Title: "Duckweed in space: as a food source and life support " Abstract: This presentation will be given by a master student of the Energy & Environmental sciences from the University of Groningen. During my thesis on duckweed (a very small and fast-growing floating aquatic plant), limitations to biomass production were encountered that may be averted in space. When growth of duckweed is possible in microgravity, the area available for plant growth is substantially higher in microgravity environments than on Earth due to water sphere formation. Duckweed has characteristics that make this plant a suitable candidate for an ecological-based life support system. An indication will be given for the amount of duckweed needed to perform basic life support functions and simultaneously providing a food source, as well as the possible pros and cons of using duckweed to provide these necessities.

1. 1|04-01-2018
1|04-01-2018
Duckweed in space
as food source and life support
Cleo Offers
Energy and Environmental Sciences
University of Groningen
Cleo.offers90@gmail.com

2. 2|04-01-2018
About me
› Bachelor Marine Biology
› Master-student Energy & Environmental sciences
› Center for Energy and Environmental Sciences, IVEM
› Currently working on thesis: duckweed as nitrogen cyclers
in the Dutch dairy system
› Interests: exobiology, biomimicry, agro-ecology, (aquatic-
)ecosystems

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What is duckweed?
› Smallest flowering plant
› Very fast growing
› Protein rich (up to 45% dry weight)

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What is duckweed?
› Optimal temperature 26°C
› Grows under low light: 20 MJ / m2
› High nutrient loading tolerance: nitrogen

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Nitrogen cycle

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Thesis research question: can duckweed
improve N-cycling?
(Parabel)
Manure
Duckweed pond
Protein-rich feed:
substitute for soy?
Local production
and nutrient cycling

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Thesis outcomes
› Nutritional value duckweed
› ↑ Sustainability feed
› Improved (local) N-cycling
› Large area needed
› Biomass production depending on weather
› System not perpetuating
› Heavy metal build-up

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Why growing duckweed in space?
› Controlled growth environment
› Converting waste streams
› CO2 conversion and O2 generation
› Food
› Increase self-sustainability of shuttle/station
› Advantages of space: more energy (?) and growth
area limitation may be solved: spherical growth

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Water in space: spheres to grow
duckweed upon?
Water forms a sphere in microgravity
Duckweeds may orientate
themselves as ‘micelles’
Hydrophobic leaves
Hydrophilic roots

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Duckweed life support system

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Example of a possible growth system
CO2
Heat
O2
Grey water + some duckweed
Duckweed
Light
Cleaner water

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Radiation
› Incorporation with water wall: + radiation shielding
› Absorbed radiation in low Earth orbit: ~6 mGy day-1

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Daily protein demand and availability
Based on daily urine nitrogen excretion of 11 g pppd

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Daily caloric demand and availability
› Based on protein demand

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CO2 absorption and O2 generation
› Humans exhale daily 1.18 kg CO2
› Consume 0.86 kg O2

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Area required
› 35 m2 in spheres: 7000 · Ø 4 cm ≈ 234 L
› 5 m2 in spheres: 1000 · Ø 4 cm ≈ 33 L

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Further beneficial characteristics
› N-fixating bacteria associated with duckweed
› (Luxury) uptake of Ca and P

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Pros and cons
› Resource savings
› Wastewater treatment
› Optimal growth conditions
achievable
› Relying on organisms for life
support
› Build-up of unwanted
substances through continued
cycling
› High water content
› Processing needed

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Feedback and questions
› Are there questions?
› You think this is a good
idea? Why (not)?
› Thank you for your attention!

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Life support: CO2 uptake
› Humans exhale ± 1.2 kg CO2 pppd
› Duckweed takes up ± 11 g CO2 MJ-1 light
Assume 20 MJ m-2 day-1 light is absorbed
› ± 220 g CO2 m-2 day-1
Large margin; CO2 absorption value for area with full
biomass coverage
› ~6 m2 duckweed pppd needed =
500-1250 small spheres (r = 2.5 cm) total 10-30 L
volume or:
125-300 spheres (r=5 cm) total 30-80 L

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Life support: O2 generation
› Humans need ±0.9 kg O2 pppd
Multiply absorbed CO2 with
32
44
> 220 g CO2 m-2 day-1*
32
44
= 160 g O2 m-2 day-1
› Duckweed area needed is ~6 – 15 m2 pppd
› Conventionally: electrolysis of ~2 kg H2O pppd

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Life support: food
› Duckweed ~2250 kcal per kg (dry weight)
› Growth per day ≈ 100 g dry weight m-2
An area of approximately 10 m2 is needed to fulfill daily caloric
requirements of one astronaut.
But: that would yield ~450 g protein

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Plant protein production from urine
nitrogen
› Daily ~11 g N excreted in human urine
› Plant protein formation: 11 · 6.25 = 68.25 g protein
› Humans need 0.8 – 1 g protein per kg body weight
per day

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LED lights and plant chlorophyll
absorbance

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Calorific demand
kcal of 2.8 burgers = 25 kg lettuce ≈ 1 kg dried duckweed

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Thesis problem: linearity dairy system
Manure
Eutrophication
Mass cultivation of soy in S-America
Soy as protein-rich cow feed

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Duckweed as nitrogen cyclers in the
dairy system
Excretion
± 175 kg N cow-1 year-1
1000 MJ m-2 year-1
10 000 GJ ha-1 year-1
(NL)
1400 kg DM ha-1 year-1
Max.110 kg N uptake ha-1 year-1
1 ha N uptake capacity: 0.6 cow year-1
Feed demand = ± 1400 kg protein cow-1 year-1
Duckweed production = max. 680 kg protein ha-1 year-1
= enough protein for 0.5 cow year-1
Duckweed
Cow
Available sunlight for
duckweed growth [NL]

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Nitrogen flows
NH3
volatilization
NH4 & NH3 uptake
Manure degradation
Bacteria N2 fixation
Protein production
Toxic to most other plants
Greenhouse gas

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Concept: aquaponics + duckweed
› Ammonia and CO2 excreted by fish
› Duckweed can bypass bacterial NH3conversion
› Less N loss from system
› Producing feed within-system
› Ecosystem mimicking

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Image from https://science.nasa.gov
Conventional life support system

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Space agriculture
› Root anchoring needed
› LEDs, controlled environment
› Area is limited
› Nutritional value of crops very low
› Psychological value: fresh food

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Why this presentation?
› Came up with an idea during my thesis: growing
duckweed in space
› Want to check it’s viability and I would like your
feedback!

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