Oxidation ditch and method of repairing oxidation ditch

摘要

PROBLEM TO BE SOLVED: To form a circulation agitation stream efficiently in a tank by a vertical shaft type aeration agitator even when an oxidation ditch (OD) has a flow straightening wall in an arc-shaped channel.SOLUTION: In the oxidation ditch, an endless circulation channel is formed by a partition wall 2 for partitioning the inside of the water tank 1 and the circulation channel is constituted of a main channel 5 and an arc-shaped channel 6 which joins ends of the main channels 5, 5 each other and which is almost semicircular when horizontally viewed and the arc-shaped shaped channel 6 is provided with the flow straightening wall 7 which is arc-shaped shaped when horizontally viewed. The vertical shaft type aeration agitator 3 is installed so that its impeller 9 is located in the main channel 5 more on the further downstream side than the end 7a of the downstream side of the flow straightening wall 7 in the arc-shaped shaped channel 6. A jetting stream which goes, by rotation of the impeller 9, to either an inner peripheral side channel 8a or an outer peripheral side channel 8b from the flow straightening wall 7 in the arc-shaped shaped channel 6 on the further upstream side than the impeller 9 is prevented from going to the upstream side by a backflow prevention plate 13 located on the side of the impeller 9 and good circulation agitation stream going to the downstream side is formed.