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Highly efficient bacterial carbon sequestration with the equivalent of 360 trees in just one bioreactor.



Unfortunately I have not been able to update my proposal due to university commitments. I just wanted to inform the judges so that they do not waste time rereading a proposal that has not changed since their original critique. Thank you for this great opportunity to spread ideas.

Cyanobacteria are the only prokaryotes known to perform oxygenic photosynthesis. Responsible for the production of 20-30% of the world's oxygen, these organisms play a very important role in carbon cycling.

These organisms sequester carbon during the day and fix nitrogen at night [1].  Energy for nitrogen fixation is obtained through fermentation which does release CO2, but this gas can be trapped at night and used for industrial purposes such as carbonated drinks and fire extinguishers. However, most of the mass is preserved as biomass.

Excess biomass will be harvested to use as a biofertiliser [2] or to convert into a biofuel. This allows for the continuous culture of bacteria by merely replacing the medium.

At a later stage bacteria will be optimised to produce specific substances. Cyanobacteria have already been shown to produce substances that have antifungal, antiviral and anticancer functions. Hydrogen produced by cyanobacteria could be used in the future as an alternative energy source [3].

What actions do you propose?

1) Isolation of Bacteria and Past Experiments

Isolation of a specific species of cyanobacteria is important because many species produce toxins. A starter culture of Arthrospira platensis and Arthrospira maxima (which make up spirulina) would be bought. These two types of cyanobacteria are most suitable because of the amount of research done into these specific species and because of the many additional benefits (e.g. fertiliser and food source).

With an optimal bioreactor cell concentrations of 4-7g/L can be obtained. A high surface-to-volume ratio allows for optimal exchange of CO2 and uniform mixing. This allows for a net biomass production of up to 24 g/m2/day in summer and just less than half of that in winter. Biomass production can also be improved by controlling the temperatures in winter [4]. In another study, 0.5 g dry cell weight/liter/day was obtained. This was equivalent to 30.2 g dry cell weight/m2/ day [5]. This is a similar biomass to that seen in spirulina production (0.21-0.25 g/L/d) [6].

Your average tree sequesters 4.5-11 kg of carbon annually [7]. Species of cyanobacteria can fix from 0.96 g/L/d to 7 g/L/d of carbon dioxide [8]. This means that just 4.5 L of a culture of Synechocystis (with a fixation of 7g/L) could sequester just as much carbon as a single tree.

An added benefit is that the biomass produced by the cyanobacteria can be used to formulate biofuels and can be engineered to produce other products such as pharmaceuticals [9]. 

2) Bioreactors

In this case a bioreactor is a vessel used to grow cyanobacteria. It ensures optimal growth conditions by controlling air and nutrient flow. 

In more urban areas the focus will be on creating extremely efficient systems that need very little maintenance. The aim will be to create a bioreactor with the maximum surface area possible with a capacity of 1000 L. This would yield 15 kg of biomass every month. The biomass would be harvested automatically and dried out at regular intervals. The time of harvesting would be determined using sensors in the bioreactor itself that would determine the density of the cyanobacteria (too high a density will impede growth). Sensor systems on the bioreactors will feedback information on the efficiency of production and allow for on-the-fly adjustments to heating and lighting as well as to alert collection services when biomass is ready for collection.

Details on how to setup the pump for aeration and harvesting can be found here.

Very low cost bioreactors can be constructed for rural areas using polypropylene bags that can hold between 20 and 40 liters each. This allows for sterile cyanobacterial cultures while still yielding similar biomass outputs per day as open air systems [10]. Urine will be investigated as a suitable medium for these bioreactors to create a very low cost solution at the loss of some efficiency [11]. Agricultural wastes will also be investigated as a source of nitrogen for culture mediums [12]. The aim in rural areas is to bring a source of income to many people who would not have a source of income, but would also be a method to bring fuels to far out areas.

Before harvesting the pH of the medium needs to be at around 10 to ensure that other bacteria would not be growing in the solution. This will be tested using a permanent pH sensor in the urban setting and pH strips in the rural setting.

3) Collection of Dry Cell Mass

Biomass will be collected every month from participating companies and delivered to a central biofuel or fertiliser processing plant. This is, however, not initially the aim of this project and would only be used to offset the maintenance costs of the system. Cyanobacterial cell mass can be used as fertiliser without any additional processing. In order for cyanobacterial cell mass to be converted into a biofuel, however, significant processing will be needed.

4) Optimisation and Engineering

Bacteria will be optimised to sequester the highest amount of carbon dioxide possible. Cyanobacteria can also be engineered for additional functions e.g. with bioluminescence for art installations, biofuel production and to produce certain pharmaceutical products. [13] [14]

Who will take these actions?


Companies that secrete large amounts of carbon dioxide as a part of their ordinary operations can get involved to reduce their net impact on the environment. It would be far easier to host a single culture tank than to plant almost 360 trees.


Governments can get involved to try to help out rural communities. By providing a source of income (through biofertiliser, biofuel or other bacterial products) to people in these areas the government can help to create jobs.

Through mass adoption goverments can reduce net emissions.

Where will these actions be taken?

Large Cities

Large cities will house the urban bioreactors. I believe that the most ideal place to start would be in a developing country in sub-Saharan Africa. This would allow for relatively low labour and development costs and would provide a good basis for a proof of concept.

Later, other cities and multinational corporations can become involved.

Rural Areas

After an initial proof of concept in an urban area, a roll out to a rural area will begin to serve as a proof of concept for further rural development.

How much will emissions be reduced or sequestered vs. business as usual levels?

Carbon Sequestration

Urban bioreactor: 3.5 kg/day, 1277.5 kg/year

Rural bioreactor (40L): 140g/day, 51.1 kg/year

Hydrogen Production

Some cyanobacteria have been shown to produce 30ml of hydrogen/liter culture/hour [15].

Urban bioreactor: 341 kW h of energy per year, 341 kg less CO2 [16]

Rural bioreactor (40L): Not efficient enough to warrant collection of H2.

What are other key benefits?

  • Food Source
  • Fertiliser
  • Source of therapeutics for cancer and infections
  • Energy Source
  • Oil production


What are the proposal’s costs?

Starter Culture

Since the purity of the final product is of concern I would buy my starter culture from a reputable supplier that can ship overseas (such as the National Center for Marine Algae and Microbiota). It would cost $175 [17].

Urban Reactor Culture Medium

Since high efficiency is key in the urban setting a special medium will be used. Investigators found that a revised medium was just as effective as the conventional medium (Zarrouk's medium) but was 5 times less expensive. The cost of the medium would be $16 for 1000L [18].

Rural Reactor Culture Medium

The focus in the rural areas would be to keep the cost of the medium as low as possible. Some previous research has shown that Spirulina grows well in human urine. Agricultural waste can also be added to the medium to provide a better source of nitrogen for the cyanobacteria to grow.

Urban Bioreactor

Polycarbonate tubing will be used. It will cost about $45 per m of tubing that has an internal diameter of 10cm. This has a volume of 40 L. Therefore about 25 m of tubing would be needed ($1125). [19]

Medium will be constantly circulated through the polycarbonate tubing.

The reactor will be placed at an angle and will face toward the south (northern hemisphere) or north (southern hemisphere).

Two pumps will be connected to the bottom of the reactor and will bubble air through the system. These pumps currently cost about $14 each [20].

Arduino basic kit with lux sensor and pH sensor: $200 [21] [22] [23]

Harvest cloth: $?

Total Cost For Reactor: $1353

Maintenance Cost: <$16 per month (medium replacement if needed) + electricity cost

Rural Bioreactor

By just using a polypropylene bag (assume $5) and a pump ($14) (if electricity is available) a simple bioreactor can be created for rural areas [10].

Total Cost For Reactor: $19

pH test strips: $4 [24]

Maintenance Cost: $0 (medium) + electricity cost

Time line

Short Term

Optimisation of 1 bioreactor (growth conditions, medium, species of cyanobacteria)

Involvement of several companies to house bioreactors and participate in a pilot project. Small scale biofuel processing plant using available university facilities.

Further involvement of city and development of single biofuel processing plant. Roll out to rural areas with biomass being used for fertiliser.

Medium Term

Adoption by multiple cities. Mass adoption in nearby rural areas and construction of centralised biofuel processing plant.

Spread to other rural areas with similar model to pilot (fertiliser and other products first, with biofuels to follow at a later stage).

Related proposals

Diatom Algae to consume excess CO2 and Nutrients

Ocean Forests – Global Ocean Restorative Development


Exploring the invisible. Microbiology at Home: A short non-laboratory manual for enthusiasts and bioartists

[1] Stenou A, Bhaya D, Bateson M et al. In situ analysis of nitrogen fixation and metabolic switching in unicellular thermophilic cyanobacteria inhabiting hot spring microbial mats. PNAS 2006;103(7):2398-2403.

[2] Sahu D, Priyadarshani I, Rath B. Cyanobacteria - as potential biofertiliser. CIBTech Journal of Microbiology 2012;1(2-3):20-26.

[3] Abed R, Dobretsov S, Sudesh K. Applications of cyanobacteria in biotechnology. Journal of Applied Microbiology 2009;106:1-12.

[4] Tredici M, Calozzi P et al. A Vertical Alveolar Panel (VAP) for Outdoor Mass Cultivation of Microalgae and Cyanobacteria. Bioresource Technology 1991;38:153-159.

[5] Watanabe Y, de la Noue J, Hall DO. Photosynthetic performance of a helical tubular photobioreactor incorporating the cyanobacterium spirulina platensis. Biotechnology and Bioengineering 1995;47(2):261-9.

[6] Mata TM, Martins AA, Caetano NS. Microalgae for biodiesel production and other applications: a review. Renew Sust Energy Rev 2010;14:217-32.

[7] Akbari H. Shade trees reduce building energy use and CO2 emissions from power plants. Environmental Pollution 2002;116:S119-S126.

[8] Lopez C, Fernandez F, Sevilla J et al. Utilization of the cyanobacteria Anabena sp. ATCC 33047 in CO2 removal processes. Bioresource Technology 2009:5904-5910.

[9] Mollers K, Cannella D et al. Cyanobacterial biomass as carbohydrate and nutrient feedstock for bioethanol production by yeast fermentation. Biotechnology for Biofuels 2014;7(64):1-11.

[10] Sathoyamoorthy P, Shanmugasundaram S. A Low-Cost Bioreactor for Cyanobacterial Biomass Production. Bioresource Technology 1994;49:279-280.

[11] Dao-lun F, Zu-cheng W. Culture of Spirulina platensis in human urine for biomass production and O2 evolution. Journal of Zhejiang University Science B 2006;7(1):34-37.

[12] Markou G, Gerogakakis D. Cultivation of filamentous cyanobacteria (blue-green algae) in agro-industrial wastes and wastewaters: A review. Applied Energy 2011;88:3389-3401.

[13] Abed R, Dobretsov S, Sudesh K. Applications of cyanobacteria in biotechnology. Journal of Applied Microbiology 2009; 106: 1-12

[14] Nozzi N, Oliver J, Atsumi S. Cyanobacteria as a platform for biofuel production. Frontiers in Bioengineering and Biotechnology 2013; 1: 1-6.

[15] Dutta D, De D, Chaudhuri S, Bhattacharya SK. Hydrogen production by Cyanobacteria. Microbial Cell Factories 2005; 4(36): 1-11.


[17] National Center for Marine Algae and Microbiota: Spirulina

[18] Raoof B, Kaushik B, Prasanna R. Formulation of a low-cost medium for mass production of Spirulina. Biomass and Bioenergy 2006;30:537-542.

[19] Polycarbonate prices

[20] Amazon: Tetra Whisper Air Pump (100 gallons)

[21] Adafruit Arduino

[22] Amazon: Light Sensor

[23] Atlas Scientific Sensor Kit

[24] Amazon: pH test strips