JP2610669B2 - Processing method of membrane module - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating a membrane module immediately after the membrane module is continuously immersed in an aqueous formaldehyde solution.

<Conventional Technology> In the field of food and medicine, when separation, purification, concentration, etc. are performed by a membrane module, sterilization or prevention of bacterial growth is a serious problem from a sanitary point of view. Thus, when the membrane module is out of service for a relatively long time, the stock solution in the membrane module is replaced with formalin to prevent harmful bacteria from growing due to nutrients in the stock solution. In this way, the membrane module is preserved in formalin during its suspension, and at the time of restart, formalin is discharged from the inside of the membrane module and the membrane surface of the membrane module is washed with pure water.

<Problem to be Solved> However, according to the experience of the present inventors, the permeated water amount of the membrane module after the water washing is considerably lower than the permeated water amount when the operation is stopped. In the case of a reverse osmosis membrane module using a reverse osmosis membrane, the reduction ratio reaches as much as 40%.

An object of the present invention is to provide a method for treating a membrane module that enables the membrane module to be operated with a high permeated water amount, based on such knowledge, in order to solve the problem.

<Means for Solving the Problems> In the method for treating a membrane module according to the present invention, after the membrane surface of the membrane module is continuously contacted with an aqueous formaldehyde solution, the membrane surface is treated with an alcohol adjusted to be alkaline. And operating the membrane module.

The present invention is applied to a membrane module using a semipermeable membrane, and is particularly effective for a module using a reverse osmosis membrane, and is particularly effective for an aromatic polyamide-based reverse osmosis membrane.

The above-mentioned case where the membrane surface is continuously contacted with the aqueous formaldehyde solution usually means that when the operation of the membrane module is stopped for a relatively long time, the remaining undiluted liquid (for example, a food processing raw material liquid) in the membrane module is discharged. After that, it is filled with formalin (a 37% aqueous solution of formalaldehyde), and the membrane module is stored in this state.

For the treatment of the film surface with the alcohol adjusted to be alkaline, a method of immersing the film surface in contact with formalin in the alcohol or a method of circulating the alcohol in a non-pressurized state can be used.

Ethanol, methanol and the like can be used as the alcohol, and sodium hydroxide, hydrazine, ammonia and the like can be used as the alkaline substance for alkalinization.

To adjust the alcohol to alkaline, the concentration should be 10 to 10
The pH may be adjusted to 9 to 12 by adding an alkaline substance to 0% alcohol.

<Description of Examples> Hereinafter, examples of the present invention will be described.

Example 1 The membrane module used was a spiral type using an aromatic polyamide reverse osmosis membrane having a membrane area of 7 m ² as the membrane, the operating pressure was 15 kgf / cm ² , and the initial permeate water amount (raw water was tap water) was 5.2 ^{m 3.}
/ d at ₂₅ ° C.

By operating this membrane module, tap water was treated with pure water for 5 days, then the operation was stopped, the remaining water was replaced with 0.5% formalin, and this state was maintained for 7 days. Seven days later, formalin was discharged, and the amount of permeated water was measured. As a result, it was 60% of the initial permeated water amount.

Therefore, 50% ethanol was adjusted to PH = 11 with sodium hydroxide, the membrane surface of the module was immersed in this alcohol for 30 minutes, and then washed with pure water for 10 minutes. After the water washing, when the amount of permeated water of the reverse osmosis membrane was measured, it had recovered to the initial amount of permeated water.

Example 2 The same procedure as in Example 1 was performed except that ethanol having a concentration of 50% was adjusted to P = 10 with hydrazine as alcohol, and the time for immersing the module membrane surface in this alcohol was set to 60 minutes. Example 1 was the same. In this case, the permeated water amount had recovered to 95% of the initial permeated water amount.

Comparative Example Compared with Example 1, the immersion treatment with alcohol was omitted, and after discharging the formalin, the membrane surface was immediately washed with pure water.
The same procedure as in Example 1 was carried out except that the sample was washed with water for minutes. The amount of permeated water after this water washing was only 62% of the initial permeated water amount, and the improvement was little compared to the permeated water amount of 60% after immersion in formalin for 7 days.

As described above, according to the method for treating a membrane module according to the present invention, even when the membrane surface of the membrane module is continuously contacted with an aqueous formaldehyde solution, the membrane surface can be recovered with good permeability by treating the membrane with an alcohol adjusted to be alkaline. In addition, during the operation of the membrane module, the growth of bacteria by immersion in formalin can be effectively prevented.

Claims (1)

(57) [Claims] 1. The membrane module according to claim 1, wherein, after the membrane surface of the membrane module is continuously contacted with an aqueous formaldehyde solution, the membrane surface is treated with an alcohol adjusted to be alkaline, and then the membrane module is operated. Processing method.