Water treatment method, surfactant for water treatment

Abstract

This invention provides a method for treating treated water and a surfactant for treating treated water that contribute to extending the lifespan of solid-liquid separation membranes. [Solution] A method for treating water to be treated is provided, comprising the steps of adding a surfactant to the water to be treated and subjecting the water to be treated to solid-liquid membrane separation. Here, it is preferable that the surfactant is added to the water to be treated to a concentration of 0.1 mg / l or more and 5000 mg / l or less. It is also preferable that the final HLB value of the surfactant is 3 or more and 20 or less.

Description

[Technical Field]

[0001] The present invention relates to a method for treating water to be treated and a surfactant for treating water to be treated. In particular, it relates to a method for treating water to be treated using a solid-liquid separation membrane and a surfactant for treating water to be treated. [Background technology]

[0002] Wastewater discharged from factories and other sources is subject to wastewater discharge standards, and in order to comply with these standards, wastewater treatment using solid-liquid membrane separation, such as the membrane bioreactor (MBR), is carried out. In wastewater treatment methods using solid-liquid separation membranes, clogging of the solid-liquid separation membrane (so-called fouling) is known to occur. When fouling occurs in a solid-liquid separation membrane, it is necessary to either wash away the blockage or replace it.

[0003] The cleaning or replacement of this solid-liquid separation membrane needs to be done approximately once a year, which poses problems in terms of cost and labor. For this reason, for example, Patent Document 1 describes a technology developed to extend the lifespan of the solid-liquid separation membrane by adding microorganisms to it. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-089627 [Overview of the project] [Problems that the invention aims to solve]

[0005] The following analysis has been conducted from the perspective of the present invention. The disclosures in the above-mentioned prior art documents are incorporated herein by reference.

[0006] In the technology described in Patent Document 1, because a wide variety of bacteria are present in activated sludge, the added microorganisms do not necessarily proliferate as intended. As a result, there is a problem in that it does not have a sufficient effect in preventing fouling of the solid-liquid separation membrane.

[0007] Therefore, the present invention aims to provide a method for treating water that contributes to extending the lifespan of a solid-liquid separation membrane in a water treatment method using a solid-liquid separation membrane, and a surfactant for treating water. [Means for solving the problem]

[0008] According to the first aspect of the present invention, The steps include adding a surfactant to the water to be treated, A step of subjecting the water to be treated, to which a surfactant has been added, to solid-liquid film separation, A method for treating water to be treated is provided, which includes this method.

[0009] According to a second aspect of the present invention, A surfactant for treating treated water, applicable to a water treatment method using solid-liquid membrane separation, A surfactant for treating treated water, which is added to treated water subjected to solid-liquid membrane separation, is provided. [Effects of the Invention]

[0010] According to each aspect of the present invention, a method for treating water that uses a solid-liquid separation membrane and a surfactant for treating water that contribute to extending the lifespan of the solid-liquid separation membrane are provided. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described in detail with reference to the drawings. The reference numerals in the drawings provided below are for illustrative purposes only and are not intended to limit the present invention to the illustrated embodiments.

[0012] First, the outline of the present invention will be described. The present invention is based on a method for treating water using a solid-liquid separation membrane, in which a surfactant is added to the water to be treated. The water to be treated includes factory wastewater, domestic wastewater, sewage, etc., and is water that is subject to treatment such as oil and grease removal and sludge removal before being discharged into the natural environment. The method for treating the water to be treated can be any method that uses a solid-liquid separation membrane, and may be a membrane separation activated sludge method or a method that treats the water to be treated under anaerobic conditions. Here, it is preferable that the surfactant is added to the water to be treated to a concentration of 0.1 mg / l or more and 5000 mg / l or less. The surfactant may be added to the water to be treated before it is fed to the solid-liquid separation membrane. For example, in a membrane separation activated sludge method, the water to be treated is fed to the solid-liquid separation membrane via a raw water tank, a conditioning tank, and an aeration tank, but the surfactant may be added to the water to be treated at any of the stages of the raw water tank, conditioning tank, or aeration tank. Furthermore, it is preferable that the final HLB value of the surfactant is 3 or more and 20 or less. Furthermore, it is preferable that the surfactant is a mixture of multiple surfactants having different initial HLB values, with a final HLB value of 3 or higher and 20 or lower. It is also preferable that the surfactant is biodegradable.

[0013] In other words, since the membrane separation activated sludge method involves the assimilation of treated water by microorganisms, those skilled in the art would have thought that adding surfactants to the treated water would hinder the growth of microorganisms and lead to a decrease in assimilation efficiency.

[0014] For example, the antibacterial properties of surfactants have been studied extensively, and the minimum inhibitory concentrations for Staphylococcus aureus, categorized by ionic type, are 2 ppm for cationic surfactants (benzalkonium chloride), 12 ppm for amphoteric surfactants (alkyldiamineethyleneglycine acetate), 1000 ppm for anionic surfactants (sodium lauryl sulfate), and 1000 ppm for nonionic surfactants (polyoxyethylene(9) alkyl ether). Therefore, adding surfactants to activated sludge tanks (raw water tanks, aeration tanks, etc.) has been considered undesirable.

[0015] However, surfactants specified as food additives (lecithin, glycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester) have LD 50 Although it has been confirmed and is known in the food industry, few persons skilled in the art who understand that it can be used for wastewater treatment can be found, and it appears not to be used. It is required to use a more biodegradable one, and it was judged that those containing groups such as ester bonds that are easily hydrolyzed are easily decomposed and suitable for wastewater treatment.

[0016] That is, when the inventors of the present application tried to add a surfactant to the treated water, they found that it did not interfere with the assimilation efficiency of microorganisms and extended the life of the solid-liquid separation membrane. In other words, the technical significance of the present invention lies in overturning the conventional technical common sense.

[0017] This will be described in more detail. First, it is considered that the fouling of the solid-liquid separation membrane proceeds in three stages. First, an increase between the membranes due to initial fouling occurs. Initial fouling is the stage where substances are first adsorbed on the membrane surface, and inorganic salts such as iron, calcium, and magnesium, soluble organic substances such as proteins, lipids, and carbohydrates, exopolymers produced by microorganisms, extracellular polymers, and microbial-derived substances of the microorganisms themselves are adsorbed on the membrane surface substances.

[0018] Subsequent to this, in the case of steady fouling, biofouling containing biofilms, microbial cells, exopolymers, and other microbial metabolites formed by the growth of microorganisms, suspended organic matter such as flocs and dead microbial cells, and inorganic salts such as iron, calcium, and magnesium form precipitation scale, and even more substances accumulate on the membrane surface and membrane pores. According to the announcement of the Environmental Microbiology Research Group of the National Institute of Advanced Industrial Science and Technology on February 23, 2017, titled "Analysis of the clogging of water treatment membranes by activated sludge using a new method," they are analyzing the causes of water treatment membrane clogging using confocal reflection microscopy and next-generation sequencers. As a result, when there is a large amount of organic matter in the raw water, dead cell membrane lipids caused by the predator-prey relationship of heterogeneous bacteria in the biofilm accumulate on the water treatment membrane, and polysaccharides are secreted extracellularly to form a biofilm under low load conditions.

[0019] The increase in transmembrane pressure (TMP) is due to the progress of membrane fouling, which reduces membrane permeability, increases the pressure between the membranes, and decreases the operating efficiency of the membrane. According to the present invention, for these initial fouling and steady fouling, it has been found that substances that cannot be removed by only water can be removed by the adsorption of surfactant molecules to fibers and fouling, and the action of the lipophilic group and hydrophilic group. In addition, for various fouling substances, surfactants require penetration and wetting action, emulsification / solubilization action, dispersion action, peeling action, and anti-redeposition action, and a mechanism for extending the increase in transmembrane pressure has been found. In addition, the removal of dead cell membrane lipids (such as phospholipids) and exopolysaccharides in the case of oligotrophic conditions, which are components of biofilms, has also been elucidated.

[0020] The membrane bioreactor (MBR) generally consists of a raw water tank, a raw water adjustment tank, an aeration (biological treatment) tank, and a treated water discharge process using a separation membrane. A screen may be provided for removal when there is a lot of garbage, and a sedimentation tank may be provided when there is a lot of soil or sand. Also, when there is a lot of oil and fat in the drainage, a flocculant may be added and separated by pressure flotation.

[0021] Separation membranes can generally be installed in anaerobic, oxygen-free, and aerobic tanks, or in membrane treatment tanks. Biologically treated wastewater is drawn in by pumps and flows through hollow fiber membranes, flat membranes, or ceramic tubes. The membrane filters out solid matter, and the treated water is discharged. These are often sold as membrane modules.

[0022] Separation membranes can be classified into three types based on their form and characteristics: immersion type (integrated), immersion type (separate tank), and external type. The immersion type (integrated) is installed within the microbial reaction tank (aeration tank, etc.), resulting in a simple process where the aeration device in the reaction tank is shared with the membrane module cleaning, and flat membranes and hollow fiber membranes can be used. The immersion type (separate tank) involves installing another tank containing the modules after the reaction tank, allowing the reaction tank MLSS concentration to be lower than the membrane separation MLSS concentration, and flat membranes and hollow fiber membranes can be used. The external type is installed separately from the reaction tank, and treated water is sent directly to the separation membrane. This type allows for the highest flow rate, reduces the number of membrane modules, and allows for the use of tubular, ceramic, and large-diameter hollow fiber membranes.

[0023] The separation membrane is a microfiltration membrane with an opening of 0.1-0.4 μm on the membrane surface. 2 In terms of size, membrane types are broadly classified into flat membranes, ceramic membranes, and hollow fiber membranes, which are commonly used. Various polymer materials are used for separation membranes, including polyvinylidene fluoride (PVDF), polyethersulfone (PES), polypropylene (PP), and polytetrafluoroethylene (PTFE).

[0024] The membrane is used by reducing the pressure on the permeate side of the membrane using a pump to achieve a differential pressure of 5-30 kPa, and the permeate flow velocity is 2000-7000 kg / m 2 It is used in h. To physically remove dirt, air sculling is used to remove dirt from the surface of the membrane by creating turbulence and shear force. However, the power cost of blowing air increases the processing cost of MBR, so technological development is underway. Also, the effect of air sculling is not completely sustained, and cleaning is performed. In actual processes, it is necessary to clean the membrane before the permeability decreases due to membrane fouling, which reduces the effectiveness of the processing process.

[0025] Many filtration membrane systems are equipped with instruments to measure the transmembrane pressure difference, which is calculated using the following formula. Pressure gauges are installed on the supply side, concentration side, and permeate side, and generally, the average of the pressures on the supply side and concentration side is calculated, and the difference with the pressure on the permeate side is determined. TMP= (Pfeed+Pconcentrate) / 2- Ppermeate Pfeed: Pressure on the membrane supply side (pressure at the membrane module inlet) Pconcentrate: Pressure on the concentration side of the membrane (pressure at the outlet of the membrane module) Ppermeate: Pressure on the permeate side (pressure after passing through the membrane) This is shown.

[0026] High TMP levels may indicate that membrane fouling or clogging is progressing, necessitating proper membrane cleaning and a review of operating conditions. TMP is an important indicator for monitoring membrane fouling and condition. While the appropriate TMP value varies depending on the system design and operating conditions, the following ranges are generally considered guidelines: 0.05-0.15 bar (5-15 kPa) for new or cleaned membranes, 0.1-0.3 bar (10-30 kPa) for membranes under normal operation, and 0.3-0.5 bar (30-50 kPa) for heavily soiled membranes. If TMP exceeds 0.5 bar (50 kPa), there is a high probability that membrane fouling is progressing, requiring membrane cleaning and a review of operating conditions.

[0027] A major drawback of the MBR method is that membrane fouling occurs during operation. As the membrane becomes fouled and clogged, its permeability decreases, reducing the effectiveness of the treatment process. It is generally understood that the rate of membrane fouling increases exponentially with increasing flow rate. While the MBR method simplifies the management of the biological tank, it presents problems such as high equipment costs and increased labor and expense due to membrane clogging requiring cleaning or replacement.

[0028] The mechanism of membrane fouling has been extensively studied, but fouling occurs as the processing time increases and in various stages depending on the flow velocity and the composition of the substances passing through the membrane. The stages of fouling formation are described as initial fouling (or conditioning fouling), steady-state fouling, and the increase in transmembrane pressure (TMP). Initial fouling mainly involves inorganic substances, organic substances, and microbial substances, while steady-state fouling is mainly caused by biofilm formation, organic aggregation, and the accumulation of inorganic scales. The accumulation of these fouling substances ultimately leads to an increase in TMP and reduces the operating efficiency of the membrane.

[0029] Chemical cleaning or treatment methods for membranes include desalination agents, disinfectants, and / or bacteriostatic agents. For example, inorganic or organic acids, caustic soda, or sodium hypochlorite are used. However, frequent chemical cleaning results in loss of equipment operating time, a decrease in the operating time of the water treatment equipment or facility being treated, a reduction in the average lifespan of the membrane, and high costs due to the large amount of chemicals used for cleaning.

[0030] When the specified surfactant of the present invention is added to a wastewater treatment process incorporating a membrane filtration system, it surprisingly removes unwanted biofilms, bacterial residues, phospholipids, etc., while maintaining and improving the flow rate, enabling the system to maintain the flow rate. The use of the specified surfactant of the present invention does not have a negative effect on permeability and does not suppress the microbial community in the aeration tank. According to the present invention, it is possible to "contact the separation membrane with the surfactant and extend the period until the membrane becomes clogged." This means that the lifespan of the membrane can be extended while maintaining the same water permeability, for example, flow rate, temperature, and pressure.

[0031] Initial fouling of the membrane is the stage in which substances are first adsorbed onto the membrane surface. This stage involves the adsorption of inorganic salts such as iron, calcium, and magnesium, soluble organic matter such as proteins, lipids, and carbohydrates, exopolymers produced by microorganisms, extracellular polymers, and microbial-derived substances from the microorganisms themselves. Subsequently, biofilms formed by microbial proliferation contain biofouling, which includes microbial cells, exopolymers, and other microbial metabolites. Suspended organic matter such as flocs and dead microbial cells, as well as inorganic salts such as iron, calcium, and magnesium, form a precipitated scale, and even more substances accumulate on the membrane surface and in the membrane pores.

[0032] In one respect, the present invention can also be described as "a method for extending the time until membrane clogging occurs in a membrane bioreactor (MBR) system by contacting the separation membrane with a predetermined surfactant." These surfactants have wetting, penetrating, emulsifying, dispersing, plasticizing / softening, and solubilizing functions for biofilms. They also have wetting, penetrating, and plasticizing / softening functions for the fibers of the filter material. The predetermined surfactant used in the method of the present invention penetrates, wets, peels off, and disperses the biofilm on the MBR membrane filter material. Due to these properties, the biofilm peels off, and long-term tests showed an improvement in the decrease in permeability.

[0033] The basic structure of surfactants is that they possess both hydrophilic and hydrophobic groups within a single molecule, exhibiting special properties such as "reduced surface tension (interfacial tension)" and "molecular aggregation and micelle formation." The reduction in surface tension (interfacial tension) is illustrated by the fact that while a water droplet placed on the surface of a glass plate forms a round hemisphere, when a surfactant is added to water, the droplet does not take on a hemispherical shape but becomes flat. This is because the hydrophilic part is submerged in the water, and the hydrophobic part protrudes into the air, resulting in a weakened surface tension, preventing the droplet from taking on a hemispherical shape and creating a flat, planar surface.

[0034] Molecular aggregation and micelle association refer to the fact that when surfactants dissolved in water are at low concentrations, they gather and arrange themselves at the interface. When the concentration of surfactant is increased, the water surface is filled with surfactant, and the surfactant forms micelles in the water with its hydrophilic groups facing outwards. When an oil that does not dissolve in water is added to the water, the micelles incorporate the oil and emulsify it. Due to these properties, surfactants are known to perform a variety of functions.

[0035] Surfactants are molecularly designed to possess a wide range of functional activities, and can be broadly categorized into four types. There are three types of "ionic surfactants," which dissociate into ions when dissolved in water. These are further classified into anionic surfactants, cationic surfactants, and amphoteric surfactants (which possess both anionic and cationic properties) depending on the type of ion they form when dissolved in water. Nonionic surfactants are those that do not dissociate into ions. Anionic, cationic, amphoteric, and nonionic surfactants are further classified in detail based on the type of hydrophilic and hydrophobic groups and the raw materials used.

[0036] Anionic surfactants, such as carboxylates (soaps) made from natural beef tallow and coconut oil, have excellent foaming and foam stability and are used for body washing. In aerobic activated sludge processes, foaming requires careful attention during aeration. Linear alkylbenzene sulfonates, which are sulfonates, have excellent cleaning power and penetration, while sulfo fatty acid methyl esters and olefin sulfonates also have excellent cleaning power, foaming power, and biodegradability.

[0037] Cationic surfactants are called "reverse soaps" because, when dissolved in water, the portion attached to the hydrophobic group dissociates into a positive ion, giving them an ionically opposite structure to soap. They strongly adsorb to negatively charged solid surfaces such as fibers and hair, providing flexibility, antistatic properties, and antibacterial effects. Structurally, they are classified into amino acid salts and quaternary ammonium salts, with the quaternary ammonium salt type being widely used for fiber flexibility, as a hair rinse base, and as a disinfectant. Due to their antibacterial properties, caution is required when using them in activated sludge processes that utilize microorganisms.

[0038] Amphoteric surfactants exhibit the properties of anionic surfactants in alkaline environments and cationic surfactants in acidic environments when dissolved in water. They are classified into carboxylate, amino acid, and betaine types, but the betaine type has low irritation to the skin and eyes and can be used in combination with other surfactants to improve its effectiveness.

[0039] Nonionic surfactants are surfactants that have hydroxyl groups that do not ionize when dissolved in water. They are less affected by water hardness and electrolytes and can be used in combination with all other surfactants. Nonionic surfactants are classified into ester type, ether type, ester-ether type, etc., according to the main bonding mechanism within the molecule. Ester-type nonionic surfactants have a structure in which a fatty acid is ester-bonded to a polyhydric alcohol such as glycerin, sorbitol, or sucrose. This type of nonionic surfactant is called the "polyhydric alcohol type."

[0040] Ether-type nonionic surfactants are primarily created by adding ethylene oxide to hydroxyl group-containing raw materials such as higher alcohols and alkylphenols. Fatty acid methyl ester ethoxylates, obtained by adding ethylene oxide to fatty acid methyl esters, are used in laundry detergents. Ether-type nonionic surfactants called polyoxyethylene alkylphenyl ethers have excellent availability due to the inclusion of a benzene ring in the hydrophobic portion. While the hydrophilic polyoxyethylene chain biodegrades easily, the hydrophobic group (alkylphenol) biodegrades slowly. Polyoxyethylene polyoxypropylene glycol, which uses polypropylene glycol in the hydrophobic group, is used as a low-foaming surfactant with minimal foaming.

[0041] Ester-ether type nonionic surfactants are formed by adding ethylene oxide to an ester consisting of a high or low alcohol (such as glycerin or sorbitol) and a fatty acid. They possess both ester and ether bonds in their molecules and are used as emulsifiers and dispersants. Both "ether type" and "ester-ether type" are types with added ethylene oxide, and are sometimes called "polyethylene glycol type." Fatty acid alkanolamide type surfactants have hydrophobic and hydrophilic groups linked by an amide bond, and have low water solubility, so they are not used alone.

[0042] The following are examples of surfactants permitted as food additives: Fatty acid esters include glycerin fatty acid esters, sorbitan fatty acid esters, and sucrose fatty acid esters. Polyols include propylene glycol fatty acid esters and polyglycerin esters. Naturally derived substances include soy lecithin, saponins, monoglycerides, and diglycerides.

[0043] HLB Surfactants are known to produce a variety of actions, including emulsification, dispersion, foaming, defoaming, wetting, and modification, and there are many different types, as described above. The actions and strengths of surfactants cannot be categorized by the four types mentioned earlier or by the subdivided salt forms, and some kind of selection criterion is necessary. The balance between hydrophilicity and lipophilicity (HLB) has become a criterion for using surfactants and a relative scale for organizing their properties and performance.

[0044] The degree of hydrophilicity and lipophilicity of a surfactant determines the type of emulsion, and HLB (Hydrophilic Balance) is a quantitative representation of this hydrophilicity and lipophilicity. This balance concept was developed by investigating the relationship between the molecular structure and properties of surfactants through emulsification experiments, quantifying it, and assigning it to surfactants as HLB. These were proposed by William Griffin in 1949 and became the selection criteria for surfactants.

[0045] HLB value is an acronym for the balance between hydrophilicity and lipophilicity. Paraffin, which lacks hydrophilic groups, is assigned an HLB of 0, while substances like polyethylene glycol, which have only hydrophilic groups and no hydrophobic groups, are assigned an HLB of 20. Surfactants that possess both hydrophilic and hydrophobic groups within a single molecule will have an HLB value in between. The greater the hydrophilicity of the hydrophilic groups relative to the hydrophobic parts of a surfactant, the higher its HLB value, indicating greater solubility in water; conversely, the opposite is true for oil-soluble surfactants.

[0046] In emulsion formation, surfactants are important factors in determining the ease and stability of emulsion formation, as well as whether it is an oil-in-water (O / W) or water-in-oil (W / O) emulsion. While HLB was experimentally determined by comparing the emulsifying power of various surfactants, numerous calculation formulas have been proposed by Griffin, Kawakami, Davis, Oda, and others. Griffin's proposed calculation formula (for high- and low-alcohol fatty acid esters) is as follows:

[0047] According to Griffin's HLB calculation formula, the HLB of polyethylene glycol-type and polyhydroxyalcohol-type nonionic surfactants is calculated as follows: The HLB of a nonionic surfactant is given by (molecular weight of the hydrophilic group / molecular weight of the surfactant) × 100 / 5. In ionic surfactants, the hydrophilicity per unit weight of the hydrophilic group is generally considerably higher than that of nonionic surfactants, and the degree of hydrophilicity per unit weight varies depending on the type of hydrophilic group. Therefore, focusing on the fact that emulsifying properties change sensitively when the HLB changes, the HLB has been experimentally established through emulsification experiments with standard oils.

[0048] An HLB value of "7" is considered the baseline (neutral). It is assumed that surfactants with an HLB of "7" or higher (or greater) exhibit hydrophilicity, while those with an HLB of "7" or lower (or less) exhibit lipophilicity. Furthermore, surfactants with an HLB of 7 to 18 are suitable for preparing oil-in-water (O / W) emulsions, while surfactants with an HLB of 1 to 5 are suitable for preparing water-in-oil (W / O) emulsions. Additionally, surfactants with an HLB of 15 or higher are suitable for solubilization, those with an HLB of 2 or higher are suitable for cleaning, and those with an HLB of 4 or lower have excellent defoaming properties.

[0049] The calculation of the HLB of a surfactant mixture is given by the following formula: Mixed System HLB = (N1)HLB·W1 + (N2)HLB·W2. (N1)HLB, (N2)HLB: HLB values ​​for each surfactant W1, W2: Weight fraction of each emulsifier (W1 + W2 = 1) The mixed HLB is also referred to as the "final HLB value." Furthermore, (N1)HLB and (N2)HLB are also referred to as "initial HLB values".

[0050] In one aspect of the present invention, the surfactant in the "method for extending the period until membrane clogging by contacting the separation membrane with a surfactant in a membrane bioreactor (MBR) system" only needs to have both hydrophilic and lipophilic groups, and the concentration in the water in contact with the membrane should be between 0.1 mg / l and 5000 mg / l. Furthermore, the HLB of the surfactant should preferably be between 3 and 20, and it is preferable that the HLB of a mixed surfactant consisting of HLB 7 and 7 is between 3 and 20. More preferably, the HLB is 5 or higher.

[0051] The following describes the experiments conducted to demonstrate the effects of the present invention.

[0052] [Experiment 1] Broth medium (Eiken Chemical Co., Ltd.) was prepared according to standard procedures, sterilized by autoclaving, and 200 ml each of Pseudomonas putida, Pseudomonas japonica, and Bacillus subtilis were cultured. After 7 days of static culture, 30 ml each of the three culture solutions was taken to prepare a mixed culture solution (90 ml). A cellulose acetate membrane with a pore size of 0.2 μm and a diameter of 47 mm was placed on an Advantec KP-47S 47 mm polysulfone holder (Advantec Toyo Co., Ltd.). 90 ml of the mixed culture solution was placed on this membrane, and aspirated under negative pressure of 0.9 MPa for 1 hour to allow the bacterial cells to adhere to the cellulose acetate membrane and cause occlusion. The inside of the holder was then washed three times with 10 ml of clean water.

[0053] The following tests, Test 1, Test 2, and Test 3, were performed sequentially on the holder with these initial settings. (Test 1) 50 ml of clean water was placed inside the holder, and aspirated under a negative pressure of 0.9 MPa for 10 minutes to confirm membrane occlusion. (Test 2) 10 ml of clean water was placed in the holder, left to stand for 5 minutes, then gently shaken for 5 minutes to drain, 50 ml of clean water was placed in the holder, and it was subjected to a suction test at a negative pressure of 0.9 MPa for 10 minutes. (Test 3) 10 ml of surfactant solution was placed in the holder, left to stand for 5 minutes, then gently shaken for 5 minutes to drain, and then washed three times with 10 ml of clean water. 50 ml of clean water was then placed in the holder, and it was subjected to a suction test at a negative pressure of 0.9 MPa for 10 minutes. Here, Test 2 is considered a control (without the addition of surfactant) for Test 3.

[0054] Furthermore, in Test 3, the HLB and concentration of the surfactant were changed as shown in the table below. To give an example, for HLB 15.7 in Table 1, the initial settings described above were performed first, Test 1 was conducted, then Test 2 was conducted using the same holder, and then Test 3 was conducted. For HLB 14.6, the initial settings were performed separately from HLB 15.7, and Test 1 → Test 2 → Test 3 were conducted consecutively.

[0055] Table 1 shows the test results when the HLB of the surfactant was changed, and Table 2 shows the test results when the concentration of the surfactant was changed. The test results for Tests 1 and 2 indicate the amount of clean water that passed through the cellulose acetate membrane after 10 minutes of aspiration. For Test 3, since all the clean water in the holder passed through the cellulose acetate membrane before 10 minutes had passed, the test result was defined as the time it took for all 50 ml of clean water in the holder to pass through the cellulose acetate membrane. Hereafter, the passage of clean water through the cellulose acetate membrane will be referred to as "filtration."

[0056] The HLB value of a surfactant indicates the final HLB value of a mixture of multiple surfactants with different initial HLB values. The initial HLB values ​​and weight fractions of each surfactant are shown below. Surfactant A (polyoxyethylene sorbitan monooleate): Initial HLB value = 15.7 Surfactant B (sorbitan monooleate): Initial HLB value = 4.3 Note that the initial HLB value represents the value published by the surfactant manufacturer. [Table 1] TIFF2026081849000001.tif41151 An example of calculating the final HLB value (HLB value in the table) for 14.6 is shown below. 14.6 = Initial HLB value of surfactant A * weight fraction + Initial HLB value of surfactant B * weight fraction = 15.7 × 0.9 + 4.3 × 0.1 =14.13+0.43 =14.56 ⇒ 14.6 (rounded to one decimal place)

[0057] [Table 2] Changing the HLB of the surfactant at a surfactant concentration of 140 mg / l TIFF2026081849000002.tif36123

[0058] Compared to Test 2 (essentially the control) which did not contain any surfactant, Test 3 showed significant filtration for all HLBs. In other words, the addition of the surfactant improved filtration efficiency, regardless of the HLB of the surfactant.

[0059] [Table 3] Changes in surfactant concentration at HLB 12.3 TIFF2026081849000003.tif31121

[0060] Compared to Test 2 (essentially the control) which did not contain surfactant, Test 3 showed significant filtration at all concentrations. In other words, an improvement in filtration efficiency was observed with the addition of surfactant, at least when the surfactant concentration was 0.14 mg / l or higher.

[0061] [Experiment 2] In Experiment 1, the cellulose acetate membrane was occluded by bacterial cells, but in Experiment 2, the membrane occluding substance was changed to the following.

[0062] Rapeseed oil (J-Oil Mills Co., Ltd.), lecithin (Wako Pure Chemical Industries, Ltd.), and zeolite #70 (Nitto Powdering Industry Co., Ltd.) were mixed (by weight) in a ratio of 7:2:1. After standing at 35°C for 24 hours, the mixture was uniformly stirred. As in Experiment 1, a cellulose acetate membrane with a pore size of 0.2 μm and a diameter of 47 mm was placed on an Advantec KP-47S 47 mm polysulfone holder, 4 g of the above mixture was added, and the oil was completely drawn out under negative pressure of 0.9 MPa. This sealed the cellulose acetate membrane.

[0063] For tests 1-3, the results were the same as in experiment 1, except that the amount of clean water used in the aspiration test was changed to 30 ml. However, for test 3, since the clean water in the holder did not completely pass through the cellulose acetate membrane during the 10-minute aspiration test, the amount of clean water that passed through the cellulose acetate membrane during the 10-minute aspiration test is shown.

[0064] [Table 4] Changing the HLB of the surfactant at a surfactant concentration of 20 mg / l TIFF2026081849000004.tif36140

[0065] Compared to Test 2 (essentially the control) without the addition of surfactant, Test 3 showed significant filtration for all HLBs. In other words, even when the clogging material of the cellulose acetate membrane was changed, the addition of surfactant improved the filtration efficiency.

[0066] [Table 5] Changes in surfactant concentration at HLB 12.3 TIFF2026081849000005.tif26139

[0067] Compared to Test 2 (control), significant filtration was observed in Test 3 at all concentrations.

[0068] [Experiment 3] In Experiment 2, a mixture of surfactant A (polyoxyethylene sorbitan monooleate) and surfactant B (sorbitan monooleate) was used, but in Experiment 3, the same test as in Experiment 2 was performed using a single surfactant. The surfactants used are as follows: Y50MB11 (Polyoxyethylene polyoxypropylene alkyl ether type) Y50MT-2200B (Polyoxyethylene polyoxypropylene decyltetradecyl ether)

[0069] [Table 6] TIFF2026081849000006.tif21138

[0070] [Experiment 4] Furthermore, the effects of surfactants on microorganisms were investigated using the following experimental methods. Broth medium (Eiken Chemical Co., Ltd.) was prepared according to standard procedures, sterilized by autoclaving, and 100 ml each of Pseudomonas putida, Pseudomonas japonica, and Bacillus subtilis nattou were cultured. After 3 days of static culture, 30 ml each of the three culture solutions was added to create a 90 ml mixture. Solutions of HLB 12.28 surfactant at 700 ppm, 70 ppm, and 7 ppm were also prepared. 9 ml of each concentration was placed in a small test tube, and 1 ml of the above-prepared microbial mixture was added to each, mixed, and allowed to stand for 10 minutes. Standard agar medium (Eiken Chemical Co., Ltd.) was prepared according to standard procedures, sterilized by autoclaving, and allowed to cool to the appropriate temperature. 1 ml of each sample was placed in a petri dish and cultured in a pour plate, and the bacterial count was measured after 48 hours.

[0071] [Table 7] TIFF2026081849000007.tif15137 As shown in the results above, no decrease in microorganisms was observed in the surfactant solutions at each concentration compared to simply diluting the culture medium with clean water, and no decrease in microorganisms was observed even at the high concentration of 700 ppm.

[0072] [Implementation Test] Based on the above laboratory-level verification, we conducted practical tests at a level where the present invention is expected to be actually applied.

[0073] [Practical Test 1] (Factory Overview) The factory where the practical test was conducted processes and manufactures prepared foods, dressings, etc. Its wastewater treatment plant uses the standard activated sludge method. The treatment flow involves raw wastewater from the manufacturing process flowing into a regulating tank, where oils and greases are removed by pressurized flotation. The wastewater is then treated with aerobic activated sludge in an aeration tank, and the treated water is separated by membrane at the rear of the aeration tank before being discharged into the river. The capacity of the adjustment tank is 100 m³. 3 The average daily flow rate is 100-150 m³. 3 / day, the aeration tank is 171m3 It is as follows.

[0074] (Type and performance of the membrane) The type of the separation membrane used in the aeration tank is a hollow fiber membrane made by Mitsubishi Chemical, with a treatment capacity of 500 m of membrane area 3 installed, and the main body material is polyolefin. There are countless holes with a diameter of 0.2 μm on the flat membrane surface, and microorganisms are not allowed to pass through and are discharged as treated water.

[0075] (Quality of the drainage water) The average value of the drainage components over one year was 0.7 KgBOD / m as the BOD volume load 3 ·day, and 0.07 KgBOD / KgSS·day as the BOD sludge load. The hexane volume load of the oil and fat components after pressure flotation was 0.11 KgN-H / m 3 ·day, and 0.011 KgN-H / KgSS·day as the hexane sludge load.

[0076] (Test method) The components of the surfactant were 0.9 parts (by weight) of Nisshin Oil Co., Ltd.'s polyoxyethylene sorbitan monooleate (HLB 15.7), to which half the amount of ethyl alcohol was added and mixed. 0.1 part (by weight) of sorbitan fatty acid ester (HLB 4.3) was added to this solution and stirred. This mixed surfactant was diluted with clear water to 7% to obtain a surfactant mixture. This mixture was continuously dropped into the drainage water every day by a metering pump so that the concentration became 20 mg / l with respect to the drainage volume.

[0077] (Results of using the surfactant) In this factory, the membrane is cleaned when the differential pressure between membranes reaches 50 KPa. However, after continuously using the surfactant, the time when the differential pressure between membranes reached 50 KPa was about 5.5 years after cleaning. Previously, before using the surfactant, it reached 50 KPa at intervals of about 1.5 years, and the membrane was cleaned. Comparing this period, the period until cleaning was extended by about 3.7 times due to the use of the surfactant. In this factory, there has been no significant change in the product types manufactured in the past seven years, and generally, the components of the drainage water have not changed significantly from the values described above.

[0078] [Implementation Test 2] (Quantity and composition of factory wastewater) The factory where the practical test was conducted processes and manufactures bento boxes and other similar products. Its wastewater treatment plant uses the standard activated sludge method. The treatment flow is as follows: raw wastewater from the manufacturing process flows into a regulating tank, oils and greases are removed by pressurized flotation, and then the wastewater is treated with aerobic activated sludge in an aeration tank. The treated water is then separated by membrane separation at the rear of the aeration tank before being discharged into the river. The regulating tank has a capacity of 250 m³. 3 The average daily flow rate is 200-250 m³. 3 / day, the aeration tank is 195m 3 That is the case.

[0079] (Types and capabilities of membranes) The separation membrane used in the aeration tank is a flat membrane manufactured by Kubota Corporation, with a processing capacity of 120 m² of membrane area. 3 Three units are installed, and the main body material is polyvinylidene fluoride (PVDS). The hollow fibers have countless holes with a diameter of 0.2 μm, preventing microorganisms from passing through, and the treated water is discharged.

[0080] (Quality of wastewater) The average annual value of wastewater components is 1.23 kgBOD / m³, with a BOD volumetric load. 3 The BOD sludge load was 0.12 kgBOD / kgSS·day. The hexane volume load, which is the oil component after pressurized flotation, was 0.18 kgN-H / m³. 3 The daily rate was 0.018 kgN-H / kgSS·day, and the hexane sludge load was 0.018 kgN-H / kgSS·day.

[0081] (Test method) Similar to Experiment 1, the surfactant was prepared by mixing 0.9 parts (by weight) of NOF Corporation's polyoxyethylene sorbitan monooleate (HLB 15.7) with half the amount of ethyl alcohol. To this solution, 0.1 parts (by weight) of sorbitan fatty acid ester (HLB 4.3) was added and stirred. This mixed surfactant was diluted with clean water to a concentration of 7% to obtain the surfactant mixture. This mixture was continuously added to the wastewater daily using a metering pump to achieve a concentration of 10 mg / l relative to the wastewater volume.

[0082] (Results of using surfactants) At this factory, membrane cleaning is performed when the intermembrane pressure difference reaches 50 kPa. However, after continuously using surfactants, the intermembrane pressure difference reached 50 kPa 18 months after cleaning. Previously, before using surfactants, the pressure reached 50 kPa in about 3 months, at which point the membranes were cleaned. Comparing these periods, the period until cleaning was extended by approximately six times with the use of surfactants. At this factory, the types of products manufactured have not changed significantly over the past three years, and the wastewater composition has generally remained largely unchanged at the values ​​described above.

[0083] (Other embodiments) The present invention is not limited to the above-described tests. For example, when manufacturing a surfactant, if a mixed formulation is created by adding a surfactant with an HLB of 10 or less to a surfactant with an HLB of 10 or more, it is desirable to mix in an organic substance that is both water-soluble and oily. Examples include alcohols, propylene glycol, glycerin, and polyethylene glycol. These substances can be mixed with the surfactant with an HLB of 10 or more, thoroughly mixed, and then the surfactant with an HLB of 10 or less can be added and mixed. Alternatively, the reverse can be done, such as adding these substances to a surfactant with an HLB of 10 or less.

[0084] Furthermore, surfactants with an HLB of 10 or less often do not dissolve in water or have a cloud point below room temperature. In such cases, it is desirable to add water-soluble and oily organic substances such as alcohols, propylene glycol, glycerin, and polyethylene glycol, as mentioned earlier, to dissolve them and raise the cloud point above room temperature. Below room temperature, precipitation is likely to occur when left standing, which is undesirable for the product. Ideally, the cloud point should be 30°C or higher, preferably 50°C or higher, and more preferably 70°C or higher. Adding more of the aforementioned organic substances can raise the cloud point, but in order not to degrade the properties of the surfactant, the amount of the aforementioned organic substance added should preferably be 10 times or less the amount of surfactant added, preferably 2 times or less, and more preferably the same amount or less (by weight).

[0085] Some or all of the above embodiments may also be described as follows, but are not limited to the following:

[0086] (Note 1) The steps include adding a surfactant to the water to be treated, A step of subjecting the water to be treated, to which a surfactant has been added, to solid-liquid film separation, A method for treating water to be treated, including the treatment of treated water.

[0087] (Note 2) The method for treating water to be treated according to Appendix 1, wherein the surfactant is added to the water to be treated to a concentration of 0.1 mg / l or more and 5000 mg / l or less.

[0088] (Note 3) The method for treating water to be treated according to Appendix 1, wherein the final HLB value of the surfactant is 3 or more and 20 or less.

[0089] (Note 4) The method for treating water to be treated according to Appendix 3, wherein the surfactant is a mixture obtained by mixing a plurality of surfactants having different initial HLB values ​​to obtain a final HLB value of 3 or more and 20 or less.

[0090] (Note 5) A surfactant for treating treated water, applicable to a water treatment method using solid-liquid membrane separation, A surfactant for treating water to be treated, which is added to water to be treated for solid-liquid membrane separation.

[0091] (Note 6) A surfactant for treating water to be treated, as described in Appendix 5, which is added to the water to be treated to a concentration of 0.1 mg / l or more and 5000 mg / l or less.

[0092] (Note 7) A surfactant for treating treated water as described in Appendix 5, wherein the final HLB value is 3 or higher and 20 or lower.

[0093] (Note 8) A surfactant for treating water to be treated, as described in Appendix 6, which is a mixture of multiple surfactants having different initial HLB values, wherein the final HLB value is 3 or more and 20 or less.

[0094] (Note 9) A surfactant for treating treated water, as described in Appendix 8, which suppresses fouling of solid-liquid separation membranes by lipids and / or polysaccharides.

[0095] Furthermore, each disclosure of the above-mentioned patent documents cited is incorporated into this document by reference and may be used as the basis or part of the present invention as necessary. Within the framework of the full disclosure of the present invention (including the claims), further modifications and adjustments to the embodiments or examples are possible based on the basic technical concept. Also, within the framework of the full disclosure of the present invention, various combinations or selections (including partial deletions) of various disclosure elements (including each element of each claim, each element of each embodiment or example, each element of each drawing, etc.) are possible. In other words, the present invention naturally includes the full disclosure, including the claims, and various modifications and alterations that a person skilled in the art could make in accordance with the technical concept. In particular, with respect to the numerical ranges described in this document, any numerical value or sub-range included within that range should be interpreted as being specifically described, even if not otherwise stated. Furthermore, each disclosure of the above-mentioned cited documents may, as necessary, be used in part or in whole as part of the disclosure of the present invention, in accordance with the spirit of the present invention, and this is also considered to be included in the disclosure of this application.

Claims

1. The steps include adding a surfactant to the water to be treated, A step of subjecting the water to be treated, to which a surfactant has been added, to solid-liquid film separation, A method for treating water to be treated, including the treatment of treated water.

2. The method for treating water to be treated according to claim 1, wherein the surfactant is added to the water to be treated to a concentration of 0.1 mg / l or more and 5000 mg / l or less.

3. The method for treating water to be treated according to claim 1, wherein the final HLB value of the surfactant is 3 or more and 20 or less.

4. The method for treating water to be treated according to claim 3, wherein the surfactant is a mixture of a plurality of surfactants having different initial HLB values, the final HLB value being 3 or more and 20 or less.

5. A surfactant for treating treated water, applicable to a water treatment method using solid-liquid membrane separation, A surfactant for treating water to be treated, which is added to water to be treated for solid-liquid membrane separation.

6. The surfactant for treating water to be treated according to claim 5, which is added to the water to be treated to a concentration of 0.1 mg / l or more and 5000 mg / l or less.

7. The surfactant for treating water to be treated according to claim 5, wherein the final HLB value is 3 or more and 20 or less.

8. The surfactant for treating water to be treated according to claim 6, which is a mixture of multiple surfactants having different initial HLB values, wherein the final HLB value is 3 or more and 20 or less.

9. The surfactant for treating treated water according to claim 8, which suppresses fouling of solid-liquid separation membranes by lipids and / or polysaccharides.

Images