Micro-bubbleswere discharged into the lower layer in a eutrophic reservoir in order to aerate and purify the contaminated waters.Water quality has been monitored in the last 1.5 year after starting the system operation. In the first one year, the water body was more mixed and overturned by the micro-bubble aerator than we expected, although the aerator was originally designed so that only the lower layer water is aerated with minimum vertical mixing.The reason of such significant mixing was that high amount of unexpected and undesirable macro-bubbles were generated at the nozzle's outlet. Nevertheless, it was found through measurements of nutrients, metals, DO, etc.that the water quality was much more improved than before and the water purification system has been running quite well.In the last July, generator's structure was modified for preventing macro-bubble generation and then microbubbles were generated more efficiently. Water quality change after improvement of the system were also reported.
A water purification system was developed and installed in the lower layer of a eutrophic reservoir . A preliminary test was conducted in order to examine its performance. The aerator generates fine air bubbles of several ten micro millimeters, so-called micro-bubbles. Dissolved oxygen, temperature, electric conductivity and other water quality items have been measured in every two weeks after starting the micro-bubble aeration in March 1999. Despite continuously operating the system, total amount of dissolved oxygen in the reservoir has decreased so far, from which the air discharge is estimated to be less than oxygen consumption due to decomposition . Nevertheless, DO concentration in the lower layer is higher than that observed in the last four years , while DO in the surface layer has been kept less than that in the last four years. These results suggest that the system functions for aerating water body to some extent, except that the air discharge is not sufficient for complete aeration , yet.
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