JPH10216487A - Washing method of membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of a recovering ability of membrane performance due to chemical washing and generation of slime during shut-down period to maintain the membrane in a good state over a long period of time by allowing a wash chemical to contact with a membrane surface at the time of long term shut-down of a membrane separation device. SOLUTION: At the time of an operation of the membrane separation device, a water passing treatment and a back washing with a permeated water or a pressurize air, etc., for a prescribed time are executed alternately, moreover, the chemical washing for several hour to ten and several hour is executed periodically. At the time of a long term shut-down of a membrane separation device, an alkali aq. soln. such as NaOH aq. soln. is supplied with a washing pump 3 to a permeated water chamber 1B and a raw water chamber 1A of a membrane module 1 from an alkali tank 2A of a wash chemical tank 2 through pipings 22, 23, 24 and 25, and after circulating through the piping 26 and 27 and the pining 29 and 30, an acid aq. soln. such as HCl aq. soln. is supplied similarly to the membrane module 1 from an acid tank 2B of the wash chemical tank 2 through the piping 21, and subjected to return circulation through the pipings 28 and 31, and in such a way, a recovery property of the membrane performance is improved by chemical washing, and washing frequency is reduced to improve an operating efficiency, and the generation of the slime, etc., at the time of the shut-down is prevented and the deterioration of the membrane is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a membrane, and more particularly to a method for recovering membrane performance by performing chemical cleaning when the operation of a membrane separation apparatus is stopped for a long time.

[0002]

2. Description of the Related Art In recent years, a membrane separation device has been widely used as a solid-liquid separation means instead of a settling tank in a wastewater coagulation / solid-liquid separation treatment.

[0003] When solid-liquid separation of the coagulation treatment liquid of wastewater is performed by a membrane separation device, contaminants adhere to and accumulate on the membrane surface over time, causing clogging, thereby deteriorating membrane separation performance. For this reason, in order to prevent the deposition and deposition of contaminants on the membrane surface, during operation of the membrane separation device, water passing treatment for a predetermined time and backwashing with permeated water or pressurized air are alternately repeated. We,
In order to remove contaminants attached and deposited on the film surface, chemical cleaning of the film is regularly performed.

Conventionally, an acidic aqueous solution and / or an alkaline aqueous solution has been used as a cleaning chemical for the periodic chemical cleaning. The frequency of this chemical cleaning varies depending on the type of wastewater, coagulation processing conditions, membrane separation processing conditions, and the like, but generally, chemical cleaning is performed once every 10 to 100 days. The time required for the regular chemical cleaning varies depending on the raw water storage tank of the apparatus, the heating capacity of the chemical liquid heating equipment, the discharge time of the cleaning wastewater, the degree of membrane contamination, and the like. Since it is preferable from the viewpoint of increasing the operation rate of the apparatus, the time is generally several hours to several tens of hours.

[0005] The operation of the membrane separation apparatus is stopped several times a year, about three days in a short case, and several months in a long time, in connection with a periodic inspection or in connection with other auxiliary equipment. Conventionally, during this long-term operation stoppage, the membrane separation device is filled with pure water or industrial water, and the membrane surface is kept immersed in the pure water or industrial water.

[0006]

As described above, even if chemical cleaning is performed periodically, contaminants gradually accumulate on the film surface, and the resilience of the film performance due to chemical cleaning gradually decreases. For this reason, conventionally, there has been a problem that the frequency of chemical cleaning increases as the time of using the film elapses.

There is also a problem that slime is generated on the membrane surface and the membrane is deteriorated during an operation stop period in which pure water or industrial water is stagnant in the membrane separation device.

[0008] The present invention solves the above-mentioned conventional problems, and prevents a decrease in the resilience of membrane performance due to chemical cleaning and the generation of slime during a shutdown period to maintain the membrane in a good state for a long period of time. An object of the present invention is to provide a washing method.

[0009]

The method for cleaning a membrane according to the present invention comprises the steps of:
The cleaning solution is brought into contact with the membrane surface.

According to the present invention, the membrane surface can be chemically cleaned for a longer period of time than the periodic chemical cleaning by using the operation stop period of the membrane separation apparatus, and the membrane performance can be periodically measured. Recovery can be significantly higher than the required chemical cleaning.

In addition, slime can be prevented from being generated by immersing the membrane surface in the cleaning solution during the operation stop period.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram of a membrane separation apparatus showing an embodiment of the present invention.

In this membrane separation apparatus, raw water is supplied to the membrane module 1 from a pipe 11, and the permeated water is treated as treated water.
The cross-flow type membrane module 1 is further discharged to the outside of the system, and the concentrated water is extracted from the pipe 13 and circulated to the pipe 11 via a circulation tank (not shown). During the operation of the membrane separation device, water passing treatment for a predetermined time and backwashing with permeated water or pressurized air are alternately and repeatedly performed, and further, chemical cleaning for several hours to several tens of hours is performed periodically. Will be

When the operation of the membrane separation apparatus is stopped for a long time, NaO is removed from the alkaline tank 2A of the cleaning chemical tank 2.
An alkaline aqueous solution such as H
The water is supplied to the permeated water chamber 1B and the raw water chamber 1A of the membrane module 1 through 2, 23, 24 and 25, and circulated through the pipes 26 and 27 and the pipes 29 and 30.

Thereafter, the acid tank 2B of the cleaning chemical tank 2
An aqueous acid solution such as an aqueous HCl solution is supplied to the membrane module 1 from the pipe 21 in the same manner as described above, and returned from the pipes 28 and 31 for circulation.

[0017] The supply of the cleaning chemicals during such a long-term operation stoppage can be carried out using cleaning equipment generally used for periodic chemical cleaning.

In the present invention, the contact between the cleaning solution and the membrane surface may be carried out while circulating the cleaning solution. When the concentration of the solution in the membrane module becomes stable, the circulation of the solution is stopped and allowed to stand. Alternatively, the circulation and the stationary may be alternately repeated.

The type of membrane to which the method for cleaning a membrane of the present invention is applied is preferably an MF (microfiltration) membrane or a UF (ultrafiltration) membrane, but the type of membrane module is not particularly limited. Alternatively, either a cross-flow type or an immersion type may be used.

Further, as shown in FIG. 1, the cleaning chemical is not limited to a combination of an alkali aqueous solution and an acid aqueous solution, but may be an alkaline aqueous solution alone or an acid aqueous solution alone. When an alkali aqueous solution and an acid aqueous solution are used in combination, the order of washing is not particularly limited.

The method of the present invention is such that the membrane is continuously contacted with the cleaning solution during the long-term shutdown period, and the contact time is one day or more, preferably three days or more. The contact may be made during the operation stop period. As shown in FIG. 1, when an alkaline aqueous solution and an acid aqueous solution are used in combination, both of them may be brought into contact with the film surface for a long period of one day or more, and only one of them may be brought into contact with the film surface for a long period of one day or more. , And the other may be brought into contact with the film surface for several hours to several tens of hours.

As the cleaning chemical, a cleaning chemical used for periodic chemical cleaning can be used. In the present invention, a cleaning chemical which requires a longer contact time can be used at a lower concentration or added. The temperature can be omitted.

The membrane cleaning method of the present invention is applied to a membrane separation apparatus used for solid-liquid separation of a coagulation treatment liquid of wastewater such as flue gas desulfurization wastewater for a long-term operation suspension period of three days or more. By doing so, it is possible to enhance the recoverability of the membrane performance, effectively prevent the membrane from deteriorating due to the generation of slime during operation stoppage, and maintain the membrane in a good state for a long time.

[0024]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 3 Wastewater treatment and chemical cleaning were performed in the apparatus shown in FIG.

A tubular MF membrane made of polypropylene (area 0.036 m ² , inner diameter 5.5 mm, pore diameter 0.2 μm)
Using a neutralized coagulation treatment liquid of a suit separation type flue gas desulfurization wastewater as raw water, a permeated water amount of 5 m ³ / m ² · day is about 100
The membrane module with reduced flux was subjected to a membrane separation treatment for ~ 600 hr and an 8 wt% NaOH aqueous solution and a 7 wt% H
Two-step chemical cleaning was performed using a Cl aqueous solution.

First, an NaOH aqueous solution was supplied to the membrane module, and the inside of the membrane module was filled with the NaOH aqueous solution.
For the time shown in FIG. Thereafter, an aqueous NaOH solution was extruded, and an aqueous HCl solution was supplied to fill the inside of the membrane module with the aqueous HCl solution and held for the time shown in Table 1.

In Examples 1 to 3, the holding time of at least one of the cleaning chemicals was set to 1 day or more, assuming chemical cleaning during the long-term shutdown of the membrane separation apparatus in Examples 1 to 3.

On the other hand, in Comparative Examples 1 to 3, the retention time of at least one of the cleaning chemicals was set to be shorter than one day, assuming conventional chemical cleaning that is regularly performed.

Pure water flux before and after the chemical cleaning,
Table 1 shows the recovery rate and the average value of the recovery rates obtained from the ratio of the pure water flux of the membrane after chemical cleaning to the pure water flux of the new membrane.
Kgf / cm ² , 25 ° C. ).

[0031]

[Table 1]

From the results shown in Table 1, the recovery of the membrane flux is reduced only by the conventional regular chemical cleaning, but the membrane is washed with the cleaning solution several times a year during the long-term operation stoppage of the membrane separation apparatus. It can be seen that a sufficient recovery can be obtained by keeping the contact.

[0033]

As described in detail above, according to the method for cleaning a film of the present invention, the recoverability of the film performance by chemical cleaning is improved, so that the frequency of chemical cleaning is reduced, the operation rate of the apparatus is improved, and the chemical cost is improved. Can be reduced. In addition, the generation of slime and the like during the operation stop period can be prevented, and the deterioration of the film can be prevented.

[Brief description of the drawings]

FIG. 1 is a system diagram of a membrane separation device showing an embodiment of the present invention.

[Explanation of symbols]

 1 Membrane module 2 Cleaning chemical tank 3 Cleaning pump

Claims (1)

[Claims] 1. A method for cleaning a membrane, wherein a cleaning agent solution is brought into contact with a membrane surface during a period when the operation of the membrane separation device is stopped for a long period of time.