JPH0698351B2 - Treatment of waste liquid containing citric acid - Google Patents

Description

TECHNICAL FIELD The present invention relates to treatment of a waste liquid containing citric acid and a salt thereof, and in particular, it is used for industrial waste liquid or chemical cleaning for producing or using citric acid. The present invention relates to a method for treating cleaning waste liquid containing citric acid or a salt thereof.

[Conventional technology]

Hitherto, a processing technique for recovering citric acid from a dilute citric acid-containing waste liquid has not been established.

In addition, for the purpose of removing various metal oxide scales mainly composed of iron oxide adhered to the metal surface of boilers and heat exchangers, an acid solution containing a corrosion inhibitor or a reducing agent added to citric acid or its salt. Cleaning with is widely performed in general.

Most of the waste liquid discharged after cleaning contains COD components and heavy metals derived from citric acid. In discharging this waste liquid, it is necessary to remove these harmful substances.

Conventionally, the following means have been adopted for COD treatment of this type of waste liquid.

In treating the waste liquid, COD is treated to below the standard value by chemically oxidizing and decomposing it with an oxidizing agent, and then neutralizing it to completely remove heavy metal ions.

When the citric acid concentration is high, calcium hydroxide is added to the waste liquid, most of the citric acid is precipitated and removed as calcium citrate, and the same operation is performed on the supernatant water as in the treatment.

Waste liquid is processed using RO (reverse osmosis membrane), and most of the COD
A method in which the components are separated by concentrating them, and the diluted liquid that has passed through RO is treated in the same manner as in.

A method of biodegradation by treatment of activated sludge with microorganisms.

Etc.

[Problems to be Solved by the Invention]

In such a treatment method, in the case of, the number of treatment days, the load of treatment chemicals are large, the treatment operation is complicated, and COD
There is a problem that results that satisfy the standard value of can not be obtained stably. In the case of, COD is treated to 10 mg / l or less, though treatment chemicals are considerably reduced compared to. Attempting to do so, the permeated water after the RO treatment had to be further chemically oxidized by an oxidizing agent.

In addition, there are problems of culturing microorganisms and the cost of equipment, and it is not practical as a treatment of unsteady waste liquid.

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, reliably treat COD caused by citric acid to 10 mg / l or less, and enable continuous treatment, and reduce the number of treatment days and treatment chemicals. Another object of the present invention is to provide a waste liquid treatment method capable of recovering citric acid, which is a valuable resource, as much as possible.

[Means for Solving the Problems]

In order to achieve the above object, in the present invention, when treating a waste liquid containing citric acid and a salt thereof, after adjusting the pH of the waste liquid to 4 or less, the dissolved citric acid and a salt thereof are treated with activated carbon. This is a method for treating a waste liquid, which is characterized by adsorption treatment.

As the waste liquid containing citric acid and its salts in the present invention, when the purpose is to recover the citric acid, the waste liquid is subjected to the above-mentioned treatment as it is, and only for the purpose of reducing COD in the waste liquid. If this is the case, it is advisable to first perform treatment using RO (reverse osmosis membrane) and then perform this treatment.

Next, the present invention will be described in detail.

First, in a process for recovering citric acid from a waste liquid containing citric acid and a salt thereof of the present invention, as shown in FIG. 1, an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid is added to the liquid to be treated 1, After adjusting the pH, the activated carbon is passed through the activated carbon layer 3 to adsorb the dissolved citric acid on the activated carbon. The adsorbed citric acid can be easily desorbed by bringing it into contact with the alkaline aqueous solution 4.

By adding the calcium agent 5 to the desorption solution, it is recovered as calcium citrate, and the activated carbon after desorption (after regeneration) is reused.

Table 1 shows the results of the adsorption test by the batch method. In the present invention, the pH of the liquid before passing through the activated carbon layer is 4 or less, particularly 2 to
It was found that 3 is preferable, and that citric acid and its salt are hardly adsorbed at pH 5 or higher.

The amount of COD that can be adsorbed per 1 kg of activated carbon when passing through the activated carbon layer is approximately
COD of 10 mg / l continuously up to 36 g (72 g as citric acid)
It can be processed as follows. Since the liquid that has passed through the activated carbon layer is acidic, it is neutralized by adding an alkaline agent.For continuous proportional neutralization, an alkaline agent such as sodium hydroxide may be used. If so, it is desirable to use bicarbonate for pH adjustment. In this case, the pH can be easily treated within the range of 7 to 7.5 by adding 2 to ³ kg per 1 m ^{3 of the} waste liquid.

When the COD value of the passing liquid reaches the upper limit of the regulation value, the activated carbon is regenerated and used repeatedly.

To regenerate the activated carbon after the adsorption, citric acid can be easily desorbed by contacting it with an aqueous solution of an alkali agent such as sodium hydroxide, potassium hydroxide or ammonium hydroxide. For desorption, regeneration can be carried out by a method of temporarily passing a necessary amount of the alkaline agent or by circulating an aqueous solution of the alkaline agent.
Since it is performed sufficiently quickly at pH 9 or higher, it is possible to perform a process to bring the pH to the same value by appropriately injecting the alkaline agent by the circulation method. This method saves and collects (desorbs) the alkaline agent. This is advantageous because the volume can be reduced.

The desorption solution is a concentrated solution of citric acid, to which calcium hydroxide (lime milk), calcium chloride, etc. are added and recovered as sparingly soluble calcium citrate. After that, it is possible to contribute to the improvement of the yield as a product by refining by the existing method.

Further, in the COD treatment of the waste liquid caused by citric acid such as the chemical cleaning of the boiler of the present invention, the high COD waste liquid is treated using RO (reverse osmosis membrane). The permeated water obtained by this is
It is a diluted concentration of about 1/100 of the stock solution. An inorganic acid is added to this waste liquid to adjust the pH, and then the activated carbon layer is passed through to adsorb the dissolved COD component citric acid with the activated carbon.
Since the activated carbon passage liquid from which citric acid has been removed is acidic, it is possible to continuously treat the waste liquid by adding an alkali and performing a neutralization treatment.

The activated carbon used for adsorption can be easily regenerated by washing with an alkaline aqueous solution and can be used repeatedly for waste liquid treatment.

FIG. 2 shows one mode thereof. That is, by passing the waste liquid 1 containing a high concentration of citric acid through the RO device 7,
Removes most of the citric acid ,. RO that became even more diluted
Inorganic acid 2 is proportionally injected into the permeate with a metering pump 8 or the like to continuously adjust the pH.

Any inorganic acid may be used in this case, but phosphoric acid, nitric acid and the like are not preferable in view of wastewater regulations. Therefore, hydrochloric acid and sulfuric acid are preferable because they are cheap in price, economical, and have no problem in drainage regulation. The activated carbon layer 3 can also be passed through, and almost all the amount of citric acid is adsorbed on the activated carbon, and the liquid that has passed through the activated carbon is proportionally injected with an alkaline agent 9 by a metering pump or the like, continuously neutralized, and continuously discharged. Is to be processed.

Regeneration of activated carbon can be performed by the method described above,
In this case, the cleaning waste liquid generated by the regeneration treatment can be treated as a liquid to be treated in the RO treatment.

[Examples] Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

Example 1 A simulated waste liquid containing citric acid shown in Table 2 was prepared and treated by the method of the present invention to confirm the citric acid adsorption effect.

The treatment is to add HCI solution first, adjust the pH of the waste liquid to 2.5,
Palm shell granular activated carbon (8-32 mesh) 440g (920ml)
Was packed in a column having a diameter of 42 mm, and water was passed at 16.5 l / h for treatment. For the adsorption effect, measure the COD of the liquid that has passed through the activated carbon,
It was confirmed by converting to the amount of citric acid.

The processing conditions and results are shown in Table 2 and FIG.

As can be seen from Fig. 3, the COD target value of treated water is 10 mg / l.
When it is less than (corresponding to 20 mg / l as citric acid), the amount of citric acid adsorbed is calculated from the cumulative value of the values calculated by the following formula at each measurement point: (concentration of citric acid in simulated waste liquid x water flow rate) -2 x ( COD of treated water x water flow rate 31.7 g of citric acid (72.0 g per 1 g of activated carbon), and the recovery rate (amount of citric acid adsorbed / total amount of citric acid in simulated waste liquid x 100) at this time was 31.7 g. ÷ (262 l × 126 mg / l × 10 ^-3 ) × 100 = 96.1%, showing a remarkable effect.

In this case, the COD amount is 15.9g (as citric acid
31.7g equivalent), and a double amount of water flow (ratio of the amount of water flow to the weight of activated carbon), a remarkable effect that COD of treated water can be treated to 10 mg / l or less up to about 600 times is recognized.

Furthermore, 2% NaOH aqueous solution 1 equivalent to the citric acid that adsorbed the activated carbon used for citric acid adsorption treatment was equivalent to 16.5 l /
When the desorption treatment of citric acid was performed by circulating washing of h, it was about 3
No change was observed in the pH of the circulating liquid in 0 minutes, and the pH value of the liquid at that time was 9.2. Next, the activated carbon layer was extruded with 2 liters of water and washed with water, and then the entire amount (desorption solution 1 + washing water 2 liters)
The amount of citric acid was determined by measuring the COD.

As a result, as shown in Table 3, 31.1 g of citric acid was desorbed and the desorption rate (that is, the regeneration rate) was 98%.

Furthermore, calcium hydroxide was added to this solution to separate and collect calcium citrate. As a result, as shown in Table 4, 39.2 g was obtained. This was a high yield corresponding to 97% of the theoretical yield. In addition, the recovery rate by this method until the citric acid in the waste liquid is separated and recovered as calcium citrate is equivalent to 91.3%, and it is possible to recover the valuable materials that had been discarded until now in a high yield.

Example 2 The activated carbon regenerated in Example 1 was adjusted to pH 2.5 with HCl and subjected to citric acid adsorption treatment again. As shown in Table 5, three kinds of waste liquids to be treated were prepared with different citric acid concentrations, and the adsorption effect was confirmed as in Example 1. The results are shown in FIG.

As can be seen from Table-3, it is shown that desorption of citric acid is easily performed by the circulation treatment with the NaOH aqueous solution.
Further, as can be seen from FIG. 4, even when the activated carbon was regenerated, it was confirmed that there was no problem in the citric acid adsorption recovery thereafter, and the same results as in Example 1 were obtained. The recovered calcium citrate can be made into a product by refining it as citric acid by an existing method.

As described above, according to the method of the present invention, citric acid can be reliably recovered from the waste liquid containing dilute citric acid, and the recovered citric acid becomes a product by refining and contributes to the improvement of yield. Depending on the treatment, the activated carbon of the recovery medium can be repeatedly used.

In addition, the apparatus can be simple, and the COD of the waste liquid caused by citric acid is processed to be below the regulation value, so that the processing cost can be reduced.

In this way, it is possible to recover citric acid, a valuable resource that was previously discarded as waste liquid, with an efficiency of 90% or more, and also to process COD of waste liquid related to citric acid. Since activated carbon, which is the medium of, can be repeatedly used, it is a method of realizing highly economical treatment.

Example 3 A simulated cleaning waste liquid shown in Table 6 was prepared, the waste liquid 1 was treated with RO7 as shown in FIG. 2, and the liquid that passed through RO was continuously supplied with H ₂ SO ₄ using a metering pump 8. 700 g of coconut shell type granular activated carbon (8-32 mesh)
(1460 ml) is passed through an activated carbon tank 3 packed in a column with a diameter of 55 mm, and the liquid that has passed through is continuously metered using a metering pump.
A series of treatments of adding NaHCO ₃ and neutralizing was performed.

The result is shown in FIG. In Fig. 5, the COD of the RO permeate and the amount of permeate change with time, but by returning the concentrate 6 of Fig. 2 to the original tank 1, the concentration of the liquid to be treated gradually increases, and In proportion to this, the COD of the permeate increases, and conversely the amount of permeate decreases in inverse proportion.

As can be seen from Fig. 5, a high-concentration waste liquid of citric acid was treated with RO, the permeated liquid that became a dilute waste liquid was pH-adjusted, and the waste liquid containing 15,000 mg / l of COD was passed through activated carbon. Could be continuously treated to a COD of 10 mg / l or less.

Also, the pH of the discharged water shows 7.0 to 7.5 from the beginning, indicating that this treatment is complete.

It can be confirmed that a series of treatment operations can be performed continuously, and the treatment effect of the present invention is clearly recognized.

As described above, according to the method of the present invention, the waste liquid containing citric acid as a main component is continuously and reliably treated to have a COD of 10 mg / l or less, a conventionally complicated operation is simplified, and a treatment chemical is used. Can also be reduced.

〔The invention's effect〕

 The present invention has the following effects.

(A) Use valuable citric acid, which was previously discarded as waste liquid
It can be recovered with an efficiency of 90% or more.

(B) The waste liquid containing citric acid as a main component can be continuously and reliably treated to a COD of 10 mg / l or less.

(C) Activated carbon is a highly economical treatment method that can be repeatedly used.

[Brief description of drawings]

1 and 2 are process drawings showing an example of the present invention, FIGS. 3 and 4 are graphs showing the relationship between the treated water COD and the citric acid adsorption amount, and FIG. It is a graph which shows the relationship between water flow rate and COD. 1 ... Waste liquid (treatment liquid), 2 ... Inorganic acid, 3 ... Activated carbon layer, 4 ... Alkaline aqueous solution, 5 ... Calcium agent, 6 ...
... Circulating water, 7 ... RO device, 8 ... Metering pump, 9 ... Alkaline agent

Claims (8)

[Claims] 1. When treating a waste liquid containing citric acid and its salt, the pH of the waste liquid is adjusted to 4 or less, and then the dissolved citric acid and its salt are subjected to adsorption treatment using activated carbon. Waste liquid treatment method. 2. The pH of the waste liquid according to claim 1, which is 2 to 3.
A method for treating waste liquid, which is characterized in that 3. The method for treating a waste liquid according to claim 1, wherein the pH of the waste liquid is adjusted with an inorganic acid selected from hydrochloric acid or sulfuric acid. 4. The method for treating a waste liquid according to claim 1, wherein the waste liquid after the adsorption treatment with activated carbon is then neutralized with an alkali. 5. The method for treating waste liquid according to claim 1, wherein the activated carbon after the adsorption treatment is regenerated by desorbing citric acid adsorbed by an alkaline aqueous solution. 6. The method for treating waste liquid according to claim 5, wherein the alkaline aqueous solution is an aqueous solution of a hydroxide selected from sodium hydroxide, potassium hydroxide or ammonium hydroxide. 7. The method for treating a waste liquid according to claim 5, wherein the regenerated alkaline aqueous solution recovers desorbed citric acid as calcium citrate by adding a calcium agent. 8. The method for treating waste liquid according to claim 5, wherein the alkaline aqueous solution after the regeneration treatment is treated using a reverse osmosis membrane.