Reservoir Water Purification With Use of Micro-Bubbles and System's Performance

Abstract

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.

An Attempt to Measure the Oxygen Transfer Rate of a Gas Dissolving Device in a Separate-Type Experiment

“…Then, the equivalent ΔDO at temperature 20 [°C], ΔDO 0(20) , was obtained using eq. (19). The water temperature correction factor was set at θ=1.02.…”

“…(13), to the required temperature has been derived in eq. (19) from the theory of aeration, eq. (1), and the existing temperature correction formulation.…”

“…It was shown that the result of the oxygen transfer rate obtained by the existing method, with the imposed water temperature of 20 [°C], is almost the same as that obtained by applying the result of the separate-type ΔDO method with temperature correction, eq. (19), to 20[°C], as shown in Fig.12. Therefore it has been verified that the separate-type equivalent ΔDO method proposed in this study is valid as a measuring method for the oxygen transfer rate of the one-pass-type gas dissolving devices.…”

“…When we vary the pressure of gas in the water treatment process, the value of the DO concentration at saturation in eqs. (13) and (19) should be corrected. When we set the value of DO concentration at saturation condition after correcting for pressure as DO s ′[mg/L], the DO concentration at saturation condition at atmospheric pressure, read from the table 26) as DO s [mg/L], and the partial pressure of the oxygen in the water treatment system as…”

“…(13) and its correction for temperature given by eq. (19) are the original ones proposed by the authors. The validity for these was verified through measurement in a laboratory.…”