JPS59213495A - Treatment of water - Google Patents

Abstract

PURPOSE:To remove easily, economically and efficiently COD from water contg. bisulfite to be discharged from a reverse osmosis membrane separator for desalting by dispensing an alkali agent to said water under aeration of said water. CONSTITUTION:Condensate is introduced into the 1st tank 1a and the pH thereof is measured with pH 6a, and if the pH decreases to <4, a pump 7a is started to supply an alkali agent via a pipe 8a to the water to adjust the pH to 4-7 and to treat the water for 5-10min. The water is then introduced into the 2nd tank 1b, where the water is treated for 60-120min under the condition of 4-7pH to oxidize most of the bisulfate in the water. The treated water is introduced into the 3rd tank 1c, where the pH is maintained in a 6-8 range and the residual bisulfite ion and sulfite ion are finally treated to make the treated water match the level of the release water. The water in the tank 3 is stagnated for 5- 30min. COD is thus considerably reduced and the treated water is released from the 3rd tank to the outside of the system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water containing bisulfite, and more particularly to a method for treating water containing bisulfite discharged from a reverse osmosis membrane separation device for desalination. .

In coastal areas and remote islands, reverse osmosis membrane separation equipment using a polymer permeable membrane is used to obtain industrial water or drinking water from seawater or salt water.

When desalinating seawater, dissolved oxygen in the seawater and residual chlorine generated from chlorine removal, which is added as a microbial countermeasure, do not have a negative effect on reverse osmosis membranes, so it is common to add reducing agents. , these dissolved oxygen and residual chlorine are removed, and acid is added to reduce p.
Adjust l■ to 4-7 and then j1! J/An1f, supplied to the device.

In addition, in some cases, once a day for 10 to 60 minutes,
Adding bisulfite at a concentration 5 to 8 times that during normal operation,
Shock treatment methods have been adopted to prevent microorganisms from multiplying within reverse osmosis membrane devices.

In addition, when the reverse osmosis membrane separation equipment is stopped, it becomes unusable due to oxidative deterioration of the membrane due to the infiltration of air while it is stopped, and the growth of microorganisms. 1iJA at pH 4-7
A method has been adopted in which the liquid in the reverse osmosis membrane separation device is replaced with the filtered liquid.1 Regardless of these methods, the reverse osmosis membrane separation device is drained immediately after the start of operation or at all times during operation. , 1 (concentrated liquid containing sulfites is discharged 8!).

Conventionally, this concentrated liquid is diluted and discharged without treatment, or it is discharged after adding an oxidizing agent7. However, it was not considered appropriate due to COD regulations, large consumption of oxidizing agents (hypochlorite, bleaching powder, chlorine gas, etc.) and toxicity when added in excess.

The present invention provides a method for treating such a bisulfite-containing concentrate exhibiting a high COD, and is a method for efficiently reducing COD by simply using air as an oxidizing agent.

However, this invention is a method for reducing the COD of water containing bisulfite discharged from a reverse osmosis membrane separation device for desalination by air aeration, and is characterized by dispensing an alkaline agent while aerating. This is a method for treating water containing bisulfite.

When bisulfite-containing water is simply aerated with air, the pentabisulfite ion is oxidized to sulfate ion by the following reaction, but at the same time, the p■■ of the liquid decreases, causing dissociation to the right term in equation (1). As the reaction progresses slowly, the oxidation reaction of formula (2) is inhibited.

HS O3-material n-+-soM-(1)S(Ji-+(
U) → 5c) 1'-i2) Therefore, in order to promote the formula (2), it is necessary to keep the pH above a certain level.

This phenomenon becomes more significant as the content of M sulfite increases. For example, in Jin's invention, such a phenomenon occurs frequently when treating a concentrated liquid containing 5001 η/e or more as bisulfite ions, which is discharged immediately after the above-mentioned shock treatment or the start of operation of the membrane separation device.

As a result of research, when processing such a concentrated liquid, it is preferable to maintain the pH at 4 or higher; however, if the pI becomes too high, charcoal scale will precipitate, so an upper limit of pH 8 is preferable. .

Bisulfite-containing concentrated water is subjected to air aeration treatment in an aeration tank, but it is necessary to add an alkaline agent to maintain the pH of the liquid at 4 to 8.

In other words, if the required amount is added all at once at the aeration tank inlet, high and low pH areas will occur depending on the position of the aeration tank, scale will occur in areas with high pf-1, and the oxidation reaction will not progress at the aeration tank outlet. The pH accordingly decreases, and as a result, the oxidation reaction is inhibited and some bisulfite or sulfite ions are discharged untreated.

Therefore, in this invention, a plurality of alkali agent injection points are provided so that an appropriate pf can be maintained in any part of the aeration tank.

Hereinafter, the present invention will be explained in detail using the drawings.

Figure 1 shows that aeration tanks are set up in multiple stages, the pH is set in the well, and each ("i"
This shows a method in which the alkaline agent is dispensed into the opening 9 and the injection amount is adjusted to the open side 1.

In this method, the aeration tank 1 has three stages (1a, lb+lc)
However, the number of stages is not limited to three, and any number of stages can be provided as required. Each aeration tank is equipped with an aeration pipe 3 connected to a blower 2 (3a, 3b, 3c).

Further, on the upstream side, for example, a concentrated water supply pipe 5 connected to the concentration (ill) of the reverse osmosis membrane separation device 4 for seawater desalination is arranged,
Famous water (pH 1i6a, (ib, 6c) is provided on the downstream side.

Furthermore, alkaline agent injection pumps 7a, 7b, and 7c are provided which are linked to each of the pH meters (3), and the alkali agent is supplied by the operation of these pumps.

From 8c, a suitable alkali filler such as sodium hydroxide, potassium hydroxide, etc. is supplied.

There is a baffle plate 9 on the front of the pH meter installed in each aeration tank.
It would be better to provide a, 9b, and 9c.

In a device designed in this way, at 11M, concentrated water containing a large amount of bisulfite is discharged from the concentration side of the reverse osmosis membrane separation device 4 for f1σ water desalination during the initial stage of operation or during shock treatment. The aeration water tank 1 is deposited to the earth flow side via the 1 agency 5. Aeration pipe 371 is connected to the aeration tank by blower 2.
First, the condensed water is treated in the first section (V-).

The residence time is relatively fast, usually within 5 to 10 minutes.
sent to the tank.

In the first inertia, pH is measured by pI-■ meter 6a, and p
When H becomes less than 4, the pump 7a is automatically started and the alkaline agent is supplied through the pipe 8a to reduce pJ-14.
It is adjusted to a range of ~7. Then, it is sent to the second tank.

The processing in the second tank is basically the same as in the first tank, but
The second tank has a relatively long residence time of about 60 to 120 minutes because it is set to carry out full-scale treatment, whereas the second tank is more of a preliminary treatment. even here,
An alkaline agent is automatically injected to maintain the pH of the liquid within the range of 4 to 7.

The water, in which most of the bisulfite has been oxidized, is then fed to a third tank for after-treatment.

The 3rd tank is the final stage in the 2nd drawing, so in order to finally process residual bisulfite ions and sulfite ions and to obtain buried water that meets the effluent standards, pi-I is 6. Adjusted and maintained within the range of ~8. The rfij residence time is usually about 5 to 30 minutes.

Treated water with COD and p i-I whose OD is greatly reduced and meets the effluent standards, (, i
[Discharged from tank 3 to the outside of the system.]

On the other hand, FIG. 2 Co1 shows another simpler embodiment of the present invention. The device C in Fig. 2 has an aeration water tank with a multi-stage alkali agent supply pipe instead. , a pH meter 16 provided downstream of the aeration water tank 11, and an alkali agent supply tube 18a, l8b having one or more nozzles,
This system includes alkaline agent injection pumps 17a, 17b, and 17c (same) connected to pump I8c (three stages are shown in Fig. 2, but they can be provided as necessary), and pump Activation is performed by a total of 16 p i-.

In the device designed in this manner, water to be treated is supplied from the concentration side of the reverse osmosis membrane separation device 14 for seawater desalination to the upstream side of the aeration tank 11 via the pipe 15. The aeration tank is provided with as many aeration pipes 13 as necessary from the upstream to the downstream side,
Air is supplied by the blower 12, and the water to be treated is gradually oxidized.

In the system shown in Fig. 2, a pf (total of 16
and pump 1.7a, depending on the detected pH value.
17b and 1Fic are activated to supply the alkali agent 20. In the figure, reference numeral 19 indicates a baffle plate, which is preferably provided.

Note that one or more nozzles are arranged at the end of the alkaline agent supply pipe connected to each pump, and these nozzles are arranged in the direction of flow in the aeration tank (upstream τljl) as shown in Figure 2. It is preferable to provide it in such a way (from the downstream side).

An example of how to operate a pump is when the detected pH is 4.
If the groove is not yet filled, start all the pumps so that a large amount of alkaline agent is dispensed. Also, the detected pll is 6
-7, start 1 or 2 units. If the pH shows 8 or higher, stop all pumps.

In short, the operation of the pump can be easily controlled so that the pll of discharged water is 6 to 8. The standard residence time is about 30 to 200 minutes, and may be adjusted depending on the COD of the treated water.

As mentioned above, in the embodiments shown in FIGS. 1 and 2, the alkaline agent is dispensed in accordance with the oxidation treatment.
Heavy by doing so! 11! (The oxidation reaction of the IIIt salt proceeds smoothly, and by the time it leaves the aeration tank, CO
D is sufficiently reduced. In addition, the pH is adjusted to rA so that the temperature can be released as is.

In this way, with this invention, condensate water discharged from reverse osmosis membrane separators for seawater desalination, which contains high concentrations of bisulfite and which has conventionally been difficult to treat economically and efficiently, can be easily and economically treated. It became possible to provide a seawater desalination system using a reverse osmosis machine using a reverse osmosis machine.

EXAMPLE Concentrated water discharged from a seawater desalination river reverse osmosis membrane separation apparatus immediately after the start of operation was treated using the apparatus shown in FIG.

The concentration of sodium bisulfite in the concentrated water was 1,200 mV/min.

The tank capacity was set to 3 for both tanks 1 to 3, and the air supply amount was 0-1n! /77f・mjn.

Residence time in tank 1 is 7 minutes, tank 2 is 70 minutes, and tank 3 is 5 minutes.
It was a minute. When the pf (total) provided in the first tank was less than 6, an alkaline agent (sodium hydroxide) was injected.The water at the first tank outlet was sampled and the amount of residual sulfite ions (bisulfite ions and sulfite ions) was added to 6111. However, 1,
It was 020■/I3. Also, 1) H was 6.2.

Next, in the second case, the pH was controlled to be 6 or more. Similarly, when sampling was performed at exit 241, the residual sulfite ion concentration was 30 μ/min, and the pf (pf) was 6.4.

In the third tank, the pH was controlled to be 6-8.

The final effluent had an IA lees sulfite ion horny/43 less than pL (7,000 pL).

Comparison The same water as above was supplied to the aeration tank of Example 9e, and the water was aerated with air for io minutes. 40 minutes after the start of aeration, the pH suddenly dropped to 2.6, and the residual ion concentration (tffi I'1''2 ion concentration) in the final treated water was 500 η/min.

1) When rum was added all at once, a considerable amount of scale precipitated at the inlet, and 1
After aeration for 20 minutes, the residual i+r and sulfur ion/concentrated IW became 50η/τ.

As is clear from the above Examples and Comparative Examples, in this invention, the alkaline agent is dispensed with care, so that the problems described in the Comparative Examples do not occur and processing can be carried out efficiently. .

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 show embodiments of the present invention, and in FIG. 1, 1 (la, lb, lc) is an aeration tank, 3 (3a, 3b, 3c) is an aeration pipe,
6 (6a, 6b, 6c) is pf (total, 7 (7a, 7b,
7c) is an alkali injection pump, 8 (8a, Fib, 8
cJ indicates an alkali agent supply pipe. On the other hand, in FIG. 2, 11 is an aeration tank, 131',
! ,' 11 questions, 3.7 (17a, I7b, 17c
) is alkali injection pump, 18 (18a, 1FJb,
18c) each shows an alkali agent supply pipe. Special feature: Applicant: Kurita Water Industries, Ltd.

Claims (1)

[Claims] A method for reducing COD of water containing bisulfite discharged from a reverse osmosis membrane separation device for desalination by air aeration, the method comprising:
A method for treating water containing bisulfite, characterized by dispensing an alkaline agent while aerating.