JPH0899025A - Method for cleaning of membrane element - Google Patents

Abstract

PURPOSE: To clean effectively the whole face of a filter membrane by feeding a specified amt. of a chem. liq. with a specified pressure and a uniform flow rate into a transmitting liq. flow path in the reverse direction of the flow of the transmitting liq. under a condition where a membrane element is immersed in a water to be treated and holding it for a specified time. CONSTITUTION: In a membrane element 2 of an immersion type separation unit used in solid-liq. separation application in activated sludge processing of an org. drainage, a transmitting liq. flow path 5 opening on the surface of a flat sheet-type membrane substrate 4 is formed and a filter membrane 6 covering the surface of the membrane substrate 4 is arranged. In cleaning of the membrane element 2 like this, a chem. liq. is fed into a transmitting liq. flow path in the reverse direction of the flow of the transmitting liq. under a condition where a membrane element 2 is immersed in a water to be treated and the chem. liq. is held for a specified time. In this case, the amt. of the chem. liq. to be fed is made to be an amount by which the chem. liq. flows equally into each membrane element being arranged in parallel, namely, about 1/5 to 1/10 of the max. transmitting and holding vol. of the membrane element and it is fed at a low pressure of at most 10kPa.

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 element of an immersion type membrane separation unit used for solid-liquid separation in the treatment of activated sludge of organic waste water.

[0002]

2. Description of the Related Art Conventionally, in the treatment of activated sludge of organic waste water, a membrane separation unit is provided, for example, in order to separate activated sludge and agglomerated sludge by immersing in activated water in a treatment tank. The membrane separation unit is as shown in FIG. 1, in which a box-shaped casing 1 having openings at the top and bottom is provided with flat plate-shaped membrane elements 2 arranged in parallel in the vertical direction, and the membrane elements are dispersed below the membrane element 2. An air conditioner 3 is provided.

The membrane element 2 has a rectangular flat plate-shaped membrane support 4 which has a permeate flow path 5 which opens to the surface of the membrane support 4 and communicates with a suction pipe (not shown). The filtration membrane 6 is disposed so as to cover the surface of the membrane and is fixed to the membrane support 4 at the peripheral portion of the filtration membrane 6. In addition, a spacer 7 such as a net or felt is interposed between the filtration membrane 6 and the membrane support 4 to secure a flow path of permeate between the filtration membrane 6 and the membrane support 4, The filtration membrane 6 is protected by the numeral 7.

When performing processing, suction means (not shown)
A negative suction pressure is applied to the permeated liquid flow path 5 through the suction pipe to remove the activated sludge and the like in the water to be treated by the filtration membrane 6.
The permeated liquid captured by the permeation liquid and permeated through the filtration membrane 6 and flowing into the permeated liquid channel 5 is taken out as treated water. At this time, due to the cutting force of the bubbles of the aerated air supplied through the air diffuser 3 and the upward flow of the water to be treated caused by the air lift action of the bubbles, the deposits on the membrane surface of the membrane element 2 are removed. ing.

Then, when the flow rate of the permeate decreases, or periodically, the membrane element 2 is cleaned with a chemical solution.

[0006]

However, while the above-mentioned immersion type membrane element is advantageous in terms of energy, it has the drawback that it is difficult to clean with a chemical solution because it is immersed in the water to be treated. is there. As a method of performing chemical cleaning, a method of taking out the membrane separation unit from the processing tank and immersing it in the chemical cleaning tank, a method of discharging all the water to be treated in the processing tank and replacing it with a chemical solution, etc. have been proposed.
All of them have a problem that they require a large-scale device and are not economical.

Further, it is difficult to remove dirt such as sludge adhering to the surface of the membrane simply by immersing the membrane element in a chemical solution, so that there is a problem that physical cleaning with a sponge or the like must be added.

The present invention solves the above problems, and an object of the present invention is to provide a method for cleaning a membrane element, which can economically and effectively clean the membrane element without using a large-scale device.

[0009]

In order to solve the above-mentioned problems, a method for cleaning a membrane element according to the present invention is a method for forming a permeate flow channel by opening a surface of a flat plate-shaped membrane support to form a permeate flow channel. Is a method for cleaning a plurality of immersion type membrane elements arranged side by side with an organic filtration membrane covering the surface of the membrane element, wherein the membrane element is immersed in the water to be treated, The chemical solution is injected in the direction opposite to the flow of the permeated solution, and the injected chemical solution is retained in the membrane element for a certain time,
At that time, the amount of the chemical liquid to be injected is about 1/5 to 1/10 of the maximum permeated liquid holding capacity of the membrane element, and the flow rate and the flow rate of 10 kP evenly flowing into the membrane elements arranged in parallel.
The injection is performed at a low pressure of a or less.

[0010]

[Function] In the membrane element immersed in the water to be treated, the pressure on the treated water side and the pressure on the permeated liquid side maintain a constant balance, and the permeation with the treated water side does not occur at any part of the filtration membrane. The pressure difference with the liquid side is constant. In this state,
When a small amount of chemical liquid is injected into the permeate liquid channel at a low pressure and kept for a certain period of time, the chemical liquid permeates evenly from the entire membrane surface to the water to be treated, and the entire surface of the filtration membrane is washed. At this time, the problem of peeling of the filtration membrane unlike the case of injecting a large amount of chemical liquid at high pressure does not occur. Further, since the chemical liquid is evenly injected into each of the juxtaposed membrane elements, a plurality of juxtaposed membrane elements are simultaneously washed.

[0011]

EXAMPLES The method for cleaning the membrane element of the present invention will be described below with reference to examples. The overall structure of the membrane separation unit according to the embodiment is almost the same as that of the conventional one described with reference to FIG. (Example 1) In a treatment tank for performing activated sludge treatment, membrane element cleaning of a membrane separation unit installed in an activated sludge mixed liquid as water to be treated was performed. 1 membrane separation unit
100 elements of m × 0.5 m × thickness 6 mm are arrayed at a pitch of 14 mm, and the maximum permeation liquid holding capacity of the arrayed membrane elements is calculated to be about 4 liters per element from the membrane area and the membrane pitch. To be done. When the amount of the chemical liquid close to or larger than the maximum permeated liquid holding capacity is injected, the problem of peeling of the filtration membrane occurs.

[0012] When the cleaning is performed, 5000 ppm of sodium hypochlorite solution is used as a chemical in the permeate flow path of the membrane element in the direction opposite to the flow of the permeate, and the flow rate is about 0.5 in about 5 minutes.
-1 liter (about 1/5 to 1/10 of the maximum permeate holding capacity of the membrane element) was injected, and the mixture was allowed to stand for about 1 hour, and a sufficient cleaning effect was obtained. At this time, a flow rate of about 200 cc / min was required to evenly inject the chemical liquid into 100 elements, but the injection pressure at this time was 5 kPa or less, and no separation of the filtration membrane occurred.

Generally, in the membrane element immersed in the water to be treated, the pressure on the water to be treated side and the pressure on the permeate side are kept in a certain balance, and the portion to be treated is treated at any part of the filtration membrane. The pressure difference between the water side and the permeate side is constant. For this reason, as described above, when a small amount of chemical liquid is injected into the permeate flow path at a low pressure in the immersed state of the membrane element and held for a certain period of time, the chemical liquid permeates uniformly from the entire membrane surface to the treated water side. As a result, the entire surface of the filtration membrane is washed. At this time, since the chemical solution evenly flows into each of the juxtaposed membrane elements, the juxtaposed membrane elements can be simultaneously washed. If a high flow rate of a chemical solution is injected into the permeate side of the membrane element, a pressure loss will occur in the permeate flow path, and only the upper part of the membrane element will be washed, or the filtration membrane will peel off. However, this problem can be avoided in the method of injecting a small amount of chemical liquid at a low pressure as described above.

Further, by carrying out chemical cleaning from the permeate side as described above, even if there is a sludge cake layer that cannot be separated by a gas-liquid mixed flow due to aeration, the sludge can be decomposed by the chemical solution, that is, sodium hypochlorite solution. The sludge cake layer can be removed during chemical cleaning or during aeration after chemical cleaning. Therefore, there is no need to perform physical cleaning with a sponge or the like one element at a time as in the conventional case, and labor can be saved significantly.

Sodium hypochlorite is consumed when decomposing activated sludge, but since it may remain in the permeate immediately after washing, the permeate immediately after washing should be returned to the treatment tank. Good. Since the amount of chemical solution to be injected is small, the amount of sodium hypochlorite is very small when viewed from the total amount of activated sludge, and even if sodium hypochlorite remains in the treatment tank, It does not affect activity.

The concentration of sodium hypochlorite to be injected may be determined in consideration of the chemical solution immersion time (that is, standing time). For example, the concentration shown in Table 1 below can be used.

[0017]

[Table 1]

The above-mentioned chemical cleaning method may be carried out while aeration is performed. In this case, however, the chemical on the membrane surface that has penetrated to the side of the water to be treated flows along with the flow of the water to be treated. It is preferable to inject half of the solution in 2 to 3 minutes and then slowly inject the remaining amount of the solution over 1 hour to maintain the state where the solution permeates from the permeate side to the treated water side at all times. . (Example 2) In the same manner as in Example 1, the membrane separation unit installed in the coagulated sludge mixed liquid as the water to be treated was washed in the treatment tank for coagulating the sludge. However,
An oxalic acid solution was used as the chemical solution.

In the coagulation treatment, what causes the clogging of the filtration membrane is, for example, an iron compound containing a coagulant. Therefore, the iron compound can be dissolved by washing with an acid such as oxalic acid as a chemical solution, and clogging can be eliminated.

In Example 1 and Example 2 described above, sodium hypochlorite was used as the treatment target of activated sludge and oxalic acid was used as the treatment target of iron compounds. Not limited to oxalic acid, various chemicals can be used depending on the object to be treated.

[0021]

As described above, according to the present invention, in the state where the membrane element is immersed in the water to be treated, each membrane element in which a small amount of the chemical liquid is arranged in parallel in the permeate passage of the membrane element at a low pressure Was injected in the direction opposite to the flow of the permeated liquid at a flow rate that evenly flows in, and the injected chemical liquid was held for a certain period of time. Thereby, in each membrane element, the chemical liquid permeates uniformly into the water to be treated from the entire membrane surface, and the entire surface of the filtration membrane is effectively washed. Therefore, the conventional problem that the chemical solution cleaning is difficult because the membrane element is immersed in the water to be treated is solved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an immersion type membrane separation unit in which a method for cleaning a membrane element of the present invention is performed.

[Explanation of symbols]

 2 membrane element 4 membrane support 5 permeate flow path 6 organic filtration membrane

Claims (1)

[Claims] 1. A plurality of side-by-side immersion type immersion filters, each having a flat plate-shaped membrane support opening to form a permeate flow channel and an organic filtration membrane disposed to cover the surface of the membrane support. A method for cleaning a membrane element, in which a chemical solution is injected into the permeate flow path in a direction opposite to the flow of the permeate while the membrane element is immersed in the water to be treated, and the injected chemical solution is kept constant in the membrane element. The amount of the chemical liquid to be injected is set to about 1/5 to 1/10 of the maximum permeation liquid holding capacity of the membrane elements, and the flow rate of the liquid evenly flowing into each of the juxtaposed membrane elements. And a method for cleaning a membrane element, which comprises injecting at a low pressure of 10 kPa or less.