JP7386105B2 - Water treatment equipment and water treatment method - Google Patents

Description

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

Groundwater pumped up from a well is treated by a water treatment device and then used for domestic, industrial, agricultural, and other purposes.
As a method for treating groundwater with a water treatment device, for example, groundwater pumped up from a well is first stored in a raw water tank, then subjected to pretreatment such as sand filtration and activated carbon treatment, and then subjected to ultrafiltration membrane or reverse water treatment. A method is known in which membrane separation treatment using a permeable membrane or the like is performed to separate permeated water and non-permeated water.

The more treatment items there are, the easier it is to remove impurities from groundwater, but this also increases the size of the water treatment equipment and increases the treatment cost. By simplifying the process without performing pretreatment, it is possible to save space and reduce costs.
However, when groundwater comes into contact with air in the raw water tank, metal ions such as iron ions dissolved in the groundwater oxidize and become metal oxides, which can clog the separation membrane used for membrane separation treatment. be.

As a method of preventing oxidation of dissolved elements in groundwater, there is a method of membrane separation treatment after adjusting groundwater to a reduced state (for example, Patent Document 1), and supplying an inert gas to a water storage tank (raw water tank) that stores pumped groundwater. A method (for example, Patent Document 2) is known.
Furthermore, an aeration prevention device (for example, Patent Document 3) is known that combines a submersible pump for pumping up groundwater from a well, a pressure tank, an intake valve, and the like to prevent air from entering a water pumping device.

Japanese Patent Application Publication No. 2011-189242 Japanese Patent Application Publication No. 2012-122189 Utility Model Publication No. 56-86374

However, in the method described in Patent Document 1, if dissolved elements in groundwater are oxidized before being adjusted to a reduced state, it is difficult to reduce the oxides, and prevention of oxidation of the dissolved elements is not necessarily sufficient.
The method described in Patent Document 2 requires periodic replenishment of gas, which is laborious and costly.
The air entrainment prevention device described in Patent Document 3 does not necessarily sufficiently prevent air incorporation.
An object of the present invention is to provide a water treatment device and a water treatment method that can save space and reduce costs while suppressing clogging of separation membranes.

The present invention has the following aspects.
[1] A submersible pump that pumps groundwater from a well,
membrane separation means for separating groundwater pumped from the well into permeated water and non-permeated water;
a raw water supply channel connecting the submersible pump and the membrane separation means;
Pressure fluctuation reducing means provided in the raw water supply flow path for reducing pressure fluctuations in the groundwater pumped from the well,
In the water treatment device, groundwater pumped up from the well is supplied to the membrane separation means while maintaining an airtight state.
[2] The water treatment device according to [1], wherein the membrane separation means includes at least one of a reverse osmosis membrane and an ultrafiltration membrane.
[3] Further comprising a return means for returning a portion of the non-permeated water to the membrane separation means,
The water treatment device according to [1] or [2], wherein a part of the non-permeated water is returned to the membrane separation means while maintaining an airtight state.
[4] A water treatment method in which groundwater pumped from a well is supplied to a membrane separation means and separated into permeated water and non-permeated water,
A water treatment method in which groundwater pumped up from the well is supplied to the membrane separation means while maintaining an airtight state while reducing fluctuations in its pressure.
[5] The water treatment method according to [4], wherein the membrane separation means includes at least one of a reverse osmosis membrane and an ultrafiltration membrane.
[6] The water treatment method according to [4] or [5], wherein a part of the non-permeated water is returned to the membrane separation means while maintaining an airtight state.

According to the present invention, it is possible to provide a water treatment device and a water treatment method that can save space and reduce costs while suppressing clogging of separation membranes.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows typically an example of the water treatment apparatus of the 1st aspect of this invention. It is a schematic diagram showing typically an example of the water treatment device of the second aspect of the present invention. 2 is a graph showing the relationship between water flow time, flux, and RO average pressure in Example 1. 2 is a graph showing the measurement results of the concentrations of total iron, iron ions, and iron oxide in non-permeated water in Example 1. 2 is a schematic diagram schematically showing a water treatment device used in Comparative Example 1. FIG. 3 is a graph showing the relationship between water flow time, flux, and RO average pressure in Comparative Example 1. 3 is a graph showing the measurement results of the concentrations of total iron, iron ions, and iron oxide in non-permeated water in Comparative Example 1.

Hereinafter, one embodiment of the water treatment method and water treatment apparatus according to the present invention will be described in detail with reference to FIGS. 1 and 2 as appropriate.
In addition, in each drawing used in the following explanation, characteristic parts may be shown enlarged for convenience in order to make the characteristics easier to understand, and the dimensional ratio of each component may differ from the actual one. There is. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be practiced with appropriate changes within the scope of the gist thereof.
Further, in FIG. 2, the same components as in FIG. 1 are given the same reference numerals, and their explanations will be omitted.

<First aspect>
(Water treatment equipment)
FIG. 1 schematically shows an example of a water treatment apparatus according to the first aspect of the present invention.
The water treatment device 1 shown in FIG. 1 includes a well 100 that is a water source, a submersible pump 21 that pumps groundwater (raw water) from the well 100, and a membrane that separates the groundwater pumped from the well 100 into permeated water and non-permeated water. It includes a separation means 10, a raw water supply channel 22 that connects a submersible pump 21 and a membrane separation means 10, and a pressure fluctuation reduction means 30 that reduces pressure fluctuations in groundwater pumped from a well 100.

The water treatment device 1 further includes a permeated water discharge means 40 for discharging permeated water from the membrane separation means 10 and a non-permeated water discharge means 50 for discharging non-permeated water from the membrane separation means 10.
Note that the pump, a solenoid valve (described later), a flow meter, a pressure gauge, etc. are electrically connected to a control section (not shown) that controls their operations.

The membrane separation means 10 is a means for separating groundwater into permeated water and non-permeated water.
The membrane separation means 10 in this example includes a reverse osmosis membrane module 11, a pump 12, a raw water channel 13, a flow meter 14, and a pressure gauge 15.
The reverse osmosis membrane module 11 may be any module that includes a reverse osmosis membrane and separates introduced groundwater into permeated water that passes through the reverse osmosis membrane and non-permeated water that does not pass through the reverse osmosis membrane. Note that the permeated water that has passed through the reverse osmosis membrane is called "treated water," and the non-permeated water that has not passed through the reverse osmosis membrane is also called "concentrated water."
Reverse osmosis membranes include nanofiltration membranes.
Examples of the form of reverse osmosis membranes include spiral membranes, hollow fiber membranes, tubular membranes, and flat membranes.
Examples of the material for the reverse osmosis membrane include polyamide, polysulfone, cellulose acetate, and polyacrylonitrile.

Examples of the reverse osmosis membrane module 11 include one in which one or more spiral-type reverse osmosis membrane elements are housed in a pressure-resistant container such as a vessel. An example of a spiral reverse osmosis membrane element is one in which a reverse osmosis membrane is wound around a water collection pipe, housed in a cylindrical casing, and telescope prevention members are attached to both end faces of the casing.

The raw water channel 13 is a connecting pipe that connects the reverse osmosis membrane module 11 and the pump 12.
A flow meter 14 and a pressure gauge 15 are provided in the raw water flow path 13.

The raw water supply channel 22 is a connecting pipe that connects the submersible pump 21 and the membrane separation means 10.
The groundwater pumped up from the well passes through the raw water supply channel 22 while maintaining an airtight state, and is supplied to the membrane separation means 10.

The raw water supply channel 22 includes a water pump 23 extending from underground to above ground, and a water pipe 24 connected to the upper end of the water pump 23 and extending horizontally.
The water pipe 24 in this example includes a first water pipe 241 upstream of the pressure fluctuation reducing means 30 and a second water pipe 242 downstream of the pressure fluctuation reducing means 30.
A submersible pump 21 is connected to the lower end of the pumping pipe 23, that is, one end of the raw water supply channel 22. The pump 12 of the membrane separation means 10 is connected to the tip of the water pipe 24 (the tip of the second water pipe 242), that is, the other end of the raw water supply channel 22.
The raw water supply channel 22 is not particularly limited as long as it is a pipe that can maintain an airtight state.

The pressure fluctuation reducing means 30 is a means for reducing pressure fluctuations of groundwater pumped up from the well 100, and is provided in the raw water supply channel 22. By reducing fluctuations in groundwater pressure, it is possible to balance the flow rate of groundwater sent from the submersible pump 21 to the raw water supply channel 22 and the flow rate of groundwater sent from the pump 12 to the reverse osmosis membrane module 11, Damage to the separation membrane can be suppressed.
The pressure fluctuation reducing means 30 in this example is a pressure tank 31.
The pressure tank 31 can store groundwater inside according to the pressure, and can absorb and reduce fluctuations in groundwater pressure, and can also store groundwater inside and discharge the stored groundwater. Accordingly, the flow rate of underground water flowing through the water pipe 24 can also be adjusted.
The pressure tank 31 is not particularly limited as long as the stored groundwater can be maintained in an airtight state, but for example, a tank filled with an inert gas such as nitrogen or carbon dioxide in the gas phase; a rubber membrane such as an accumulator, etc. It is preferable to use a tank in which the inside of the tank is filled with a pressure-accumulating gas sealed in the tank, and the pressure can be accumulated by compression and expansion of the pressure-accumulating gas.

The permeated water discharge means 40 is a means for discharging permeated water from the membrane separation means 10.
The permeated water discharge means 40 includes a permeated water flow path 41, and a flow meter 42 and a pressure gauge 43 provided in the permeated water flow path 41.

The non-permeated water discharge means 50 is a means for discharging non-permeated water from the membrane separation means 10.
The non-permeated water discharge means 50 includes a non-permeated water flow path 51, and a flow meter 52 and a pressure gauge 53 provided in the non-permeated water flow path 51.

(Water treatment method)
An example of a water treatment method using the water treatment device 1 will be described.
First, the submersible pump 21 is driven to pump up groundwater from the well 100. Next, the pump 12 is driven to supply the groundwater pumped up from the well 100 to the membrane separation means 10 while maintaining an airtight state. When the groundwater passes through the raw water supply channel 22, the pressure fluctuation reducing means 30 reduces the fluctuation in the pressure of the groundwater. That is, the groundwater pumped up from the well 100 is supplied to the membrane separation means 10 while maintaining an airtight state while reducing fluctuations in its pressure.

The groundwater that has passed through the pump 12 passes through the raw water channel 13 while maintaining an airtight state and is supplied to the reverse osmosis membrane module 11. At this time, a flow meter 14 and a pressure gauge 15 provided in the raw water channel 13, a flow meter 42 and a pressure gauge 43 provided in the permeated water channel 41, a flow meter 52 and a pressure gauge provided in the non-permeated water channel 51, It is preferable to adjust the pressure of groundwater and the amount of water relative to the reverse osmosis membrane using the pump 12 while monitoring 53.
The groundwater supplied to the reverse osmosis membrane module 11 is separated into permeated water that passes through the reverse osmosis membrane and non-permeated water that does not pass through the reverse osmosis membrane.

The permeated water that has passed through the reverse osmosis membrane passes through the permeated water channel 41 and is stored in a water receiving tank (not shown).
On the other hand, non-permeated water that has not passed through the reverse osmosis membrane passes through the non-permeated water flow path 51 and is disposed of, for example, by being discharged into a sewage system.

(effect)
According to the water treatment device and water treatment method of the first aspect of the present invention, groundwater pumped from a well is supplied to the membrane separation means while maintaining an airtight state while reducing fluctuations in its pressure, and permeates the groundwater. Separates into water and non-permeable water. In other words, since groundwater pumped up from a well is supplied to the membrane separation means without coming into contact with air, metal ions dissolved in the groundwater are unlikely to oxidize before the groundwater is supplied to the membrane separation means, and the separation membrane blockage can be suppressed.
In addition, in the water treatment device and water treatment method of the first aspect of the present invention, groundwater pumped up from a well is directly supplied to the membrane separation means, so the process can be simplified, saving space and reducing costs. can be achieved.
Moreover, in the water treatment apparatus and water treatment method according to the first aspect of the present invention, groundwater is supplied to the membrane separation means while reducing pressure fluctuations in the groundwater by the pressure fluctuation reducing means, so that the raw water supply channel is connected to the submersible pump. It is possible to balance the flow rate of groundwater sent to the reverse osmosis membrane module with the flow rate of groundwater sent from the pump to the reverse osmosis membrane module in the membrane separation means, and damage to the separation membrane can be suppressed.

(Other aspects)
The water treatment device and water treatment method of the first aspect of the present invention are not limited to the embodiments described above.
In the first aspect, the pressure fluctuation reducing means is a pressure tank provided in the raw water supply channel, but the raw water supply channel itself may be used as the pressure fluctuation reducing means. However, when the raw water supply channel is used as pressure fluctuation reducing means, it is preferable to increase the diameter or length of the raw water supply channel. In particular, it is preferable to increase the diameter or length of the water pipe. Specifically, the diameter of the water pipe is preferably 13 to 1000 mm, and the length is preferably 10 to 600 m.

In the first embodiment, a reverse osmosis membrane is used to separate groundwater into permeated water and non-permeated water, but the separation membrane used for membrane separation is not limited to reverse osmosis membranes, and includes, for example, ultrafiltration membranes, precision It may also be a filtration membrane or the like. As the separation membrane, a reverse osmosis membrane or an ultrafiltration membrane is preferable, and a reverse osmosis membrane is more preferable.
Moreover, although the membrane separation means of the water treatment apparatus of the first aspect includes one reverse osmosis membrane module, the membrane separation means may include a plurality of reverse osmosis membrane modules arranged in parallel. In this case, it is preferable that the raw water flow path is branched in the middle and connected to each reverse osmosis membrane module, and the pump of the membrane separation means is preferably a boost pump.

<Second aspect>
(Water treatment equipment)
FIG. 2 schematically shows an example of a water treatment device according to the second aspect of the present invention.
The water treatment device 2 of the second embodiment is the same as the water treatment device of the first embodiment, except that it further includes return means 60 for returning a portion of non-permeated water to the membrane separation means 10.
That is, the water treatment device 2 shown in FIG. 2 includes a well 100 that is a water source, a submersible pump 21 that pumps groundwater (raw water) from the well 100, and a system that separates the groundwater pumped from the well 100 into permeated water and non-permeated water. a raw water supply flow path 22 that connects the submersible pump 21 and the membrane separation means 10, a pressure fluctuation reduction means 30 that reduces pressure fluctuations in groundwater pumped from the well 100, and non-permeable water. and return means 60 for returning a part of the membrane separation means 10 to the membrane separation means 10.
The water treatment device 2 further includes a permeated water discharge means 40 for discharging permeated water from the membrane separation means 10 and a non-permeated water discharge means 50 for discharging non-permeated water from the membrane separation means 10.

The membrane separation means 10, the raw water supply channel 22, the pressure fluctuation reduction means 30, the permeated water discharge means 40, and the non-permeated water discharge means 50 are the same as in the first embodiment, and therefore their explanations will be omitted.

The return means 60 is a means for returning part of the non-permeated water to the membrane separation means 10.
The return means 60 includes a return flow path 61 , a solenoid valve 62 that opens and closes the return flow path 61 and adjusts the pressure of non-permeated water returned to the membrane separation means 10 , and a flow meter 63 .
The return flow path 61 in this example has one end connected to the middle of the non-permeated water flow path 51 and the other end connected to the middle of the second water supply pipe 242, so that a part of the non-permeated water flows into the non-permeated water flow. The water is returned to the membrane separation means 10 through the water pipe 51, the return channel 61, and the second water pipe 242 in this order.
The non-permeated water passing through the return channel 61 is preferably returned to the membrane separation means 10 while maintaining an airtight state.

(Water treatment method)
An example of a water treatment method using the water treatment device 2 will be described.
First, the submersible pump 21 is driven to pump up groundwater from the well 100. Next, the pump 12 is driven to supply the groundwater pumped up from the well 100 to the membrane separation means 10 while maintaining an airtight state. When the groundwater passes through the raw water supply channel 22, the pressure fluctuation reducing means 30 reduces the fluctuation in the pressure of the groundwater. That is, the groundwater pumped up from the well 100 is supplied to the membrane separation means 10 while maintaining an airtight state while reducing fluctuations in its pressure.

The groundwater that has passed through the pump 12 passes through the raw water channel 13 while maintaining an airtight state and is supplied to the reverse osmosis membrane module 11. At this time, a flow meter 14 and a pressure gauge 15 provided in the raw water channel 13, a flow meter 42 and a pressure gauge 43 provided in the permeated water channel 41, a flow meter 52 and a pressure gauge provided in the non-permeated water channel 51, It is preferable to adjust the pressure of groundwater and the amount of water relative to the reverse osmosis membrane using the pump 12 while monitoring 53.
The groundwater supplied to the reverse osmosis membrane module 11 is separated into permeated water that passes through the reverse osmosis membrane and non-permeated water that does not pass through the reverse osmosis membrane.

The permeated water that has passed through the reverse osmosis membrane passes through the permeated water channel 41 and is stored in a water receiving tank (not shown).
On the other hand, non-permeated water that has not passed through the reverse osmosis membrane passes through the non-permeated water flow path 51 and is disposed of, for example, by being discharged into a sewage system. At that time, by opening the electromagnetic valve 62 as necessary, a part of the non-permeated water is diverted in the middle of the non-permeated water flow path 51 and passed through the return flow path 61, and a part of the non-permeated water is diverted in the middle of the second water pipe 242. , and the groundwater pumped up from the well 100. As a result, a portion of the non-permeated water is returned to the membrane separation means 10 through the non-permeated water channel 51, the return channel 61, and the second water pipe 242 in this order.
When returning a portion of the non-permeated water to the membrane separation means 10, it is preferable to return a portion of the non-permeated water to the membrane separation means 10 while maintaining an airtight state.

(effect)
According to the water treatment device and water treatment method of the second aspect of the present invention, similar to the water treatment device and water treatment method of the first aspect, the groundwater pumped from the well is processed until it is supplied to the membrane separation means. Meanwhile, metal ions dissolved in groundwater are less likely to be oxidized, and clogging of the separation membrane can be suppressed. In addition, the process can be simplified, and space and cost can be reduced. Moreover, it is possible to balance the flow rate of groundwater sent from the submersible pump to the raw water supply channel and the flow rate of groundwater sent from the pump to the reverse osmosis membrane module in the membrane separation means, and damage to the separation membrane can be suppressed.

(Other aspects)
The water treatment device and water treatment method of the second aspect of the present invention are not limited to the embodiments described above.
In addition, in the second aspect, other aspects regarding the common parts with the first aspect are the same as the first aspect, and therefore description thereof will be omitted.

In the second embodiment, the other end of the return flow path is connected to the middle of the second water pipe, but the other end of the return flow path may be connected to the middle of the first water pipe, or It may be connected in the middle of the water flow path. However, since the pressure and water volume of the mixture of groundwater and non-permeated water supplied to the reverse osmosis membrane can be adjusted while monitoring, the other end of the return flow path is located midway through the first water pipe or the second water pipe. preferably connected to.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following Examples are not intended to limit the scope of the present invention.

[Example 1]
In this example, groundwater was treated as follows using the water treatment apparatus 2 shown in FIG. 2.
In this example, an aqueous solution of iron sulfate was intentionally added to the groundwater as shown below in order to confirm the effect on the separation membrane due to oxidation of metal ions dissolved in the groundwater.
Further, as the reverse osmosis membrane, a product name "RO Membrane Filter (model number: BW60-1812-75)" manufactured by As One Corporation (membrane area: 0.5 m ² ) was used.

First, the submersible pump 21 was driven to pump groundwater from the well 100. Next, the pump 12 was driven to supply the groundwater pumped up from the well 100 to the membrane separation means 10 while maintaining an airtight state. At that time, the groundwater flowing through the raw water supply channel 22 was temporarily stored in the pressure tank 31, and the stored groundwater was discharged into the raw water supply channel 22, thereby reducing fluctuations in the pressure of the groundwater. Furthermore, before the groundwater pumped from the well 100 was stored in the pressure tank 31, an aqueous solution of iron sulfate was added to the groundwater so that the total iron concentration in the groundwater was 4.8 mg/L. In addition, as an aqueous solution of iron sulfate, after adding iron (II) sulfate heptahydrate (FeSO _{4.7H 2} O) to pure water whose pH at 25 ° C. was adjusted to 2.5, The container was replaced with argon in a closed container until the amount of dissolved oxygen became 0 mg/L. Further, when adding the aqueous solution of iron sulfate to groundwater, the aqueous solution of iron sulfate was kept in a closed container (not shown) and added to the groundwater using a pump (not shown). The pH of the groundwater to which the iron sulfate aqueous solution was added at 25°C was 7.5.
Next, the groundwater was separated into permeated water and non-permeated water using the reverse osmosis membrane module 11.
The permeated water that passed through the reverse osmosis membrane was discharged from the membrane separation means 10 by the permeated water discharge means 40, and the non-permeated water that did not pass through the reverse osmosis membrane was discharged from the membrane separation means 10 by the non-permeated water discharge means 50. At that time, the electromagnetic valve 62 is opened to divert part of the non-permeated water in the middle of the non-permeated water flow path 51 and allow it to pass through the return flow path 61, and the water is pumped up from the well 100 in the middle of the second water pipe 242. The collected groundwater was combined with groundwater and returned to the membrane separation means 10. The water flow conditions were set to 2600 mL/min for the flow meter 14, 113 mL/min for the flow meter 42, and 49 mL/min for the flow meter 52.

The amount of permeated water per unit time and per unit membrane area at 25° C. was measured until 115 hours had passed since the start of water flow, and the flux (permeation flux) was calculated. In addition, the average pressure of the reverse osmosis membrane (RO average pressure) was measured using a pressure gauge. The results are shown in Figure 3.
Generally, when membrane filtration is performed at a constant pressure, the flux tends to decrease when the separation membrane is clogged.
As shown in FIG. 3, in this example, the RO average pressure and flux remained approximately constant even after 100 hours or more of water flow, indicating that no blockage of the reverse osmosis membrane occurred.

In addition, the concentration of total iron and the concentration of iron ions in the non-permeated water after 115 hours had passed from the start of water flow were measured using a product name "Portable Absorption Photometer DR890" manufactured by HACH, and the total iron concentration was determined. The iron ion concentration was measured using the Feroo Ver method and the 1.10 phenanthroline method. In addition, the iron oxide concentration in the non-permeated water was determined by subtracting the iron ion concentration from the total iron concentration. The results are shown in Figure 4.
As shown in FIG. 4, the total iron concentration and iron ion concentration in the non-permeated water were both 16 mg/L, and no iron oxide was contained in the non-permeated water. That is, since the iron ions in the groundwater are not oxidized, it can be said that in this example, the groundwater pumped up from the well was supplied to the membrane separation means in an airtight state.

Further, when 115 hours had passed since the start of water flow, the amount of dissolved oxygen in the non-permeated water immediately after being discharged from the non-permeated water channel 51 was measured and found to be 0 mg/L. Therefore, it can be said that the amount of dissolved oxygen in the non-permeated water returned to the membrane separation means 10 is 0 mg/L, so in this example, a part of the non-permeated water is transferred to the membrane separation means 10 while maintaining an airtight state. It can be said that it was sent back.

[Comparative example 1]
In this comparative example, groundwater was treated as follows using the water treatment device 3 shown in FIG. 5.
The water treatment device 3 shown in FIG. 5 includes a well 100 that is a water source, a submersible pump 21 that pumps groundwater (raw water) from the well 100, a raw water tank 70 that stores the groundwater pumped from the well 100, and a water tank 70 that stores the groundwater pumped from the well 100. a membrane separation means 10 for separating permeated water and non-permeated water; a permeated water discharge means 40 for discharging permeated water from the membrane separation means 10; and a non-permeated water discharge means 50 for discharging non-permeated water from the membrane separation means 10; A return means 60 returns part of the non-permeated water to the membrane separation means 10, an addition means 80 adds sulfuric acid to the groundwater pumped from the well 100, and supplies the groundwater pumped from the well 100 to the raw water tank 70. It includes a first treated water flow path 91 and a second treated water flow path 93 that connects the raw water tank 70 and the membrane separation means 10.
The membrane separation means 10 of the water treatment apparatus 3 is the same as the membrane separation means 10 shown in FIG. 2, except that the pump 12 is a boost pump.
The permeated water discharge means 40 of the water treatment device 3 is the same as the permeated water discharge means 40 shown in FIG.
The non-permeated water discharge means 50 of the water treatment device 3 is the same as the non-permeated water discharge means 50 shown in FIG.
The return means 60 of the water treatment device 3 is the same as the return means 60 shown in FIG. 2 except that the other end of the return flow path 61 is connected to the second water flow path 93 to be treated.

The raw water tank 70 is provided with an aeration means 71. The aeration means 71 is arranged approximately horizontally near the bottom of the raw water tank 70, and includes an aeration tube 71a, a blower 71b that supplies gas to the aeration tube 71a, and a gas diffuser 71b that supplies the gas supplied from the blower 71b to the aeration tube 71a. A gas supply pipe 71c is provided.
The addition means 80 includes a tank 81 containing sulfuric acid, a sulfuric acid supply pipe 82 that supplies sulfuric acid to the raw water tank 70, and a pump 83 provided in the middle of the sulfuric acid supply pipe 82.
A solenoid valve 92 is provided in the first treated water flow path 91 .
A pump 94, a flow meter 95, two pre-filters 96, and a pressure gauge 97 are provided in the second treated water flow path 93 in this order from the raw water tank 70 side.
Note that the pump, solenoid valve, flow meter, pressure gauge, etc. are electrically connected to a control section (not shown) that controls their operations.
As the reverse osmosis membrane, Nitto Denko Corporation's product name "ESPA2-LD4040" (membrane area: 7.43 m ² ) was used.
As the pre-filter 96, the product name "Wide Cartridge Filter (model number: ZW-PP10-500L)" manufactured by Z Kogyo Co., Ltd. was used.
Furthermore, in Comparative Example 1, a well 100 different from the well used in Example 1 was used. The concentration of total iron in the groundwater in the well 100 used in Comparative Example 1 was 5.2 mg/L.

First, the submersible pump 21 was driven to pump groundwater from the well 100. The solenoid valve 92 was opened to supply groundwater pumped up from the well 100 to the raw water tank 70. At that time, the pump 83 was driven and sulfuric acid was added to the groundwater passing through the first water to be treated channel 91 so that the pH of the groundwater at 25° C. was 6.0.
Next, by driving the blower 71b, air was supplied to the aeration pipe 71a in the raw water tank 70 through the gas supply pipe 71c, and the groundwater in the raw water tank 70 was aerated.
Next, the pump 94 and the pump 12 were driven to draw out the groundwater from the raw water tank 70 and supply it to the membrane separation means 10 through the prefilter 96.
Next, the groundwater was separated into permeated water and non-permeated water using the reverse osmosis membrane module 11.
The permeated water that passed through the reverse osmosis membrane was discharged from the membrane separation means 10 by the permeated water discharge means 40, and the non-permeated water that did not pass through the reverse osmosis membrane was discharged from the membrane separation means 10 by the non-permeated water discharge means 50. At that time, the electromagnetic valve 62 is opened, a part of the non-permeated water is diverted in the middle of the non-permeated water flow path 51 and passed through the return flow path 61, and a part of the non-permeated water is diverted in the middle of the second water flow path 93, specifically, On the upstream side of the pump 94, it was combined with groundwater drawn from the raw water tank 70 and returned to the membrane separation means 10.
In Comparative Example 1, the groundwater pumped from the well is stored in the raw water tank and supplied to the membrane separation means after being aerated in the raw water tank, so the groundwater pumped from the well is in an airtight state. This means that it was supplied to the membrane separation means without being retained. The water flow conditions were set to 25.0 L/min for the flow meter 14, 1.7 L/min for the flow meter 42, and 0.7 L/min for the flow meter 52.

The amount of permeated water per unit time and per unit membrane area at 25° C. was measured for 23 hours after the start of water flow, and the flux (permeation flux) was calculated. In addition, the average pressure of the reverse osmosis membrane (RO average pressure) was measured using a pressure gauge. The results are shown in FIG.
As shown in FIG. 6, after 20 hours of water flow had passed, the RO average pressure rose to twice that at the start of water flow, indicating that the reverse osmosis membrane was clogged.

Furthermore, the concentration of total iron and the concentration of iron ions in the groundwater in the raw water tank 70 at the time point when 23 hours had passed since the start of water flow were measured in the same manner as in Example 1. Further, the concentration of iron oxide in the underground water in the raw water tank 70 was determined by subtracting the concentration of iron ions from the concentration of total iron. The results are shown in FIG.
As shown in FIG. 7, the concentration of total iron in the groundwater in the raw water tank 70 is 5.2 mg/L, the concentration of iron ions is 4.4 mg/L, and the concentration of iron oxide is 0.8 mg/L. It was L. This means that while the groundwater pumped up from the well 100 was stored in the raw water tank 70, 15% of the total iron in the groundwater was oxidized to iron oxide. This iron oxide is thought to be the cause of blockage of the reverse osmosis membrane.

Generally, when the pH of water to be treated, such as groundwater, is lowered, metal ions dissolved in the water to be treated tend to be less likely to be oxidized. In addition, the pre-filter removes suspended matter (dust, sand, etc.) from the water, and by removing suspended matter from the water, it plays a role in protecting the reverse osmosis membrane.
However, in Comparative Example 1, in which groundwater pumped up from a well was supplied to the membrane separation means without maintaining an airtight state, the pH of the groundwater was lowered to 6.0, and the groundwater that had been pretreated with a prefilter was passed through the membrane separation means. Despite being fed to the separation means, iron oxides formed in the groundwater, increasing the RO average pressure during water treatment and blocking the reverse osmosis membranes.

1, 2, 3 Water treatment equipment 10 Membrane separation means 11 Reverse osmosis membrane module 12, 83, 94 Pump 13 Raw water channel 14, 42, 52, 63, 95 Flow meter 15, 43, 53, 97 Pressure gauge 21 Submersible pump 22 Raw water supply channel 23 Lifting pipe 24 Water pipe 241 First water pipe 242 Second water pipe 30 Pressure fluctuation reduction means 31 Pressure tank 40 Permeated water discharge means 41 Permeated water flow path 50 Non-permeated water discharge means 51 Non-permeated water flow Channel 60 Return means 61 Return flow path 62, 92 Solenoid valve 70 Raw water tank 71 Aeration means 71a Diffuser pipe 71b Blower 71c Gas supply pipe 80 Addition means 81 Tank 82 Sulfuric acid supply pipe 91 First treated water flow path 93 Second Treated water flow path 96 Pre-filter 100 Well

Claims (10)

A submersible pump pumps groundwater from a well,
membrane separation means for separating groundwater pumped from the well into permeated water and non-permeated water;
a raw water supply channel connecting the submersible pump and the membrane separation means;
Pressure fluctuation reducing means provided in the raw water supply flow path for reducing pressure fluctuations in the groundwater pumped from the well,
The pressure fluctuation reducing means is a pressure tank,
In the water treatment device, groundwater pumped up from the well is supplied to the membrane separation means while maintaining an airtight state. The water treatment apparatus according to claim 1, wherein the pressure tank is capable of keeping groundwater stored inside the tank in an airtight state. 3. The pressure tank is a tank filled with an inert gas, or a tank filled with an accumulating gas sealed in a rubber membrane, and capable of accumulating pressure by compressing and expanding the accumulating gas. water treatment equipment. The water treatment apparatus according to any one of claims 1 to 3 , wherein the membrane separation means includes at least one of a reverse osmosis membrane and an ultrafiltration membrane. further comprising a return means for returning a portion of the non-permeated water to the membrane separation means,
The water treatment device according to any one of claims 1 to 4 , wherein a part of the non-permeated water is returned to the membrane separation means while maintaining an airtight state. A water treatment method in which groundwater pumped from a well is supplied to a membrane separation means to separate permeated water and non-permeated water,
A water treatment method , wherein groundwater pumped from the well is supplied to the membrane separation means while maintaining an airtight state while reducing fluctuations in pressure of the groundwater using a pressure tank . 7. The water treatment method according to claim 6, wherein the pressure tank is capable of keeping groundwater stored inside the tank in an airtight state. According to claim 6 or 7, the pressure tank is a tank filled with an inert gas, or a tank in which the inside of the tank is filled with a pressure accumulation gas sealed in a rubber membrane, and the pressure can be accumulated by compression and expansion of the pressure accumulation gas. water treatment methods. The water treatment method according to any one of claims 6 to 8 , wherein the membrane separation means includes at least one of a reverse osmosis membrane and an ultrafiltration membrane. The water treatment method according to any one of claims 6 to 9 , wherein a part of the non-permeated water is returned to the membrane separation means while maintaining an airtight state.

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