METHOD FOR CLEANING WATER IN TANK FOR BREEDING AQUATIC ANIMAL

摘要

PURPOSE:To prevent the increase of NO level in a water tank by arranging an aeration step, a filtration step, a returning step and a denitrification step in a specific state. CONSTITUTION:Water in a water tank 1 is passed through an aeration tank 5 and a sand-filtration column 4 to effect the filtration of SS with a filter layer 4 and the nitration of NH3 to NO by nitrifying bacteria and is circulated to the water tank 1. A part of the liquid discharged from the aeration tank 5 is introduced into a denitrification tank 9 operated under anaerobic condition and filled with a reducing agent 8 and a microorganisms supported on a medium. NO is reduced and decomposed to N2 by this process. The denitrified water 10 is passed through the former stage 11 and the middle stage 12 of the aeration tank 5 operated under aerobic condition and filled with microorganisms supported on a medium M and most part of the water is returned from the latter stage 13 through a sand filtration column 4 to the water tank 1. The medium M supports microorganisms capable of oxidizing and decomposing unreacted reducing agent and a part of the medium M supports also nitrifying bacteria.