Study on design and performance of two-layer floating bead biofilter for recirculating aquaculture system

Based on the filtration of sand filter bed, a solid and nitrification biofilter of floating plastic bead was designed and tested. In the biofilter, the bead was layered automatically in water according to the size and gravity of plastic bead. With two types of diameter 5 mm gravity 0.94 and diameter 2 mm gravity 0.5 beads, the biofilter performed well in solid separation and ammonia nitrification. The bead filter performances were tested in a recirculating aquaculture system. When pump power was 0.75 kW and flow quantity was 20 m~3·h~ -1, the recirculating culture system could support 10 m~3 water in culture density of 16 kg·m~ -3 Amur sturgeon. Suspended solid filtering rate was 90% and ammonia nitrification capacity was 149 g·m~ -3·d~ -1. Within water exchanged period of two weeks, the water quality was as following, SS≤100 mg·L~ -1, Ammonia≤1.0 mg·L~ -1, Nitrite≤0.18 mg·L~ -1 and Nitrate 24≤mg·L~ -1. After 15 days' culture, fish survival rate was 99% and growth rate was 50%. The experiment result showed that the bead biofilter could meet the need of recirculating aquaculture system in solid separation and ammonia nitrification.