We’re pleased to share the Seasteading Institute(TSI)’s Guest Blog article written by Rutger De Graaf-van Dinther. Rutger is the co-founder of DeltaSync and Blue21, which are determined to realize the first sustainable floating islands in French Polynesia. His scientific vision is also featured in the Seasteading book published by Joe Quirk.
How cities will save the rainforests with floating production
Cities use vast areas of agricultural land all over the planet for their energy and food supply. To achieve the Paris climate agreement, even more space is needed to capture all the CO2 that cities produce. By implementing floating algae production systems, cities can find this space and even save huge areas of agricultural land. This is shown by a recent study of Blue21, Rotterdam University of Applied Sciences and TU Delft who evaluated the potential of these systems in two very different coastal cities: Rotterdam and Manila. Rotterdam can save 12 times its own area. For Manila, 74 times the city area in agricultural land can be saved. These particular saved areas do not have to be created by cutting rainforest or cultivating other nature areas. Therefore, if coastal cities all over the world would start using floating production, the world’s rainforest can be saved.
Cities: from parasites to solution space
Cities are still huge importers of resources such as food, while they mainly produce waste. Citizens in urban areas also account for the majority of global greenhouse gas emissions. This so-called parasitic metabolism causes various environmental problems such as air and water pollution, CO2 emissions and a high dependency on global networks for critical resources. However, the concentration of people and industries in large cities also make cities a unique solution space for technological innovations. A promising solution for cities to use waste as a resource is using wastewater and CO2 in algae systems to produce biofuel. Algae can fix carbon up to 50 times as fast as land based vegetation. However, in dense urban environments, the space for these systems is often scarce and expensive. The water offers a new perspective here because it can provide the required space for floating algae systems, in particular in coastal cities where a large part of the urban population is located.
How floating algae systems can make a difference
The study of Dal Bo Zanon et al (2017) published in the Journal of Cleaner Production shows how floating algae systems can change the urban parasitic metabolism. Two very different coastal cities were used as case study: the city of Rotterdam, the Netherlands, as developed coastal city and the city of Manila, the Philippines as rapidly developing coastal city. Figure 1 demonstrates the system. Nutrients from domestic wastewater and CO2 emissions from industries are used in open algae ponds with selective environments to encourage the most productive algae (Mooij et al., 2013). The fats that algae produce are used for biofuel production. The proteins are used to feed fish in so-called aquaponics systems. In these systems, the waste excrements of the fish are used for cultivation of fruits and vegetables. Because food and energy production on the water is much more efficient than on land, space on land is saved and CO2 emissions of the cities are reduced.
Towards circular coastal cities
How much food can floating algae systems produce? The calculation model of Dal Bo Zanon shows that cities can produce a large part of their own food. This is contrary to current practice in which cities import almost everything. By using all waste nutrients, floating algae systems can supply 29% of the total vegetal consumption and 20% of the total protein consumption of the city of Rotterdam. For Manila, floating algae systems can provide 22% of the city’s vegetal consumption and 37% of the total protein consumption. Moreover, the model shows that floating production in Rotterdam can be at least 130 times as efficient as land based agriculture. For Manila, the efficiency is even better: to achieve the same food production on land, 189 times as much space would be needed.
Figure 1. How CO2 and wastewater can be productively used by cities (Source: Blue21/ Dal Bo Zanon et al., 2017)
Next steps
Now we have proven the benefits of floating production systems on paper, we want to demonstrate it in practice. The next step is the design and realization of a real-time monitored floating production pilot project to recycle wastewater and CO2 and produce energy and food. For this purpose we are looking for coastal cities all over the world to build the pilot and help them to become more resilient for climate change.
More information
The full study can be downloaded at: https://www.blue21.nl/wp-content/uploads/2017/03/Journal-of-Cleaner-Production.pdf
Acknowledgements
Funding for this study or preliminary studies was provided by Centre of Expertise Deltatechnology, Topsector Water, Municipality of Rotterdam and Blue21.
Literature
Dal Bo Zanon, B, Roeffen, B, Czapiewska, De Graaf-Van Dinther, R.E.; and Mooij, P.R. (2017) Potential of floating production for delta and coastal cities. Journal of Cleaner Production 151, 10-20
Mooij, P.R., Stouten, G.R., Tamis, J., van Loosdrecht, M.C.M., Kleerebezem, R. (2013) Survival of the fattest. Energy Environ. Sci. 6, 3404–3406. doi:10.1039/c3ee42912a
