Abstract: The surface of the floating filtering balls were attached by growing biofilms and absorbed the ions in suspended solid particles when the floating type ofbio-filters were applied to effluent treatment in a closed-reeirculating aquaculture. The biofllms and absorbed suspended particles led to plug the gap of float balls, and to increase in the resistance to water flow, even to stop water flowing. So, regular backwashing is important in the normal function of the filtering. In this study, a floating Wpe of bio-fiiter with back back- wash and effluent treatment was designed based on the structural characteristics and fimctional requirements of the float type of bio-filter and tested in practice, with good performance. It was found that the advice showed accurate action, and flowing elimination of the effluent, and that a backwash needed 10 min, and water consumption of 1.5 m3.

Key words: bio-filter, backwashing, sewage discharge device