JP2008289958A - Membrane filtration system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable more efficient reduction of transmembrane pressure difference by carrying out short-time washing a plurality of times. <P>SOLUTION: A membrane filtration system comprises a raw water tank 1 temporarily storing raw water, a membrane module 2 filtering the raw water, a raw water pump 3 supplying the raw water in the raw water tank to the membrane module, a treated water tank 4 storing treated water filtered by the membrane module, a compressor 5 supplying pressurized air into the membrane module, and a backwashing water pump 6 supplying the treated water to the membrane module as washing water. In a membrane module washing process, the membrane module 2 is washed plural times until its transmembrane pressure difference becomes a predetermined value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane filtration system suitable for the treatment of fresh water such as surface water and groundwater, rainwater storage, industrial wastewater, sewage such as sewage, and seawater such as ballast water.

  Conventionally, in the field of water treatment, raw water (for example, fresh water such as surface water, groundwater, rainwater storage water, industrial wastewater, sewage such as sewage, seawater such as ballast water) is filtered and used for domestic water, industrial water, and agricultural water. As a method of obtaining, for example, a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, or a reverse osmosis membrane is used.

  The membrane has a high separation performance with respect to solids such as microorganisms, algae and clay in the raw water, and its application in the water treatment field is expanding. In recent years, it is common to use a hydrophilic material as the material of the membrane. Even when a hydrophobic material is used, it has been studied to improve the filtration performance by hydrophilizing the membrane surface with a sulfuric acid solution of potassium dichromate or the like (see, for example, Patent Document 1).

  However, when the raw water is continuously passed through the membrane, the solute in the raw water accumulates on the outer surface of the membrane or in the pores of the membrane, and the filtration resistance may increase and the filtration performance may deteriorate.

  Therefore, in such a membrane filtration system, physical cleaning with filtered treated water or compressed air is performed at a preset cycle or when the membrane shows a predetermined differential pressure increase, and the membrane outer surface or membrane pores Of the deposits inside, reversible ones are removed.

  On the other hand, deposits that are difficult to remove by such physical cleaning gradually accumulate on the outer surface of the membrane and in the membrane pores, so when the membrane differential pressure exceeds the preset upper limit value, membrane filtration treatment Is stopped and chemical cleaning is performed to remove deposits that could not be removed by physical cleaning.

And even if chemical cleaning is performed, it is impossible to remove deposits such as the membrane surface and inside, and recovery of the membrane differential pressure is not recognized, or when the usage period of the membrane exceeds a certain period, The membrane is replaced when it is judged that it has reached the end of its life.
Japanese Patent Laid-Open No. 5-23553

  In such a membrane filtration system, the membrane filtration process must be stopped each time chemical cleaning, filtration membrane replacement, or the like is performed. For this reason, it is necessary to reduce the frequency of chemical cleaning and filtration membrane replacement as much as possible, increase the operating rate of the membrane filtration system, and reduce the cost required for chemical cleaning and membrane replacement.

  The present invention has been made in consideration of such circumstances, and can increase the amount of treated water to increase the system operation rate, reduce the cost required for chemical cleaning and membrane replacement, and reduce the total running cost. The object is to provide a membrane filtration system.

  (1) A membrane filtration system according to the present invention, as described in claim 1, is a raw water tank that temporarily stores raw water, a membrane module that filters raw water, and raw water that supplies raw water from the raw water tank to the membrane module. A pump, a treated water tank for storing treated water filtered by the membrane module, a compressor for supplying pressurized air into the membrane module, and a backwash water pump for supplying treated water as washing water to the membrane module In the membrane filtration system, the membrane module is washed a plurality of times until a predetermined membrane differential pressure is reached.

(2) The membrane filtration system according to the present invention is characterized in that, in the above (1), the membrane module is washed a plurality of times until the rate of increase of the membrane differential pressure with respect to a predetermined period becomes constant.
(3) Furthermore, the membrane filtration system according to the present invention is characterized in that, in the above (1) or (2), an upper limit value of the number of times of cleaning is set in advance.
(4) Further, in the membrane filtration system according to the present invention, in the above (1) to (3), the time during which reverse water flow is measured by measuring the membrane differential pressure or flow rate during reverse water flow, It is characterized in that it is determined by the time during which the slope of becomes constant.

  According to the present invention, the membrane differential pressure can be more effectively reduced by performing a plurality of short-time cleaning operations.

Hereinafter, an embodiment of a membrane filtration system of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of a membrane filtration system according to the present invention.
The membrane filtration system is a raw water tank 1 for temporarily storing raw water guided by a water pump (not shown), a raw fiber for filtering the raw water, for example, a hollow fiber type membrane module 2, and supplying raw water from the raw water tank 1 to the membrane module. Raw water pump 3, treated water tank 4 for storing treated water filtered by the membrane module 2, a compressor 5 for supplying pressurized air into the membrane module 2, and treated water as washing water to the membrane module 2 And a backwash water pump 6.

In FIG. 1, 7 _{1 to} 7 ₈ denote pipes, and _{8 a to 8} k denote valves. Pipe 7 ₁ a pipe connecting the bottom portion of the lower side and the membrane module 2 in the raw water tank 1, the valve 8a, 8b is interposed. Pipe 7 ₂ in pipe connecting the upper part of the treatment water tank 4 and the top of the membrane module 2, the valve 8c, 8d is interposed. Pipe 7 ₃ by a pipe connected to the bottom of the membrane module 2, the valve 8e is interposed. Pipe 7 ₄ in pipe connected to the upper side of the membrane module 2, the valve 8f is interposed. Pipe 7 ₅ a pipe connected to the pipe 7 _4, the valve 8 is interposed. Pipe 7 ₆ in pipe connecting the bottom side of the compressor 5 and the membrane module 2, the valve 8h is interposed. Pipe 7 ₇ a pipe to be connected to the _second pipe 7 is branched from the pipe 7 ₆ connected to the compressor 5, the valve 8i is interposed. Pipe 7 ₈ a pipe connecting the bottom of the treating tank 4 and a pipe 7 _2, valve 8k is interposed.

The operation of the membrane filtration system of FIG. 1 is as follows.
In the membrane filtration system, raw water is guided to the raw water tank 1 by a water pump (not shown). Then, raw water is introduced into the membrane module 2 by pressurization of the raw water pump 3, and the treated water that has permeated the membrane module 2 is stored in the treated water tank 4. The normal cleaning is performed by repeating the reverse pressure water step (1) and the raw water rinsing step (2) in the following procedure a plurality of times until a predetermined membrane differential pressure is reached.

(1) Reverse pressure water process
The valves 8b, 8d, 8g, and 8i are closed, and the treated water in the treated water tank 4 is caused to flow backward from the treated water side of the membrane module 2 by the backwash water pump 6 with the valves 8c, 8j, and 8k opened. bottom of the raw water side pipe 7 ₃ or, or discharged from the membrane module 2 pipe 7 of the upper portion of the raw water side _4. At this time, swinging the membrane module 2 from the raw water side of the pipe 7 ₆ of the membrane module 2 by flowing a pressurized air by a compressor 5.

(2) Raw water rinsing process
The valves 8a and 8b and the valve 8f above the membrane module 2 are opened, the raw water pump 3 is started, and the membrane module 2 is rinsed. At this time, the rinse water may be circulated to the raw water tank 1. In addition, rinsing can be performed more effectively while the compressed air is allowed to flow from the compressor 5, but the compressed air may be stopped to reduce the power cost.

According to the above embodiment, in the membrane filtration system including the raw water tank 1, the membrane module 2, the raw water pump 3, the treated water tank 4, the compressor 5, and the backwash water pump 6, By repeating the time cleaning a plurality of times until the membrane differential pressure reaches a predetermined pressure (P ₁ ), the membrane differential pressure can be more effectively reduced as shown in FIG.

  In the above embodiment, the case where the membrane module 2 is cleaned a plurality of times for a short time until the membrane differential pressure reaches a predetermined pressure has been described, but the present invention is not limited to this. For example, cleaning may be performed a plurality of times until the rate of increase in the film differential pressure with respect to a predetermined period becomes constant, or an upper limit value of the number of times of cleaning may be set in advance. Alternatively, the time for reverse water flow may be determined by measuring the membrane differential pressure or flow rate during reverse water flow and the time during which the slope of either value becomes constant.

  3 and 4 are characteristic diagrams showing the relationship between the washing time and the membrane differential pressure during reverse water flow, and the materials of the hollow fibers used in the membrane module are different. In FIG. 3, it is clear that the membrane differential pressure becomes substantially constant from about 5 minutes for the lines (a) and (c) and about 3 minutes for the line (b). Also, in FIG. 4, the membrane differential pressure is substantially reduced from about 2 minutes for the line (a), about 5 minutes for the line (b), and about 4 minutes for the line (c). It is clear that it will be constant.

  FIG. 5 and FIG. 6 are characteristic diagrams showing the relationship between the cleaning time and the cleaning flow rate during reverse water flow, and the materials of the hollow fibers used in the membrane module are different. FIG. 5 shows the data of the membrane module similar to FIG. 3, and FIG. 6 shows the data of the membrane module similar to FIG. In FIG. 5, it is clear that the cleaning flow rate is substantially constant from about 5 minutes for the lines (a) and (c) and about 3 minutes for the line (b). In FIG. 6, the cleaning flow rate is approximately constant for line (a), the cleaning time is approximately 2 minutes, for line (b), the cleaning time is approximately 5 minutes, and for line (c), the cleaning flow rate is approximately constant from approximately 4 minutes. It is clear.

In the above embodiment, as shown in FIG. 2, physical cleaning is performed a plurality of times, and the film differential pressure is lowered to ΔP1, ΔP2, ΔP3, and ΔPk to obtain a constant film differential pressure (P ₁ ). However, the present invention is not limited to this, and as shown in FIG. 7, physical cleaning is performed a plurality of times to lower the film differential pressure to ΔP1, ΔP2, ΔP3, ΔPk, and the final film differential pressure is constant (P ₁ ) May be adjusted to be slightly inclined.

  In addition to the above, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

An explanatory view of a membrane filtration system concerning an embodiment of the present invention is shown. In the membrane filtration system of FIG. 1, it is a characteristic view which shows the relationship between the elapsed time at the time of performing physical cleaning of multiple times, and a membrane differential pressure | voltage. It is a characteristic view which shows the relationship between the washing | cleaning time by this invention, and the membrane differential pressure at the time of reverse water flow. It is a characteristic view which shows the relationship between the washing | cleaning time by this invention, and the membrane differential pressure at the time of reverse water flow. It is a characteristic view which shows the relationship between the washing | cleaning time by this invention, and the washing | cleaning flow volume at the time of reverse water flow. It is a characteristic view which shows the relationship between the washing | cleaning time by this invention, and the washing | cleaning flow volume at the time of reverse water flow. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time at the time of performing physical cleaning of multiple times, and a membrane differential pressure | voltage.

Explanation of symbols

1 ... raw water tank, 2 ... raw water pump, 3 ... membrane module, 4 ... treatment water tank, 5 ... compressor, 6 ... backwash water _{pump, 7} 1-7 8 _... piping, 8A～8k ... valve.

Claims (4)

A raw water tank for temporarily storing raw water, a membrane module for filtering raw water, a raw water pump for supplying raw water from the raw water tank to the membrane module, a treated water tank for storing treated water filtered by the membrane module, and a membrane module A membrane filtration system comprising a compressor for supplying pressurized air therein and a backwash water pump for supplying treated water as wash water to the membrane module;
A membrane filtration system, wherein a membrane module is washed a plurality of times until a predetermined membrane differential pressure is reached in the membrane module washing step. 2. The membrane filtration system according to claim 1, wherein the membrane module is washed a plurality of times until the rate of increase of the membrane differential pressure with respect to a predetermined period becomes constant. The membrane filtration system according to claim 1 or 2, wherein an upper limit value of the number of times of washing is set in advance. 4. The membrane according to any one of claims 1 to 3, wherein the reverse water flow time is determined by the time during which the gradient of any value becomes constant by measuring the differential pressure or flow rate during reverse water flow. Filtration system.

Images