JPS583742B2 - Method for neutralizing recycled waste liquid from ion exchange equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for neutralizing recycled waste liquid from an ion exchange device, and in particular to a method for neutralizing recycled waste liquid containing a large amount of organic matter without generating a precipitate, and a process for neutralizing the recycled waste liquid. The present invention relates to a neutralization treatment method for efficiently removing organic matter from the inside.

In recent years, the water quality of water sources used for industrial water has become increasingly polluted, and industrial water containing large amounts of organic matter has no choice but to be used as raw water for ion exchange equipment such as water purification equipment. be.

When such raw water is treated with a water purification device, a coagulation sedimentation device is generally installed as a pretreatment, but the coagulation sedimentation device does not remove all of the organic matter in the raw water, and only some of the organic matter is removed. The organic matter will be supplied to the pure water production equipment.

Furthermore, most of the organic substances contained in natural water are adsorbed by anion exchange resins, and most of them are desorbed when the anion exchange resin is regenerated.

Therefore, the organic matter present in the raw water is contained in the recycled waste liquid of the anion exchange resin in a concentrated form, and in some cases, the COD concentration may reach 100 ppmasO or more.

The recycled waste liquid containing a large amount of organic matter cannot be discharged simply by neutralizing it, but it is necessary to remove the organic substances in the recycled waste liquid by some method.

A possible method for removing the organic matter is to perform coagulation and precipitation treatment on the liquid after neutralization, but the organic matter is organic matter that could not be removed by coagulation and precipitation treatment, which is a pretreatment for the water purification equipment. Therefore, even if this is subjected to coagulation and precipitation treatment again, the removal effect is small.

Another possibility is to decompose the organic matter using an oxidizing agent such as sodium hypochlorite, but this method requires a large amount of oxidizing agent and is therefore not an economical method. The best way is to do so.

There are two types of activated carbon: powder activated carbon and granular activated carbon, but the former is difficult to regenerate and is disposable, whereas the latter can be activated and reused by roasting and recycling, so the latter is more cost-effective.

However, the adsorption capacity of the above-mentioned organic substances by granular activated carbon is not so large, and it is currently desired that an even better treatment method be developed.

On the other hand, when acidic waste liquid and alkaline waste liquid generated from pure water production equipment are mixed and neutralized, a large amount of insoluble precipitates are generated in the neutralized liquid, which is a problem that occurs during the regeneration process of cation exchange resin. Acidic waste liquid contains a large amount of cations such as calcium ions, magnesium ions, and sodium ions along with excess acid, and alkaline waste liquid generated from the anion exchange resin regeneration process contains excess alkali as well as chlorine ions, sulfate ion,
Contains large amounts of anions such as carbonate ions and silica.

Therefore, when the two are mixed, insoluble precipitates caused by calcium carbonate and the like are generated, and it is currently necessary to separate these insoluble precipitates.

Conventionally, when neutralizing recycled waste liquid containing a large amount of organic matter, two operations have to be carried out: separation of insoluble precipitates and removal of organic matter from the neutralized liquid, which imposes a heavy economic burden.

The present invention solves the above-mentioned conventional problems, and neutralizes both recycled waste liquids without generating insoluble precipitates.
Another object of the present invention is to efficiently adsorb organic substances to granular activated carbon during the neutralization process and to dramatically increase the adsorption capacity of granular activated carbon.

That is, in neutralizing the recycled waste liquid of the ion exchange device, the present invention separates the acidic waste liquid discharged from the cation exchange resin regeneration process and the alkaline waste liquid discharged from the anion exchange resin regeneration process into separate receiving tanks. The first step is to take out both waste liquids from the receiving tank and instantly mix them so that the pH of the mixed liquid is 3 or less.The mixed liquid is aerated or deaerated to remove free carbonic acid from the mixed liquid, An ion exchange device consisting of a second step in which the acidic mixed solution from which carbonic acid has been removed is passed through a granular activated carbon layer to remove organic matter in the solution, and a third step in which an alkali is added to the granular activated carbon treated solution to re-neutralize it. This invention relates to a method for neutralizing recycled waste liquid.

The present invention will be explained in detail below.

In general, most of the organic substances present in natural water are hydrophilic organic acids with high or low molecular weight, and are therefore adsorbed as organic acids on anion exchange resins. During regeneration, it is desorbed into the regeneration waste liquid as a sodium salt of an organic acid.

These organic acids generally have high solubility, but the pH of the waste liquid
When is made small, that is, on the acidic side, the solubility of organic acids decreases as the acidity increases, and at the same time, the affinity for water decreases, so the adsorption capacity of the organic substance of activated carbon tends to increase.

For example, this tendency was confirmed when the equilibrium adsorption amount of organic matter by activated carbon was measured for an alkaline waste liquid of an anion exchange resin having the composition shown below.

The method for measuring the equilibrium adsorption amount of organic matter by activated carbon is as follows:
A certain amount of the alkaline waste liquid mentioned above was collected into four beakers, and hydrochloric acid was added to adjust the pH of the waste liquid to 7. 0,
The equilibrium adsorption amount of COD by granular activated carbon was measured using a conventional method for four types of samples with different pH values adjusted to 4.5, 3.0, and 2.0.

That is, 500 ml of each sample was collected in four Erlenmeyer flasks, and 32
Granular activated carbon Diamond Hope 00 crushed to 5 mesh or less
8 (registered trademark) at 50 mg, 100 mg, and 20 mg, respectively.
Add 0 mg and 300 mg at a time and adsorb organic matter while shaking at a constant temperature for 120 minutes. COD of the filtrate
Measure the concentration and determine the COD of activated carbon at each concentration.
The equilibrium adsorption amount was calculated.

By such a method, the pH was adjusted to 7.0, 4. 5,
When the equilibrium adsorption amount was measured for four types of samples, 3.0 and 2.0, as shown in Figure 1, each F
It matched well with the reund lich adsorption isotherm, X=aCn, and a linear relationship was obtained on the double-log graph.

For example, pH 7.0 at a COD concentration of 100 to a s O /l. 0 and pH 3. From FIG. 1, the COD equilibrium adsorption amount of the sample of 0.0 and 2.0 mg as. o/g,
180 mga s0/g, and it was confirmed that when the pH was 3, the amount of COD adsorbed increased by about 3.5 times compared to the neutral case.

As described above, the equilibrium adsorption amount of organic matter contained in the recycled waste liquid of anion exchange resin by activated carbon is dramatically increased when the organic matter is adsorbed at a waste liquid pH of 3 or less compared to when the organic substance is adsorbed at a waste liquid pH of 7. I found out that.

Therefore, when treating organic matter in the recycled waste liquid with activated carbon, it is preferable to lower the pH of the waste liquid and adsorb it on the acidic side.

On the other hand, when acidic waste liquid and alkaline waste liquid are mixed and neutralized, insoluble precipitates that are generated are caused by calcium carbonate, etc., but this is because a large amount of calcium ions are present in the acidic waste liquid, and a large amount of calcium ions are present in the alkaline waste liquid. This is because a large amount of carbonate ions are present.

Therefore, in order to prevent the generation of calcium carbonate, it is recommended to carry out the following neutralization method.

That is, both waste liquids are mixed and the pH of the mixed liquid is first made acidic to 3 or less.

If the mixed solution becomes acidic, carbonate ions become free carbonic acid, so even if calcium ions coexist therein, no calcium carbonate precipitate is generated.

Next, free carbonic acid is removed by aeration of this mixed solution, and then an alkali is added to the acidic mixed solution from which free carbonic acid has been removed to adjust the pH to around neutrality.

Once free carbonic acid is removed in this way, no precipitate of calcium carbonate will be formed even if the pH is made neutral in the presence of calcium ions.

The present invention skillfully combines the above two technical findings, by mixing both waste solutions to a pH of 3 or less, then removing free carbonic acid from this acidic mixture, and then removing the free carbon dioxide from this acidic mixture. Organic matter is effectively removed by passing the liquid through the granular activated carbon, and finally, an alkali is added to the granular activated carbon treatment liquid to re-neutralize it, making the recycled waste liquid near neutral.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is an explanatory diagram showing a flow of an example of an embodiment of the present invention, in which an acidic waste liquid 1 discharged from a cation exchange resin regeneration process and an alkaline waste liquid 2 discharged from an anion exchange resin regeneration process are illustrated. They are received separately in an acid waste liquid receiving tank 3 and an alkaline waste liquid receiving tank 4, respectively.

The size of both receiving tanks should be such that if the ion exchange equipment is used in batches, such as with a fixed bed, the capacity can accommodate at least one batch of regenerated waste liquid, or if the regenerated waste liquid is constantly discharged, such as in a continuous ion exchange equipment. When using a tank, it is preferable to use a tank that allows retention for at least 10 minutes.

Next, each waste liquid is taken out using the acid waste liquid pump 5 and the alkaline waste liquid pump 6, and both waste liquids are instantaneously mixed using an instant mixer such as an ejector 7, and the p of the mixed waste liquid is
H is 3 or less.

Generally, recycled waste liquid from an ion exchange device such as a water purification device has a larger alkali equivalent than an acid equivalent, and therefore it is necessary to replenish the insufficient acid.

In the embodiment shown in FIG. 2, acidic waste liquid 1 and alkaline waste liquid 2 are mixed at constant flow rates, and the pH of the waste liquid is detected by a pH controller 8 installed immediately after the ejector 7.
An acid injection pump 9 linked to an H controller 8 adds acid 10 to bring the pH of the waste liquid below 3, but there are other methods, such as adding a constant flow of alkaline waste liquid 2 as shown in FIG.
is passed through the ejector 7 using the pump 6, while the acidic waste liquid 1
A control valve 11 linked to a pH controller 8 using a pump 5
The acidic waste liquid 1 may be introduced while adjusting the flow rate so that the pH of the mixed liquid waste liquid becomes 3 or less.

In this way, if the alkali equivalent is greater than the acid equivalent, the liquid level in the acid waste liquid receiving tank 3 will gradually decrease;
The acid injection pump 9 is driven by the signal from the liquid level gauge 12 to replenish the acid waste liquid receiving tank 3 with acid 10 up to a constant liquid level.

Note that when comparing the acid equivalent and alkali equivalent of both waste liquids, it goes without saying that if the acid equivalent is larger, alkali should be replenished.

In this way, by instantaneously mixing the two waste liquids and making the pH acidic to 3 or less, no insoluble precipitate is generated in the mixed liquid.

Regarding pH, as shown in Figure 1,
The lower the pH, the greater the adsorption capacity of organic matter by granular activated carbon.

However, if the pH of the waste liquid is lowered too much, the amount of alkali ultimately added will increase, which is undesirable in terms of running costs.Usually, the pH of the waste liquid after mixing is preferably in the range of 2 to 3.

When mixing both waste liquids to bring the pH to 3 or less, it is not preferable to mix slowly as insoluble precipitates tend to occur and a time lag occurs in the pH controller 8, which is not preferable, so it is necessary to mix both waste liquids instantly. There is.

As a means for instantaneously mixing both waste liquids, it is desirable to use an ejector 7 as shown in FIG. 2, but a so-called line mixer may also be used.

When both the waste liquids are mixed and the pH is made below 3, the carbonate ions contained in the alkaline waste liquid 2 become free carbonic acid, so this mixed liquid is transferred to the decarboxylation tower 13 as shown in Fig. 2. to remove free carbonate.

The decarboxylation tower 13 shown in FIG. 2 is filled with a filler 14 such as a Raschig ring, and air is circulated from the bottom of the tower by a blower 15, but the decarbonation tower 13 is not limited to this, for example, a vacuum deaerator, etc. Free carbonic acid may be removed using

Next, the decarboxylated acidic mixed liquid is passed through an adsorption tower 18 filled with granular activated carbon 17 using a decarboxylated liquid pump 16, and organic substances contained in the mixed liquid are adsorbed and removed.

When the acidic mixed solution is passed through the granular activated carbon layer, the adsorption capacity for organic matter increases as shown in Figure 1, so the organic matter in the mixed solution can be effectively removed. , it becomes possible to dramatically increase the throughput.

In addition, if the two waste liquids are mixed to have a pH of 3 or lower and the carbonate ions are changed to free carbonate, and the liquid is passed through the granular activated carbon as it is, carbon dioxide gas will be generated within the granular activated carbon layer, and the granular activated carbon layer will become in a state of one-sided flow. Therefore, it is not preferable to remove free carbonic acid using a decarboxylation tower and then pass the liquid through the granular activated carbon layer.

In addition, the adsorption tower 18 is not limited to a single bed, for example, two
The liquid is passed through a series of columns, and when the first column is saturated with organic matter, the granular activated carbon in the first column is replaced with recycled carbon, and then the granular activated carbon in the first column is replaced with recycled carbon.
By using a so-called multi-tower merry-go-round method in which the liquid is passed through the columns, the utilization efficiency of the granular activated carbon can be further increased.

Since the treated liquid from which organic matter has been removed by passing through the adsorption tower 18 has a low pH, it is mixed with the alkali 19 using the ejector 7' to be re-neutralized, and the pH of the treated liquid can be discharged. Near neutrality.

At this time as well, the amount of alkali to be added is adjusted by the control valve 11' which is interlocked with the pH controller 8' provided immediately after the ejector 7'.

It is preferable that the alkali to be added be a caustic soda solution with a low concentration, but in some cases, the alkaline waste liquid 2 discharged from a pure water production apparatus may also be used.

However, if the alkaline waste liquid 2 is used, the neutralized liquid will contain some organic substances, so care must be taken when the alkaline waste liquid 2 has a large amount of organic substances.

As explained above, according to the present invention, it is possible to neutralize the regenerated waste liquid of an ion exchange device without generating any insoluble precipitates, and therefore there is no need to install an insoluble precipitate separation device that was previously required. Furthermore, since the organic matter contained in the recycled waste liquid can be efficiently removed, the life of the granular activated carbon can be dramatically increased.

Note that the present invention is applicable not only to recycled waste liquid from water purification equipment, but also to various ion exchange equipment that desalts liquids containing organic matter using cation exchange resins and anion exchange resins.

Examples of the present invention will be described below.

Example An analysis of the compositions of the acidic waste liquid discharged from the cation exchange resin regeneration process and the alkaline waste liquid discharged from the anion exchange resin regeneration process of the boiler water purification water production equipment revealed the following. Ta.

Next, neutralization treatment according to the present invention was carried out based on the flow shown in FIG.

In other words, an acidic waste liquid of 9 m/H and an alkaline waste liquid of 14 m/H are mixed in an ejector, and the pH immediately after the ejector is 2.5.
35% hydrochloric acid was injected using an electroservo-equipped injection pump so that the concentration was ~3.0.

The acidified mixture is then decarboxylated by flowing into the upper part of a decarboxylation tower with an inner diameter of 770 mm and a height of 2,740 mm, which is filled with a cylindrical Raschig ring made of vinyl chloride (inner diameter 40 mm, length 30 mm). Free carbon dioxide in the acidic mixture was removed by blowing air at about 650 Nm/H from the bottom of the column with a blower.

Next, the mixed liquid from which free carbonate was removed was poured into a tube with an inner diameter of 1,800 mm filled with 6 m of granular activated carbon Diahope 008.
The organic matter in the mixed solution was adsorbed by passing the liquid through two adsorption towers each having a height of 4,500 mm and a height of 4,500 mm.

Next, a 0.3% caustic soda solution was added to the treated liquid in the adsorption tower to neutralize the pH of the treated liquid to around 7.

At this time as well, the ejector was used as a mixer, the pH of the waste liquid immediately after the ejector was measured with a pH controller, and the flow rate of the caustic soda solution was adjusted using an articulated valve linked to the pH controller.

By the neutralization treatment method of the present invention as described above, transparent neutralized water containing insoluble precipitates of 5 ppm or less and COD of 10 ppm as O or less was obtained.

Furthermore, the point at which the COD value of the treated water reached 10 ppmaso was set as the flow-through point of the granular activated carbon, and it was possible to process 2,750 m of the acidic mixture from which free carbonic acid had been removed.

On the other hand, for comparison, a pH 7
When the neutralized water before and after was passed through a granular activated carbon tower, insoluble precipitates were found to be less than 5 ppm and COD was 10 ppm.
Treated water with a concentration of less than m aS O was obtained. Similarly, the point at which the COD value of the treated water reached 10 ppmas0 was set as the flow-through point of the granular activated carbon, and the throughput at this time was 450 m.

[Brief explanation of the drawing]

Figure 1 is a graph showing the COD equilibrium adsorption isotherm at each pH of the alkaline waste liquid discharged from the reprocessing of anion exchange resin in a water purification equipment.The vertical axis is the COD equilibrium adsorption amount, and the horizontal axis is the COD Indicates concentration. FIG. 2 is an explanatory diagram showing a flow of one example of an embodiment of the present invention, and FIG. 3 is an explanatory diagram showing a flow of another embodiment regarding a part of FIG. 1... Acidic waste liquid, 2... Alkaline waste liquid, 3... Acid waste liquid receiving tank, 4... Alkaline waste liquid receiving tank, 5...... Acid waste liquid Pump, 6...
・Alkaline waste pump, 7... Ejector, 8.
...pH controller, 9...acid injection pump,
10...Acid, 11...Control valve, 12.
...Liquid level gauge, 13...Decarbonation tower, 14.
...Filler, 15...Blower, 16...
... Decarbonation liquid pump, 17 ... Granular activated carbon, 18 ... Adsorption tower, 19 ... Alkali.

Claims (1)

[Claims] 1. When neutralizing the recycled waste liquid from the ion exchange equipment, the acidic waste liquid discharged from the cation exchange resin regeneration process and the alkaline waste liquid discharged from the anion exchange resin regeneration process are received in separate receiving tanks. The first step is to remove both waste liquids and instantly mix them to bring the pH of the mixture to 3 or less.The mixture is aerated or deaerated to remove free carbonic acid from the mixture, and then the free carbonic acid is removed. A recycled waste liquid from an ion exchange device, which consists of a second step of passing an acidic mixed solution through a granular activated carbon layer to remove organic matter in the liquid, and a third step of adding an alkali to the granular activated carbon treated solution to re-neutralize it; Neutralization method.