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ARS Home » Southeast Area » Auburn, Alabama » Soil Dynamics Research » Research » Publications at this Location » Publication #383693

Research Project: Enhancing Production and Ecosystem Services of Horticultural and Agricultural Systems in the Southeastern United States

Location: Soil Dynamics Research

Title: Mass-balance process model of a decoupled aquaponic system

item KALVAKAALVA, ROHIT - Auburn University
item SMITH, MOLLIE - Auburn University
item AYIPIO, EMMANUEL - Auburn University
item BLANCHARD, CAROLINE - Auburn University
item Prior, Stephen - Steve
item Runion, George
item WELLS, DANIEL - Auburn University
item BLERSCH, DAVID - Auburn University
item ADHIKARI, SUSHIL - Auburn University
item PRASAD, RISHI - Auburn University
item HANSON, TERRY - Auburn University
item WALL, NATHAN - Auburn University
item HIGGINS, BRENDAN - Auburn University

Submitted to: Agricultural Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2023
Publication Date: 8/21/2023
Citation: Kalvakaalva, R., Smith, M., Ayipio, E., Blanchard, C., Prior, S.A., Runion, G.B., Wells, D., Blersch, D., Adhikari, S., Prasad, R., Hanson, T., Wall, N., Higgins, B.T. 2023. Mass-balance process model of a decoupled aquaponic system. Agricultural Systems. 66(4):955-967.

Interpretive Summary: Little attention has been given to constructing detailed mass-balance models of non-traditional systems such as aquaponics. Data collected over a full calendar year included weekly water quality, greenhouse gases, system water flows, and biosolid nutrients were used for the model. Four separate model variations were created to account for seasonal changes. The model was also able to predict nitrate, phosphate, and formation of N2 gas. The model was able to predict changes in system outputs based on upstream operational changes with some limitations.

Technical Abstract: Nitrate and phosphate contained in aquacultural effluents are known to have adverse environmental effects in the form of eutrophication. Aquaponics presents a viable solution to many issues faced by aquaculture fish production via utilizing nitrate and phosphate rich effluent for crop production. Herein, we present a mass-balanced process model based on a large pilot-scale aquaponics facility growing Nile Tilapia and cucumbers in Auburn, AL to better understand how upstream operational changes affect downstream processes. This includes changes to makeup water and feed inputs to help simulate fish, sludge and cucumber yields, as well as greenhouse gas emissions (GHG) and soluble nutrient concentrations. Data were collected from the aquaponics system for a full calendar year and included weekly water quality and GHG sampling and daily metering of system water flows. Biosolids were also collected from the system for elemental analysis and formed the stoichiometric basis for the process model (in addition to soluble nutrient and greenhouse gas data). The resultant stoichiometric mass-balance was used to drive processes within the model constructed using SuperPro designer software. Four separate model variations were created to account for seasonal changes in parameters. The model was run based on weekly (approximate) parameters that coincided with weekly water sampling. Model outputs from the three unit procedures (fish tank, clarifier, and sumps) for nitrate averaged ~440, 441, & 307 mg/L and 25, 27, & 20 mg/L of phosphate. This was compared to a measured average of 442, 406, & 298 mg/L of nitrate and 31, 31, & 20 mg/L of phosphate. The model was also able to predict N2 gas formation as well as irrigation rates based on set stoichiometry and flow splitting, respectively. The constructed model shows promise in predicting changes in system outputs based on upstream operational changes with some limitations. Thus, the model can be recommended for predictions across large time scales.