Date of Award

Fall 2020

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Stephen Jones

Second Advisor

Paula Mouser

Third Advisor

Todd Guerdat

Abstract

The United States imports more seafood than any other country in the world. Supporting the development of a sustainable aquaculture industry will allow the United States to meet domestic seafood demand and compete in international markets. However, conventional aquaculture production methods such as pond and net pen systems are limited in capacity to meet the market demands for variety and local production. Instead, recirculating aquaculture systems (RAS) are a promising option for domestic aquaculture expansion. RAS is a controlled environment agriculture production model which is location-independent, offers significant water conservation, and optimizes environmental conditions to maximize fish production year round. Similar to other animal agriculture production facilities, RAS effluents must be treated to prevent pollution in waterways, but the cost of effluent treatment is a primary obstacle for expanding the RAS industry in the United States. Terrestrial animal agriculture producers are able to offset operating costs through the re-utilization and monetization of manures as a fertilizer for land-based crops. Similarly, RAS effluents contain the nutrients required for plant production. However, the high water content of RAS effluents makes the treated waste stream better suited for reuse as a fertilizer in hydroponic cropping systems. The development of a naturally-derived fertilizer from RAS effluents would benefit the hydroponic industry by creating a circular nutrient economy, reducing reliance on finite mineral reserves currently used to make nutrient salts, and by enabling USDA Organic certification for producers to increase crop value and profit margins.

Highly dissolved plant essential macro- and micro-nutrients and low amounts of total organic carbon are two essential characteristics for a successful hydroponic nutrient solution. Additional treatment is required to mineralize particulate-bound nutrients and remove organic carbon before RAS effluent can be a viable hydroponic nutrient solution. Microbial digestion is a commonly used treatment method to mineralize solids and remove organic carbon in municipal and terrestrial agriculture wastes. Using both aerobic and anaerobic microbial digestion treatment methodologies, the objectives of this research were to 1) characterize nutrient mineralization of RAS effluent, 2) characterize organic carbon mass reduction, 3) and evaluate the microbially-treated effluent relative to commercially available hydroponic nutrient solutions. The effluent from a pilot-scale RAS was collected and analyzed to develop a nutrient profile and to determine organic carbon concentrations before and after anaerobic and aerobic treatment in batch reactors. Bioreactors were operated until stabilization was observed in total suspended solids (TSS) concentrations. An evaluation of the nutrient profile and organic carbon concentrations before and after microbial digestion was used to determine the viability of developing a naturally-derived hydroponic nutrient solution from RAS effluent. Results indicated that both treatment methods significantly mineralized particulate-bound nutrients in RAS effluent and successfully reduced organic carbon concentrations. Anaerobic treatment resulted in a 76% reduction in the TSS concentration and a 47% reduction in the organic carbon concentration of the effluent. After anaerobic treatment, the percent of the total concentration that was dissolved increased by a factor of 3.13 for phosphorus, 1.36 for calcium, and 1.24 for manganese. Aerobic treatment resulted in a 62% reduction in the TSS concentration of the effluent. After aerobic treatment, the percent of the total concentration that was dissolved increased by a factor of 1.39 for phosphorus, 1.22 for aluminum, and 1.10 for boron. A significant degree of denitrification was observed in the anaerobic treatment. As a result of denitrification, the nutrient ratios of the anaerobically treated effluent were different than the nutrient ratios of the aerobically treated effluent. The mass reduction of nitrogen via denitrification must be considered when determining which treatment method to use to meet the nutrient needs of a specific crop. RAS waste treatment systems must maximize plant-available nutrient mass while reducing the mass of dissolved organic carbon (DOC). Additional research is needed to optimize bioreactor operating parameters and to support the development of a two-stage effluent treatment system employing both anaerobic and aerobic treatment processes to capitalize on the benefits of both treatment methods.

This research provides a framework for future research focusing on the optimization of RAS waste treatment for use in hydroponic cropping systems.

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