Energy and water use of a small-scale raft aquaponics system in Baltimore, Maryland, United States

Abstract

Aquaponics is a form of aquaculture that integrates hydroponics to raise edible plants and fish. There is growing interest in aquaponics because it can be practiced in non-traditional locations for agriculture such as inside warehouses and on marginal lands, and it can provide locally grown products without using synthetic pesticides, chemical fertilizers, or antibiotics. Yet questions remain about the ecological and economic sustainability of aquaponics. The objective of this study was to describe the operating conditions, inputs (energy, water, and fish feed) and outputs (edible crops and fish) and their relationship over two years for a small-scale raft aquaponics operation in Baltimore, Maryland, United States. The system had roughly 1% water loss per day and used an average of 35,950L for replenishment per year. Predicted values suggest rainfall could completely replace the existing water needs. The average energy use was 19,526kWh for propane and electricity per year at a cost of $2055 US dollars. The largest uses of electricity were in-tank water heaters. Comparing inputs to outputs, 104L of water, 0.5kg feed, and 56kWh energy ($6 in energy costs) were needed to produce 1kg of crops; and 292L of water, 1.3kg feed, and 159kWh of energy ($12 in energy costs) were needed to produce a 1kg increase in tilapia. Raising tilapia was a net loss, while raising crops was a net gain when comparing market prices to energy costs. Understanding energy, water, and feed use in aquaponic systems is essential to inform farm business plans. These data can serve as a point of comparison to other small-scale aquaponic systems, and inform future work on life cycle assessments of aquaponics.