| The evaluation and modelling of the nitrogen and solids dynamics in recirculating aquaculture systems was carried out in three different parts. The first part evaluated the effect of two settling unit sizes (large and small), three solid removal periods (each 48, 24, or 12-hours), and three percentages of water exchanged (9, 18, and 36% of the total volume) on nitrogen budget, water quality, and fish production performance. The second part evaluated the effect of high (47% P) and low (32% P) protein diets on mass and energy balance and resource use. In the third part of the thesis, the nitrogen and solids models were built, parameterized, calibrated, and validated. The large settling units had higher inorganic nitrogen concentrations and removed lower amounts of dry matter and protein than small settling units. Dissolved oxygen and chlorophyll-a concentrations, pH, water temperature, and fish variables (feed conversion rate, biomass gained, dry matter, and protein retention efficiency) were not significantly affected by the size of the settling units. The level of protein in the diets had a negligible effect on the mass balance of the feed ingredients in the system. The level of protein in the diet also had an insignificant effect on the amount of nitrogen lost from the system. The protein levels in the affected the environmental cost on-farm. The nitrogen model predicted with adequate accuracy (less than 10% of average relative error) the fish nitrogen retained, dissolved nitrogen (ammonia-N, nitrite-N, and nitrate-N concentrations), and the phytoplankton N concentrations, and the phytoplankton N concentrations. The solids model predicted with adequate accuracy (less than 10% of relative error) most of the system solids. Fraction of uneaten feed did not affect the solids accumulated in the system, while an increase in protein digestibility decreased the solids in the rearing, settling, and biofilter units. (Abstract shortened by UMI.)... |
