WATER-TREATMENT AND WASTE CHARACTERIZATION EVALUATION OF AN INTENSIVERECIRCULATING FISH PRODUCTION SYSTEM

A combination of two different technologies used for fish production w as evaluated at the North Carolina State University (NCSU) Fish Barn' facility. The combined system included the ECOFISH tank, developed at the Norwegian Hydrotechnical Laboratory (NHL) at SINTEF (Trondheim, N orway) and water treatment and recycle technology designed at NCSU. Ap proximately 2170 fingerling tilapia (Oreochromis niloticus, Oreochromi s mis niloticus x Oreochromis aureus) were grown from 3.6 to 507 g in 177 days in a 20 m(3) four-zone tank. The system design included paten ted particle traps at the bottom of each zone to remove feed waste and excrement, sludge collectors where the removed particles settled, a r otating screen filter for suspended solids removal, a high-rate linear -path trickling biological filter for nitrification, and two down-flow columns for oxygen injection. The measured suspended solids level in the tank zones were usually less than 7.5 mg l(-1) Based on six effici ency tests with a mean total ammonia nitrogen (TAN) concentration in t he culture tank of 0.62 mg l(-1), the biofilter removed approximately 65% on a single pass through the filter, with an average removal rate per unit of filter surface area of 0.33 g TAN m(-2) day(-1). Sampling every 4 h over a 24-h period showed variability in concentrations and TAN removal rates by the biofilter. Six efficiency tests on the sludge collectors and the screen filter showed 80% and 41% suspended solids removal efficiency, respectively, based on the influent and effluent c oncentrations. On a daily basis, the sludge collectors and the screen filter each removed about 18% of feed volatile solids input, respectiv ely, based on three 24-h periods studied. Fresh water use averaged app roximately 1500 1 day(-1), which was about 7% of the system volume. (C ) 1997 Elsevier Science B.V.