Coupled aquaponics is the integration of recirculating aquaculture systems (RAS) and hydroponic cropping systems (HCS) into one system with shared culture water. Water conservation, revenue diversification, location-independent food production, and a reduced reliance on synthetically derived fertilizer salts have been identified as potential benefits of coupled aquaponic production. Despite these potential benefits, it has been difficult for producers to achieve success at the commercial scale. This review discusses how traditional linear coupled aquaponic system designs are not suited for intensive production due to a lack of scalability and water flow rate optimization to meet the differing requirements for finfish, vegetables, and water treatment with practices commensurate with the individual RAS and HCS industries. An alternative design for intensive coupled aquaponics is presented that utilizes a parallel unit process approach for independent hydraulic retention time optimization of each system component. The production benefits and scaling opportunities for each of the primary components in an aquaponics system are discussed. A review of recently published coupled aquaponics literature demonstrates that a system utilizing a parallel unit process design can result in more intensive fish production and a greater nutrient supply for plant production, leading to the potential for greater economic and space use efficiency.

Coupled aquaponics is the integration of recirculating aquaculture systems (RAS) with hydroponic cropping systems (HCS) into a single system with shared water treatment units. Potential benefits of integration include water conservation, reduced reliance on finite mineral fertilizers, and intensive year-round location-independent production of lean proteins and fresh vegetables. However, coupled aquaponic practitioners have found minimal commercial success to date. This has been mostly due to the use of system designs which are not based on contemporary water treatment principles, especially those for commercial aquaculture. Instead, conventional coupled aquaponic system design has been based on a linear framework assuming fish wastes are readily utilized as plant fertilizers, with minimal emphasis on waste treatment or individual component hydraulic retention times. The result has been economic failures due to misbalancing the cost of inputs, the value of the outputs, and the time required to reach a marketable harvest size for both crops: fish and plants. This manuscript provides theoretical calculations based on existing standards in commercial RAS and HCS for sizing plant, fish, and biofiltration units focused on nitrogenous waste production from fish. Successful integration of HCS and RAS is defined as achieving industry standard production timelines for lettuce (seed to harvest time of 35 days) and Nile tilapia (fry to a 624 g average harvest weight in 35 weeks). Equations and examples to calculate lettuce yield, daily lettuce nitrogen requirement, fish feed rates to achieve specific nitrogen production rates, and fish tank and biofilter volumes are provided.

Controlled environment agriculture (CEA) technologies are required to meet current and future food production demand as the global population rises, arable land decreases, and minerals for fertilizer production are depleted. Hydroponics and recirculating aquaculture systems (RAS) are intensive production methods that can provide season-independent vegetables and seafood in urban settings but are limited by a reliance on fertilizing solutions made from finite mineral reserves and the treatment and disposal costs of nutrient rich effluent, respectively. The development of a capture and reuse system where RAS effluent is solubilized to become plant-available and utilized as a hydroponic nutrient solution would aid both industries and increase food security in urban food deserts. Aerobic mineralization is used in domestic wastewater treatment to reduce solid content and solubilize particulate-bound nutrients. Preliminary studies have also shown that aerobic mineralization can be an effective method for RAS effluent treatment. Aerobic batch reactors were used to mineralize RAS effluent in this study. Suspended solids reduction achieved in the reactors was measured throughout the experiment and the plant-availability of twelve nutrients was determined before and after treatment. It was shown that aerobic mineralization can effectively reduce particulate-bound solids and solubilize nutrients to increase plant utilization in RAS effluent.

Operation and effluent treatment costs are limiting factors for the success of recirculating aquaculture systems (RAS) in meeting seafood demand in the United States. Adopting a capture-and-reuse waste management model similar to terrestrial agriculture farmers would allow RAS farmers to monetize effluent and offset production costs. The moisture content and nutrient profile of RAS effluent makes it a potential option for use as a hydroponic fertilizer. Treatment of RAS waste is needed to mineralize particulate-bound nutrients before becoming a viable hydroponic nutrient solution. Anaerobic treatment (AT), a method used by municipal and agricultural waste treatment facilities to reduce total solids, has been shown to successfully mineralize particulate-bound nutrients from RAS effluent. Continuously mixed anaerobic batch bioreactors were used to evaluate the degree to which AT may mineralize particulate-bound nutrients in solid RAS waste. Concentrations of twelve different macro- and micro-nutrients were analyzed in the waste before and after treatment. Effluent samples were analyzed to determine the fraction of each nutrient in the solid and aqueous forms. This study showed that AT is an effective method to mineralize particulate-bound nutrients in RAS effluent and the mineralization rate data may be used to design a pilot-scaled flow-through RAS effluent treatment system.

Controlled environment agriculture (CEA) optimizes growth parameters for vegetable and aquaculture production and can be used to address growing global food insecurity. Recirculating aquaculture systems (RAS) generate a nutrient-dense effluent that may result in environmental pollution, but with treatment and integration with hydroponic vegetable production may be repurposed as a naturally derived nutrient solution. This work developed a preliminary model using the system feed rate to calculate a plant-essential nutrient discharge rate in RAS effluent. Loading rate equations were created to calculate the daily mass of nutrients entering the system through fish feed, and discharge rate equations were created to calculate the grams of each nutrient discharged in the effluent per kilogram of feed. Data from previous published work were used for validation. The loading-rate percentage discharged for nutrients present in the effluent was between 2.71% and 64.5%, with several nutrients being prominent pollutants and all being required for vegetable growth. This work provides the preliminary framework for calculating nutrient discharge rates, which can be used to mitigate pollution or develop more precise, naturally derived hydroponic nutrient solutions for a circular bioeconomy in CEA.