Sharp (Osaka, JP) earned U.S. Patent 7,662,288 for a more efficient semiconductor wastewater treatment system using micro-nano bubbles and microorganisms.
There are three kinds of bubbles. (i) Normal bubbles ascend in water, and upon reaching the surface, they burst with a pop and disappear. (ii) Micro bubbles, which are microscopic bubbles with a diameter of not more than 50 microns, shrink in water and eventually disappear (totally dissolved). (iii) Nano bubbles, which are bubbles smaller than the micro bubbles (with a diameter of not more than 1 micron and usually 100 nm to 200 nm), are said to be able to exist in water permanently. The micro nanobubbles can be defined as the bubbles with the micro bubbles and the nano bubbles mixed together.
According to inventors Kazuyuki Yamasaki, Kazuyuki Sakata and Kazumi Chuhjoh, micro-nano bubbles are used in a production device and a detoxification device as one example of the upstream treatment devices which perform specified treatment on ultra pure water used in semiconductor manufacturing. The micro-nano bubbles are used again in the waste water treatment by a waste water pretreatment device and another waste water treatment device in the subsequent step.
Since the micro-nano bubbles are reused, the efficiency of the micro-nano bubbles is enhanced. Moreover, according to the inventors, treatment water is pretreated with the microorganisms activated by micro-nano bubbles and propagate in a polyvinylidene chloride filler material and which is introduced into the waste water treatment device in the subsequent step. The system makes it is possible to reduce the waste water treatment load in the waste water treatment device in the subsequent step.
The treatment water containing air micro-nano bubbles and nitrogen micro-nano bubbles is introduced into a biological treatment tank or a deep biological treatment tank having a submerged membrane. Consequently, in the biological treatment tank or the deep biological treatment tank, the activity of microorganisms can be increased by the air micro-nano bubbles, while the activity of anaerobic microorganisms can be increased by the nitrogen micro-nano bubbles.
In the viewpoint of energy saving, the deep biological treatment tank is more effective than the general biological treatment tank. More specifically, in treatment water containing air micro-nano bubbles and nitrogen micro-nano bubbles, micro bubbles accumulate in treatment water for only four to five minutes, whereas nano bubbles accumulate in treatment water for a month and therefore even without the oxygen feeding process by aeration, dissolved oxygen can be maintained for a long time due to the effect by the air micro-nano bubbles.
FIG. 1 is a schematic view showing a water treatment system using micro-nano bubbles
An experimental device corresponding to the waste water pretreatment device (30) in the first embodiment shown in FIG. 1 was manufactured. The filler-type air micro-nano bubble treatment tank (1) in the experimental device had a capacity of 300 L, while the air micro-nano bubble replenishing tank (4) had a capacity of 80 L.
After a trial run of the experimental device for approximately two days, waste water discharged from a semiconductor plant was continuously introduced as treatment water into the filler-type air micro-nano bubble treatment tank and the air micro-nano bubble replenishing tank. The measured dissolved oxygen concentration in the treatment water was 0 ppm. After three days for stabilization of water quality, the dissolved oxygen concentration in the treatment water was measured in an outlet pipe L4 of the air micro-nano bubble replenishing tank, and the result was 6 ppm.