|Summerfelt, Steve - FRESH WATER INSTITUTE|
|Davidson, John - FRESH WATER INSTITUTE|
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2004
Publication Date: January 17, 2005
Citation: Summerfelt, S., Davidson, J., Brazil, B.L. 2005. Net dissolved organic carbon production in recirculating salmonid culture system. Aquaculture America Conference. Book of Abstracts 2005 Pg 441. Technical Abstract: Ozonating a coldwater recirculating system (RAS) can help control the accumulation of fine suspended solids, micro-organisms, and components of dissolved organic carbon (DOC) that can negatively impact fish health and production efficiency. Ozone can oxidize relatively large non-biodegradable organic molecules and produce smaller and more readily biodegradable molecules as well as induce micro-flocculation of fine solids, which enhances their removal from the recirculating water. Ozone can also inactivate micro-organisms when a dissolved ozone concentration can be maintained for a sufficient time. However, maintaining a dissolved ozone concentration for a given time requires overcoming the reaction kinetics of dissolved ozone decay, which is dependent upon the concentration of ozone demanding compounds, e.g., DOC and nitrite, and on the water temperature. During this study the goal was to model the rate of DOC accumulation within a coldwater RAS. A commercial-scale RAS used to growout food-size rainbow trout and arctic char was operated under three different configurations (different biofilter configuration, fish species and ozonation versus no ozonation) that were each evaluated over a range of make-up water flows (e.g., R = 91.5-98.9) and feeding rates (e.g., 78-159 kg/day). Fish were fed approximately every 3 hour during a 24-hr photoperiod. 24-hr composite samples were collected from the water flows entering and exiting the RAS and the culture tank after quasi-steady-state conditions had been achieved. Water samples were analyzed for DOC concentration (mg/L). The mean feed-specific DOC production constant was estimated from the DOC data using the steady-state model for waste accumulation in a RAS that was first reported by Liao and Mayo (1972). DOC accumulation in the RAS operated under steady-state conditions was controlled by the rate of DOC production i.e., the feeding rate (rfeed, kg feed per day) multiplied by the mean feed-specific DOC production constant (DOC, kg waste per kg feed) by the efficiency that water treatment units remove the waste (frem, unit less), by the fraction of water flow (Q, L/min) that was reused (R, dimenstion less), and by the concentration of DOC in the make-up flow (DOCnew, mg/L). Results indicate that 'DOC ranged from 0.031-0.045 kg DOC per kg feed and that the DOC treatment efficiency in the recirculating system was approximately 10 - 15%, depending upon conditions.