Direct greenhouse gas emissions from a commercial pilot-scale aquaponics system

Authors: KALVAKAALVA, ROHIT - Auburn University; Prior, Stephen - Steve; SMITH, MOLLIE - Auburn University; Runion, George; AYIPIO, EMMANUEL - Auburn University; BLANCHARD, CAROLINE - Auburn University; WALL, NATHAN - Auburn University; WELLS, DANIEL - Auburn University; HANSON, TERRILL - Auburn University; HIGGINS, BRENDAN - Auburn University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2022
Publication Date: 10/27/2022
Citation: Kalvakaalva, R., Prior, S.A., Smith, M., Runion, G.B., Ayipio, E., Blanchard, C., Wall, N., Wells, D., Hanson, T.R., Higgins, B.T. 2022. Direct greenhouse gas emissions from a commercial pilot-scale aquaponics system. Journal of the ASABE. 65(6):1211-1223. https://doi.org/10.13031/ja.15215.
DOI: https://doi.org/10.13031/ja.15215

Interpretive Summary: Little attention has been given to the direct greenhouse gas emissions (GHG=CO2, CH4, N2O) from non-traditional systems such as aquaponics. Findings from this study shed light on how operational variables can affect direct GHG emissions from an aquaponics facility. Based on our results, we recommend the use of non-organic substrates for plant growth to reduce CO2 emissions. Likewise, we also recommend avoiding the addition of citric acid or other organic carbon sources to prevent additional N2O production and denitrification. Within clarifiers, we suggest implementing a faster separation process with frequent solid removals to avoid anaerobic conditions and reduce CH4 emission. Information from this study will aid in calibrating a mass-balance process model to track nutrient flows under changing operating conditions. Most importantly, this study will allow for a basic framework to quantify direct GHG emissions from other types of aquaponics systems.

Technical Abstract: Agricultural production systems have been known to be a large contributor to global greenhouse gas (GHG) emissions and many studies have focused on the mitigation of trace gas emissions from open field and other traditional crop production practices. Little attention has been given to the direct emissions from non-traditional systems such as aquaponics. Here we determine the direct trace gas emissions (CO2, CH4, N2O) from a semi-commercial aquaponic facility located in Auburn, AL. We also determine how emissions from unit operations differ based on a series of parameters. The system included a fish tank which held tilapia, a solids settling clarification system, and a climate controlled greenhouse in which cucumber plants were grown in substrate. The study was separated into three seasons in which the first sought to find differences based on pH treatments and the last two sought to compare differences between Perlite and pinebark substrates. Measurements indicated differences between aerated and non-aerated portions of the fish tank and high CH4 levels from the clarification system which indicated anaerobic activity. Results from the plant study showed significant relationships with various selected parameters with pH having a negative correlation with N2O efflux and pinebark averaging higher CO2 efflux values compared to the Perlite substrate. This study begins to address recommendations for better management practices, as well as provides a framework for future studies on aquaponic systems.