Nutrient Transfer in Aquaponic Systems – Optimizing microbial processes for greater circularity and economic viability

Abstract

The trend towards sustainable process design in modern industries combines the goal of improving process efficiency with a conscientious shift towards resource conservation. Aquaponics, a system that involves co-cultivating fish and plants, is a waste-conscious food production system. The primary system inputs - water and fish feed - are supplied to the aquaculture component and then transferred downstream to an area of plant cultivation. The upstream aquaculture component is organized in the form of a recirculating aquaculture system (RAS), while the downstream portion is most often a hydroponic greenhouse and as such takes the form of two recirculating loops that have a variable degree of connectivity. Aquaponics, just as its parent fields of aquaculture and hydroponics, falls under the umbrella of closed environment agriculture (CEA) systems. Unlike aquaculture and hydroponic cultivation systems, aquaponics relies heavily on endogenous microbial communities to remineralize nutrients and eliminate fish-toxic waste products. To date, efforts to improve nutrient use efficiency in aquaponic systems have primarily focused on nitrogen metabolism within the biofilter, with research around the utilization of other nutrient streams (solid waste) relegated to waste disposal. This dissertation addresses this shortcoming by investigating the processes underlying microbial colonization and nutrient remineralization in aquaponics, along with an analysis of the potential to improve system efficiency and sustainability through solids revalorization. These efforts demonstrate the capacity of bioprocess innovation to bridge the commercialization gap that has thus far limited widespread adoption of this type of high intensity, yet sustainable, food production systems. While there are already hundreds of aquaponics operations developing globally, achieving industrial scale production at similar scales to land-based aquaculture and hydroponic facilities has yet to be accomplished. Therefore, this dissertation aims to better understand nutrient flows and remineralization and how they can be utilized to improve food production and resource-use efficiency. Chapter 2 discusses how plants can guide microbial colonization in aquaponic systems, Chapter 3 reviews the advent of ecosystem-specific microbiota and microbiome databases, Chapter 4 introduces a novel nutrient remineralization system that converts fish solids into a fertilizer for CEA, and finally, Chapter 5 expands this technology to include the generation of methane from fish solids. In conclusion to these four chapters, a discussion section contextualizes the experiments within the larger umbrella of microbial and nutrient flow and how this relates to sustainable process design.