A Four-tank Water Recirculation System with a Hydrocyclone Prefilter and a Single Water Reconditioning Unit

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Abstract
In a four-tank recirculation system serviced by a single biological filter, hydrocyclone prefilters removed over 87% of the particulate matter greater than 77 μm (3 x 10-3 in) in diameter. Biological nitrification occurred on a substrate of 25 mm (1 in) diameter, Actifil (R) polypropylene biorings contained in a 0.29-m3 (10-ft3) fiberglass tank. The four 0.9 m3 (32-ft3) tanks were stocked with 1200 rainbow trout (Salmo gairdneri), averaging 66.9 g (0.148 lb) each. Fish were thinned every 2 weeks to maintain approximately constant density. During the first 62 days of the 248-day test when the filter was being conditioned, the fish had essentially no growth. Over the last 186 days the average weight increased from 71.4 to 294.1 g (0.157 to 0.648 lb) resulting in a specific growth rate of 0.76%/day. Recirculation and makeup water rates were 130 and 5 L/minute (34 and 1.3 gal/minute), respectively. Chlorinated makeup water was passed through a small ultraviolet irradiator where chlorine was oxidized ...