Rooftop vertical aquaponics systems for sustainable urban farming

Unlike traditional farming, an urban farming is the practice of cultivating crops either in indoor or outdoor spaces of the buildings. It refers to the farming activities in urban areas, which are commonly used for income or food. The rooftop vertical farming helps to overcome limited agricultural land use such as Singapore. Food security is a global concern that refers to the availability, accessibility, and stability of safe and nutritious food. As such, urban farming would help transform the agri?food industry into one that is highly productive and employs climate?resilient, resource?efficient, and sustainable technologies, thereby contributing to Singapore’s ‘30 by 30’ goal set by the Singapore Food Agency ? to reduce reliance on food imports and sustainably produce 30% of the country’s nutritional needs by 2030. Aquaponics has recently emerged as a sustainable and innovative agricultural system to produce plants and fish simultaneously to conserve land and water. It combines a Recirculating Aquaculture System (RAS) and hydroponics. It involves a process known as nitrification, whereby ammonia from fish waste is oxidized into nitrite by ammonia oxidizing bacteria, and converted into nitrates by nitrite oxidizing bacteria, mainly Nitrobacter spp. and Nitrospira spp. The nitrates and other residual nutrients are then taken up by the hydroponic plants. The symbiotic relationship in an aquaponics system may improve nutrient retention efficiency, reduce water usage and waste discharge to the environment, and increase profitability by simultaneously producing both fish and vegetables.   Aquaponics systems with optimized operating conditions to balance required amount of nutrients between fish and vegetables growing contribute to increase local food production and sustainable urban farming.