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PHOTOSYNTHETIC ENERGY AND ECOLOGICAL RECYCLING 1
Photosynthetic Energy and Ecological Recycling:
The Architectural Potential of Algae Cultivation
GUNDULA PROKSCH
University of Washington, Seattle, WA
Ecological Design is defined as "effective
adaptation to and integration with nature's
processes."1 Until recently, it has included the
development of sustainable materials and
employing bio-mimicry both functionally and
formally.2 Today, more and more projects are
taking the concept further by integrating plant
material and living systems directly, like living
machines and algae farming. They discover
sunlight-driven photosynthesis as the central
force to generate renewable energy. As the
primary biological process of solar energy
translation that supports all life on earth,
photosynthesis converts common waste
products of respiration and combustion
together with sunlight and water into two vital
substances: sugar and oxygen.3 In terms of
material science, photosynthesis represents a
remarkably elegant process by virtue of
chlorophyll's photosynthetic properties.4 It sets
the standard for any technology and material
performance interacting with the energy
embodied in daylight.
Photosynthesis can do even more; it sets up a
co-dependency between energy production and
ecological recycling. Currently, most renewable
energy sources like hydroelectric, solar, wind,
tidal, and geothermal, target the electricity
market as "clean" energies without pollution
and carbon dioxide emissions.5 Photosynthesis-
based systems reach beyond renewable energy
production; they are capable of actively
improving the health of the environment
through the sequestration of CO2 and
wastewater treatment. Rethinking plant
material as a "smart" material allows for the
production of renewable energy while playing
an essential role in zero-waste systems
inspired by cyclical natural processes. Still
underutilized in the built environment, these
closed-loop systems generate a synthesis
between energy generating technologies and
resource sustainability (Figure 1A).
In this context, algae cultivation stands out as
an extremely efficient living system because of
its high productivity rates and low resource
needs, as well as its ability to sequester
pollutants. In comparison with terrestrial
plants, algae show a higher photosynthetic
efficiency and oil production. Although
photovoltaic cells have a higher efficiency and
energy production per area, algae-based
energy is almost 30 times less expensive per
unit than energy generated by photovoltaic
technology. After factoring in land value,
energy derived from algae can still be
produced at 30% of the cost of photovoltaic-
based energy (Figure 1B).
2
Photosynthetic+efficiency+
(%+of+solar+radiation)
Useable+Energy per+
Area+of+Land (MJ/m22
/year)
Unit+of+Energy
per+USD (MJ/$)
11%
1.16
5% 6%
Photovoltaics
Corn++
Algae
28.50
33.33
Photovoltaics
Corn++(Ethanol)
Algae(+Biofuel)
Useable+Energy+per+Combined+
+Land+and+Cost (MJ+/$+/+m )
689
570
2,033
Photovoltaics
Corn++(Ethanol)
Algae(+Biofuel)
594
61
20
Photovoltaics+
(London,+150kW/m2)
Corn++(Ethanol)
Algae+(Biofuel)
(Low+yield+of+15g/m2/day)
A.+ClosedOLoop+System
B.+Comparison+of+Photovoltaic+v.+Photosynthesis
Advanced algae cultivation technologies –
some still in the laboratory and scientific
testing phase – instantaneously inspire
architects and designers on speculative
projects and design competitions. Many recent,
innovative design proposals integrate algae
cultivation and redefine how designers think
about the relationship for sunlight, matter, and
renewable energy. Given algae's energetic
potential and cleansing benefits, this paper
analyzes algae farming methods, their
emerging architectural applications and
integration into closed-loop systems. Algae
cultivation and its architectural integration
promises to revolutionize ecological design and
become a potent tool to address the causes of
climate change.
Figure 1: Photosynthesis
PHOTOSYNTHETIC ENERGY AND ECOLOGICAL RECYCLING 3
ALGAE FARMING
Humans have been harvesting algae for food
and medicinal purposes for over 2500 years,
and began cultivating it approximately 300
years ago.6 Currently, macro- and microalgae
are commercially cultivated worldwide.7 One of
the earliest mentions of algae as fuel occurred
in 1953 in Algal Culture: From Laboratory to
Pilot Plant.8 In his introduction to the edited
volume, John S. Burlew – inspired by MIT
research into rooftop micro-algae production –
suggests harnessing algae’s extremely efficient
photosynthesis process to produce oils,
effectively accelerating the natural process
through which fossil fuels are formed.9 In the
1960s Stanford University scientists Oswald and
Golueke released their paper "The Biological
Transformation of Solar Energy," documenting
their studies on a closed-looped algae-to-fuel
production process.10
US government-supported research into the
potential of algae as a biofuel surged during the
energy crisis of the 1970s.11 Funding dwindled
in the 1980s, and government funding has only
recently resurged again in response to the
growing interest in alternative energies,12
leading to an expansion of testing and
innovation in algal fuel production and
wastewater processing.13 According to biologist
Peer Schenk, international awareness of climate
change and the need for reduced CO2 emissions
has focused scientific attention on the potentials
of algal biofuels.14 Since algae farming can
occur without disrupting domestic agriculture,
some governments and food industries are
highly invested in its success.15
Productivity and Resource Efficiency
Microalgae, autotrophic organisms often living
as single cells and floating as plankton, are
among the fastest growing, most efficient and
adaptive organisms on the planet.16 They can
produce up to 3,000-15,000 gallons
oil/acre/year.17 Their very high energy content
of 18.5 - 35 MJ/kg rivals coal (averages at 24
MJ/kg) and exceeds the energy density of wood,
wastewater sludge, and agricultural by-
product,18 making them an excellent energy
source. Algae have a quick harvest cycle of only
1-10 days19 and can be harvested batch-wise
nearly all-year-round,20 providing a reliable and
continuous supply. Besides energy in the form
of biofuel, commercial algae cultivation has
numerous uses. These include production of
food, food supplements,21 fish feed, bioplastics,
chemical feedstock, pharmaceuticals, fertilizer,
and soil enhancements.22
Algae can tolerate salt and wastewater streams
and thereby greatly reduce freshwater use. In
nutrient-rich, eutrophic water they thrive even
more abundantly.23 As a positive by-product,
they clean the water as a means of pollution
control. Algae farming couples CO2-neutral fuel
production with CO2 sequestration and O2
production. Numerous studies indicate that
photosynthesis performed by algae significantly
contributes to a reduction of atmospheric CO2
levels.24 Increased CO2 concentration will
further increase the rate of growth as long as
there is an abundance of other limiting
nutrients.25
FARMING TECHNIQUES
System designs for algae farming range from
low-tech ponds to high-tech bioreactors, with
each design varying the balance of yields, land,
water, and energy usage, susceptibility to
contamination, initial costs, and operating costs.
In all cases the growth occurs over the course
of 1-10 days after which the algae mass is
extracted and pressed for oil. The oil is then
refined into a useable source, typically
biodiesel.26 Other forms of energy exploitation
are possible, including biogas, methane,
ethanol, and biobutanol, but the economic
payback is lower.27
Open Pond System
The open pond system is the most commonly
employed growing technique today. It utilizes
shallow lakes, constructed ponds or raceway
ponds, in which the water is circulated by
gravity or paddlewheels (Figure 2A). The major
advantages of open ponds are their low
construction and operation costs, but their
economic margins are also lower than more
controlled systems. Open ponds require large
areas of land and are susceptible to
contamination, evaporation losses, poor light
utilization, temperature swings, and bad
weather. To minimize many of the problems
associated with an open system, the pond can
be enclosed with a transparent or translucent
barrier, which effectively turns it into a
greenhouse.
4
PLASTIC(BAG
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WATER
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PROCESSOR
ADDED(C02
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NUTRIENTS
ALGAE
CONCRETE(POND
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OUTPUT
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BIOREACTORS
COMPUTER7
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RECYCLED(
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PLANT(+(NUTRIENTS
A.#Open(Pond#System
B.#Low(Tech#Vertical#Bioreactor
biofuel‐1.jpg
C.High(Tech#Bioreactor
D.#Experimental#3DMS#Triangle#Bioreactor
Figure 2: Algae Cultivation Methods
PHOTOSYNTHETIC ENERGY AND ECOLOGICAL RECYCLING 5
!Yield&
(g/m2/day)
&
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&
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Initial&Cost& Operating&
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Vertical Growth Systems
To increase the productivity per areal footprint,
various vertical algae growing systems have
been developed. All of these are primarily
capitalizing on the fact that most algae thrive
best in indirect, diffuse light.28 As a
consequence algae can be grown in three-
dimensional space rather than on a surface (like
terrestrial plants), as long as the light can
penetrate into the depth of the volume. The
simplest vertical systems, or low-tech
bioreactors, cultivate algae in clear, poly-
ethylene plastic bags hung vertically from racks
to expose all sides to light (Figure 2B). The
individual bags are connected by circulation
tubes through which water is mechanically
pumped. In these closed systems the yield is
higher and algae is not vulnerable to
contamination. The use of simple materials
keeps the construction costs low, but might also
require additional structure and enclosure to
protect the cultivation from weather
fluctuations.29
Closed Photo-Bioreactor Systems
Closed bioreactors are initially up to 10 times
more costly than open pond systems but have 5
to 10 times higher yields per areal footprint
than conventional methods. They achieve this
by maximizing the absorption of nutrients and
energy in a minimal volume of water under
controlled conditions. The algae are typically
grown in glass tubes through which water is
continuously pumped. This mixing is necessary
to prevent sedimentation of the algae cells and
to support even distribution of CO2 and O2. The
design goal of all growing structures30 is to
maximize the surface-to-volume ratio and
provide light saturation at optimal light
intensities.
The world’s largest photo-bioreactor in Klötze,
Germany consists of 500km of glass tubes in a
12,000m2 green house. The total volume of the
system is ca. 600m3; a constant flow speed of
25m per minute guarantees an optimized light
exposure (Figure 2C).31 A very recent bioreactor
variation, the 3D Matrix System increases the
photosynthetic active area per areal footprint
even further.32 This "airlift reactor" consists of
triangular-shaped bioreactors from poly-
carbonate tubing (Figure 2D). Flue gases are
introduced at the bottom of the hypotenuse and
flow up while the media containing the algae
flows in the opposite direction. The ascending
bubbles and downward current generate
vortices that intensify the matter exchange
(assimilation), which determines the growth
rate. Even when tested under sub-optimal
lighting conditions,33 the reactor is one of the
most productive algal cultivation systems ever
built.34
Figure 3: Comparison of Algae Growing Systems
6
Evaluation of Algae Farming Techniques
Despite the development of more advanced
bioreactor technology, the open-pond system
is still the predominant, commercial system
because it is initially cheaper and nevertheless
produces a profitable yield, even if it is not
nearly as productive as controlled systems
(Figure 3). This very land-intensive operation
can be installed on marginal and non-arable
land and therefore potentially opens up new
economic opportunities for arid or coastal
regions.35 The system's vulnerability to
contaminations and the higher land cost in
urban areas limits the possibility for its
integration in public space and cities.
When integrating algae cultivation in cities or
areas of higher density and land cost,
bioreactors are the technology of choice to
minimize the area needed, while increasing the
yields by 5-10 times. Closed systems minimize
evaporation and therefore control resource
input and biochemical reaction rates carefully.
Depending on the construction system used,
from low-tech plastic bags to high-tech
fiberglass bioreactors, controlled systems
require a higher initial investment.
Simultaneously, the necessary structure and
compactness makes them more applicable for
architectural integration, both spatially and
infrastructurally. Bioreactors can potentially be
connected to urban infrastructures and even
building systems for resource recycling and
pollutant sequestration at its source and
energy production where it is needed.
SYNERGIES AND BUILDING INTEGRATION
Algae’s nutritional and chemical requirements
offer opportunities for establishing synergies
between algae production and industrial,
urban, and building utilities. Commonly,
connections of algae cultivation with industrial
plants that produce CO2- or nitrogen-heavy
byproducts establish benefits and higher
yields. Architecturally, the integration of algae
farming in urban centers, in connection with
urban infrastructure and building systems is
equally promising.
Current case studies and investigations
emphasize four different aspects and benefits
of algae farming. (1) Instead of remaining a
hidden, utilitarian amenity, speculative design
projects have started to interweave the
infrastructures of algae cultivation with cities
and building systems. Algae bioreactor façades
harness solar energy and reveal the new
technology. (2) Controlled systems can be
installed as effective CO2 filters and additional
power sources for buildings or neighborhoods,
which utilize CO2 rich exhausts. (3) Other pilot
projects utilize algae's ability to thrive in
nutrient rich wastewater to improve
wastewater treatment practices. (4) And
integrated in complex, closed-loop systems,
algae cultivation can help to establish net-zero
or perhaps even carbon-negative building
performance.
Solar Energy Harvesting
In 2009 the Institute of Mechanical Engineers
recommended integrating algae cultivation into
the existing building stock as a strategy to deal
with climate change. Building-integrated
photo-bioreactors are designed to efficiently
collect solar radiation on the surface of
buildings. Prefabricated bioreactor panels
present a manageable form for algae farming
on the domestic and small commercial scale.36
These units are more accessible from the
commercial point of view and are an ideal bolt-
on solution for a retrofit scenario. In addition
to lowering the atmospheric CO2 level and
providing a natural source of energy, the algae
growth infrastructure can act as thermal buffer
(if integrated in a double skin façade), lead
potentially to reduced energy demand, and
improve building performance.
Process Zero: Retrofit Resolution, the winner of
Metropolitan Magazine’s The Next Generation
2011 Design Competition, translates this vision
into a design proposal. It uses energy-
generating algae to power a 1960s-era General
Services Administration office building in Los
Angeles.37 A 25,000 sq ft microalgae bioreactor
system generates 9% of the renovated
building’s power supply. A modular system of
algae tubes wraps the building and absorbs
solar radiation while reclaiming CO2 and
building wastewater to produce lipids for fuel
production on-site.38 The bioreactor tubes are
protected from intense sunlight through a thin-
film photovoltaic shading system to avoid
overexposure (Figure 4A).39 They are part of a
full-scale closed system of holding tanks and
filtration ponds to complete the bio-energy
network.40 The panelized, tubular algae skin
expresses the alternative energy production
PHOTOSYNTHETIC ENERGY AND ECOLOGICAL RECYCLING 7
and environmental system also architecturally
and equips the building with more than a
"metaphoric green cast."41
The emerging technology of bioreactors has
not yet been installed on the side of the
building nor integrated with high performance
double skin facades. It is only a matter of time,
judging from the success of other alternative
energy systems, such as solar thermal,
photovoltaic, and living machines, when this
technology will be integrated into buildings.
Currently the main concern for realizing this
step is a question of scale in terms of
efficiency, harvesting, and processing of the
biomass.42
Carbon Dioxide Emissions
Carbon-absorbing algae cultivation and
existing carbon-emitting power plants or
building exhausts can be combined to both
clean emissions and increase algae yield.
Several pilot programs have found that small
concentrations of algae can be used to “scrub”
gas emissions from power plants, absorbing as
much as 85% of CO2 gasses. A test system run
by the Swedish energy company Vattenfall
absorbs greenhouse gas emissions from a coal-
fired power plant in Germany. Flat-panel airlift
reactors cultivate algae “broth” through which
gas emissions are pumped. The resulting
biomass is used for biofuel or fish feed.43
An innovative architectural application of this
synergetic affect is Carbon TAP, the winner of
UCLA’s WPA 2.0 Competition. Carbon TAP
(Tunnel Algae Park) advocates taking
advantage of concentrated CO2 resources from
underwater vehicular tunnels and urban
infrastructures in cities. With the CO2 exhaust
of the Brooklyn-Battery Tunnel as primary case
study, Carbon TAP develops a new eco-
landscape or algae farm in the Upper Bay north
of Governor's Island. The algae feed off
underwater “bladders” of CO2 collected from
the tunnel in sealed large-scale bioreactors on
the surface of the bay. The farm is integrated
into a public park, which doubles as an
operable bridge between Manhattan and
Brooklyn.44
The project is notable for its integration with
existing urban infrastructure, utilizing a "out of
sight" source of CO2, and generating an index
for the otherwise invisible tunnel below. It
imagines algae cultivation as part of a
functional urban landscape, while taking
advantage of the necessity of substantial CO2
sources for algae production as well as its
"cleaning" effect through carbon dioxide
sequestration (Figure 4B).
Wastewater Treatment
Algae's ability to utilize the nutrients in
wastewater calls for integration with water
treatment processes. Solar Aquatic is one of
the first living machines to use algae in
translucent, light transmitting tanks for
wastewater treatment. This ecologically
engineered system has operated continuously
since 1989 at Ocean Arks International in
Rhode Island.
More recently, many municipalities are
announcing plans to integrate algae technology
in their wastewater treatment facilities while
harnessing their additional benefits. Rotating
Algal Contactors RAC's, also referred to as
algaewheels,45 are algae-based applications for
wastewater treatment currently in the testing
phase in several American cities. RAC
technology employs a series of rotating
photosynthetic algal contactors, which are
propelled by a constant airflow and are
designed specifically to grow large amounts of
algae. Each wheel provides optimal conditions
for algal growth while removing nutrients from
the water and increasing the energy efficiency
of the treatment process.
Algae and bacteria grow in a symbiotic
relationship, even though algae metabolize
sewage far more rapidly than bacterial
treatment by converting organic matter to
plant life. This natural growth process of algae
removes nutrients, such as nitrates and
phosphates, from the treated effluent water,
which therefore can no longer harm lakes and
streams. The process helps to eliminate
greenhouse gas emissions by sequestering CO2
and eliminating N2O as a byproduct of
conventional water treatment methods. The
photosynthesis process generates also oxygen,
which replaces the need for costly mechanical
oxidation of the wastewater. In addition,
algaewheels significantly improve the energy
efficiency of water treatment; they use 50 to
75% less energy than other biological
processes and generate 95% less waste solids.
The valuable byproduct of algal biomass is an
8
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MANHATTAN
GOVERNORS
ISLAND
BROOKLYN
A
B
C
D
E
D
vegetal terraces
CO2 bladder
SECTION A
algae bio-reactor
wetland tray algae bio-reactor
valve
access
access
promenade promenade
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tulip poplar bosque
CO2 bladder algae bio-reactoralgae bio-reactor
wetland
tray
algae bio-reactoralgae bio-reactor
valve
access
access
valve
wetland
access
promenade promenade
SECTION B
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CO2 bladder
promenade promenadepromenade
vertical gardens (beyond)
SECTION C
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xed-pier CO2 bladder
algae bio-reactor
algae bio-reactor
valve
access
access
promenadewetland tray
(wind turbine beyond)
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CO2 bladder (xed) cycloidal drive propeller system
(embedded in CO2 bladder)
promenade
to brooklyn
landing + overlook
SECTION D
?
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?
The rotating pier is driven by an integrated
cycloidal drive propeller system located at
its free end. This system of locomotion is
highly maneuverable, allowing for near
instantaneous change of thrust direction.
The rotating Governors Island pier
connects to the existing Brooklyn-Battery
tunnel ventilation system via a matrix of
exible ducting that links to the shaft’s 53
existing fans and motors.
The oating pier follows a scheduled
pivoting sequence connecting to Brooklyn
and Manhattan each once every hour.
The xed Battery pier is connected to the
landside ventilation shaft and is able to
function independently from the other two
pier elements.
The rotating pier departs on the half hour
for the Brooklyn Waterfront.
Like the Battery pier, the xed Brooklyn
pier is able to function independently as a
storage and delivery system. It is also
home to the processing facility for the
entire NYC industrial algae complex.
The rotating pier departs on the hour for
the Battery in Manhattan.
0’
plan scale: 1”=200’
100’50’ 200’ 400’
0’
section scale: 1”=40’
20’10’ 40’ 80’
Carbon T.A.P.
As federal, state and local governments consider large-scale
investments in the renovation and replacement of urban infrastr uctures,
we see a unique opportunity to reexamine the role of these sy stemic
networks and their eect on our contemporary urban landscapes.
In the scenario outlined herein, a new type of green infrastru cture is
deployed at urban locations comprising concentrated sources o f CO2
production. This new infrastructure utilizes a proprietary sy stem of
industrial-scale algal agriculture to sequester and consume gre enhouse
gas emissions (in particular CO2) in order to limit their introduction into
the atmosphere, while simultaneously creating a new economic
resource through the production of oxygen, biofuels, biop lastics,
nutraceuticals and/or agricultural feeds. In the scenario shown, this new
infrastructure manifests itself as a series of pier-like armatu res linked to
the ventilation system for the Brooklyn-Battery tunnel
What is unique about this proposition is not just the introdu ction of
large-scale green infrastructure in the context of a city, bu t rather the
use of this infrastructure to create an exceptional public re alm amenity
for the city. Rather than considering urban infrastructure s as a
necessary evil only to be hidden or mitigated, we view the reno vation
and re-imagination of these systems as opportunities to create new
forms of civic and social domain which have the capacity to po sitively
transform the American urban landscape.
Our proposal for a new infrastructural typology that is one par t climate
action; one part agricultural production; one part ecological p reserve;
one part public realm; and one part economic catalyst represen ts what
should be the aspiration for all newly deployed urban infrastru ctures –
the ability to fundamentally improve the economic and social qu ality of a
city, as well as the associated lives of its current and future residents.
HOW IT WORKS
1) Algae are one of the most robust classications of life on earth. Thriving on every
continent, they are highly adaptive to any physical environment where they are able to
derive energy from photosynthesis and the uptake of organic carbon, particularly in the form
of CO2.
3) Capturing even a small fraction of these CO2 emissions would oer an enormous
food source for large-scale algae production. However, the challenge of these sources is
holding the CO2 before it is delivered to some vessel containing the algae.
4) In our scenario, we use a two-part system for the capturing of CO2 and providing its
controlled delivery to an industrial-scale algae bioreactor. In this system, CO2 emissions
are captured and held in what is essentially a giant bladder or rigid balloon which is
congured to deliver CO2 to a series of 20,000-sq.-ft. bioreactors that can be detached
for harvesting and processing of their algae crop.
2) Atmospheric CO2 concentrations are not high enough for industrial-scale production
of algae. However, concentrated CO2 sources such as Coal/CoGen power plants or
manufacturing facilities oer potential sources of high-level CO2 concentrations. Vehicular
tunnels in particular can produce hundreds of millions of cubic feet of CO2 per year.
TUNNE L AL G A E PARK
5) Many of these concentrated CO2 sources are sited near bodies of water, allowing the
CO2 bladder to function as essentially a large pier or an expanded waterfront. As the
volume of CO2 needed and produced is quite large, thoughtful integration of the pier into
its urban context is an absolute. That said, we propose that these algal piers become the
sites of a new typology of public open space that bundles waterfront access with
productive green infrastructures.
6) With 18 vehicular tunnels of greater than 2,000 feet across the U.S., and thousands
of coal and natural gas driven power plants, deployment of adaptations of this system have
the potential to reinvigorate a wide range of urban environments throughout the country.
rigid CO2 bladder
algae bio-reactor
tunnel ventilation system
vehicular tunnel tubes
(CO2 emmision source)
new public realm typology
(rigid CO2 bladder below)
PORT IS: CHRISTOPHER MARCINKOSKI + ANDREW MODDRELL
1
4
3
2
5
6
7
8
9
10
11
12
13
14
15
16
18
17
19
20
1
22
21
24
23
25
27
26
The Battery Landing
2The Hive
3Entry Bosque
4Recreation Pool
5Algae Bioreactor (typ.)
6Wetland Tray (typ.)
7The Promenade
8Gov. Island Overlook
Vertical Botanic Gardens
10
Recreation Pool
11
Vegetal Terrace
12
Algae Bioreactor (typ.)
13
Tulip Poplar Grove
14
Event Plaza
15
Vegetal Terrace
16
Wetland Tray (typ.)
9The Point
17
18 The Hive
BBT Ventilation Tower
Gov. Island Landing
19
Brooklyn Landing
20
Wetland Tray (typ.)
21
Algae Bioreactor (typ.)
22
Event Plaza
23
Collection Area
24
25
26 Processing Plant
26 Entry Bosque
B.'Algae'Farming'as'Landscape';'Carbon'TAP'
C.'Wastewater'Treatment';'Rotating'Algal'Contactors'RAC
Figure 4: Case Studies
PHOTOSYNTHETIC ENERGY AND ECOLOGICAL RECYCLING 9
OCE
Energy2
Generation
I
C
O
2
+
N
2
0
T
H
E
R
M
A
L
H
E
A
T
WASTE WOOD
FERTILIZER
LUMBER
BIO-CHAR
O
M
A
S
S
B
I
O
-
O
I
L
(
2
/
3
)
B
I
O
-
O
I
L
(
1
/
3
)
METHANE
NUTRIENT SOLIDS
TIME-RELEASE SOIL AMENDMENT
(FERTILIZER)
SAWMILL
B
SUN LIGHT
SUN LIGHT
Digestion
Anaerobic
ALGAE
AACT
Photosynthesis
alternative energy source, which can improve
the energy balance even further. Overall, RAC
technology provides one of the most
environmentally friendly solutions to
wastewater treatment available today.46
Closed-loop Systems
Algae's ability to sequester CO2, produce
energy, and absorb pollutants can be
integrated into a sequence of processes that
build on each other by using the byproduct of
one cycle as the resource for the next. Multiple
interlocking cycles can create a self-sustaining,
net-zero system. Green Power House (GPH)
uses newly-developed Algae Aquaculture
Technology (AACT) within a system that inputs
two resources abundant in Montana: sunlight
and woody debris waste from a lumber mill.47
The system uses three separate but
interrelated processes to create two important
outputs: nutrient-rich soil amendment and
energy, both of which are necessary
components of a successful, resource-efficient
timber operation (Figure 5).
(1) Eight algae ponds of the AACT cover the
floor of the GPH greenhouse. Sunlight, CO2 and
N2O from the Organic Carbon Engine (OCE)
provide nutrients for algae growth. Ponds are
managed and harvested separately for
maximum yield. (2) The anaerobic digester
breaks down algae sludge harvested from
ponds inside the greenhouse by using a
process similar to that found in a buffalo's
stomach to produce methane and nutrient-rich
solid matter (digestate). The methane is used
in the OCE to start gasification process. (3)
The Organic Carbon Engine (OCE) converts
waste wood into biochar, bio-oil, CO2, and N2O
through gasification (pyrolysis). Waste gases
are pumped into the algae ponds to accelerate
algae growth and increase yields while
simultaneously managing CO2 emissions and
creating a carbon-negative cycle48.
Figure 5: Green Power House - Closed-Loop System
10
CHALLENGES AND LIMITATIONS
The primary challenge algae cultivation faces
when optimized for efficient energy and biofuel
production is the question of scale. All
currently existing operations work at relatively
large scale.49 For large operations the
availability of all resources in one place – a
concentrated CO2 source, water, infrastructure,
and land – is critical. Other important factors in
this context are the high costs of harvesting
and processing the algal biomass.50 Algae can
be produced in large quantities, but at the
same time efficient harvesting needs to be
available on site. Multiple tons of biomass must
be harvested, processed, and refined almost
daily. A selected location needs to be able to
handle both, the production of algae as well as
the processing of the end product.
The Institute of Mechanical Engineers suggests
the large-scale introduction of algae cultivation
into the built environment by integrating
growth facilities into the urban fabric.51 While
the growing happens dispersed on available
vertical and horizontal surfaces in discrete
photo-bioreactors, a local, combined energy
center contains and coordinates all processing
and generation. The center is linked up to a
district heating/cooling network as well as the
grid for surplus production. Mixed-use
developments with an energy demand profile
sufficient to merit running a combined heat
and power unit for more than 5,000hrs/yr are
ideally suited for this scheme. The
implementation of this concept is scalable, but
larger processing plants and systems will
benefit most from economies of scale.52
To set scale in perspective, experts suggests
that algal cultivation is primarily indicated
where algae performs multiple functions, such
as CO2 sequestration, wastewater treatment,
and nutrient recovery, because expenses for
cultivation and harvesting do not have to be
adequately offset by increased fuel production
alone.53 Given the growing architectural
interest in algae integration, more research
needs to be conducted on the efficiencies and
scale of algae farming. An interesting question
remains, in how far algae cultivation could
happen on smaller scale and in smart networks
following the trend of other alternative energy
production towards decentralization.
CONCLUSION
The architectural integration of algae
cultivation opens a new dimension to ecological
design by combining carbon neutral/negative
energy production with ecological recycling of
environmental pollutants. With its high
ecological performance, algae production
generates a multi-fold contribution towards
improving the health of the environment. On
the infrastructural scale, it improves the
environmental footprint of power plants,
industrial processes and large urban
infrastructures. As demonstrated in design
projects for innovative parks, it can become
part of the urban landscape. Through urban
and building integration, it can be connected to
the waste stream and exhaust of the existing
urban infrastructure. On the smallest scale,
algae cultivation can potentially improve the
performance of individual buildings, for
example, through the integration of novel
façade technologies.
Besides sequestering CO2, algae can mitigate
other environmental challenges. It treats
wastewater by using the pollutants as nutrients
for its own growth. Algae can grow in waste
and salt water and can be cultivated on
marginal land54; therefore it does not
contribute to the strain on freshwater
resources or compete for arable land with
other crops. On the contrary, as a source for
fertilizer and soil amendment, it helps to re-
establish the nutrient cycle, improve depleted
soil, and reduces the petrochemical fertilizer
production.
These unique benefits of algae cultivation
initiate a rethinking of the relationships
between sunlight, alternative energy and
material recycling. Although currently
monopolized by industrial-scale operations
focusing on the efficiency of biofuel production,
the recent interest by architects and designers
in algae technologies shows that these new
relationships have strong potential for future
development of algae-integrated buildings and
closed-loop systems to mitigate climate
change.
PHOTOSYNTHETIC ENERGY AND ECOLOGICAL RECYCLING 11
ENDNOTES
1 Van der Ryn, Sim, and Stuart Cowan, Ecological
design (Washington, D.C.: Island Press, 1995), 18.
2 Benyus, Janine M., Biomimicry: innovation inspired
by nature. (New York: Perennial, 2002)
3 Van der Ryn, 32.
4 Lim, C. J., and Ed Liu, Smartcities + eco-warriors.
(Abingdon [England]: Routledge, 2010), 19.
5 Schenk, Peer, Skye Thomas-Hall, Evan Stephens,
Ute Marx, Jan Mussgnug, Clemens Posten, Olaf
Kruse, and Ben Hankamer, "Second Generation
Biofuels: High-Efficiency Microalgae for Biodiesel
Production," BioEnergy Research, 1 (1) 2008: 20.
6 Tseng, C. K., "Commercial cultivation," in The
Biology of Seaweeds, ed. C. S. Lobban and M. J.
Wynne. (Oxford: Blackwell Scientific Publication,
1981), 680-725.
7 See: Modern Uses of Cultivated Algae, http://www.
ethnoleaflets.com/leaflets/algae.htm (assessed Sep.
3, 2011)
8 Burlew, John S., ed. Algal Culture: From Laboratory
to Pilot Plant. (1953)
9 ibid, 6-8
10 Oswald, W. J., and C. Golueke, "Biological Trans-
formation of Solar Energy," Advances in Applied
Microbiology, 2 (1960): 223-262.
11 Benemann, John R., Overview: Algae Oil to Biofuel,
NREL (February 2008), (accessed Sep. 10, 2011)
12 Pienkos, Philip T. and Al Darzins, The Promise and
Challenges of Microalgal-Derived Biofuels, AFDC
(May 2009), (accessed Sep. 10, 2011) 436-437.
13 Biomass Program: Algal Biofuels, USDOE,
(accessed Sep. 10, 2011)
14 Schenk, 21
15 Biomass Program
16 See: http://electrictreehouse.com/tag/bioreactor/
(assessed Sep. 3, 2011)
17 Suzanne Goldenberg, "Algae to Solve pentagon’s
fuel problem," Guardian.co.uk, Feb. 13, 2010. http://
www.guardiannews.com/ (assessed Sep. 5, 2011)
18 IMECHE Report: Institution of Mechanical
Engineers, Geo-Engineering Giving Us the Time to
ACT?, London, August 2009, 16.
19 Schenk, 24.
20 ibid, 20.
21 Food supplements and ingredients such as omega-
3 fatty acids or natural food colorants and dyes are
produced from algae.
22 http://en.wikipedia.org/wiki/Algaculture (assessed
Sep. 5, 2011)
23 ibid, 26.
24 http://www.algomed.de (assessed Sep. 3, 2011)
25 IMECHE Report, 16.
26 The algae oil can also easily be mixed with other
fuels such as gasoline or jetfuel.
27 Schenk, 28.
28 To optimize the photosynthetic reaction, most
algae species require indirect, middle-intensity light
levels, which equal a light intensity of 1,000-10,000
lux. Direct sun light causes low efficiencies, photo-
inhibition, or even photo-bleaching (Schenk, 30).
29 Kizililsoley, Mustafa and Helvacioglu, Soner.
“Microalgae Growth Technology Systems.” Soley
Institute Presentation at IIMSAM, New York, NY,
2008, 27.
30 Four geometries are commonly utilized for photo-
bioreactores: tubes, plate, annular and “plate airlift,”
each differently prioritizing surface area, light
penetration, and water mixing speed (Schenk, 33).
31 http://www.algomed.de (assessed Sep. 5, 2011)
32 Pulz, Otto, “Evaluation of GreenFuel’s 3D Matrix
Algae Growth Engineering Scale Unit.” IGV Institut
für Getreideverarbeitung, Sep. 2007, 6.
33 Schenk, 31.
34 In field tests, it exhibited an average productivity
of 98 g/m²/day (Pulz, 11).
35 Schenk, 23.
36 IMECHE Report, 16.
37 See: Giving new meaning to 'livingwall'... http://
www.worldarchitecturenews.com/index.php?fuseacti
on= wanappln.projectview&upload_id=16709
(assessed Sep. 5, 2011)
38 ibid
39 http://www.process-zero.com/ (assessed Sep. 4,
2011)
40 http://www.metropolismag.com/nextgen/ng_story
.php?article_id=4726 (assessed Sep. 10, 2011)
41 ibid
42 Bioreactor expert René Wijffels of Wageningen
University in the Netherlands states that his main
concern for integrating algae production in buildings
is whether the surface area is significant enough.
43 See: MNN: Power plant testing CO2-scrubbing
algae, http://www.mnn.com/earth-matters/climate-
weather/stories/power-plant-testing-co2-scrubbing-
algae (assessed Sep. 5, 2011)
44 See: PORT CARBON TAP competition boards,
http://portarchitects.com/project/urban-algae/
(assessed Sep. 4, 2011)
45 http://www.algaewheel.com/algaewheel-
technology/ (assessed Sep. 10, 2011)
46 http://continuingeducation.construction.com/article.
php?L=227&C=698&P=1 (assessed Sep. 10, 2011)
47 Green Power House is located at the lumber mill of
F.H. Stoltze Land and Lumber Co. near Columbia
Falls, Montana.
48 See: BioCycle article: http://www.jgpress.com/
archives/_free/002388.html (assessed Sep. 5, 2011)
49 See: Benemann, John R., MICROALGAL BIOFUELS:
A BRIEF INTRODUCTION, http://advancedbio
fuelsusa.info/wpcontent/uploads/2009/03/microalga
e-biofuels-an-introduction-july23-2009-
benemann.pdf, (assessed Sep. 6, 2011)
50 ibid
51 IMECHE Report, 14-19.
52 IMECHE Report, 17.
53 Benemann
54 Schenk, 23