Purification of deep water in a dam lake using micro-bubbles and/or Eco-Bio-Ring

This study is aiming at finding an efficient method to purify deep water in Midorikawa-dam Lake in Kumamoto Pref., Japan. The biological oxygen demand (BOD) of the water at first was 46 mg/L in the worst case. In the test, micro-bubbles were periodically supplied into the water in 80 L tank by a multi-fluids-mixer patented by Sadatomi and Kawahara. The bubbling rate were changed as QG = 1.0 L/min and 2.0 L/min to study its effect. In addition, the Eco-Bio-Ring including aerobic bacteria (Bacillus bacterium), sold by Big Bio Co. Ltd., Japan, were immersed in two tanks of the three in order to study its effect. As a result, it was cleared that QG = 1.0 L/min was enough to reduce the BOD to about 6-10 mg/L within two weeks, and the Eco-Bio-Ring was effective to reduce turbidity