CAPTURING A WASTED OPPORTUNITY: CHARACTERIZATION OF AQUACULTURE EFFLUENT AS A NUTRIENT SOURCE FOR HYDROPONICS

Aquaculture accounted for 44% percent of the 167 million tons of seafood consumed worldwide in 2014. Capture fisheries have continued to decline at a steady rate, while the aquaculture industry has grown at nearly 6% annually in the last decade. With such growth in the aquaculture industry, there is a correlational increase in the amount of nutrient rich waste produced. In the United States, EPA regulations for wastewater discharge requires expensive and energy intensive treatment to remove excess nutrients from aquaculture effluent before its return to a watershed. Costs associated with waste removal systems can be mitigated through the adaptation of a nutrient rich RAS waste stream into an integrated agricultural production system which effectively monetizes the effluent treatment process. Previous waste-solids capture research suggests that the macro- and micro-nutrients in the captured solids from recirculating aquaculture systems (RAS) exist in equal or greater concentrations than the nutrient profiles required for terrestrial farming. Therefore, nutrient supplementation of aquaculture effluent may not be necessary before integrating this waste stream into hydroponic production systems. Through characterization of wastewater nutrients in terms of plant-availability, optimization of hydroponic productivity, utilization of a waste stream, and economic viability may be improved for aquaculture systems at any scale.

The University of New Hampshire Agricultural Engineering research program is profiling the effluent and culture stream nutrient production from tilapia in RAS. Tilapia will be fed one of three types of aquaculture diets of differing protein contents and the effluents characterized via mass balance analysis. Following nutrient profiling, the feed with the most applicable nutrient profile will be integrated into a coupled RAS and hydroponic system. Understanding plant-availability of nutrients in RAS will enable an engineered approach to optimizing integrated agricultural production systems for environmentally and economically cost efficient nutrient utilization.

Based on the results of the RAS plant-available nutrient production rate characterization, a strategy will be developed to liberate the micro- and macro-nutrients from plant-unavailable form (i.e. organic particulate waste). The goal of this research is to develop and maintain a consistent nutrient solution for the production of plants using hydroponic systems. Stocking density, feed protein content, and nutrient assimilation vary across aquaculture production cycles making it difficult to maintain consistent concentrations of a nutrient solution. Through production cycle management and monitoring Electrical Conductivity (EC), IAFS can simultaneously grow multiple cohorts of fish and plants to maintain constant production which allows for consistent fish and plant production via waste nutrient assimilation. As RAS scales up, the ability to reduce and monetize the waste stream becomes more appealing. Characterization of nutrient production rates combined with system integration results in the recycling of water and nutrients to improve the economic viability and environmental sustainability of RAS technology.