A future powered by algae?
There are lots of astonishing things that algae can do: they are a vegetable that doesn´t need fertilizers, irrigation or farmland; a source for bio-fuel that doesn’t compete with land crops; and a plant that grows and soaks up CO2 much faster than land plants.
This can sound like an all-in-one solution ready to solve major contemporary challenges like the climate crisis, future food security and ecologically sustainable energy production.
But is it really that easy? What could that look like?
This project aims to share more specific knowledge by rendering fictive scenarios. Hypothetical questions are posed and answered by animated miniature worlds based on researched and calculated data.
How big would algae walls by the highway have to be to soak up all CO2-emissions?
Sources:
total emissions from traffic (germany): 159 000 000 tons/year
total km of german highway ("autobahn"):12.993 km
bioreactor productivity:29 g/day/m²
CO2 capture by algae:1,8 tons of CO2 per ton of algae
Calculations:
m2 of bioreactors ("algae walls") needed: emissions / co2 capture / productivityheight of algae walls: m2 needed / 4 (two walls, double sided) / autobahn kilometers
If we wanted all CO2-emissions from traffic in Germany to be soaked up by growing algae, we would need to build 280m high algae farm walls along all the highways - on both sides. That is about as high as the Eiffel Tower: its tip is 324m high. How we would be to contruct such walls in a stable manner, how to maintain them, and what other effects they would have is open.
With how big of an algae tank could cars be co2-neutral?
Sources:
algae bioreactor productivity:67 mg per litre and day
CO2 capture by algae:1,8 tons of CO2 per ton of algae
CO2 emissions per km driven: 110 g per km
average kilometers driven per year: 14000 km per car per year
Calculations:
daily CO2 emissions per car: emission per km * average kilometers per dayalgae tank needed: daily CO2-emissions / CO2 capture / bioreactor productivity
If a tank full of algae was to compensate the CO2 emissions of a car, that tank would need to be 42m long. Of course the algae produced in that tank would need to be harvested regularly and used productively, because if the algae is let to simply decay, all the captured carbon is released back into the atmosphere during the decay process. A car would also have more emissions if it had to pull along such a long and heavy tank, so in reality, that would require an even longer algae trailer.
How much land could be spared by making E10-fuel from seaweed?
Sources:
yields corn-bioethanol: 2010 l/ha/year
yields seaweed-bioethanol: 23400 l/ha/year
average kilometers driven per year: 14000 km per car per year
pure bioethanol in E10-fuel: 10%
Calculations:
bioethanol per car and year: average kilometers per year * average fuel consumption * 10%
farming area for corn needed: total yearly bioethanol / corn yield
farming area for seaweed needed: total yearly bioethanol / seaweed yield
Producing Bioethanol from seaweed would require less than a tenth of the the surface required for corn-based Ethanol production.
How many electric busses could be powered of bioreactors on the roofs of the pentagon?
Sources:
algal oil productivity:1014 GJ/ha/year
energy needed for electric busses:125 kWh
public bus figures (berlin):300000 km/day in total with 1600 busses
Calculations:
total energy from pentagon roofs: area (~5ha) * productivity
average kms driven per day by one bus: total kms / number of busses
number of electric busses that could be powered: total daily energy / energy per km electric bus / average kms driven by a bus
If all the roofs of the pentagon were covered with algae farms, energy harvested from them could power 18 electic busses around the clock.
How much land and water could everyone spare if they replaced cabbage they ate with sea lettuce?
Sources:
global cabbage production: 71778764 t/year
global land for cabbage production: 2470275 ha
water footprint cabbage: 280 m³/t
world population: 7500000000
Calculations:
average cabbage footprint per person and day: global production * water footprint / world population
total cabbage farmland per person: global cabbage farmland / world population
If we replaced the average cabbage consumption with seaweed, every person would require 3m² less farmland and 7 litres less water per year.
How big of an algae tank would feed astronauts on the way to Mars?
Sources:
nutrition microalgae (porphyridium): 30g fat, 50g carbs, 10g protein
algae bioreactor productivity:67 mg per litre and day
Calculations:
algae tank needed: algae needed per day * 4 astronauts / productivity
A tank with the diameter of a space-craft and a length of about 5m would provide astronauts with a steady production of enough algae to cover their basic nutrition needs.
How fast does seaweed grow compared to corn?
On 2m² of farmland, you can produce about 1kg of corn as opposed to 150kg of seaweed, annually.
For how long would a backpack full with algae supply enough oxygen to breathe?
Sources:
oxygen in space suits:1,5 pounds for 7 hours
algae tank productivity:67 mg per litre and day
CO2 capture by algae:1,8 tons of CO2 per ton of algae
Calculations:
constant algae production in backpack: productivity * volume
O2 produced by backpack: molar mass O2 ÷ molar mass CO2 * CO2 capture * productivity
A 50l backpack full of algae can only produce about 0,1% of the oxygen needed by humans to survive.
How much seaweed soaks up the CO2 of one steak?
Sources:
CO2 emissions per kg beef:27kg/kg
carbon content macroalgae: 30%
molar masses: Carbon: 12 g/mol; CO2: 46 g/mol
Calculations:
co2 absorption macroalgae: carbon content / molar mass carbon * molar mass CO2
co2 emissions per steak: CO2 emissions beef * weight steak
seaweed needed: CO2 emissions steak / CO2 absorption macroalgae
If you wanted to compensate the CO2-emission of a steak with seaweed, you would need to grow and use (maybe also eat?) 35kg of seaweed.
How big would my personal CO2-footprint compensating seaweed farm have to be?
Sources:
carbon content macroalgae: 30%
molar masses: Carbon: 12 g/mol; CO2: 46 g/mol
macroalgae yields: 73 t/ha/year (dry)
Calculations:
carbon fooprint per person and year (german): total: 11,6 t/year
co2 absorption macroalgae: carbon content ÷ molar mass carbon * molar mass CO2
seaweed farm area needed: total CO2 emissions ÷ CO2 absorption ÷ seaweed yields = 0,14ha
For the average person in Germany, you would need a 1444 ha large seaweed-farm to capture your carbon emissions. The produced seaweed would need to be harvested and used productively - if the seaweed is left to dacay naturally, the captured carbon is released back into the atmosphere in the process.