TW202302473A - Method for suppression of biofouling in water and water treatment equipment - Google Patents

Abstract

A method for treating a water containing a chlorine-based oxidizer while suppressing a fouling of a reverse osmosis membrane, comprising adding a biofouling inhibitor or slime control agent to the water containing a chlorine-based oxidizer, adding reducing agent to the water which the biofouling inhibitor or slime control agent has been added, and then subjecting the water which the reducing agent has been added to treatment with the reverse osmosis membrane.

Description

Water system biofouling suppression method and water treatment device

The invention relates to a method for inhibiting reverse osmosis membrane fouling and a water treatment method. More specifically, the present invention relates to methods for inhibiting the formation of biofilm on the reverse osmosis membrane and the damage of the reverse osmosis membrane itself, inhibiting the fouling of the reverse osmosis membrane, and inhibiting the formation of biofilm on the reverse osmosis membrane and the damage of the reverse osmosis membrane itself , and a method of treating water containing chlorine-based oxidants.

Reverse osmosis membranes are used in liquid concentration, desalination, pure water production and other water treatment. When the reverse osmosis membrane is used in water treatment, etc., it is polluted by various substances, or the permeation flux is reduced, or the selectivity is reduced. As membranes used for reverse osmosis membranes, cellulose acetate membranes, polyether membranes, crosslinked aramid membranes, and the like are known.

Furthermore, as the raw water of the water treatment apparatus, for example, industrial water, tap water, well water, river water, lake water, factory waste water, etc. are used. Chlorine-based oxidants such as sodium hypochlorite are often added to tap water. In addition, chlorine-based oxidants are also added to well water or recycled water for the purpose of inhibiting microbial growth. Since free chlorine originating from chlorine-based oxidizing agents added to water may attack the reverse osmosis membrane, it is preferable to remove residual free chlorine before the reverse osmosis membrane.

On the other hand, when adjusting the reproduction conditions of organisms and treating water that is prone to sludge formation, bacteria multiply in the reverse osmosis membrane, which may clog the reverse osmosis membrane (biofouling). To inhibit biofouling or sludge formation, biological sludge inhibitors or sludge control agents are sometimes used.

For example, Patent Document 1 discloses a pre-treatment method for reverse osmosis membrane treatment of water containing an oxidizing agent with a reverse osmosis membrane device, which is characterized in that nitrous acid and/or its salt are added to the water containing the oxidizing agent to reduce and remove the oxidizing agent. Add oxidizing chemicals to the water after adding nitrous acid and/or its salt. Patent Document 1 discloses one or two or more species selected from the group consisting of chlorsulfuric acid, a salt of chlorsulfuric acid, and a stabilized hypobromous acid-based sludge control agent as an oxidizing chemical.

Patent Document 2 discloses a method of using a composite semipermeable membrane, which is characterized in that when the composite semipermeable membrane formed by a microporous membrane and a cross-linked polymer film containing a special structural unit is subjected to reverse osmosis operation, it contains 0.5~5000ppm The aqueous solution of pH 4~7 of chlorine-based bactericide is sterilized, and then washed with an aqueous solution containing 1.0~5000ppm reducing agent to repeatedly use the composite semipermeable membrane.

Patent Document 3 discloses a forward osmosis treatment method, which includes the following steps: in a forward osmosis membrane having a first surface and a second surface, the first surface is contacted with a feed solution, and the second surface is soaked with A drive (draw) solution with a higher osmotic pressure than the inflow solution, so that the water contained in the inflow solution passes through the forward osmosis membrane and moves from the first side to the second side; before the osmosis step, Adding a chlorine-based bactericide to any one of the inflow solution and the draw solution; adding a reducing agent to at least one of the inflow solution and the draw solution after the bactericide addition step and before the permeation step Reductant addition step.

Patent Document 4 discloses a press-in water production system, which is a press-in water production system for producing press-in water for crude oil production using fresh water obtained by passing seawater through a reverse osmosis membrane, and is equipped with: a bactericide adding device for adding a chlorine-based bactericide to seawater ; A residual chlorine concentration measuring device for measuring the residual chlorine concentration in seawater with a chlorine-based bactericide added by a bactericide adding device; it is installed at the rear of the residual chlorine concentration measuring device, and the seawater is added to the seawater with a chlorine-based bactericide A reducing agent adding device for the dechlorination of residual chlorine in the reductant; a reverse osmosis membrane obtained by permeating seawater with a reducing agent added by the reducing agent adding device to obtain pressurized water; based on the residual chlorine measured by the residual chlorine concentration measuring device Concentration, an arithmetic control device that controls the amount of chlorine-based fungicide added to the fungicide adding device. [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2016-221500 [Patent Document 2] Japanese Patent Application Laid-Open No. 59-26101 [Patent Document 3] Japanese Patent Laid-Open No. 2015-188787 [Patent Document 4] Japanese Patent Laid-Open No. 2016-22458

[Issues to be solved by posting a name]

The purpose of the present invention is to provide a method for inhibiting the formation of biofilm on the reverse osmosis membrane and the damage of the reverse osmosis membrane itself, inhibiting the fouling of the reverse osmosis membrane, and inhibiting the formation of biofilm on the reverse osmosis membrane and the damage of the reverse osmosis membrane itself, and A method of treating water containing chlorine-based oxidizing agents. [Means to solve the problem]

As a result of examining in order to achieve the said object, this invention including the following embodiment was completed. [1] A method for treating water containing a chlorine-based oxidant, comprising: adding a biofouling inhibitor or a sludge control agent to water containing a chlorine-based oxidant, adding a biofouling inhibitor or a sludge control agent to water after adding a biofouling inhibitor or a sludge control agent Reducing agent, followed by the treatment of the water after adding the reducing agent using reverse osmosis membrane.

[2] A method for inhibiting fouling of a reverse osmosis membrane, comprising: adding a biofouling inhibitor or a sludge control agent to water containing a chlorine-based oxidant, and adding a reducing agent to water after adding a biofouling inhibitor or a sludge control agent. agent.

[3] The method of [1] or [2], wherein the biofouling inhibitor or sludge control agent contains an isothiazolone compound. [4] The method according to any one of [1] to [3], wherein the reducing agent is sulfurous acid, sulfite or bisulfite. [5] The method according to any one of [1] to [4], wherein the chlorine-based oxidizing agent is perchloric acid, perchlorate, chloric acid, chlorate, chlorous acid, chlorite, hypochlorite acid, hypochlorite or chlorine.

[6] The method as in [3], wherein the isothiazolone compound is 5-chloro-2-methyl-4-isothiazol-3-one, 2-methyl-4-isothiazol-3-one, 4, 5-dichloro-2-n-octyl-4-isothiazol-3-one, 2-n-octyl-4-isothiazol-3-one, 1,2-benzisothiazol-3-one, N- Methyl-1,2-benzisothiazol-3-one or N-(n-butyl)-1,2-benzisothiazol-3-one. [Invention effect]

If the method of the present invention is used, the formation of biofilm on the reverse osmosis membrane and the damage of the reverse osmosis membrane itself can be suppressed, and the fouling of the reverse osmosis membrane can be suppressed. According to the water treatment method of the present invention, water containing chlorine-based oxidants can be treated while effectively inhibiting the formation of biofilm on the reverse osmosis membrane and the damage of the reverse osmosis membrane itself. The method of the invention can prolong the service period of the reverse osmosis membrane and reduce the frequency of replacing or cleaning the reverse osmosis membrane.

The method for treating water containing chlorine-based oxidants includes: adding a biofouling inhibitor or sludge control agent to water containing chlorine-based oxidants, and adding a reducing agent to the water after adding the biofouling inhibitor or sludge control agent , followed by the treatment of the water after adding the reducing agent using a reverse osmosis membrane. Also, the method for inhibiting fouling of reverse osmosis membranes of the present invention includes: adding a biofouling inhibitor or a sludge control agent to water containing a chlorine-based oxidant, and adding a reducing agent to the water after adding the biofouling inhibitor or sludge control agent .

Examples of the chlorine-based oxidizing agent used in the present invention include perchloric acid, perchlorate, chloric acid, chlorate, chlorous acid, chlorite, hypochlorous acid, hypochlorite, chlorine, etc. . Chlorine can also be generated in systems using electrodes. As perchlorate, chlorate, chlorite, and hypochlorite, sodium salt, potassium salt, calcium salt, magnesium salt, aluminum salt, etc. are mentioned, Preferably, a sodium salt is mentioned. Among these, sodium hypochlorite is preferably used in the present invention.

The amount of chlorine-based oxidants contained in the water before adding biofouling inhibitors or sludge control agents is not particularly limited, but in terms of chlorine mass concentration, relative to the volume of water, it is usually 0.1~10mg/L, preferably 0.3~ 2 mg/L. The chlorine mass concentration can be measured by the DPD method using N,N-diethyl-1,4-phenylenediamine according to JIS K 0400-33-10:1999.

As the biofouling inhibitor or sludge control agent used in the present invention, for example, 2,2-dibromo-3-nitropropionamide, isothiazolone compound, ammonia, chloramine, chlorsulfuric acid, stabilized times Bromic acid-based sludge control agents (trade name "ORPERSION E266 series" manufactured by ORGANO Co., Ltd., trade name "STABLEX" manufactured by Nalco Corporation) and the like. Among these, those containing an isothiazolone compound are preferable. Examples of isothiazolone compounds include 5-chloro-2-methyl-4-isothiazol-3-one, 2-methyl-4-isothiazol-3-one, 4,5-dichloro-2-n- Octyl-4-isothiazol-3-one, 2-n-octyl-4-isothiazol-3-one, 1,2-benzisothiazol-3-one, N-methyl-1,2-benzene Aisothiazol-3-one, N-(n-butyl)-1,2-benzisothiazol-3-one, etc. The biofouling inhibitor or sludge control agent is preferably added in the form of granules, powder, aqueous solution or liquid.

The amount of biofouling inhibitor or sludge control agent added varies with the type of biofouling inhibitor or sludge control agent used. For biofouling inhibitors or sludge control agents that can be converted to total chlorine, the amount added is usually 0.01~50mg/L relative to the volume of water. For example, in the case of sodium chloraminesulfonate, the amount to be added is usually 0.1-10 mg/L, preferably 0.5-3 mg/L in terms of total chlorine relative to the volume of water. When stabilizing the hypobromous acid-based sludge control agent, the amount to be added is usually 0.01-3 mg/L, preferably 0.02-0.2 mg/L in terms of total chlorine relative to the volume of water. In the case of 2,2-dibromo-3-nitropropionamide, the amount to be added is usually 0.1-10 mg/L, preferably 0.2-6 mg/L in terms of total chlorine relative to the volume of water.

For biofouling inhibitors or sludge control agents that are difficult to convert to total chlorine, the amount added is usually 0.005~5mg/L relative to the volume of water. For example, in the case of isothiazolone compounds such as 5-chloro-2-methyl-4-isothiazol-3-one, the amount added is usually 0.01~2mg/L, preferably 0.03~1mg/L relative to the volume of water. L.

Examples of the reducing agent used in the present invention include nitrous acid, nitrite, sulfurous acid, sulfite, bisulfite, thiosulfuric acid, and thiosulfate. Examples of nitrite, sulfite, bisulfite and thiosulfate include sodium salt, potassium salt, calcium salt, magnesium salt and aluminum salt, preferably sodium salt. Among these, sodium bisulfite or sodium sulfite is preferably used. The reducing agent is preferably added in the form of an aqueous solution.

The amount of reducing agent added is not particularly limited, but it is preferably 1 g equivalent or more, more preferably 1.5-4 g equivalent, and more preferably 2-3 g equivalent relative to 1 g equivalent of the chlorine-based oxidizing agent contained in the water before adding the reducing agent. . Also, 1 g equivalent is a value obtained by dividing the mass of 1 mole by the valence. In the present invention, a residual chlorine meter can be installed in the piping of a water treatment facility through which water containing a chlorine-based oxidizing agent passes to measure the mass concentration of chlorine, and based on the measured value, the amount of the reducing agent added can be adjusted. In order to adjust the amount of reducing agent added, a control system can be combined.

Chlorine-based oxidants can inhibit microbial reproduction, but on the other hand, they will corrode the reverse osmosis membrane. If the chlorine-based oxidizing agent is reduced by the reducing agent, the effect of inhibiting the growth of microorganisms will disappear, and fouling will easily occur in the reverse osmosis membrane. Therefore, in the present invention, first, a biofouling inhibitor or a sludge control agent is added to water containing a chlorine-based oxidizing agent, and then a reducing agent is added to reduce the chlorine-based oxidizing agent. Biofouling inhibitors or sludge control agents, because the content of the reducing agent is almost the same and does not decrease even if the reducing agent is added, so even after the chlorine-based oxidizing agent is consumed due to the reduction reaction, the inhibitory effect on the growth of microorganisms can still be maintained. Fouling in the permeable membrane.

Also, the reverse osmosis membrane used in the present invention is a semipermeable membrane for separating low molecular substances or ions from water by using reverse osmosis. Reverse osmosis prepares concentrate and permeate through a semi-permeable membrane, and applies a pressure exceeding the osmotic pressure on the concentrate side to allow water to permeate to the permeate side. The material used for the semipermeable membrane is not particularly limited, for example, polyamide, polyamide, polyimide, cellulose and the like. The reverse osmosis membrane is usually integrated with other components and used in the form of a membrane module. Examples of the membrane module include a housing storage method membrane module, a tank immersion type membrane module, and the like. Housing storage method Membrane module is the one that stores and integrates the reverse osmosis membrane, its support body, flow path material and other components in the housing. Examples of the case housing type membrane module include, for example, a module using a flat membrane such as a spiral type module, a module using a tubular membrane such as a capillary type module, or a hollow fiber type module.

Next, an Example and a comparative example are shown, and this invention is demonstrated more concretely. However, the following examples do not limit the scope of the present invention.

Comparative example 1 Waste water was treated with a UF membrane device, and water of the water quality shown in Table 1 (hereinafter referred to as treated water) was prepared. In addition, since the concentration of inorganic substances in the water to be treated is low, it was confirmed that no scale originating from inorganic materials was generated on the reverse osmosis membrane during the implementation of Examples and Comparative Examples. EC is electrical conductivity, and BOD is biochemical oxygen demand (Biochemical Oxygen Demand).

A reverse osmosis membrane module using ES20 (reverse osmosis membrane manufactured by Nitto Denko Co., Ltd.) was installed in the water treatment device shown in FIG. 2 . In such a way that the amount of sodium hypochlorite (chlorine oxidizing agent) added is 1 mg/L and sodium bisulfite (reducing agent) is 1.5 mg/L, the water to be treated is introduced into the water treatment device shown in Figure 2 , for water treatment. After 15 days from the start of the water flow, the pressure difference of the module rose sharply, and the device automatically stopped.

Comparative example 2 The reverse osmosis membrane module using ES20 is installed in the water treatment device shown in Figure 3. So that the added amount of sodium hypochlorite (chlorine oxidizing agent) is 1 mg/L, the added amount of sodium bisulfite (reducing agent) is 1.5 mg/L, 5-chloro-2-methyl-4-isothiazoline-3- The addition amount of ketone (biofouling inhibitor) is 0.5 mg/L, and the water to be treated is passed into the water treatment device shown in Fig. 3 for water treatment. After 16 days from the start of water supply, the pressure difference of the modules rose sharply, and the device automatically stopped. Also, it can be seen that if 0.5 mg/L of 5-chloro-2-methyl-4-isothiazolin-3-one (biofouling inhibitor) is added to the organic wastewater of the water quality shown in Table 1, no biofilm will occur . A biofilm is created between the point of addition of the reducing agent and the point of addition of the biofouling inhibitor, which builds up on the reverse osmosis membrane.

Example 1 The reverse osmosis membrane module using ES20 is installed in the water treatment device shown in Figure 1. So that the added amount of sodium hypochlorite (chlorine oxidizing agent) is 1 mg/L, and the added amount of 5-chloro-2-methyl-4-isothiazolin-3-one (biofouling inhibitor) is 0.5 mg/L. Sodium bisulfate (reducing agent) is added in an amount of 1.5mg/L, and the water to be treated is fed into the water treatment device shown in Figure 1 for water treatment. Even after 50 days have passed since the start of water supply, the pressure difference of the module has hardly changed.

The concentration of sodium hypochlorite in the water after adding the biofouling inhibitor and before adding the reducing agent was 1.0 mg/L, and the concentration of 5-chloro-2-methyl-4-isothiazolin-3-one was 0.5 mg/L. After adding the reducing agent and before the reverse osmosis membrane device, the concentration of sodium hypochlorite in the water is 0.15mg/L (reduction of about 85%), and the concentration of 5-chloro-2-methyl-4-isothiazolin-3-one is 0.37 mg/L (decrease about 26%). It can be seen that the difference of the biofouling inhibitor is not reduced compared to the chlorine-based oxidizing agent which is greatly reduced by adding the reducing agent. Also, the concentration of sodium hypochlorite was analyzed by the DPD method (diethyl-p-phenylenediamine method), and the concentration of 5-chloro-2-methyl-4-isothiazolin-3-one was analyzed by the HPLC method (high-speed liquid chromatography method). )analyze.

1: Treated water 2: Chlorine oxidizing agent adding device 3: Adding device for reducing agent 4: Reverse osmosis membrane device 5: concentrated water 6: see through water 7: Adding device for biological fouling inhibitor or sludge control agent

[ Fig. 1 ] is a diagram showing a configuration example of a water treatment device of the present invention. [ Fig. 2 ] is a diagram showing a configuration example of a conventional water treatment device. [ Fig. 3 ] is a diagram showing a configuration example of a conventional water treatment device.

1: Treated water

2: Chlorine oxidizing agent adding device

3: Adding device for reducing agent

4: Reverse osmosis membrane device

5: concentrated water

6: see through water

7: Adding device for biological fouling inhibitor or sludge control agent

Claims (5)

A method of treating water containing a chlorine-based oxidant, comprising: adding a biofouling inhibitor or a sludge control agent to water containing a chlorine-based oxidant, Add reducing agent to the water after adding biofouling inhibitor or sludge control agent, Next, the water after adding the reducing agent is treated with a reverse osmosis membrane. A method for inhibiting fouling of a reverse osmosis membrane, comprising: adding a biofouling inhibitor or a sludge control agent to water containing a chlorine-based oxidant, and adding a reducing agent to the water after adding the biofouling inhibitor or sludge control agent. The method according to claim 1 or 2, wherein the biofouling inhibitor or sludge control agent comprises an isothiazolone compound. The method according to claim 1 or 2, wherein the reducing agent is sulfurous acid, sulfite or bisulfite. The method of claim 1 or 2, wherein the chlorine-based oxidizing agent is perchloric acid, perchlorate, chloric acid, chlorate, chlorous acid, chlorite, hypochlorous acid, hypochlorite or chlorine.

Images