JPS6078689A - Operation of reverse osmosis apparatus - Google Patents

Abstract

PURPOSE:To prevent the propagation of a microorganism during the stop period of a reverse osmosis apparatus and to eliminate membrane deterioration or the closure of a flowline, by intermittently supplying water to be treated containing chlorine from the inlet side of a high pressure pump during the stop period of the reverse osmosis apparatus. CONSTITUTION:A supply pipe 7 of chlorine such as sodium hypochlorite is connected to the adequate place of the raw water intake side line of a high pressure pump P4 and this high pressure pump P4 is intermittently operated during a stop period to supply chlorine-containing seawater into a reverse osmosis module 5. The time of intermittent supply may be determined corresponding to a period when chlorine in the module 5 looses sterilizing activity and it is usually sufficient to supply chlorine in frequency of about 1 time/2-5 days. The chlorine concn. of intermittently supplied seawater may be determined with due regard to equilibrium with adverse influence of membrane deterioration due to oxidation imparted to sterilizing action and the membrane and a pref. chlorine concn. is 0.5-2mg/l.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a reverse osmosis device, and more particularly to a method of operating a reverse osmosis membrane to prevent deterioration of a reverse osmosis membrane caused by microorganisms when the device is stopped.

The field of application of reverse osmosis equipment is gradually expanding as a device for concentrating low-molecular substances in solutions or separating solvents to high purity.In particular, seawater desalination equipment is increasing in number and scale. It is following a rapidly increasing trend.

By the way, in desalination facilities that use reverse osmosis to desalinate seawater, brine, etc., the operating rate fluctuates significantly due to changes in the demand for produced water and the amount of produced water due to changes in water temperature. It becomes a big problem. In other words, in seasons with heavy rainfall, natural ice can be used in a hurry, reducing the demand for relatively expensive desalinated water.
If desalination equipment is stopped for a long period of time in response to this demand reduction period, effective chlorine such as sodium hypochlorite, which is added as a disinfectant during steady operation, will disappear, and microorganisms contained in seawater will osmose through reverse osmosis. They propagate within the membrane module, causing problems such as membrane deterioration and blockage of flow paths inside the module. In addition, in the summer, water temperature rises and the amount of water produced per unit module increases, so the operating pressure is lowered in order to maintain a constant recovery rate of produced water, but for seawater desalination, the operating pressure is lowered. If the salt removal rate is increased, the salt removal rate will decrease. Therefore, in order to maintain the fresh water quality and appropriate operating pressure, there is a method of suspending some of the reverse osmosis modules to reduce the operating rate, but in this case as well, microbial growth may occur in the reverse osmosis modules that are not in use. Problems such as membrane deterioration and flow channel blockage occur. To deal with these problems, measures have been taken to encapsulate formalin solution inside the module while it is inactive, or to preserve the membrane element in formalin solution to prevent or kill microorganisms. However, from the perspective of environmental conservation, the formalin solution after use cannot be discharged as it is, creating problems with wastewater treatment.Furthermore, since formalin is a poisonous substance, the permeated water cannot be used as it is after restarting operation. Complete removal requires a considerable amount of time. In particular, when desalinated water is used for drinking purposes, many places prohibit formalin treatment as described above to avoid contamination with poisonous substances.

For this reason, most of the reverse osmosis equipment currently installed is designed for continuous operation, and the reality is that they overproduce large amounts of desalinated water even during the rainy season when natural water is abundant. It is. However, operating reverse osmosis equipment incurs a considerable economic burden, including electricity and labor costs, so during periods when natural water is abundant, the equipment must be shut down or production volume reduced. It is necessary to realize a collection plan that can reduce the amount of water and make effective use of inexpensive natural water, and in order to do so, it is necessary to ensure that the membrane deterioration and flow channel blockage as described above are prevented when the reverse osmosis equipment is stopped. It is necessary to establish an operating method that will prevent this and allow operation to resume without any problems when necessary.

Under the above circumstances, the present invention was completed as a result of various studies in an attempt to establish a method for preventing deterioration of reverse osmosis membranes during suspension of operation. During this period, chlorine-containing seawater or brine is intermittently supplied into the reverse osmosis device from the inlet side of the high-pressure pump to prevent the growth of microorganisms that may be introduced into the reverse osmosis module. .

With normal reverse osmosis equipment, there is a concern that microorganisms will breed even during operation, so chlorine is continuously injected into the seawater to prevent this, but there are reducing substances present in the seawater kettle water. Since this process reduces and consumes chlorine, the time for this chlorine to effectively exert its disinfecting power is extremely short. Therefore, when the operation is stopped, the bactericidal activity of chlorine in the membrane module is lost, and microorganisms begin to multiply rapidly. - Chlorine, which exhibits antibacterial activity, also acts as a strong oxidizing agent, and if the concentration is too high, it will have a negative effect on general-purpose reverse osmosis membranes (cellulose acetate, etc.), so large amounts cannot be injected, and during continuous operation. The limit for the amount of chlorine injected is approximately 0.2 to 2 my/l. At this level of concentration, 2 to 3
The bactericidal effect of chlorine is lost within a few days.

The present invention attempts to compensate for the decrease in the bactericidal activity of chlorine during operation stoppage by using some method to maintain a high-stage bacteria-activating atmosphere inside the reverse osmosis membrane module at all times, and specifically, even during operation stoppage. Seawater or brine containing chlorine is intermittently supplied into the reverse osmosis device from the inlet side of the high-pressure pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and effects of the present invention will be specifically explained below with reference to the drawings. FIG. 1 is a flowchart showing an embodiment of the present invention, in which seawater sucked and sampled by a seawater intake pump P1 is temporarily stored in a water receiving tank l, and then sent to a filter 2 by a filtration pump P2. The seawater from which insoluble impurities have been removed by the filter 2 is stored in the temporary water tank 8, and then sent from the booster pump P3 to the cartridge filter 4, and from the high pressure pump P4 to the reverse osmosis module 5, where it is desalinated water W. and concentrated water B. ■ indicates a pressure adjustment valve for adjusting the operating pressure. This prevents the proliferation of microorganisms during operation of such a reverse osmosis device. For this purpose, for example, a chlorine supply pipe is connected to a suitable place on the line connecting the water intake pump P0 and the water receiving tank 1, and an appropriate amount of chlorine is continuously supplied from there.

Therefore, during operation, chlorine at an appropriate temperature is always mixed into the raw water side of the reverse osmosis module, and there is almost no breeding of microorganisms, but when the operation is stopped, the chlorine is consumed by reducing substances in the raw water as mentioned above. Microorganisms begin to proliferate within the module 5 after 2 to 8 days without losing its bactericidal action. Therefore, in the present invention, as shown in the figure, for example, a chlorine (mainly sodium hypochlorite is used) supply pipe 7 is connected to an appropriate place on the raw water suction side line of the high-pressure pump P4, and the high-pressure pump P4 is is operated to supply chlorine-containing seawater into reverse osmosis module b. The timing of intermittent feeding may be determined depending on the timing when the chlorine in the module 5 loses its bactericidal activity, and normally once every 2 to 5 days is sufficient. Further, the operating time during one intermittent operation is approximately 8 to 10 minutes, which is sufficient to supply chlorine-containing seawater into the module 5. That is, according to the present invention, for example, 8
By simply operating the device for about 10 minutes, the inside of module b can be kept in a highly sterilizing active state, and deterioration of the reverse osmosis membrane due to the proliferation of microorganisms can be prevented. The chlorine concentration of the seawater that is intermittently supplied should be determined by taking into account the balance between the bactericidal effect and the negative effect on the crotch (deterioration of the membrane due to oxidation), and the preferred chlorine concentration is 0.5 to 2 mg/l. be. In addition, microorganisms are blocked by the reverse osmosis membrane and module 5
Since the chlorine-containing seawater remains on the raw water side of module 5, the purpose can be fully achieved by simply supplying the chlorine-containing seawater to the raw water side of module 5. In this sense, it is better to keep the operating pressure as low as possible during intermittent operation. This is advantageous because power costs can be reduced.

FIG. 2 is a flow diagram showing another embodiment of the present invention, in which a plurality of reverse osmosis modules M0 to M5 are arranged in parallel, and the valve v
The freshwater production crisis can be freely controlled by opening and closing 0 to v1o. That is, when the demand for fresh water is large, all valves v0 to v1o are opened and modules 5a to
On the other hand, during the rainy season when natural ice is plentiful, for example, valves V1 to ■3 and ■6 to V8 are closed.

Production volume will be reduced by suspending 5C, etc.

In this case, as mentioned above, there is a risk of microbial growth in the idle module, so in the present invention, the valves v1 to ■ and v6 to v8
The module is opened to supply chlorine-containing seawater into the idle modules M, M2, and M3, maintaining the inside of the modules in a highly sterilizing active state. In the case of equipment in which a plurality of modules are arranged in parallel in this manner, the raw water to be treated to which chlorine has been added can be used as is as the chlorine-containing seawater that is intermittently supplied to the idle modules. In addition, in reverse osmosis equipment with this arrangement, the bactericidal activity in each idle module decreases2.
It is also possible to reduce the amount of water produced or perform granulation by switching the valve every ~5 days and repeating suspension and operation every 2 to 5 days.

The present invention is generally constructed as described above, but the point is that by supplying chlorine-containing seawater or brine at regular intervals to the module during the suspension period, it is possible to maintain the interior of the module in a high-stage bacterial activation state at all times. Therefore, the proliferation of microorganisms during this time is reliably prevented, and all problems such as membrane deterioration and channel blockage can be solved. Moreover, as mentioned above, the intermittent supply of chlorine-containing seawater only needs to be carried out once every 2 to 5 days for a short period of about 2 to 10 minutes, so the power cost required for this treatment is extremely small. Therefore, during the rainy season when natural ice is abundant, it is possible to virtually stop the reverse osmosis equipment or reduce the number of water producers, making effective use of inexpensive natural water, and reducing the operating costs of the reverse osmosis equipment during this time. It became possible to reduce the Furthermore, in the present invention, since the same chlorine as used during steady operation is used as a sterilizing agent, there is no risk of deterioration of water quality as in conventional formalin sterilization. Moreover, with the formalin sterilization method, fresh water cannot be obtained because formalin washing is required for several hours after restarting operation, but with this invention, it is possible to restart operation.
It is possible to enjoy extremely practical benefits, such as being able to recover purified water immediately after the water is removed.

Next, Examples and Comparative Examples will be presented to clarify the effects of the present invention.

Comparative Example 1 A seawater desalination equipment (using a cellulose acetate reverse osmosis membrane) as shown in Figure 1 was used and operated continuously for about 10 months while supplying sodium hypochlorite at a concentration of 1 my/l in terms of chlorine. After that, the operation was stopped, and after being left as it was for about 80 days, the operation was restarted, and the processing capacity before and after the restart was compared.

The results are shown in Table 1. Although the treatment capacity before the shutdown was good, the approximately 80-day shutdown caused microorganisms to grow inside the equipment and deteriorated the permeation membrane, resulting in a drop in the salinity of the produced water after restarting. has increased significantly, and the salt removal rate has decreased by 10%.

Table 1 Example 1 A solenoid valve and a timer are installed in the chlorine supply pipe 7 of the device shown in FIG.
and connected to high pressure pump P4.

This equipment was operated for 18 months, with operation stopped during the rainy season in response to fluctuations in water demand and produced water. During this period, there were 8 stoppages of 80 days or more, so a timer was set so that the solenoid valve would open for 5 minutes every 3 days after the stoppage and the high pressure pump P4 and booster pump P3 would operate. Then, the pressure regulating valve V was fully opened and the seawater inside the module 5 was exchanged at low pressure, and the same seawater exchange was repeated once every 8 days.
We investigated the processing ability of menstrual retirement.

The results are shown in Table 2, and there is almost no decline in processing ability even after 18 months of retirement, including a period of suspension of 8 or more yuan.

Table 2 Example 2 In a parallel type reverse osmosis separator as shown in Figure 2,
During the summer period when the water temperature is high (four months from July to October), valves V□ and V6 were closed to suspend module M and reduce the amount of water produced. Valve v1 twice a week during this period
and ■6 for 5 minutes, and then add raw water containing chlorine to module 5.
supplied inside.

Then, after the summer passes and the water temperature drops, valve v1,■
6 and restarted desalination using module M1 to compensate for the decrease in water production due to the drop in water temperature.

As a result, no performance deterioration was observed due to the long-term suspension of Module M engineering.

[Brief explanation of the drawing]

FIG. 1.2 is a flow diagram illustrating an embodiment of the invention. 1...Water tank, 2...Filter, 8...Filtering water tank, 4...Cartridge filter,
5, M1 to M5... Reverse osmosis membrane module, W... Permeated water, B... Brine (concentrated liquid). Applicant Kobe Steel, Ltd.

Claims (1)

[Scope of Claim] An operation method for preventing deterioration of the reverse osmosis membrane during a period when the device is stopped in a reverse osmosis device for obtaining fresh water by passing seawater, brine, etc. through the reverse osmosis membrane under high pressure, the method comprising: 1. A method for operating a reverse osmosis membrane, which comprises intermittently supplying treated water containing chlorine to the reverse osmosis device from the inlet side of a high-pressure pump during a period when the osmosis device is stopped.