Plant and fish production performance, nutrient mass balances, energy and water use of the PAFF Box, a small-scale aquaponic system

Aquaponics is an integrated farming concept that combines fish and hydroponic plant production in a recirculating water system. This food production system promises a reduced environmental footprint when compared to conventional farming systems. However, questions regarding its sustainability remain and there is a lack of data on its performance. A small-scale aquaponic system named PAFF Box (Plant And Fish Farming Box) consisting of a ship container topped by a greenhouse was studied. Plant yield in ebb-and-flow and deep water culture (DWC) hydroponic beds, lettuce, basil and tilapia production capacity and water and energy consumption were investigated. Additionally, all macro-and micronutrient mass balances were analyzed in order to give a better picture of their dynamics and recycling ability. Thanks to the daily inputs of tap water, and 42 g of feed per m(2) of plant beds, DWC beds showed 3-10 fold higher plant yields than ebb and flow. The production of 1 kg of vegetable in DWC consumed 244 L of water and 84.5 kWh of electricity and 1 kg increase of tilapia consumed 278 L and 96.2 kWh. The system was very efficient in water use for fish production but alternative solutions for warming the water and fine-tuned pumping setup are required to decrease energy needs. Key nutrients such as potassium, phosphorus, iron, copper, zinc, manganese and molybdenum, remained low in solution. Nitrate, calcium, boron and sodium concentrations increased quickly and only water exchange could control their accumulation meanwhile a low daily water exchange rate of 3.6% implicated a high nutrient loss in the environment. In the willingness to decrease aquaponics environmental footprint, this study indicates that improved designs could be explored such as decoupled aquaponic systems.