JP5190908B2 - Water treatment method and water treatment apparatus - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment apparatus for performing membrane separation by supplying pretreated water that has undergone pretreatment to a polyamide-based reverse osmosis membrane, and in particular, preventing biofouling (biological degradation) of a reverse osmosis membrane. Useful as technology.

  Conventionally, membrane separation technology using polyamide-based reverse osmosis membranes has been widely used in the fields of seawater and canned water desalination, production of pure water for electronics industry and medical use, treatment of various wastewater, recovery of valuable materials, etc. Yes.

  In the practical application of separation technology using reverse osmosis membranes, the most important problem is that microorganisms and their metabolites accumulate on the membrane surface as microorganisms propagate in the liquid to be treated and on the reverse osmosis membrane. The problem is that the permeation rate is reduced, and metabolites etc. deteriorate the membrane material.

  Therefore, various methods for sterilizing microorganisms have been proposed. As a general method, there is a method of adding a bactericide to the liquid to be treated constantly or intermittently, and chlorine has been widely used as a bactericide.

  As the reverse osmosis membrane, a composite membrane having a functional membrane made of a crosslinked polyamide as an active layer on a polysulfone porous support is mainly used. However, sterilization with chlorine has the disadvantage that it causes deterioration particularly for polyamide-based reverse osmosis membranes, so a new sterilization method is required when using polyamide-based high-performance composite reverse osmosis membranes. It has become.

  For this reason, in Patent Document 1 below, as a method of using a bactericide that can be sterilized at all times and can replace chlorine with respect to a polyamide-based synthetic reverse osmosis membrane, an organic bond chlorine compound such as chloramine is added to the untreated stock solution. A method for producing purified water to be added is disclosed.

  Patent Documents 2 to 3 below disclose water treatment methods in which chloramine is added to a stock solution and membrane separation is performed with a reverse osmosis membrane, followed by dechloramination and further ion exchange.

  However, chloramine has a smaller bactericidal action against microorganisms than conventional bactericides (for example, sodium hypochlorite), and has the effect of suppressing further growth (growth inhibitory effect) for microorganisms that have once grown. However, sterilization and sterilization cannot be performed sufficiently.

  For this reason, the method of adding chloramine to the raw water immediately before being supplied to the reverse osmosis membrane as in a conventional water treatment apparatus cannot sufficiently disinfect and sterilize microorganisms that already exist. There was a problem that biological degradation of the reverse osmosis membrane gradually occurred.

Japanese Patent Publication No. 8-11173 Japanese Examined Patent Publication No. 7-102309 Japanese Patent Publication No. 8-24908

  Accordingly, an object of the present invention is to provide a water treatment method and a water treatment apparatus that can effectively prevent biological deterioration of a reverse osmosis membrane during operation by utilizing the growth inhibitory effect of chloramine.

The above object can be achieved by the present invention as described below.
That is, the water treatment method of the present invention is a water treatment method in which pretreated water that has undergone pretreatment is stored in a storage tank and then supplied to a polyamide-based reverse osmosis membrane for membrane separation. While performing the separation to obtain the pretreated water , chloramines are added to the pretreated water in any flow path before being supplied to the storage tank.

  According to the water treatment method of the present invention, membrane separation is performed by a separation membrane that can remove bacteria during pretreatment, so that sterilized pretreatment water is obtained and is supplied to the flow path before being supplied to the storage tank. Since chloramines are added, bacterial growth can be suppressed and the sterilized state can be maintained. Thus, in the present invention, the bacteria that have once proliferated are not sterilized and removed with chloramines, but are sterilized by utilizing the inhibitory effect of chloramine on the pretreated water sterilized by the separation membrane. Therefore, the biological deterioration of the reverse osmosis membrane during operation can be effectively prevented.

  In the above, the polyamide-based reverse osmosis membrane is used as a spiral separation membrane element in which a separation membrane, a supply-side channel material and a permeation-side channel material are wound around a perforated central tube. Is preferred. Such a spiral separation membrane element has a large effective membrane area per volume, and thus the membrane separation efficiency is high. However, since the problem of biological degradation described above is likely to occur, the present invention having the above-described effects can be obtained. Especially useful.

  The separation membrane capable of removing bacteria is preferably a microfiltration membrane or an ultrafiltration membrane. Since the microfiltration membrane or ultrafiltration membrane has high removal performance against bacteria and a relatively large permeation flux, membrane separation in the pretreatment of the present invention can be suitably performed.

On the other hand, the water treatment apparatus of the present invention comprises a pretreatment means for performing membrane separation with a separation membrane capable of removing bacteria, a storage tank for storing pretreatment water supplied from the pretreatment means, and a pretreatment means before being supplied to the storage tank. It is characterized by comprising a drug addition means for adding chloramines to the pretreated water in any flow path and a polyamide-based reverse osmosis membrane for membrane separation of raw water supplied from the storage tank.

  According to the water treatment apparatus of the present invention, since the pretreatment means performs membrane separation by the separation membrane from which bacteria can be removed, the pretreatment water that has been sterilized is obtained, and the flow path before this is supplied to the storage tank Since chloramines are added to the medicine by means of drug addition, bacterial growth can be suppressed and the sterilized state can be maintained. Thus, in the present invention, the bacteria that have once proliferated are not sterilized and removed with chloramines, but are sterilized by utilizing the inhibitory effect of chloramine on the pretreated water sterilized by the separation membrane. Therefore, the biological deterioration of the reverse osmosis membrane during operation can be effectively prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of a water treatment apparatus of the present invention.

  In the water treatment method of the present invention, pretreated water that has undergone pretreatment is stored in a storage tank and then supplied to a polyamide-based reverse osmosis membrane for membrane separation. In the water treatment method according to the present invention, chloramines are added to any flow path before being supplied to the storage tank while performing membrane separation using a separation membrane capable of removing bacteria to obtain the pretreated water. It is characterized by that. Such a water treatment method of the present invention can be preferably carried out using the water treatment apparatus of the present invention.

  That is, as shown in FIG. 1, the water treatment apparatus of the present invention stores pretreatment means 10 that performs membrane separation using a separation membrane 11 that can remove bacteria, and pretreatment water 21 that is supplied from the pretreatment means 10. A storage tank 20, a chemical addition means 30 for adding chloramines to any flow path before being supplied to the storage tank 20, and a polyamide-based reverse osmosis membrane 40 for performing membrane separation of raw water supplied from the storage tank 20; Is provided.

  The pretreatment means 10 is not limited to a separation apparatus that performs only membrane separation, as long as it performs membrane separation using a separation membrane 11 that can remove bacteria, and biological treatment (activated sludge method, biological membrane method, carrier method). Etc.), a processing apparatus that combines chemical reaction processing and membrane separation may be used. In the present embodiment, an example in which sewage secondary treated water is treated using a treatment apparatus that combines activated sludge treatment and membrane separation is shown.

  The separation membrane 11 in the present invention preferably has an average pore size of 0.01 to 3 μm, more preferably 0.1 to 1 μm. As the separation membrane 11, for example, a microfiltration membrane or an ultrafiltration membrane is preferably used, and if the microfiltration membrane can be sufficiently sterilized, it is preferable to use a microfiltration membrane because the permeate flow rate is high.

  In the pretreatment means 10 of this embodiment, for example, sewage secondary treated water is membrane-separated by the separation membrane 11 while being aerated, and pretreated water is obtained as the permeate.

  The pretreated water thus pretreated is sucked by the pump 16 and supplied to the storage tank 20 through the pipe 15 and the pipe 17.

  The storage tank 20 stores the pretreatment water 21 supplied from the pretreatment means 10, and bacteria are likely to grow in the pretreatment water 21 that is retained by contact with air. In addition, the storage tank 20 can serve as a buffer tank with the reverse osmosis membrane 40 that is generally continuously operated when the pretreatment means 10 requires reverse flow cleaning.

  For this reason, the present invention is particularly effective when the pretreatment means 10 that requires the backwashing of the separation membrane 11 is provided. Note that the method of adding chloramines to the storage tank 20 makes it difficult to adjust the concentration when the liquid level of the pretreatment water 21 in the storage tank 20 fluctuates, and requires a stirring device. There are many disadvantages, and if these are neglected, bacteria are likely to grow.

  The drug addition means 30 is for adding chloramines to any flow path (pipe 15 or pipe 17 or the like) before being supplied to the storage tank 20. The flow path to be added is sterilized by the separation membrane 11 and is in a state of aseptic or low bacterial count. In this embodiment, an example of adding to the pipe 15 while adjusting the flow rate using the valve 32 is shown.

  Chloramines are compounds in which hydrogen of an ammoniacal nitrogen compound is replaced with chlorine, and include chloramine T, chloramine B, etc. in addition to monochloramine and dichloramine. The addition of chloramines is preferably performed so that the concentration after addition is 1 to 5 ppm, more preferably 2 to 3 ppm. The addition of chloramines may be performed continuously or intermittently. Chloramines can be continuously added to the separation system because the deterioration of the membrane can be minimized with respect to the polyamide-based synthetic membrane.

  The drug addition means 30 includes a container 31 for storing such an aqueous solution of chloramines, and a valve 32 provided in a pipe 33 extending from the container 31.

  In the present invention, it is also possible to add a scale inhibitor. In this case, for example, a scale inhibitor addition means 38 including a container 35 for storing the scale inhibitor and a valve 36 provided in a pipe 37 from the container 35. Is provided. It is preferable to adjust the pretreatment water after adding chloramines and scale inhibitors to pH 6-8.

  Note that when the separation membrane 11 is backwashed, membrane separation by the separation membrane 11 is interrupted, and addition of chloramines and the like is interrupted. Backflow cleaning is generally performed by removing components deposited on the surface of the separation membrane 11 by supplying cleaning water from a supply path (not shown) to the permeate side of the separation membrane 11 and backflowing the cleaning water. it can.

  The polyamide-based reverse osmosis membrane 40 performs membrane separation of raw water supplied from the storage tank 20, and the pretreated water 21 in the storage tank 20 is sucked by the pump 22, passes through the pipe 23, and the polyamide-based reverse osmosis membrane. 40 is supplied as raw water. The polyamide-based reverse osmosis membrane 40 mainly removes dissolved salts, organic substances, decomposition products of organic substances, and the like.

  The polyamide-based reverse osmosis membrane 40 is preferably a cross-linked polyamide-based composite membrane from the viewpoint of a large permeation flux and good blocking performance. In addition, the reverse osmosis membrane 40 may have any form such as a flat membrane, a tubular membrane, and a hollow fiber membrane. However, in the present invention, the separation membrane, the supply side channel material, and the permeation side channel material are perforated. It is preferable to use a spiral separation membrane element wound around the central tube.

  The permeate 42 separated by the polyamide reverse osmosis membrane 40 is stored in a storage tank 41, and is discharged into a river, for example, or reused as industrial water. Further, the concentrated solution after membrane separation is discharged into, for example, a river.

  In the present invention, when chloramines are harmful, a step of removing chloramines may be added after the membrane separation step by the polyamide-based reverse osmosis membrane 40. When removing chloramines, for example, sulfite, bisulfite, or the like can be used. Thereafter, the reaction product can be removed by ion exchange.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used for industrial water production, various wastewater treatment, valuable material recovery, and the like.

  Examples and the like specifically showing the configuration and effects of the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.

Example Using the water treatment apparatus shown in FIG. 1, while treating the sewage secondary treated water with an activated sludge apparatus, it was filtered and separated with a microfiltration membrane (average pore diameter of 0.1 μm), and the concentration of the permeate was reduced. Monochloramine was added so as to be 2 to 3 ppm. Furthermore, sulfuric acid as a scale inhibitor was added so that the pH was 7.0. After storing this in a storage tank (residence time 2 hours), a permeation flow rate 0.5 m ³ / (m ² · d) using a spiral type separation membrane element (polyamide type, HYDRANAUTICS, ESPA1 (low pressure type)) Membrane separation was performed at a recovery rate of 75%.

  The result is shown in FIG. 2, and the permeation flux hardly decreased even after 100 days. In addition, when the microbe density | concentration of the permeate of a microfiltration membrane was investigated, it was 0 cfu / 100 ml.

Comparative Example In Example 1, water treatment was performed using the water treatment apparatus shown in FIG. 1 under the same conditions except that chloramines were not added. At that time, the recovery rate was changed to 65%, 75%, and 70%. The results are shown in FIG. 3, and the decrease in permeation flux due to microbial fouling was significant regardless of the recovery rate.

The schematic block diagram which shows an example of the water treatment apparatus of this invention The graph which shows the time-dependent change of the permeation flux in an Example Graph showing change with time in permeation flux in comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pretreatment means 11 Separation membrane 20 Storage tank 21 Pretreatment water 30 Drug addition means 40 Polyamide type reverse osmosis membrane

Claims (6)

In the water treatment method in which pretreatment water that has undergone pretreatment is stored in a storage tank and then supplied to a polyamide-based reverse osmosis membrane for membrane separation,
Water, wherein chloramines are added to the pretreated water in any flow path before being supplied to the storage tank while performing membrane separation using a separation membrane capable of removing bacteria Processing method. The water treatment method according to claim 1, wherein the concentration after addition of the chloramines is 1 to 5 ppm. The polyamide-based reverse osmosis membrane, the separation membrane, supply-side passage material and permeation-side passage material, according to claim 1 or as spiral separation membrane element is wound around a central tube of perforated The water treatment method according to 2 . The water treatment method according to claim 1, wherein the separation membrane capable of removing bacteria is a microfiltration membrane or an ultrafiltration membrane. Pretreatment means for performing membrane separation with a separation membrane capable of removing bacteria;
A storage tank for storing pretreated water supplied from the pretreatment means;
A chemical addition means for adding chloramines to the pretreated water in any flow path before being supplied to the storage tank;
A polyamide-based reverse osmosis membrane that performs membrane separation of raw water supplied from the storage tank;
A water treatment apparatus comprising: The water treatment apparatus according to claim 5, wherein the concentration after addition of chloramines by the chemical addition means is 1 to 5 ppm.

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