| Recirculating aquaculture systems (RAS) accumulate large amounts of nitrate due to the conversion of ammonia waste products into nitrate via microbial nitrification. High nitrate levels have been shown to negatively impact the health of many aquaculture species. A sustainable option for nitrate removal in RAS is assimilation into plant biomass through the use of integrated constructed wetland systems. A dynamic optimization model was developed to determine the optimal operation of a horizontal sub-surface flow constructed wetland (HSSF-CW) leading to minimal freshwater lost to evapotranspiration, while maintaining a target concentration of total inorganic nitrogen (TIN) in the RAS.;Bench and pilot-scale studies were carried out to determine weekly TIN recovery and evapotranspiration rates of Salicornia, which were used in the dynamic optimization model. Bench-scale TIN assimilation ranged from 79-89 g m-2 yr-1, with a water budget of 1,300-1,360 L m-2 yr-1, based on a weekly initial concentration of 20 mg L-1. The pilot-scale HSSF-CW removed an average of 81% TIN, 72% total nitrogen, 68 % PO4, 77% total suspended solids, and 82% volatile suspended solids per 6-day run, with effluent alkalinity increasing an average of 43%, and pH increases of 0.4. Fresh-water lost to evapotranspiration was 6.2 L m-2 d -1, with an additional 21 L m-2 retained in the wetland after each run.;The rates of evapotranspiration and nutrient assimilation exhibited significant seasonal variation. Nutrient assimilation closely followed first order reaction kinetics, suggesting that pollutant assimilation over time could be modeled accordingly. Increases in the alkalinity and pH of the effluent could contribute to offsetting decreases in the pH and alkalinity encountered in a RAS via nitrification. The ability of the wetland to harvest rainwater would also make up for much, of the water lost to evapotranspiration. The model developed in this study can assist in the optimal design and management of an integrated RAS/HSSF-CW system by determining the size of wetland needed to maintain target water quality parameters for a given fish/shrimp biomass, and indicating the optimal times for running effluent through the CW over the course of a year. |
