Life cycle assessment of a decoupled biofloc aquaponics facility across seasons

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

Submitted to: Journal of Cleaner Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2023
Publication Date: 10/22/2023
Citation: Kalvakaalva, R., Smith, M., Prior, S.A., Runion, G.B., Ayipio, E., Blanchard, C., Wells, D., Blersch, D., Adhikari, S., Prasad, R., Hanson, T., Higgins, B.T. 2023. Life cycle assessment of a decoupled biofloc aquaponics facility across seasons. Journal of Cleaner Production. 429:139356. https://doi.org/10.1016/j.jclepro.2023.139356.
DOI: https://doi.org/10.1016/j.jclepro.2023.139356

Interpretive Summary: Global population growth spurs advancement in methods to provide sufficient, nutritious food while reducing environmental impacts. Aquaponics, a system that uses aquaculture wastewater for hydroponic plant production is a solution to environmental shortcomings of traditional aquaculture. We used life cycle assessments (LCA) as a “cradle-to-grave” approach to quantitatively assess environmental impacts. This study utilized a process engineering model to aid in scenario analyses, which allowed for tracking of water, carbon, and nutrient flows, and also included direct greenhouse gas emission (CO2, CH4, and N2O) from unit operations since other LCAs had not included these or made emission factor assumptions. Including these direct emissions enabled comparison of direct facility emissions versus emissions from upstream inputs such as electricity and fish feed.

Technical Abstract: Aquaponics promises a more sustainable approach to food production by repurposing waste from aquaculture for production of crop plant. Previous life cycle assessments have been published on the environmental impacts of coupled aquaponics using recirculating aquaculture systems, however, impacts from decoupled biofloc aquaponics systems remain unknown. Decoupled systems offer many operational advantages over coupled systems, and the objective of this study was to use life cycle assessment to quantify their environmental impacts. Data from a multi-greenhouse aquaponics system was collected over a one-year period to generate a life cycle inventory. A previously published mass balance model was also used to analyze alterative operational scenarios. Both avoided burden and mass allocation approaches were considered given the high sensitivity of the model toward the former. Results showed that electricity, heating fuel, and feed made up 40%, 22%, and 24% of global warming potential (GWP), similar to other aquaponics studies. These inputs similarly dominated cumulative energy demand. A switch to renewable electricity sources could reduce GWP by over 40% in scenario analysis. Eutrophication impacts of the decoupled biofloc aquaponics system ranged from 8.93x10-3 to 5.27 x10-2 kg N-eq per kg fish depending on the scenario. While better than aquaculture alone, these rates were over four times higher than coupled aquaponics due to discharge of nutrient-containing waters after plant production. Efforts to balance fish and plant production are especially critical in decoupled systems, as is re-use of post-plant effluent. These results show that careful consideration of operational decisions is important when trying to minimize the environmental footprint of decoupled aquaponics systems.