JPH07136475A - Washing of reverse osmosis membrane module in cooncentration of milk - Google Patents

Abstract

PURPOSE:To wash a reverse osmosis membrane module to rapidly restore the capacity thereof at the time of the concn. of milk by a simple method. CONSTITUTION:In a washing method restoring the capacity of a reverse osmosis membrane module by washing the module lowered in water transmission flux or changed in a prohibiting ratio by the accumulation of a fouling substance on the surface of a membrane at the time of the concn. of milk, the reverse osmosis membrane module is washed with at least one or more chemical agent among an aq. acid soln. and an aq. peracetlc acid soln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a reverse osmosis membrane having a reduced water permeation flux or a changed rejection rate due to deposition of fouling substances such as proteins and microorganisms on the membrane surface during milk concentration. The present invention relates to a cleaning method for cleaning a module to restore performance.

[0002]

2. Description of the Related Art A membrane separation device equipped with a reverse osmosis membrane module as a concentration / separation means does not require heat energy and can perform a continuous concentration / separation operation. Therefore, it is widely used in various industrial fields including food. Has been converted. However, in such membrane separation treatment, so-called fouling substances such as proteins, saccharides, and microorganisms are deposited and deposited on the membrane surface on the feed side of the undiluted solution when the treatment is performed for a long time or due to concentration of the undiluted solution. However, the permeation flux of the membrane separation device and the separation efficiency are lowered.

In this milk concentration, proteins and saccharides are deposited, and the permeation flux and the separation efficiency of the membrane separator are significantly reduced with time. Heretofore, as a method for cleaning the film whose performance has been deteriorated by the fouling substance and recovering the performance, there has been proposed a cleaning method using an oxidizing agent such as hydrogen peroxide or chlorine, an alkaline aqueous solution or the like.
However, even if this method is applied to a reverse osmosis membrane module whose performance has deteriorated when fouling substances are deposited and deposited on the membrane surface during milk concentration, membrane deterioration is promoted due to small membrane resistance, and practical performance recovery is achieved. Can't expect. Thus, there is a demand for an effective method for promptly recovering the performance of the reverse osmosis membrane module used for such milk concentration by a simple method.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in order to meet the above-mentioned demand, and when milk is concentrated,
It is an object of the present invention to provide a cleaning method for quickly recovering the performance of a reverse osmosis membrane module with a simple method.

[0005]

According to the present invention, when milk is concentrated, a fouling substance is deposited on the membrane surface to wash the reverse osmosis membrane module having a reduced water permeation flux and a changed rejection rate. In the cleaning method for recovering performance, the reverse osmosis membrane module is at least one of an acid aqueous solution and a peracetic acid aqueous solution.
It is characterized in that the above-mentioned chemicals are used for circulating cleaning.

As the acid aqueous solution used in the present invention,
A nitric acid aqueous solution is preferably used, and it is not necessary to make the concentration particularly high, and when the concentration is lower than pH 5, recovery of performance may not be sufficiently achieved.
It is suitable that it is -5. Further, the concentration of the peracetic acid aqueous solution used in the present invention does not need to be particularly high, and when the concentration is lower than 0.001% by weight, performance recovery may not be sufficiently achieved, and therefore 0.001 to 10% by weight. Is preferred.

The reverse osmosis membrane module used in the present invention may be any one as long as the membrane performance and material are not deteriorated by the above acid aqueous solution or peracetic acid aqueous solution. For example, polysulfonated polyethersulfone type, polyvinyl alcohol type or polyamide type composite membrane. Is mentioned. These films are not deteriorated by the nitric acid aqueous solution or the peracetic acid aqueous solution having the above concentration.

In the cleaning method of the present invention, it is preferable to add a circulating cleaning step with water before circulating cleaning the reverse osmosis membrane module with at least one chemical of an acid aqueous solution and a peracetic acid aqueous solution. It is preferable that this circulation cleaning with water is operated at a circulation flow rate higher than that at the time of milk concentration and at a circulation flow rate of the allowable maximum differential pressure of the reverse osmosis membrane module or less. However, the presence or absence of the water washing is appropriately selected in view of the total washing time and the cost of the chemicals used after the water washing. In addition, even after circulating cleaning with chemicals,
It is preferable to add a circulating washing step with water to flush out the washed chemicals. In the case of circulating cleaning with at least one or more chemicals of the acid aqueous solution and the peracetic acid aqueous solution, circulation cleaning with one chemical is usually sufficient, but if further performance recovery is desired, the dirty chemicals should be removed. Circulation cleaning may be carried out again as a new aqueous acid solution or peracetic acid solution. However, the presence / absence of the cleaning using the chemical again is appropriately selected in view of the cost of the overall cleaning time and the chemicals.

[0009]

As described above, according to the present invention, when milk is concentrated, fouling substances are deposited on the surface of the membrane, and the reverse osmosis membrane module in which the water permeation flux is reduced and the blocking rate is changed is formed into a membrane. The performance can be promptly restored by washing with a simple method without deterioration.

[0010]

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

Example 1 Polyvinyl alcohol composite film (NTR-manufactured by Nitto Denko)
729HF-S4), 50 L of commercially available milk was concentrated twice at a circulating flow rate of 10 L / min and an operating pressure of 30 kg / cm ² , and the permeation rate in a 0.15% NaCl aqueous solution was 6.3 tons / min. The performance of which the rejection rate was 93.0% in the day, the permeation rate decreased to 1.3 ton / day due to the membrane fouling by the fouling substance, and the rejection rate was 99.1.
% Has changed. Therefore, when water was washed for 30 minutes at a circulation flow rate of 20 L / min and an operating pressure of 1 kg / cm ² , 0.15% NaCl was added.
The permeation rate is 5.0 ton / day and the rejection rate is 9 in aqueous solution.
Recovered to 7.6%, then using a nitric acid solution of pH 1.8, circulating flow rate 10 L / min, operating pressure 0.5 kg / cm ² 30
After washing for a minute, the permeation rate was recovered to 6.3 ton / day and the blocking rate was recovered to 95.7% in a 0.15% NaCl aqueous solution. Then, the product was further washed with a 0.5% aqueous solution of peracetic acid for 30 minutes at a circulating flow rate of 10 L / min and an operating pressure of 0.5 kg / cm ² , and a permeation rate of 0.15% NaCl aqueous solution was 6.
3ton / day, blocking rate recovered to 93.2%.

Example 2 Concentration was carried out in the same manner as in Example 1 except that a polyamide-based composite membrane (NTR-759HR-S4 manufactured by Nitto Denko) was used in place of the polyvinyl alcohol-based composite membrane. Permeation rate of 6.5 tons in 0.15% NaCl aqueous solution
n / day, the rejection rate was 99.7%, but the permeation rate was 1.3 ton /
It decreased to day and the blocking rate changed to 99.9%. Therefore, at a circulating flow rate of 20 L / min and an operating pressure of 1 kg / cm ² , 30
After washing with water for 0.1 minutes, the permeation rate in a 0.15% NaCl aqueous solution recovered to 4.8 ton / day and the blocking rate recovered to 99.9%.
Then, using a nitric acid aqueous solution having a pH of 1.8, the circulation flow rate is 10 L /
After washing for 30 minutes at operating pressure of 0.5 kg / cm ² , the permeation rate was 6.0 ton / da in 0.15% NaCl aqueous solution.
y, the blocking rate recovered to 99.9%. Then further
0.15% when washed with a 0.5% aqueous solution of peracetic acid for 30 minutes at a circulating flow rate of 10 L / min and an operating pressure of 0.5 kg / cm ^2.
The permeation rate in the NaCl aqueous solution was 6.5 ton / day, and the blocking rate was recovered to 99.8%.

Example 3 A washing operation was performed in the same manner as in Example 1 except that the washing with water was not performed in Example 1, and 0.15% NaC was added before the start of the treatment.
l Permeability in aqueous solution was 6.4 ton / day, rejection rate was 92.5%, but permeation rate decreased to 1.4 ton / day due to membrane fouling by fouling substances.
The blocking rate of the reverse osmosis membrane module changed to 98.8%,
When washed with an aqueous nitric acid solution having a pH of 1.8 at a circulation flow rate of 10 L / min and an operating pressure of 0.5 kg / cm ² for 30 minutes, 0.15
% Aqueous solution, the permeation rate recovered to 5.4 ton / day and the blocking rate recovered to 95.7%. Then, using a 0.5% aqueous solution of peracetic acid, a circulation flow rate of 10 L / min and an operating pressure of 0.5
After washing with kg / cm ² for 30 minutes, the permeation rate in a 0.15% NaCl aqueous solution was 6.1 ton / day, and the blocking rate was 93.
Recovered to 4%.

Example 4 A cleaning operation was carried out in the same manner as in Example 1 except that the water cleaning and the circulation cleaning using a nitric acid aqueous solution were not carried out. The permeation rate was 0.15% NaCl aqueous solution before starting the treatment. Was 6.4 ton / day, the blocking rate was 93.2%, but due to membrane fouling by fouling substances, the permeation rate was reduced to 1.2 ton / day, and the blocking rate changed to 99.2%. The reverse osmosis membrane module was washed with a 0.5% peracetic acid aqueous solution for 30 minutes at a circulation flow rate of 10 L / min and an operating pressure of 0.5 kg / cm ² , and the permeation rate was 5.6 ton / day in the 0.15% NaCl aqueous solution and the inhibition rate was Has recovered to 94.8%.

Claims (3)

[Claims] 1. A cleaning method for recovering performance by cleaning a reverse osmosis membrane module in which fouling substances are deposited on the surface of a membrane when milk is concentrated to reduce the water permeation flux and the blocking rate is changed. A method for cleaning a reverse osmosis membrane module in milk concentration, which comprises circulatingly cleaning the osmosis membrane module with at least one chemical agent selected from an aqueous acid solution and an aqueous peracetic acid solution. 2. The method for cleaning a reverse osmosis membrane module in milk concentration according to claim 1, wherein the acid aqueous solution is a nitric acid aqueous solution and has a pH of 1 to 5. 3. The method for cleaning a reverse osmosis membrane module in milk concentration according to claim 1, wherein the aqueous solution of peracetic acid has a concentration of 0.001 to 10% by weight.