JP7579149B2 - Water treatment method and water treatment device - Google Patents

Description

The present invention relates to a water treatment method and a water treatment device.

Water treatment devices that have a reverse osmosis membrane (RO membrane) are known as devices that remove impurities from the water to be treated. In these devices, the water to be treated (raw water) is supplied to the RO membrane at a specified supply pressure, and the RO membrane separates the water to be treated (permeated water) and concentrated water. This makes it possible to obtain treated water (permeated water) from which impurities have been removed.

In water treatment equipment having an RO membrane, chemicals such as antiscalant and slime control agents have been conventionally injected into the raw water to prevent clogging (fouling) caused by the generation of scale and slime on the membrane surface of the RO membrane. In such chemical injection, it is required to adjust the injection amount of chemicals according to the degree of fouling in order to effectively suppress fouling while suppressing deterioration of the RO membrane caused by excessive chemical injection. In response to this requirement, a method has been proposed in which an increase in the water flow differential pressure of the RO membrane (the pressure difference between the supply pressure of raw water supplied to the RO membrane and the outflow pressure of concentrated water flowing out from the RO membrane) is detected and the injection amount of chemicals is adjusted based on the detection results (see, for example, Patent Documents 1 and 2).

JP 2011-224543 A International Publication No. 2020/158645

However, simply monitoring the increase in the water flow differential pressure across the RO membrane does not adequately take into account the effects of fouling, and is not a sufficient solution to the above-mentioned requirements.

The object of the present invention is to provide a water treatment method and water treatment device that effectively suppresses fouling while suppressing deterioration of the reverse osmosis membrane.

In order to achieve the above-mentioned object, the water treatment method of the present invention includes a step of injecting an agent into the water to be treated, and a step of supplying the water to be treated with the agent injected therein to a reverse osmosis membrane to separate it into permeate water and concentrated water, and the step of injecting the agent includes a step of detecting the current water temperature of any of the water to be treated supplied to the reverse osmosis membrane, the permeate water flowing out from the reverse osmosis membrane, and the concentrated water flowing out from the reverse osmosis membrane, a step of detecting the current supply pressure of the water to be treated supplied to the reverse osmosis membrane, or the differential pressure between the current supply pressure and the current outlet pressure of the concentrated water flowing out from the reverse osmosis membrane, and a step of adjusting the amount of the agent injected into the water to be treated based on an initial value of any of the water temperatures detected in advance when the reverse osmosis membrane is started to be used, an initial value of the supply pressure or differential pressure detected in advance when the reverse osmosis membrane is started to be used, the detected current water temperature, and the detected current supply pressure or differential pressure. In one aspect, the step of adjusting the amount of chemical injected includes converting an initial value of the supply pressure or differential pressure to a value at the detected current water temperature, and adjusting the amount of chemical injected into the water to be treated based on the converted initial value of the supply pressure or differential pressure and the detected current supply pressure or differential pressure; in another aspect, the step of adjusting the amount of chemical injected includes converting the detected current supply pressure or differential pressure to a value at standard temperature, and adjusting the amount of chemical injected into the water to be treated based on the converted current supply pressure or differential pressure and the initial value of the supply pressure or differential pressure converted to a value at the standard temperature .

The water treatment device of the present invention also includes a reverse osmosis membrane device having a reverse osmosis membrane that separates the water to be treated into permeate and concentrated water; a chemical injection device that injects a chemical into the water to be treated that is supplied to the reverse osmosis membrane device; a temperature sensor that detects the temperature of the water to be treated that is supplied to the reverse osmosis membrane device, the permeate flowing out from the reverse osmosis membrane device, and the concentrated water flowing out from the reverse osmosis membrane device; a pressure sensor that detects the supply pressure of the water to be treated that is supplied to the reverse osmosis membrane device, or the differential pressure between the supply pressure and the outlet pressure of the concentrated water flowing out from the reverse osmosis membrane device; and a control device that adjusts the amount of chemical injected by the chemical injection device based on an initial value of any of the water temperatures detected by the temperature sensor when use of the reverse osmosis membrane is started, an initial value of the supply pressure or differential pressure detected in advance by the pressure sensor when use of the reverse osmosis membrane is started, any of the current water temperatures detected by the temperature sensor, and the current supply pressure or differential pressure detected by the pressure sensor . In one aspect, the control device converts the initial value of the supply pressure or differential pressure to a value at any of the detected current water temperatures, and adjusts the amount of drug injected by the drug injection device based on the converted initial value of the supply pressure or differential pressure and the detected current supply pressure or differential pressure; in another aspect, the control device converts the detected current supply pressure or differential pressure to a value at standard temperature, and adjusts the amount of drug injected by the drug injection device based on the converted current supply pressure or differential pressure and the initial value of the supply pressure or differential pressure converted to a value at standard temperature.

This water treatment method and water treatment device makes it possible to accurately grasp the increase in pressure over time of the water being treated that is supplied to the reverse osmosis membrane that is caused by fouling, and to inject chemicals in an amount that appropriately reflects the effects of fouling.

As described above, according to the present invention, it is possible to effectively suppress fouling while suppressing deterioration of the reverse osmosis membrane.

1 is a schematic diagram showing a configuration of a water treatment device according to an embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings.

The water treatment device 10 of this embodiment is a device that removes impurities contained in raw water (water to be treated) to produce treated water, and has a reverse osmosis membrane (RO membrane) device 11. The RO membrane device 11 has an RO membrane that separates the raw water into concentrated water containing impurities and permeated water from which the impurities have been removed. The RO membrane device 11 is connected to a raw water line L1 that supplies raw water to the RO membrane device 11, a permeated water line L2 that supplies the permeated water flowing out from the RO membrane device 11 to a treated water tank or a use point, and a drainage line L3 that discharges the concentrated water flowing out from the RO membrane device 11 to the outside.

The water treatment device 10 also has a pressure pump 12 provided in the raw water line L1, a pressure sensor 13 and a temperature sensor 14 also provided in the raw water line L1, and a flow sensor 15 provided in the permeate line L2. The pressure pump 12 has a function of adjusting the supply pressure (raw water pressure) of the raw water supplied to the RO membrane device 11 through the raw water line L1 by controlling the rotation speed by an inverter (not shown), and the pressure sensor 13 has a function of detecting the raw water pressure. The temperature sensor 14 has a function of detecting the water temperature (raw water temperature) of the raw water supplied to the RO membrane device 11, and the flow sensor 15 has a function of detecting the flow rate of the permeate flowing out of the RO membrane device 11 and flowing through the permeate line L2. The temperature sensor 14 may be configured to detect the water temperature of either the permeate or concentrated water flowing out of the RO membrane device 11, i.e., it may be provided in the permeate line L2 or the drainage line L3.

The water treatment device 10 further includes a chemical injection device 16 that injects chemicals such as scale inhibitors and slime control agents into the raw water supplied to the RO filtration device 11, and a control device 17 that controls the operation of the water treatment device 10, including adjusting the amount of chemicals injected by the chemical injection device 16.

The chemical injection device 16 has a chemical tank 21 that stores the chemical, and a chemical injection pump 22 that is connected to the raw water line L1 via a chemical supply line L4 and injects the chemical stored in the chemical tank 21 into the raw water line L1. The location where the chemical is added is not limited to the location shown in the figure as long as it is upstream of the membrane filtration device 2, and may be, for example, between the pressure pump 12 and the pressure sensor 13. The type of chemical added may be a pH adjuster or a reducing agent in addition to the above-mentioned scale inhibitor and slime control agent.

During normal operation of the water treatment device 10, the control device 17 controls the pressure pump 12 so that the flow rate of the permeate detected by the flow sensor 15 is constant (preset target flow rate). For example, when the water temperature changes, the viscosity of the water changes, and the flow rate of the permeate separated by the RO membrane also changes. In response to this change, the control device 17 controls the rotation speed of the pressure pump 12 through an inverter. That is, when the water temperature decreases, the viscosity of the water increases, and as a result, the flow rate of the permeate separated by the RO membrane decreases. Therefore, the control device 17 increases the rotation speed of the pressure pump 12 to compensate for this decrease, thereby increasing the raw water pressure. Also, when the water temperature increases, the viscosity of the water decreases, and as a result, the flow rate of the permeate separated by the RO membrane increases. Therefore, the control device 17 reduces the rotation speed of the pressure pump 12 to counteract this increase, thereby reducing the raw water pressure. In this way, the control device 17 adjusts the flow rate of the permeate flowing through the permeate line L2 to the set flow rate by adjusting the rotation speed of the pressure pump 12, i.e., the raw water pressure.

In addition, the control device 17 adjusts the amount of drug injected by the drug injection device 16 based on the values detected by the pressure sensor 13, the temperature sensor 14, and the flow rate sensor 15. Two methods for adjusting the amount of drug injected by the control device 17 are described below.

(First Adjustment Method)
The occurrence of RO membrane fouling usually appears as a change in the flow rate of the permeate because it clogs the pores of the membrane, but as described above, when flow rate control is performed to maintain the flow rate of the permeate flowing through the permeate line L2 constant, it appears as a change (increase) in the raw water pressure. Therefore, by calculating the increase, the degree of fouling can be accurately grasped, and it becomes possible to inject an appropriate amount of chemicals accordingly. However, the raw water pressure not only changes depending on the degree of RO membrane fouling, but also changes depending on the water temperature as described above. Therefore, in order to accurately calculate the increase in raw water pressure caused by fouling, it is necessary to compare the current raw water pressure with the raw water pressure at the start of use of the RO membrane (initial raw water pressure) directly, but with a value obtained by correcting the initial raw water pressure taking into account the influence of fluctuations in water temperature, that is, the value obtained by converting the initial raw water pressure into the pressure at the current water temperature.

Therefore, the adjustment of the injection amount of the chemical agent by the first adjustment method is performed as follows. As a premise, the control device 17 stores the initial value of the raw water pressure (initial raw water pressure) detected in advance by the pressure sensor 13 when the RO membrane is started to be used, and the initial value of the raw water temperature (initial raw water temperature) detected in advance by the temperature sensor 14. Note that the initial raw water pressure and initial raw water temperature may be those immediately after the RO membrane is started to be used, but are preferably those obtained after a certain period of time has passed since the start of use and the performance has stabilized, and may be the moving average value. In addition, the initial raw water pressure and initial raw water temperature are newly obtained every time the RO membrane is replaced with a new one, and are stored and updated in the control device 17.

First, the pressure sensor 13 detects the current raw water pressure, and at the same time, the temperature sensor 14 detects the current raw water temperature. In practice, the moving average of the detection values by each sensor 13, 14 is calculated, and these are acquired (detected) as the current raw water pressure and raw water temperature. Then, using information (table, function, etc.) of the temperature correction coefficient pre-stored in an internal storage device or an external server, the temperature correction coefficient at the detected current raw water temperature and the temperature correction coefficient at the initial raw water temperature pre-stored in the control device 17 are acquired. The temperature correction coefficient is a coefficient for correcting the permeation flux of the RO membrane measured at an arbitrary temperature to a value of a standard temperature (e.g., 25°C), and the temperature correction coefficient for each temperature is provided by the manufacturer for each type of RO membrane. The temperature correction coefficient at the initial raw water temperature may be acquired in advance at the start of use of the RO membrane and stored in the control device 17. When each temperature correction coefficient is acquired, the initial raw water pressure is converted to a value at the current raw water temperature based on the acquired temperature correction coefficient. Specifically, when the initial raw water pressure is _P0 , a converted initial pressure _PRO obtained by converting the initial raw water pressure into a value at the current raw water temperature is given by the following formula (1).
P _R0 = P ₀ × (K _i /K ₀ ) (1)
Here, K _i is the temperature correction coefficient at the current raw water temperature, and K ₀ is the temperature correction coefficient at the initial raw water temperature.

Then, the converted initial pressure calculated by the above formula (1) is compared with the detected current raw water pressure, and the amount of the chemical to be injected by the chemical injection device 16 is determined based on the result. Specifically, if the current raw water pressure is higher than the converted initial pressure, it is determined that fouling has occurred, and the chemical is injected at an injection amount according to the difference. That is, the pressure difference between the current raw water pressure and the converted initial pressure corresponds to the increase in raw water pressure caused by fouling, and the larger the pressure difference, the more the fouling is determined to have progressed, and a larger injection amount of the chemical is injected. The injection amount at this time may be increased or decreased continuously or in stages according to the above pressure difference. On the other hand, if the current raw water pressure is equal to or lower than the converted initial pressure, it is determined that fouling has not occurred, and the injection of the chemical is stopped, or the chemical is injected at a preset minimum injection amount. In this way, the increase in the raw water pressure caused by fouling is accurately grasped, and the chemical is injected at an injection amount that appropriately reflects the effect of fouling.

Depending on the usage status of the treated water (permeate) at the point of use, for example, the target flow rate (set flow rate) in the above-mentioned permeate flow rate control may be changed from the start of use of the RO membrane. In anticipation of such a case, the converted initial pressure calculated by the above formula (1) may be further corrected taking into account the influence of the change in the permeate flow rate, and the corrected converted initial pressure may be compared with the detected current raw water pressure. As a prerequisite, the control device 17 stores the permeate flow rate (initial permeate flow rate) detected in advance by the flow sensor 15 when the RO membrane is started to be used, and preferably stores the initial permeate flow rate calculated as a moving average value after a certain time has passed since the start of use of the RO membrane and the performance has stabilized. In this case, the initial permeate flow rate stored in the control device 17 is reset and updated every time the RO membrane is replaced.

When the pressure sensor 13 and the temperature sensor 14 detect the current raw water pressure and raw water temperature, respectively, the flow rate sensor 15 simultaneously detects the current flow rate of the permeated water. In practice, like the current raw water pressure and raw water temperature, a moving average of the detected values by the flow rate sensor 15 is calculated, and this is acquired (detected) as the current flow rate of the permeated water. Then, based on the detected current flow rate of the permeated water and the initial permeated water flow rate pre-stored in the control device 17, the converted initial pressure calculated by the above formula (1) is corrected. Specifically, if the initial permeated water flow rate is _Q0 and the current permeated water flow rate detected by the flow rate sensor 15 is _Qi , the corrected converted initial pressure P _C0 is given by the following formula (2).
P _C0 = P _R0 × (Q _i /Q ₀ ) (2)
It should be noted that, as _Q0 and _Qi in the formula (2), target flow rates (set flow rates) in the above-mentioned flow rate control can be used instead of the flow rates that are actually detected.

The corrected converted initial pressure thus obtained is compared with the detected current raw water pressure, and the amount of drug injected by the drug injection device 16 is adjusted based on the result. The specific adjustment method is the same as that described above.

(Second Adjustment Method)
In the second adjustment method, in order to offset the effect of water temperature fluctuations on the raw water pressure, instead of converting the initial raw water pressure to pressure at the current water temperature as in the first adjustment method, the initial raw water pressure and the current raw water pressure are each converted to pressure at a standard temperature (e.g., 25°C), and the amount of chemical injected by the chemical injection device 16 is adjusted based on the result of comparing them. As a result, as in the first adjustment method, the increase in the raw water pressure over time that is caused by fouling can be accurately grasped, and the chemical can be injected at an injection amount that appropriately reflects the effect of fouling. In the second adjustment method, as shown below, the detection values from the sensors 13 to 15 are used to adjust the amount of chemical injected, but in practice, it is preferable to use the moving average value of each, as in the first adjustment method.

In the second adjustment method, first, as a premise, a converted initial pressure obtained by converting the initial raw water pressure into a value at a standard temperature is stored in the control device 17. In this case, the converted initial pressure P _R0 ' is given by the following formula (3) where the initial raw water pressure is P ₀ and the temperature correction coefficient at the initial raw water temperature is K ₀ .
P _R0 '=P ₀ /K ₀ (3)
Like the initial raw water pressure and the initial raw water temperature in the first adjustment method, this converted initial pressure is newly acquired every time the RO membrane is replaced with a new one, and is stored and updated in the control device 17.

Then, when the current raw water pressure and raw water temperature are detected by the pressure sensor 13 and the temperature sensor 14, respectively, a temperature correction coefficient for the detected current raw water temperature is acquired, and the current raw water pressure is converted to a value at the standard temperature based on the acquired temperature correction coefficient. Specifically, if the current raw water pressure is _Pi and the temperature correction coefficient for the current raw water temperature is _Ki , the converted raw water pressure P _Ri obtained by converting the current raw water pressure to a value at the standard temperature is given by the following formula (4).
P _Ri =P _i /K _i (4)

The converted raw water pressure calculated in this way is compared with the converted initial pressure (see formula (3) above) previously stored in the control device 17, and the amount of drug injected by the drug injection device 16 is adjusted based on the result. In other words, the amount of drug injected is determined depending on the extent to which the converted raw water pressure exceeds the converted initial pressure, and the specific method of determination is the same as in the first adjustment method.

In the second adjustment method, taking into consideration the influence of changes in the flow rate of the permeated water, the converted initial pressure (see formula (3) above) stored in advance in the control device 17 may be corrected based on the flow rate ratio of the permeated water at the start of use of the RO membrane to the present, as in the first adjustment method, and the corrected converted initial pressure may be compared with the converted raw water pressure calculated by formula (4) above. In this case, the corrected converted initial pressure P _C0 ' is given by the following formula (5), where Q ₀ is the initial permeated water flow rate (or the target flow rate of the permeated water at the start of use of the RO membrane) and Q _i is the current permeated water flow rate (or the target flow rate of the current permeated water) detected by the flow sensor 15.
P _C0 '=P _R0 '×(Q _i /Q ₀ ) (5)

The corrected converted initial pressure thus obtained is compared with the converted raw water pressure calculated by the above formula (4), and the amount of drug injected by the drug injection device 16 is adjusted based on the result. In other words, the amount of drug injected is determined depending on the extent to which the converted raw water pressure exceeds the corrected converted initial pressure, and the specific method of determination is the same as in the first adjustment method.

In both of the above-mentioned two adjustment methods, the increase in raw water pressure caused by fouling is calculated using the detection value of the raw water pressure by the pressure sensor 13, but the detection value of the RO membrane water flow differential pressure (the difference between the raw water supply pressure and the concentrated water outflow pressure) may be used instead of the raw water pressure. That is, in the first adjustment method, the increase in raw water pressure caused by fouling can be accurately calculated by converting the water flow differential pressure at the start of use of the RO membrane to a value at the current raw water temperature and comparing the converted value with the current RO membrane water flow differential pressure. In addition, in the second adjustment method, the increase in raw water pressure caused by fouling can be accurately calculated by converting the water flow differential pressure at the start of use of the RO membrane and the current water flow differential pressure to values at standard temperature and comparing them. However, in order to detect the water flow differential pressure of the RO membrane, in addition to the pressure sensor 13 installed in the raw water line L1, another pressure sensor needs to be installed in the drain line L3, which incurs additional costs. For this reason, as described above, it is preferable to calculate the increase in raw water pressure caused by fouling using the raw water pressure detected by the pressure sensor 13.

REFERENCE SIGNS LIST 10 Water treatment device 11 Reverse osmosis (RO) device 12 Pressure pump 13 Pressure sensor 14 Temperature sensor 15 Flow rate sensor 16 Chemical dosing device 17 Control device 21 Chemical tank 22 Chemical dosing pump L1 Raw water line L2 Permeate line L3 Drain line L4 Chemical supply line

Claims (12)

A water treatment method comprising: injecting a chemical into water to be treated; and supplying the water to which the chemical has been injected to a reverse osmosis membrane to separate the water into permeate and concentrated water,
The step of injecting the agent comprises:
Detecting the current water temperature of any of the water to be treated that is supplied to the reverse osmosis membrane, the permeated water that flows out from the reverse osmosis membrane, and the concentrated water that flows out from the reverse osmosis membrane ;
Detecting a current supply pressure of the water to be treated that is supplied to the reverse osmosis membrane, or a differential pressure between the current supply pressure and a current outlet pressure of concentrated water that flows out from the reverse osmosis membrane;
and adjusting the amount of the agent injected into the water to be treated based on an initial value of any one of the water temperatures detected in advance when the reverse osmosis membrane is started to be used, an initial value of the supply pressure or differential pressure detected in advance when the reverse osmosis membrane is started to be used, the detected current water temperature, and the detected current supply pressure or differential pressure,
A water treatment method, the step of adjusting the amount of the chemical injected includes converting an initial value of the supply pressure or differential pressure to a value at the detected current water temperature, and adjusting the amount of the chemical injected into the treated water based on the converted initial value of the supply pressure or differential pressure and the detected current supply pressure or differential pressure . 2. The water treatment method according to claim 1, wherein adjusting the amount of the agent to be injected includes determining the amount of the agent to be injected based on a result of comparing an initial value of the converted supply pressure or differential pressure with the detected current supply pressure or differential pressure. the step of injecting the agent further comprises the step of detecting a current flow rate of permeate exiting the reverse osmosis membrane;
2. The water treatment method of claim 1, wherein adjusting the amount of drug injection includes correcting an initial value of the converted supply pressure or differential pressure based on the detected current flow rate and an initial value of the flow rate detected in advance when use of the reverse osmosis membrane is started, and determining the amount of drug injection based on a result of comparing the corrected initial value of supply pressure or differential pressure with the detected current supply pressure or differential pressure. 4. The water treatment method according to claim 1, wherein the initial value of the supply pressure or differential pressure is converted to a value at the detected current water temperature based on a temperature correction coefficient at the detected current water temperature and a temperature correction coefficient at an initial value of either of the water temperatures. A water treatment method comprising: injecting a chemical into water to be treated; and supplying the water to which the chemical has been injected to a reverse osmosis membrane to separate the water into a permeate and a concentrate,
The step of injecting the agent comprises:
Detecting the current water temperature of any of the water to be treated that is supplied to the reverse osmosis membrane, the permeated water that flows out from the reverse osmosis membrane, and the concentrated water that flows out from the reverse osmosis membrane;
Detecting a current supply pressure of the water to be treated that is supplied to the reverse osmosis membrane, or a differential pressure between the current supply pressure and a current outlet pressure of concentrated water that flows out from the reverse osmosis membrane;
and adjusting the amount of the agent injected into the water to be treated based on an initial value of any one of the water temperatures detected in advance when the reverse osmosis membrane is started to be used, an initial value of the supply pressure or differential pressure detected in advance when the reverse osmosis membrane is started to be used, the detected current water temperature, and the detected current supply pressure or differential pressure,
A water treatment method, wherein the step of adjusting the amount of the chemical injected includes converting the detected current supply pressure or differential pressure to a value at standard temperature, and adjusting the amount of the chemical injected into the treated water based on the converted current supply pressure or differential pressure and an initial value of the supply pressure or differential pressure converted to a value at standard temperature. The water treatment method of claim 5, wherein adjusting the amount of the chemical to be injected includes determining the amount of the chemical to be injected into the treated water based on a result of comparing an initial value of the converted supply pressure or differential pressure with the converted current supply pressure or differential pressure. the step of injecting the agent further comprises the step of detecting a current flow rate of permeate exiting the reverse osmosis membrane;
The water treatment method of claim 5, wherein adjusting the amount of injection of the agent includes correcting an initial value of the converted supply pressure or differential pressure based on the detected current flow rate and an initial value of the flow rate detected in advance at the start of use of the reverse osmosis membrane, and determining the amount of injection of the agent based on a result of comparing the corrected initial value of the supply pressure or differential pressure with the converted current supply pressure or differential pressure. 8. The water treatment method according to claim 5, wherein the detected current supply pressure or differential pressure is converted to a value at a standard temperature based on a temperature correction coefficient at the detected current water temperature, and an initial value of the supply pressure or differential pressure is converted to a value at a standard temperature based on a temperature correction coefficient at an initial value of either of the water temperatures. 9. The water treatment method according to claim 4 , wherein the temperature correction coefficient is a coefficient for correcting a permeation flux of the reverse osmosis membrane measured at an arbitrary temperature to a value at a standard temperature. The water treatment method according to claim 1 , further comprising the step of adjusting the supply pressure to adjust the flow rate of the permeated water flowing out from the reverse osmosis membrane to a set flow rate. A reverse osmosis membrane device having a reverse osmosis membrane that separates the water to be treated into permeate and concentrated water;
A chemical injection device that injects a chemical into the water to be treated that is supplied to the reverse osmosis membrane device;
a temperature sensor for detecting the temperature of any of the water to be treated that is supplied to the reverse osmosis membrane device, the permeated water that flows out from the reverse osmosis membrane device, and the concentrated water that flows out from the reverse osmosis membrane device;
a pressure sensor for detecting a supply pressure of the water to be treated that is supplied to the reverse osmosis membrane device, or a differential pressure between the supply pressure and an outflow pressure of concentrated water that flows out from the reverse osmosis membrane device ;
a control device that adjusts the amount of drug injected by the drug injection device based on an initial value of any one of the water temperatures detected in advance by the temperature sensor when use of the reverse osmosis membrane is started, an initial value of the supply pressure or differential pressure detected in advance by the pressure sensor when use of the reverse osmosis membrane is started, any one of the water temperatures detected by the temperature sensor, and the current supply pressure or differential pressure detected by the pressure sensor ,
The control device converts the initial value of the supply pressure or differential pressure to a value at any of the detected current water temperatures, and adjusts the amount of the drug injected by the drug injection device based on the converted initial value of the supply pressure or differential pressure and the detected current supply pressure or differential pressure . A reverse osmosis membrane device having a reverse osmosis membrane that separates the water to be treated into permeate and concentrated water;
A chemical injection device that injects a chemical into the water to be treated that is supplied to the reverse osmosis membrane device;
a temperature sensor for detecting the temperature of any of the water to be treated that is supplied to the reverse osmosis membrane device, the permeated water that flows out from the reverse osmosis membrane device, and the concentrated water that flows out from the reverse osmosis membrane device;
a pressure sensor for detecting a supply pressure of the water to be treated that is supplied to the reverse osmosis membrane device, or a differential pressure between the supply pressure and an outflow pressure of concentrated water that flows out from the reverse osmosis membrane device;
a control device that adjusts the amount of drug injected by the drug injection device based on an initial value of any one of the water temperatures detected in advance by the temperature sensor when use of the reverse osmosis membrane is started, an initial value of the supply pressure or differential pressure detected in advance by the pressure sensor when use of the reverse osmosis membrane is started, any one of the water temperatures detected by the temperature sensor, and the current supply pressure or differential pressure detected by the pressure sensor,
The control device converts the detected current supply pressure or differential pressure to a value at standard temperature, and adjusts the amount of the drug injected by the drug injection device based on the converted current supply pressure or differential pressure and the initial value of the supply pressure or differential pressure converted to a value at standard temperature.

Images