Liquid purification or separation – Processes – Utilizing electrical or wave energy directly applied to...
Reexamination Certificate
1999-02-24
2001-03-06
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Utilizing electrical or wave energy directly applied to...
C210S764000, C210S805000
Reexamination Certificate
active
06197203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filtration method for water employing a membrane filter, and a filtration apparatus.
2. Description of the Prior Art
FIG. 3
is a perspective view showing the construction of a conventional filtration apparatus.
FIG. 4
is a schematic representation of a construction of different conventional filtration apparatus.
FIG.
3
and
FIG. 4
show a filtration apparatus in which an ultramembrane filter, a micromembrane filter or a nonwoven fabric is disposed in a filtration tank into which air is blown. The growth of algae on the membrane surface results in a layer of material that makes membrane filtration impossible because of hydraulic resistance of the algae layer. This can occur within one to two weeks after a new membrane is placed in service for recirculation of pool water and fish breeding water, for drinking water from river water and for filtration of sewage treated with activated sludge.
As a countermeasure for fouling of the membrane filter as described above, sponge balls are usually placed in the filtration tank to remove the algae layer on the membrane filter. The sponge balls contact the filtration surface of the membrane facilitating peeling of the algae off the surface. However, this measure has a small removal effect along with having a drawback that the sponge balls are drained together with the sludge accumulated in the filtration tank, requiring a cost for supplementing the sponge balls. Otherwise, sodium hypochlorite is added into the filtration tank to prevent growth of algae or to disinfect algae. The effective chlorine concentration, then, should be maintained at a certain level, for example at 0.5 ppm, in this method. Chlorine residuals are toxic to aquatic life in receiving waters and the by-products of chlorinating may be carcinogenic. Moreover, growth of microorganisms for decomposing inactivated algae in the activated sludge is inhibited with added chlorine, thereby colloidal organic substances produced from incomplete decomposing of inactivated algae may foul of the membrane filter.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to solve the foregoing problems, thereby preventing a membrane filter from fouling.
The above object can be achieved by the following method and apparatus.
In one aspect, the present invention provides a filtration method in which process water is irradiated with UV light, and the UV irradiated process water is aerated and filtered.
In another aspect, the present invention provides a filtration apparatus comprising UV irradiation means for irradiating process water with UV light, filtration means with a membrane filter for filtrating the UV irradiated process water, and air diffusing means for blowing air below the membrane filter.
In yet another aspect, the present invention provides a filtration apparatus comprising UV irradiation means for irradiating process water with UV light, filtration means with a membrane filter for filtrating the UV irradiated process water, air diffusing means for blowing the air to the filtration means, and means disposed between the air diffusing means and membrane filter to generate circulating flow.
Pore size of the membrane filter is preferably in the range from 0.1 through 1 &mgr;m.
According to the construction described above, algae and spores in process water to be fed to the filtration tank are biologically inactivated by UV irradiation. The inactivated algae and spores are rejected with a membrane filter having a pore size of 0.1 to 1 &mgr;m and remain in the filtration tank. The inactivated algae and spores in the filtration tank are decomposed by microorganisms in the activated sludge, which microorganisms appear and inhabit the filtration tank with the benefit of blown air.
REFERENCES:
patent: 5389254 (1995-02-01), Sherman
patent: 5451317 (1995-09-01), Ishida et al.
patent: 5614088 (1997-03-01), Nagai et al.
patent: 5651889 (1997-07-01), Wataya et al.
“Prevention Membrane-Fouling by USV Irradiation in Membrane Separation Process for Drinking Water Treatment”, The Water Environment Society of Japan; vol. 18, No. 11 (1995) pp. 924-928.
Inaba Toshiaki
Ishida Hiroshi
Uragami Itsuo
Chiyoda Kohan Co., Ltd.
Heslin & Rothenberg, P.C.
Hoey Betsey Morrison
Simmons David A.
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