Ammonia and Nitrite Removal by the Fluidized Bed Biofilter in a Recirculation Water Culture Fish System

A closed recirculating water fish culture system can save water resource,keep water temperature and prevent outside pollution.But the fish culture density in a recirculation water system was limited by the accumulation of toxic ammonia and nitrite.Water reuse systems facilitate fish culture densities by employing biofilter to remove ammonia and nitrite and a continuous flow of recirculating water to bring oxygen to the fish.In order to decrease the cost and improve the fish production per unit water,a new method of water treatment having a good result of purification and a high loading rate needs to be developed.The fluidized bed biofilter technology combines the best features of both trickling filters and activated sludge suspended growth system.The media materials become suspended in upflow water currents through the biofilter.Fluidized bed biofilter can reduce the clogging that often occurs in submerged fixed bed biofilter.So,high-rate nitrification in a fluidized bed biofilter and recirculating water fish culture system is designed for industrial application scale,with the optimized parameters.The unit of fluidized bed biofilter can remove 30~50 m3 water per hour.The natural porosint,cheaper,facile fluidized media materials were selected.Compared with fix bed biofilter at same conditions,the nitrification and hydraulic loading rate of fluidized bed biofilter is as three times as those of fix bed biofilter.The biofilm is observed and analyzed by electron microscope and the technology of bacterial separation and cultivation.Biotechnology production,immobilized photosynthetic bacteria,is used in fish culturing and preventing disease.Nitrobacter is selectively reared and dividing unit is designed to be helpful for ammonization and nitrification raising purification rate of water in fluidized bed biofilter.The closed recirculating water fish culture system using fluidized bed biofilter can improve treatment efficiency and cut costs.The capital investment required to construct a fluidized bed biofilter is under half that needed for the extensions to conventional biofilter.Maximum carps fish load is 25±2 kg·m-3 in closed recirculating water fish culture system,saving water 85%～90%.Total ammonia N and nitrite N in influent are 1.3 mg·L-1 and 0.068 mg·L-1,respectively,while,they are 0.2 mg·L-1 and 0.024 mg·L-1 in effluent in fluidized bed biofilter,and fish can grow normally.The removal rate of total ammonia N and nitrite N are 80%~95% and over 65%,respectively.