Model-based environmental assessment of aquaponics as a nature-based solution for wastewater use in hydroponics, guided by decision support

Optimising resource-flows such as energy, water, and nutrients from waste streams to a 2nd or 3rd usage can potentially decrease the environmental footprint of agricultural products. With its two main trophic levels, fish in recirculating aquaculture systems (RAS) and plants in hydroponics (HP), the decoupled multi-loop aquaponics system (DAPS) is the first step towards a functioning multi-trophic agricultural production system. The two highly independent controlled environment agriculture (CEA) systems of RAS and HP are highly optimised. Combining these systems, however, creates an imbalance and induces a dynamic problem that can significantly influence both trophic systems. RAS as the upstream sub-system, provides water and nutrients to the downstream HP. The source and demand however have 1) different water quality parameters as pH and nutrient profiles, and 2) processes that underlie different time constants as RAS delivers waste water with a relatively constant rate and composition throughout the year. This often results in the discharge of water and nutrients, creating environmental concerns. Using automated nutrient management systems like NutriSense within aquaponics could minimise or eliminate the need for water and nutrient discharging. In a simulation study with aquaponics production systems, we have compared water and nutrient use in DAPS with and without nutrient-selective management and used HP as a baseline. Simulation data were used to calculate environmental indicators such as water footprint using life cycle assessment (LCA). We conclude that DAPS combined with a nutrient-selective management system is a suitable solution for food production especially in arid regions, in terms of water and nutrient savings.