Field investigation and simulation of nutrient control in a fish-hatchery wastewater stabilization pond system
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The aquaculture sector has been the fastest growing animal food producer since the 1970’s. With such a fast growth rate, ecological problems have arisen due to the lack of ability to control nutrient run off in coastal systems. Conversely, land-based fisheries provide an ecologically sustainable solution to controlling the effects of pollution by regulating the effluent wastewater. A land-based fishery’s wastewater stabilization pond system (WSPS) in south-central Ontario, Canada, was characterized for its treatment of phosphorus (P) after experiencing occasional exceedances of their effluent compliance limits. An iron and aluminum oxide based media implemented as an advanced filtration was investigated as a possible treatment solution. Background testing was performed to characterize the water column as well as the sediment-water interface. The WSPS was characterized as two distinct systems. The primary loading system consisted of two slow flow but high concentration of P ponds that remove the majority of P. The primary system also had the greatest potential for P desorption from the sediments if the overlying P concentrations were to change. The secondary system is a polishing system with the majority of the flow but minimal P loading and removal. An iron and aluminum oxide based medium was characterized for its P removal. Three lab-scale tests were run; a short-term semi batch test to predict the maximum P removal using Langmuir’s isotherm, a long-term semi-batch test to quantify the total P removal, and a column flow-through test to better quantify the medium’s P removal as a lab-scale simulation of a field implementation. The medium removed around 9 mgP/gmedia depending on the particle size and contact time. Langmuir’s isotherm severely under predicted the maximum removal capacity in comparison to the long-term physical tests. A hydrodynamic simulation coupled with a water quality model was developed to investigate the impacts on the WSPS if the advanced P filtration system using the proprietary medium previously investigated was implemented. The maximum treatment flow modelled without significant continuity errors removed 31.8% of the inlet P load. Suggestions for siting the advanced P filtration system have been discussed based on the needs of the fishery.