The potential of city rooftops for fish farming and plant cultivation has been explored by an international team of researchers.

In an era of growing urbanisation and increasing food insecurity, urban aquaponics offers an innovative way forward, say Qiuling Yuan and Fanxin Meng from Beijing Normal University, China, who led the study.

Aquaponics is a system that integrates fish farming with soil-free plant cultivation to create a symbiotic relationship between fish and vegetables. Water is recirculated from fish tanks to plant beds, where bacteria convert fish waste into nutrients for plants.

The water is then returned to the fish tanks, creating a closed-loop system that minimises water use and waste. Rolled out at scale, it could enhance urban food security while reducing environmental impacts.

The research focuses on the city of Beijing, as a case study to evaluate the potential of rooftop aquaponics (RA) and ground aquaponics (GA) in terms of water efficiency, energy consumption, and carbon emissions. The researchers identified potential areas for urban aquaponics in Beijing by analysing building types and sizes within the city's built-up areas.

They found that commercial buildings offered the most potential for rooftop aquaponics, with an area of 3.4 square kilometres. Educational and industrial buildings also showed significant potential, covering 2.3 and 1.9 km² respectively.

The study also considered ground aquaponics in suburban areas, where protected agricultural areas could be converted into aquaponics systems.

A life-cycle assessment revealed that both rooftop and on-the-ground systems consumed significantly less water than traditional greenhouses, saving 42-44% of water onsite. However, aquaponics systems required 2.3 to three times more energy and produced 1.1 to 2.1 times more carbon emissions than traditional greenhouses.

Despite these higher energy demands, the farm-to-table approach of aquaponics reduced energy, water and carbon impacts by 14-44% when including off-farm activities.

The study also explored the economic feasibility of urban aquaponics. While the initial costs of setting up aquaponics systems were higher than traditional agriculture, the economic benefits were substantial.

The high selling prices of aquaponics products resulted in incomes eight to 12 times higher than those from traditional greenhouses.

To optimise the sustainability of aquaponics systems, the researchers proposed various strategies, including the use of renewable energy sources, optimised fish feed and improved material choices. Such streamlining could reduce onsite energy consumption and carbon emissions by 80-85 percent.

The study also highlighted the potential for urban aquaponics to increase local vegetable self-sufficiency by 15% and avoid 82% of the energy, water and carbon footprint associated with upstream food supply chains.

The findings of this research underscore the potential of urban aquaponics to transform cities into self-sufficient 'edible cities' with reduced environmental footprints. The study provides a framework for assessing and optimising future agricultural modes, offering insights for urban stakeholders aiming to enhance agricultural sustainability.

The paper Shaping Resilient Edible Cities: Innovative Aquaponics for Sustainable Food–Water–Energy Nexus is available in Engineering journal.