and
acidity
from
climate
change
could
have
an
effect
not
only
on
macroalgal
distribution
and
Author's personal copy
Process
Safety
and
Environmental
Protection
9
0
(
2
0
1
2
)
467–474
473
biodiversity,
but
also
on
their
physiology
and
photosynthetic
performance.
We
project
it
could
take
up
to
5
years
(2013–2018)
to
get
an
initial
demonstration
10,000
ha
forest
operating
eco-
nomically
in
a
near-shore
sheltered
water
environment
(involving
an
investment
of
about
$20
million).
This
forest
may
be
located
where
there
are
sufficient
existing
nutri-
ents
that
nutrient
recycling
needs
would
be
minimal
and
inexpensive.
It
could
take
another
10
years
(2018–2028)
to
get
many
shel-
tered
water
10,000-ha
forests
operating.
Initial
forests
may
be
located
where
there
are
sufficient
existing
nutrients
that
nutri-
ent
recycling
needs
would
be
minimal
and
inexpensive.
The
sheltered
water
approach
could
involve
as
much
as
0.3%
of
the
ocean’s
surface
(1
million
km2).
In
this
case,
‘sheltered
water’
may
be
the
entire
Mediterranean
Sea,
the
Gulf
of
California,
and
other
such
bodies
of
water
where
tropical
storms
are
rare
or
enclosed,
perhaps
4
million
km2.
Sheltered
water
can
be
any
depth.
Occupying
a
quarter
of
the
available
sheltered
water
may
be
a
challenge,
but
all
the
sheltered
water
operations
will
put
only
a
small
dent
in
humanity’s
CO2debts.
Open
ocean
operations
are
needed.
The
reason
OMA
expansion
can
be
so
rapid
is
that
the
basic
technology
involves
low-tech
components,
such
as
har-
vesting
nets,
large
geosynthetic
(plastic)
bags,
and
pipes,
with
the
methane
feeding
into
existing
natural
gas
and
diesel
power
plants.
Also,
many
sheltered
waters
suffer
from
an
over-
abundance
of
anthropomorphic
nutrients.
During
these
10
years
(2018–2028)
the
first
open-ocean
10,000-ha
forest
could
be
developed
with
an
investment
of
per-
haps
$100
million.
But
it
could
take
another
7
years
(2028–2035)
to
get
many
open-ocean
10,000-ha
forests
operating.
Note
the
long-term
goal
of
9%
ocean
coverage
(32
million
km2)
is
daunting
from
an
occupied
space
and
necessary
technology
perspective.
This
surface
area
represents
most
of
every
ocean
gyre.
On
the
other
hand,
collecting
and
removing
plastics
from
ocean
gyres
could
be
another
OMA
product.
Other
issues
that
may
slow
deploying
OMA
and
carbon
storage
include
gathering
start-up
or
expansion
nutrients
and
energy
infrastructure.
In
the
steady
state,
Ocean
Afforestation
nutrients
cycle
in
a
tight
circle.
When
increasing
the
size
of
the
algal
forest,
nutrients
must
come
from
outside
the
tight
cir-
cle.
Where
there
are
anthropomorphic
nutrients,
the
nutrient
diversion
recreates
a
more
pre-human
environment.
In
either
case,
about
140
million
metric
tons
of
nitrogen
are
needed
for
each
increase
of
Ocean
Afforestation
area
by
0.35%
of
total
ocean
area.
It
appears
necessary
to
increase
Ocean
Afforesta-
tion
area
at
0.35%
per
year
for
several
decades
in
order
to
drop
atmospheric
CO2below
350
ppm
before
the
end
of
the
century.
Whatever
fuel
is
produced
will
require
transportation
and
conversion.
When
the
OMA
energy
product
is
pure
bio-CH4,
it
is
identical
to
natural
gas.
Currently
inexpensive
natural
gas
is
displacing
coal
as
the
fuel
of
choice
for
electricity
genera-
tion.
The
world
is
already
building
more
power
plants
fueled
by
natural
gas
and
the
associated
liquefied
gas
transportation
systems.
Those
power
plants
fueled
by
bio-CH4and
outfitted
with
exhaust
capture
can
continue
generating
energy,
cap-
turing,
and
storing
bio-CO2.
New
infrastructure
required
for
OMA
produced
energy
is
not
likely
to
be
a
limiting
factor
to
rapid
expansion.
New
infrastructure
for
other
products:
fish
and
other
macroalgal
products
may
be
important
for
economics
but
the
volumes
are
so
much
less
that
building
their
demand
and
infrastructure
is
not
likely
to
limit
forest
expansion.
Quickly
implementing
Ocean
Afforestation
would
be
an
effort
on
the
order
of
putting
a
man
on
the
moon,
but
both
less
expensive
and
likely
a
much
better
return