Agro-urban Architecture

The increased competition for land between cities and agricultural areas, the increasing use of renewable raw materials and the scarcity of fossil fuels are forcing us to rethink current energy, agricultural and urban planning concepts. Up until now, urban agriculture has predominantly taken place on horizontal areas in the form of small-scale urban gardening or, on a larger scale, as agricultural areas in towns and cities. Also possible are vertical forms of agricultural production in multi-storey buildings. For economic, urban food production, recycling aspects and the intelligent networking of material flows such as thermal energy, waste water, exhaust air and emissions, as well as for the flexibility to produce not only basic nutrition but also health-oriented, functional foods, active ingredients and recyclable materials are of fundamental importance. They require the development of new agricultural areas through intelligently-networked microagricultural systems with multifunctional application potential.

Algae bioreactor for the facade
As part of the “Resource Efficiency” research focus of the Augsburg University of Applied Sciences, an industrial photobioreactor for the cultivation of algae on buildings has been developed with cooperation partners in the Federal Ministry of Education and Research's project “Next Generation Biofilm”. Conventional agriculture with typical agricultural plants can only be practised on vertical surfaces with considerable effort. A viable alternative is the combination of microalgae as agricultural plants and photobioreactors as vertical agricultural systems.

Microalgae have a high protein, vitamin and mineral content and are therefore suitable, for example, as a food supplement and for pharmaceutical use, but also as a high-quality fertilizer for food production. In an algae bioreactor, biomass is produced under solar radiation by adding CO2 and a nutrient medium or water, and is subsequently harvested. Previous techniques, mostly involving microalgae in liquid (submers), are less efficient in terms of resource and energy consumption. New possibilities are opened up by airborne (emerse) processes with terrestrial microalgae. Compared to conventional algae bioreactors, the use of aerosols (mist) can reduce water consumption by around 90 % water and energy by 20 – 40 %, because mixing and drying processes are no longer necessary. In addition, the air-guided bioreactors are only around half as heavy as their submerged counterparts. This makes them suitable for subsequent wall mounting or as a replacement for existing facades.

Reactor types for building integration
Various reactor types were analysed in the project, including freestanding systems as well as reactors inside buildings and facade-integrated solutions. Building integration was researched under the biotechnological conditions for algae production using plate, foil, hollow-chamber and tube reactors. In addition to the design function, the reactors can also perform additional technical functions in the building such as filtering the air, converting carbon dioxide into oxygen and contributing to thermal insulation.

The thermally-insulated elements provide shading and have an adiabatic cooling capacity due to the atomisation of the nutrient medium. As a result of the research in the laboratory, an initial facade demonstrator in the form of a tubular reactor has been created. The system is easy to control and can be compared to conventional aquatic systems. Another type based on hollow chamber reactors is currently being developed. During the research project, various cultivation and harvesting methods were also tested. In the current prototype, the algae grow directly on the inner surfaces of the glass tubes. The aerosol, which supplies nutrients and liquid, is generated with an ultrasonic atomizer and distributed with the aid of a fan. This creates negative pressure in the closed system so that the aerosol is directed through the reactor. The condensate is collected again and can be reused. Light is a decisive factor for the growth of micro-organisms, which is why the fronts of the steel construction are fully glazed. To protect the reactor from overheating in the summer, the irradiation can be reduced using switchable electrochromic glazing or the adiabatic cooling capacity increased through additional evaporation. The control unit, which contains all the technical components, is located below the meander-shaped glass tubes.
 

Urban agriculture of the future
In order to investigate the actual installation situation on the facade, the reactor element will be installed as a facade-integrated variant in a window soffit of the Augsburg University of Applied Sciences and monitored metrologically. Factors contributing to the broad implementation of microagricultural systems in urban spaces will be analysed in a follow-up project. The use of photobioreactors in buildings enables the selection of the optimal microorganisms for each location, the adjustment of their growth conditions and the use of constructional synergies and existing material flows. In order to produce biomass as economically as possible and to optimise integration into an urban environment, aspects such as urban development, architectural integration, energy and material flow networking and technical and biological systems should be further explored.