JP2007125526A - Operation method of reverse osmosis membrane separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable long-term stable operation by inhibiting a deterioration in membrane flux of an RO device for carrying out desalting and/or removal of organic matter. <P>SOLUTION: In an operation method of a reverse osmosis membrane separator for carrying out desalting and/or removal of organic matter, water to be treated whose pH has been adjusted to 9.5-13 by addition of an alkali is used as flushing water to temporarily flush the reverse osmosis membrane separator. By carrying out flushing with the alkaline water to be treated during operation, a membrane surface is washed effectively to inhibit the deterioration of the membrane flux, which enables a stable operation for the long term. Almost all of supply water does not permeate a membrane during the flushing, therefore concentration on the membrane surface does not occur, which prevents the problems of scale generation on the membrane surface even when the supply water is alkaline. As a result, the necessity of a pretreatment device or the like for scale prevention is eliminated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an operation method of a reverse osmosis membrane separation device (RO device), and in particular, suppresses a decrease in membrane surface permeation flux of a RO device that performs desalination and / or organic matter removal, and enables long-term stable operation. The present invention relates to a method for operating an RO device.

  RO devices are used in a wide range of fields such as fresh water production processes, food / pharmaceutical water production processes, and wastewater recovery processes. In particular, in recent years, the number of cases in which RO devices are used in the wastewater recovery process has been increasing rapidly for the purpose of reducing the cost of wastewater for use and reducing the environmental burden.

  Usually, the RO device has an arrangement called a Christmas tree as shown in FIG. 2 for the purpose of increasing the water recovery rate with respect to the supplied water. That is, in FIG. 2, a first RO vessel group (RO vessel group is also referred to as a “bank”) 1 in which four RO vessels (RO means main bodies) 1A, 1B, 1C, 1D incorporating RO elements are arranged in parallel. The second RO bank 2 in which two RO vessels 2A and 2B are arranged in parallel constitutes a Christmas tree type multi-stage RO device.

  The water to be treated, that is, the supply water (RO feed water) of the RO device first flows into the first bank 1 and is separated into permeated water and concentrated water. Subsequently, the concentrated water in the first bank 1 flows into the second bank 2 and is again separated into permeated water and concentrated water. The permeated water of the first bank 1 and the permeated water of the second bank 2 merge and are transferred to the subsequent processing step. On the other hand, the concentrated water in the second bank 2 is discharged out of the system or transferred to a wastewater treatment facility or the like. Usually, the Christmas tree structure in the RO device is often composed of two or three banks, depending on the required water recovery rate.

  When such an RO device is used in a wastewater treatment process, particularly a wastewater recovery process in which the concentration of organic components in the treated water is relatively high, microorganisms propagate on the membrane surface due to the high TOC concentration of the treated water. Due to the occurrence of biofouling caused and the inflow of non-ionic surfactants, which are biometabolite-based organic matter or biodegradable organic matter discharged from biological treatment means installed in the wastewater treatment process, into the RO device Due to the membrane surface blockage, the amount of permeated water of the RO device tends to decrease, and therefore there is a problem that the membrane must be frequently washed. This problem tends to be particularly noticeable in recent years.

  In Japanese Patent No. 3321179, a method for adjusting the pH of RO water supply to 10 or more alkaline and constantly passing water through the RO device is proposed. However, since this method performs alkaline RO treatment, scale generation on the membrane surface is proposed. For the purpose of suppressing the hardness, the hardness removing device or the alkalinity removing device must be installed in the front stage of the RO device, and there is a drawback that the equipment configuration and operation management become complicated.

  Japanese Patent Application Laid-Open No. 11-128919 proposes a method of temporarily setting the pH of RO water supply to 10 to 12 during continuous RO operation and taking out the membrane permeated water as treated water during this pH adjustment. However, in this method, even if the operation time is short with the pH of the RO water supply being alkaline, if it is carried out without pretreatment measures for scale prevention, scale is generated on the membrane surface and the membrane surface is blocked. There is a fear. On the other hand, providing a pretreatment device for scale prevention makes the facilities complicated as described above.

In addition, as described in, for example, Japanese Patent Application Laid-Open No. 2004-58022, it is known to perform alkaline cleaning on a membrane separation apparatus such as an RO apparatus. The alkali cleaning of the membrane separator is carried out by completely stopping the normal operation of the membrane separator, that is, by completely stopping the flow of water to be treated and the sampling of permeate. In addition to stopping the process, the water to be treated in the system is also discharged, and then a cleaning line is formed between the cleaning liquid storage tank and the membrane separation device to enter the cleaning process. Then, the cleaning liquid is circulated, and the primary side (concentrated water side) and the secondary side (permeated water side) of the membrane are immersed in the cleaning liquid, and the recirculation is performed, and the cleaning liquid is discharged. In such chemical cleaning with alkali, complicated procedures such as switching to a cleaning line must be taken, and the water flow stoppage time is long and it leads to a decrease in operating efficiency. Therefore, the number of chemical cleaning times can be reduced as much as possible. It is desired.
Patent 33211179 JP 11-128919 A JP 2004-58022 A

  In the RO apparatus for performing desalting and / or organic matter removal, the present invention can suppress a decrease in the membrane surface permeation flux without requiring a pretreatment apparatus for scale prevention, and enables long-term stable operation. An object of the present invention is to provide a method for operating an RO device.

  The operating method of the reverse osmosis membrane separation device of the present invention is the operating method of the reverse osmosis membrane separation device having reverse osmosis membrane separation means for desalting and / or organic matter removal, wherein alkali is added to adjust the pH to 9.5. The water to be treated as 13 is used as flushing water, and the reverse osmosis membrane separation means is temporarily flushed.

  The operation method of the reverse osmosis membrane separation device according to claim 2 is the operation method according to claim 1, wherein the reverse osmosis membrane separation device is a rear stage to which the upstream reverse osmosis membrane separation means and the concentrated water of the upstream reverse osmosis membrane separation means are supplied. A multi-stage reverse osmosis membrane separation device comprising a reverse osmosis membrane separation means, wherein the flushing step is a step of supplying flushing water only to the upstream reverse osmosis membrane separation means and then flushing, followed by flushing water to the upstream reverse osmosis membrane. And a step of supplying and flushing the separation means and the downstream reverse osmosis membrane separation means in series.

  The operation method of the reverse osmosis membrane separation device according to claim 3 is the reverse osmosis membrane separation device according to claim 1 or 2, wherein the reverse osmosis membrane separation device includes a reverse osmosis membrane separation means main body having a reverse osmosis membrane, an inlet / exhaust pipe for water to be treated In the normal operation where the permeated water is sampled, the permeated water drain pipe that has permeated through the reverse osmosis membrane and the concentrated water drain pipe that has an on-off valve are used. At the same time, the on-off valve is closed, or the permeated water is taken out by reducing the opening, and in the flushing step, the opening and closing of the reverse osmosis membrane separation means main body is continued while the treated water is continuously introduced. By opening the valve or increasing the opening, most of the water to be treated introduced into the reverse osmosis membrane separation main body is discharged from the concentrated water discharge pipe.

  According to a fourth aspect of the present invention, there is provided a reverse osmosis membrane separation apparatus operating method according to the third aspect, characterized in that an alkali addition means for injecting alkali into the introduction / drain pipe of the water to be treated is provided.

  In addition, flushing is the primary side (concentrated water side) of the membrane without allowing most of RO feed water to permeate the membrane by opening the on-off valve of the concentrated water discharge pipe while continuing the operation of the feed water pump. This is the operation of draining and discharging the concentrated water out of the system. At this time, since most RO water supply does not permeate the membrane, almost all of the water supply flows through the membrane surface on the primary side, so that a large amount of water flows at a faster flow rate than during normal operation in which permeate is sampled. Thus, the dirt blocking the membrane surface can be washed away effectively.

  According to the present invention, by flushing with alkaline treated water during the operation of the RO device, the membrane surface is effectively washed to suppress a decrease in membrane surface permeation flux, and stable operation can be performed over a long period of time. Can be done.

  At the time of this flushing, most of the RO water supply does not permeate the membrane, and therefore no concentration on the membrane surface occurs, so that even if the RO water supply is alkaline, the problem of scale generation on the membrane surface does not occur. Therefore, a pretreatment device for preventing scale is not necessary.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a method for operating an RO apparatus of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system diagram showing an embodiment of a method of operating an RO device according to the present invention.

  In the RO apparatus shown in FIG. 1, two RO vessels 1A and 1B are arranged in parallel to form a first bank (bessel group) 1 in the front stage, and a second bank 2 in the rear stage is composed of only one RO vessel 2A. This is a two-stage Christmas tree-type RO device configured.

  Each RO vessel 1A, 1B, 2A contains one or more RO elements. In addition, the banks 1 and 2 are provided with water supply pipes 11 and 13A, permeate water pipes 12 and 15, and concentrated water pipes 13 and 16, respectively.

  In the first bank 1, water supply branch pipes 11a and 11b branched from the water supply pipe 11 are connected to the RO vessels 1A and 1B, and water to be treated is supplied in parallel to the RO vessels 1A and 1B. Further, the permeated water that has passed through the RO membrane in each of the vessels 1A and 1B is collected from the permeated water branch pipes 12a and 12b to the permeated water pipe 12, and passes through the permeated water discharge pipe 14 together with the permeated water of the second bank 2 in the subsequent stage. It is discharged out of the system. On the other hand, the concentrated water of each of the vessels 1A and 1B is collected from the concentrated water branch pipes 13a and 13b to the concentrated water pipe 13 and sent to the RO vessel 2A as the water supply for the second bank 2 in the next stage.

  In the RO vessel 2A of the second bank 2 as well, the permeate that has permeated the RO membrane passes from the permeate pipe 15 through the permeate discharge pipe 14 and the permeate from the RO vessels 1A and 1B of the first bank 1 outside the system. Is discharged. On the other hand, the concentrated water is discharged out of the system through the concentrated water pipe 16. This concentrated water pipe 16 is provided with a throttle valve AV2.

In this RO apparatus, a chemical injection pipe 18 having a chemical injection pump P ₂ for injecting alkaline chemicals from the chemical tank 3 is provided on the upstream side of the water supply pump P ₁ of the water supply pipe 11. A concentrated water discharge pipe 17 having an on-off valve AV1 branches off from the concentrated water pipe 13 of the first bank 1.

In the present invention, in such an RO device, during normal operation (water sampling operation) in which the following operation is performed, the valve AV1 is closed and the valve AV2 is set to be open so as to have a predetermined water recovery rate. and, by operating the water supply pump _{P 1,} the treated water from the pipe 11, the first bank 1 of the RO vessel 1A through piping 11a, the 11b, and the pressure supplied to 1B, the permeate piping 12a, 12b, 12 , 14 and discharged outside the system. On the other hand, the concentrated water is introduced into the RO vessel 2A of the second bank 2 through the pipes 13a, 13b, 13, and 13A, and the permeate is discharged out of the system through the pipes 15 and 14. The concentrated water in the second bank 2 is discharged out of the system through the pipe 16.

  The concentrated water is discharged or sent to a wastewater treatment device at the subsequent stage. The permeated water is further fed to a subsequent processing device.

  After such normal operation is performed for a predetermined time, flushing is performed as follows.

First, while operating the water supply pump P ₁ as in normal operation, by operating the chemical feed pump P _2, while adjusting the pH9.5~13 by adding an alkali chemical to the water to be treated, the valves AV1 open. As a result, most of the water flowing into the RO vessels 1A, 1B of the first bank 1 in the previous stage is discharged outside the system through the pipes 13a, 13b, 13, 17 without passing through the RO membrane.

  By this operation, a large amount of alkaline water flows at a high flow rate on the membrane surfaces of the RO vessels 1A and 1B of the first bank 1, thereby cleaning each membrane surface.

As described above, after flushing only the first bank 1, the valve AV1 is closed and the valve AV2 is opened while the pumps P ₁ and P ₂ are operated. As a result, most of the alkaline water flowing into the first bank 1 in the preceding stage flows into the RO vessel 2A of the second bank 2 via the pipes 13a, 13b, 13, 13A, and most of the water that has flowed in further flows into the RO membrane. Without passing through the pipe 16 and discharged from the system.

  By this operation, a large amount of alkaline water flows in series and at a high flow rate in series on the membrane surface of the RO vessel 1A, 1B of the first bank 1 and the membrane surface of the RO vessel 2A of the second bank 2. Each membrane surface is cleaned.

In this way, the flushing of the first bank 1, after making subsequent first bank 1 and a continuous flushing of the second bank 2, open during normal operation the AV2 stops the chemical feed pump valve P ₂ Adjust it every time and resume normal operation. At this time, usually may resume operation by adjusting the opening of the valve AV2 after a predetermined time has elapsed stops the chemical feed pump P _2.

  The RO apparatus according to the present invention is generally an RO apparatus provided in a fresh water production process, a food / medicine water production process, and a wastewater recovery process. It is slightly acidic to neutral water of about ˜7. Accordingly, in the present invention, water adjusted to have a pH of 9.5 to 13 by adding an alkaline chemical such as sodium hydroxide (NaOH) to such neutral treated water is used as flushing water. To perform the flushing process. This is due to the following reason.

  That is, microorganisms cannot live in the alkaline region. Therefore, by adjusting the pH of the flushing water to 9.5 or higher, it is possible to create an environment where there are nutrients but microorganisms cannot live, without the need for the addition of an expensive slime control agent as in the past. Biofouling can be prevented. In addition, it is known that nonionic surfactants or biological metabolite-based organic substances that may lower the membrane surface permeation flux are desorbed from the membrane surface in the alkaline region, and the pH should be 9.5 or higher. This makes it possible to suppress adhesion to the film surface.

  However, if the pH of the RO water supply at the time of flushing is too high, the RO membrane exceeds the limit of alkali resistance and easily breaks, and the cost of adding chemicals is high. The pH of the solution is 13 or less.

  From the viewpoints of the effect of suppressing microorganisms, the effect of cleaning organic matter, the effect of removing dirt, the cost of chemical injection, and the protection of the membrane, the pH of the RO water supply during flushing is particularly preferably 10-12.

  The alkali for pH adjustment can be added at any position before the water to be treated flows into the RO vessel. However, as shown in FIG. It is efficient to inject the line.

  In the present invention, the frequency of such flushing is not particularly limited and is appropriately determined according to the quality of the water to be treated, the RO treatment conditions, and the like, but is usually 5 to 60 at a rate of once every several hours to 10 days. It is preferable to carry out for about minutes. In particular, as described above, when performing flushing of only the first bank and thereafter performing continuous flushing from the first bank to the second bank, or further performing subsequent flushing, the time for each flushing is 5 to 30. The total flushing time is preferably about 10 to 60 minutes.

  Although FIG. 1 shows a Christmas tree type RO device in which two RO vessels are arranged in parallel in the first bank and one RO vessel is provided in the second bank, the present invention is applied. The RO device is not limited to the one shown in FIG. 1, and as shown in FIG. 2, four RO vessels are arranged in parallel in the first bank, and two RO vessels are arranged in parallel in the second bank. It may be a thing. Further, the present invention is not limited to a Christmas tree type RO device, and it may be composed of only one stage of RO vessel or RO bank, or one stage of RO vessel may be connected in multiple stages.

  In the case of a Christmas tree type RO device, the number of banks and the number of vessels are not particularly limited, but the number of banks is usually two or three. However, it goes without saying that a multi-stage configuration of four or more stages may be used. Further, the number of RO vessels in each bank is appropriately set according to the amount of treated water and the processing capacity of the RO vessel, but in general, the number is larger on the upstream side and smaller on the downstream side. Normally, in the case of two stages, the number of vessels in the first bank: the number of vessels in the second bank = 2: 1 is set. In the case of three stages, the number of vessels in the first bank: second bank The number of vessels is often set at a ratio of the number of vessels: the number of vessels in the third bank = 4: 2: 1. The number of vessels in the final stage may be one.

  In any case, as described above, each RO vessel has a built-in RO element, and one vessel contains one or more RO elements.

  Each bank (vessel group) is provided with a water supply pipe, a permeate pipe, and a concentrated water pipe. And in each bank, the feed water branch pipe branched from the feed water pipe is connected to each RO vessel, and to-be-processed water is supplied to each vessel in parallel. Further, the permeated water that has passed through the membrane in each vessel is collected in a permeated water pipe and discharged. On the other hand, the concentrated water of each vessel is collected in the concentrated water pipe and sent to the next-stage water supply pipe as the water supply for the next-stage bank. In the next stage, water flows in the same manner and RO treatment is performed.

  The concentrated water piping of the upstream bank is connected to the water supply piping of the next bank, but there is a piping that branches at any position of the concentrated water piping of each stage and discharges the concentrated water out of the system. The concentrated water discharge pipe is provided with an open / close valve. The final stage concentrated water discharge pipe may be provided by branching from the concentrated water pipe, or may be combined with the concentrated water pipe.

  In addition, at least the concentrated water pipe in the final stage is provided with a throttle valve so that the operating pressure of the RO vessel in the bank in the final stage can be adjusted. When the concentrated water pipe and the concentrated water discharge pipe are shared, the on / off valve may be omitted and a throttle valve may be substituted for the on / off valve.

  The on-off valve and throttle valve are preferably automatic valves, but may be manual valves. The on / off valve and throttle valve are automatic valves, and the flushing process can be automatically incorporated during normal operation by automatically controlling the opening / closing and on / off of the chemical injection pump with a timer.

  In the case of a multi-stage RO device such as a Christmas tree type RO device, especially when an ultra-low pressure RO membrane is used or when water to be treated having a large osmotic pressure is treated, the RO membrane in the preceding bank (or vessel) is contaminated. Therefore, as described above, it is preferable to perform the flushing of only the preceding bank (the vessel group) and then sequentially perform the flushing of the preceding bank and the succeeding bank (the vessel group) sequentially. Therefore, for example, in the case of an RO device composed of three banks, after flushing only the first bank, continuous flushing from the first bank to the second bank is performed, and then the first bank to the second bank. → It is preferable to perform continuous flushing of the third bank.

However, it is also possible to directly perform flushing of all banks directly without performing flushing of only the preceding bank. In this case, for example, in RO apparatus of FIG. 1, is operated while keeping dosing pump P ₂ was operated water pump P _1, the throttle valve AV2 open while closing the opening and closing valve AV1. As a result, alkaline water flows from the RO vessels 1A, 1B of the first bank 1 into the RO vessels 2A of the second bank 2, and is discharged from the pipe 16, whereby the membrane surface of each RO vessel is cleaned.

  However, in this case, contaminants adhering to the film surface of the preceding bank flow into the succeeding bank, so after flushing only the preceding bank, continuous flushing between the preceding bank and the succeeding bank is performed. Compared with the case, as shown in Example 2 described later, the cleaning effect is slightly inferior. Therefore, as described above, it is preferable to first perform flushing of only the preceding bank and discharge the contaminants in the preceding bank to the outside of the system, and then perform continuous flushing between the preceding bank and the succeeding bank.

  Such a method of operating the RO device of the present invention is particularly effective when the treated water having a TOC concentration of 3 mg / L or more, which is likely to block the membrane surface, is used as RO water supply.

  According to the present invention, the membrane surface can be effectively cleaned by a simple operation such as opening / closing a valve or operating a chemical injection pump without stopping the operation as in the case of conventional chemical cleaning using alkali. In addition, since scale measures are not required, it can be easily applied to existing facilities.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
Example 1
TOC concentration 3 mg / L, aggregation and sedimentation and filtration the liquid crystal factory total effluent conductivity 100 mS / m, after the activated carbon treatment, ^1m 3 / hr, the recovery rate of 75% for at passing water RO apparatus shown in FIG. 1 Went. The pH of the RO water supply at this time was 5. As the RO element of each RO vessel 1A, 1B, 2A, ES-20 (manufactured by Nitto Denko), which is an ultra-low pressure RO membrane, was used.

Flushing was carried out by adding 4 wt% NaOH aqueous solution from chemical tank 3 to RO feedwater to pH of RO water with chemical feed pump P ₂ is 11, once every 4 hours, only the first bank 1 Flushing was performed for 15 minutes, followed by continuous flushing from the first bank bank 1 to the second bank 2 in the order of 15 minutes.

  The relationship between the operation days and the membrane surface permeation flux at this time is shown in FIGS.

(Example 2)
The RO apparatus was operated under the same conditions as in Example 1 except that only flushing of the first bank 1 was not performed and only continuous flushing of the first bank 1 → second bank 2 was performed for 30 minutes. The relationship between the operation days at this time and the membrane surface permeation flux is shown in FIG.

(Comparative Example 1)
The RO device was operated under the same conditions as in Example 1 except that the flushing was not performed. The relationship between the operation days at this time and the membrane surface permeation flux is shown in FIG.

  The following is clear from FIG.

In Example 1, the membrane surface permeation flux hardly decreased, and the membrane surface permeation flux was about 0.77 m ³ / m ² · day even 90 days after the start of water flow. On the other hand, in Example 2, the membrane surface flux was improved as compared with Comparative Example 1 in which flushing was not performed, but after 90 days, the membrane surface flux was 0.68 m ³ / m ² · day. A decrease was seen compared to Example 1 in which continuous flushing of the first bank and the second bank was performed after flushing of one bank. In Comparative Example 1 in which flushing was not performed, the membrane surface permeation flux after 90 days was 0.55 m ³ / m ² · day, and a marked blockage of the RO membrane surface was observed.

(Example 3)
The RO device was operated under the same conditions as in Example 1 except that the pH of the RO water supply during flushing was 9.5. The relationship between the operation days at this time and the membrane surface permeation flux is shown in FIG.

(Comparative Example 2)
The RO device was operated under the same conditions as in Example 1 except that the pH of the RO water supply during flushing was set to 7. The relationship between the operation days at this time and the membrane surface permeation flux is shown in FIG.

(Comparative Example 3)
The RO device was operated under the same conditions as in Example 1 except that the pH of the RO water supply during flushing was set to 8. The relationship between the operation days at this time and the membrane surface permeation flux is shown in FIG.

  From FIG. 4, it can be seen that when the pH of the flushing water is 9.5 or higher, a decrease in the membrane surface permeation flux is not observed and stable operation is possible.

It is a systematic diagram which shows embodiment of the operating method of RO apparatus of this invention. It is a systematic diagram which shows the structure of a general Christmas tree type RO apparatus. It is a graph which shows the relationship between the operation days in Examples 1, 2 and Comparative Example 1, and a membrane surface permeation flux. It is a graph which shows the relationship between the operation days and the membrane surface permeation flux in Examples 1 and 3 and Comparative Examples 2 and 3.

Explanation of symbols

1 First bank (first RO vessel group)
2 Second bank (second RO vessel group)
1A, 1B, 1C, 1D, 2A, 2B RO vessel 3 Chemical tank

Claims (4)

  In a method for operating a reverse osmosis membrane separation apparatus having a reverse osmosis membrane separation means for desalting and / or removing organic matter, water to be treated, which has been adjusted to pH 9.5 to 13 by adding alkali, is used as flushing water. A method for operating a reverse osmosis membrane separation apparatus comprising a step of temporarily flushing an osmosis membrane separation means.   2. The multi-stage reverse osmosis membrane separation device according to claim 1, wherein the reverse osmosis membrane separation device includes a first-stage reverse osmosis membrane separation unit and a second-stage reverse osmosis membrane separation unit to which the concentrated water of the first-stage reverse osmosis membrane separation unit is supplied. In the flushing step, the flushing water is supplied only to the first-stage reverse osmosis membrane separation means and then flushed, and then the flushing water is serially connected to the first-stage reverse osmosis membrane separation means and the second-stage reverse osmosis membrane separation means. A method of operating a reverse osmosis membrane separation device, comprising: supplying and flushing.   In claim 1 or 2, the reverse osmosis membrane separation device comprises a reverse osmosis membrane separation means main body having a reverse osmosis membrane, an introduction / exhaust pipe for water to be treated, a discharge pipe for permeated water that has permeated the reverse osmosis membrane, Concentrated water discharge pipe having an on-off valve, and during normal operation for collecting permeated water, water to be treated is introduced into the reverse osmosis membrane separation means body and the on-off valve is closed, or The permeated water is taken out by reducing the opening, and in the flushing step, the on-off valve is opened or the opening is increased while the introduction of treated water into the reverse osmosis membrane separation means body is continued. Thus, most of the treated water introduced into the reverse osmosis membrane separation main body is discharged from the concentrated water discharge pipe.   4. The method of operating a reverse osmosis membrane separation apparatus according to claim 3, wherein alkali addition means for injecting alkali into the introduction / exhaust pipe of the water to be treated is provided.

Images