Denitrification Woodchip Bioreactor Treatment of Wastewater From Land-Based Recirculating Aquaculture Systems.

Denitrification “woodchip” bioreactors are a natural treatment technology ideally suited to mitigate point and non-point sources of nitrate from multiple types of agriculture and industry. A new application for “managed denitrification” practices is the treatment of the small, concentrated outflows from recirculating aquaculture systems (RAS). As aquaculture is the fastest growing segment of global animal agriculture production, land-based, closed-containment RAS are poised to significantly contribute to the market-driven demand for responsibly produced seafood. However, the “environmentally-friendly” marketability of these systems depends upon their ability to treat waste and mitigate negative point-source water quality impacts. Denitrification bioreactors  are a  potentially ideal treatment option for RAS wastewater as (1) nitrate-nitrogen is the primary effluent water-quality concern, (2) effluent water temperatures are fairly consistent (>10 ºC), and (3) controlled effluent flow rates allow for a consistent design hydraulic retention time.  This poster describes The Conservation Fund Freshwater Institute’s recent activities in the area of woodchip bioreactors for RAS wastewater nitrate mitigation. Six bioreactors, designed in triplicate, each receive wastewater from a closed-containment aquaculture system that produces 22 tonnes of fish annually. A design procedure for agricultural drainage bioreactors in Iowa was modified to design these bioreactors for a consistent retention time. This work-in-progress study will provide insight into woodchip bioreactor design criteria for treatment of RAS wastewater and an overall feasibility assessment of this novel treatment process for aquaculture production systems.