Low-head, roughing filters for enhancing recycle water treatment for aquaculture

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Summerfelt, Steven
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E. Robert Baumann
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Civil, Construction, and Environmental Engineering

The engineering aspects of producing walleye in recycle culture systems was studied. To recycle (i.e., reuse) the water, treatment processes were required to maintain water quality for the growth and health of the cultured walleye. The major treatment processes were aeration, clarification and nitrification. The goal of this research was to evaluate unit processes for recycle aquaculture systems that are amenable for converting abandoned water and waste water treatment plants into commercial sites for culturing walleye;A three-unit aquaculture pilot plant was equipped for growing walleye from fingerling to food-size fish. The growth of the walleye was observed in two closed-systems and a single-pass system for a period of two years. Normal operating conditions within the closed-systems required water replacement only for solids flushing and evaporation, which was approximately 5-10% of the system volume per day;Within the pilot plant, two clarification processes were used for removing organic solids from the recirculating water: sedimentation basins and roughing filters. The design of the pilot plant permitted the use of a range of hydraulic and solid loading rates to evaluate these clarification processes. Nitrification was evaluated using submerged, static-media, biological filters over a range of hydraulic and ammonia loading rates. Acceptable levels of oxygen and carbon dioxide were maintained by bubbling compressed air through diffusers in the culture tank and in separate columns;A study on nitrification and clarification within submerged, static-media filters indicated that: (1) biofilters had greater nitrification rates than roughing filters acting as their own clarifiers; (2) increased hydraulic loading rate tended to increase the oxygen and ammonia consumption rates within the biofilters; (3) increasing the rate captured suspended solids were removed from the clarification process improved nitrification within the biofilters and overall water quality;The generation and treatment of carbon dioxide within recycle aquaculture systems was reviewed, and design criteria for CO[subscript]2 control within recirculating systems were developed;This research demonstrated that walleye could be grown from fingerling (5-8 cm) to food-fish size in approximately two years within recirculating systems at an average temperature of 24°C.

Fri Jan 01 00:00:00 UTC 1993