Liquid purification or separation – With means to add treating material – Directly applied to separator
Reexamination Certificate
1998-12-08
2001-09-04
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
With means to add treating material
Directly applied to separator
C210S361000, C210S332000, C210S346000, C210S407000
Reexamination Certificate
active
06284135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an immersion type membrane filter apparatus and a method for operating the membrane filter apparatus.
2. Description of the Related Art
Conventionally, solid-liquid separation has been performed in many instances of waste water treatment, collection of valuable substances in water, and like treatments. A solid-liquid separation method employs a membrane filter apparatus which uses a membrane unit composed of a plurality of membrane elements, such as precision filtration membranes or ultrafiltration membranes. In this case, in the membrane element, pressure is applied on the side of water to be treated, or a negative pressure is generated on the side of treated water with respect to each membrane, so that only water permeates through the membranes.
However, in the membrane element, adhesion to the membrane surface of solid matter such as suspended solid causes generation of filtration resistance in addition to resistance intrinsic to the membrane material itself. As adhesion of solid matter proceeds, the associated filtration resistance increases, impairing permeability of the membrane element. In the case of fixed-rate filtration, the pressure difference between untreated water and treated water, i.e., the differential filtration pressure, increases. As a result, energy required for filtration increases. In the case of fixed-pressure filtration, the water permeation rate, i.e., the rate of water permeating through the membrane, decreases. Thus, there is provided a membrane filter apparatus in which the velocity of water flowing along membrane surfaces is increased, or in which the membrane surfaces are cleaned by means of, for example, sponge balls or carriers, thereby minimizing adhesion of solid matter to the membrane surfaces.
In the case of an immersion-type membrane filter apparatus, in which a membrane unit is immersed in water, an aerator is disposed under the membrane element so as to discharge air for aeration of membranes. An air lift action of the discharged air causes a shear force to be applied to membrane surfaces, thereby cleaning the membrane surfaces by means of a mixed flow of air and water (refer to Japanese Patent Publication No. 4-70958).
To uniformly and efficiently supply air discharged from the aerator into gaps between membranes, the membrane unit is disposed within an enclosure, which is open upward and downward, and the aerator is disposed within the enclosure at a lower portion thereof (refer to Japanese Patent Publication No. 7-20592). Alternatively, the membrane unit is disposed within the enclosure, which is open upward and downward, the aerator is disposed within the enclosure at a lower portion thereof, and flow-smoothing means is disposed between the membrane unit and the aerator (refer to Japanese Patent Laid-Open (kokai) No. 8-281080) or a skirt member is disposed at the lower end of the membrane unit (refer to Japanese Patent Laid-Open (kokai) No. 8-281083).
The conventional immersion-type membrane filter apparatus can uniformly supply air discharged from the aerator into each gap between membranes, but involves a problem that, as air rises within each gap between membranes, a flow of bubbles is gradually biased toward a widthwise central portion of the membrane surface.
FIG. 1
shows a schematic view of a conventional immersion-type membrane filter apparatus.
In
FIG. 1
, numeral
10
denotes a treatment tank for accommodating water to be treated, which is supplied there into through a line L
1
; numeral
11
denotes a membrane element; numeral
12
denotes a membrane; numeral
13
denotes a frame; numeral
14
denotes a water manifold nozzle attached to the top end of the frame
13
; and a line L
2
for discharging treated water is connected to the water manifold nozzle
14
. A pump P is disposed in the line L
2
in order to pump out treated water. A plurality of membrane elements
11
are arrayed adjacent to each other to constitute a membrane unit.
An aerator
15
is disposed under the membrane unit for cleaning the surfaces of the membranes
12
, and is connected to an unillustrated air source through a line L
3
. Air discharged from the aerator
15
is supplied, in the form of bubbles
16
, to the membrane element
11
uniformly along an entire bottom end S
1
thereof. The bubbles
16
, together with water, rise within each gap between the membranes
12
. To guide air discharged from the aerator
15
upward, a skirt element
17
is disposed between the membrane unit and the aerator
15
.
Since the membrane elements
11
extend along a predetermined length within the treatment tank
10
, the opposite side edge portions of the frame
13
and water to be treated present in the vicinity of the edge portions produce resistance to the bubbles
16
which are rising within each gap between the membranes
12
. Accordingly, as the bubbles
16
rise within each gap between the membranes
12
, the bubbles
16
are gradually biased toward a widthwise central portion of the surface of the membrane
12
. As a result, the amount of the bubbles
16
is reduced at the opposite side portions of a top end S
2
of each membrane element
11
. That is, the bubbles
16
flow at a relatively high rate in a trapezoidal region AR
1
and at a relatively low rate in triangular regions AR
2
and AR
3
. Consequently, sludge is removed by action of the bubbles
16
from the surface of the membrane
12
in the region AR
1
, whereas sludge tends to adhere to the surface of the membrane
12
in the regions AR
2
and AR
3
due to impairment in the cleaning effect of the bubbles
16
, thus failing to clean the entire surface of the membrane
12
. Further, the gaps between the membranes
12
are clogged with sludge, SS, colloid, or a like substance, resulting in a failure to maintain good filtration over a long period of time.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems in the conventional membrane filter apparatus and to provide a membrane filter apparatus capable of cleaning the entire surface of a membrane and maintaining good filtration over a long period of time, as well as to provide a method for operating the membrane filter apparatus.
To achieve the above object, the present invention provides a membrane filter apparatus comprising a treatment tank, a membrane unit, a tubular (rectangular-tube-like) skirt element, an aerator, a partition, and gas supply means. The membrane unit is disposed within the treatment tank and is composed of an array of membrane elements. The skirt element is disposed at a bottom portion of the membrane unit. The aerator is disposed under the skirt element for the purpose of discharging gas. The partition is disposed at a bottom portion of the membrane unit and, together with the skirt element, defines a compartment within the skirt element. The gas supply means supplies gas into the compartment.
The gas discharged from the aerator becomes bubbles. The bubbles are supplied into and rise within the compartment, thereby increasing their rising force upon entry into gaps between membranes.
Since the gas is supplied into the compartment by the gas supply means, the flow rate of bubbles along the opposite side edge portions of the membrane unit can be increased while the bubbles are flowing upward within the gaps between the membranes.
Accordingly, the entire surface of each membrane can be cleaned, thereby preventing clogging by sludge, SS, colloid, or a like substance within each gap between the membranes and thus preventing an increase in filtration resistance. Therefore, good filtration can be maintained over a long period of time.
Further, power required for filtration can be reduced, and the frequency of manual periodic cleaning, chemical cleaning, or like cleaning can be decreased.
Preferably, the skirt element has a rectangular cross section, and the compartment is formed along two walls of the skirt element.
Preferably, the skirt element has a rectangular cross section, and the compartment is
Arent Fox Kintner Plotkin & Kahn
Cecil Terry K.
Drodge Joseph W.
Sumitomo Heavy Industrie's, Ltd.
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