JPS58166982A - Treatment of waste water containing sodium terephthalate - Google Patents

Abstract

PURPOSE:To accelerate the settling of formed precipitates and to make the sepn. and dehyration of the precipitates easy by adding chlorides or nitrates of alkaline earth metals to waste water contg. sodium terephthalate, under alkaline or neutral conditions. CONSTITUTION:Waste water contg. sodium terephthalate is put into a neutralzing reaction vessel, and a hydrochloric acid is added thereto to neutralize the water. A soln. of calcium chloride is added to the water to allow the water to react, thereby forming the precipitate of calcium terephthalate. The precipitate is transferred into a settling tank, where the calcium terephthalate is settled, and supernatant liquid is released. The liquid contg. precipitate in the lower layer is transferred into a dehydrator, by which the liquid containing the precipitates is separated to solids and filtrate. The filtrate is released. Hydrochloric acid, sulfuric acid, nitric acid or mixed acid thereof are usable for the acid to be used for the mertralization. There are calcium chloride, calcium nitrate, barium chloride, etc. for the chlorides or nitrates of alkaline earth metals.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wastewater treatment method for separating terephthalic acid from wastewater during alkaline weight reduction processing of polyester fiber knitted fabrics and significantly reducing the high B-OD of the wastewater. In order to improve the feel of polyester fiber knitted fabrics, treatment with a sodium hydroxide solution is carried out to reduce the weight of polyester fiber knitted fabrics by about 20%.
This is called alkali weight loss processing.

Alkaline weight loss processing wastewater contains an extremely large amount of terephthalic acid produced by the decomposition of polyester, and the BOD of the wastewater often reaches approximately to, ooppm, which corresponds to approximately 6°700ppm as TOC. death,
Moreover, since it is strongly alkaline with a pH of about 13.5, wastewater cannot be discharged as is.

Treatment methods for alkali reduction processing wastewater include neutralization followed by activated sludge treatment, and treatment methods such as acidifying with hydrochloric acid to precipitate terephthalic acid, removing it through filtration and dehydration, and then performing activated sludge treatment. is being carried out.

The former method has drawbacks such as an abnormally high BOD of wastewater, requiring a vast site for installing an aeration tank and a huge amount of equipment costs, and requiring technology to manage microorganisms.

The latter is a treatment method shown in the flowchart of FIG. 1, and the reaction formula is as follows.

c6H4(COONa)2+NaOH+3Hc1→c6
H4(cOoH)2+ aNaCl 10H20 Put the alkali weight loss processing wastewater into a reaction tank, and add hydrochloric acid to it.
) When added until reaching I4, sodium terephthalate decomposes and liberates as terephthalic acid. This is transferred to a settling tank for precipitation, and the 1-U layer of clear liquid is transferred to a neutralization tank.

The lower sediment mixture is separated into a terephthalic acid solution and a terephthalic acid solution using a filter, and the filtrate is transferred to a neutralization tank.

In the neutralization tank, sodium hydroxide solution is added to neutralize the wastewater, which is then diluted and discharged, or further treated using an activated sludge method. This acid precipitation method requires a large amount of hydrochloric acid to make the wastewater strongly acidic with a pH of 4, and sodium hydroxide to neutralize the acid precipitation separated wastewater, and the cost of these chemicals is high. In addition, there are major drawbacks such as severe damage to reaction tanks, settling tanks, filters, etc. due to hydrochloric acid.

As will be described in detail later, the present invention is a method in which a chloride or nitrate of an alkaline earth metal is added to wastewater from an alkaline weight reduction process, and terephthalic acid is precipitated and separated as an alkaline earth metal terephthalate. Regarding alkaline earth metal compounds, several methods for using them in wastewater treatment are known, but these are different from the method of the present invention in object, purpose, action, and effect.

For example, as a flocculant to remove phosphorus from wastewater.
Aluminum sulfate, ferric sulfate, slaked lime, etc. are used, and the reaction when slaked lime is used is as shown in the following equation.

3HPO knee +5Ca' +40H--Ca5(OH)
(PO4)3+ 3H20, that is, phosphoric acid, is precipitated and separated as poorly soluble calcium hydroxyphosphate, and the separation effect is significantly affected by pH, and in actual sewage, the minimum concentration is reached at pH 10.5 to 11. In this case, the purpose is to remove phosphorus and not to reduce BOD, and the type of wastewater, treatment agent, and chemical reaction are also different from the method of the present invention.

In addition, for wastewater containing hexavalent chromium from electroplating, sulfuric acid is added to bring the pH to 3 or less, hydrogen sulfite is used as a reducing agent) IJ chromium is added to make trivalent chromium, and then sodium hydroxide is added to bring the pH to 7. 0 to 7.5,
There is a method of separating chromium as a precipitate of chromium hydroxide.

In order to improve the precipitation state during this neutralization, calcium chloride is added, but this causes the reaction between sodium hydroxide and calcium chloride to produce poorly soluble calcium hydroxide. This is because sulfate ions and calcium chloride in wastewater react to produce insoluble calcium sulfate, and these fine particles serve as nuclei to co-precipitate chromium hydroxide.

In this case, the purpose is not to reduce BOD, but to
The purpose of the present invention is to remove valent chromium, and the effect of calcium chloride is to generate nuclei and coprecipitate chromium hydroxide. Therefore, the use of alkaline earth metal salts in the present invention is completely different from the use of alkaline earth metal salts in the present invention. differ.

As described above, the present invention can easily and sufficiently remove terephthalic acid from waste liquid containing sodium terephthalate,
The purpose is to treat wastewater without causing damage to machinery or equipment.

That is, the present invention provides alkaline earth metal terephthalate by adding alkaline earth metal chloride or nitrate to alkaline wastewater containing sodium terephthalate or after adding an acid to the alkaline wastewater to make it neutral. This is a wastewater treatment method that generates a precipitate and separates it.

A flowchart of an example of implementing the present invention is shown in FIG. Put the alkali weight loss processing wastewater into a neutralization reaction tank and neutralize it by adding hydrochloric acid. A solution of calcium chloride is added to this and reacted to form a precipitate of calcium terephthalate. The chemical reaction at this time is as shown in the following equation.

C6H4(COONa)2+CaCl2→C6H4(C
OO)2Ca+2NaC1 Next, this product is transferred to a settling tank to precipitate calcium terephthalate, and the supernatant liquid is discharged. The lower layer of the sediment-containing liquid is transferred to a dehydrator to separate solids and filtrate, and the filtrate is discharged.

Another embodiment includes adding calcium chloride to the alkaline reduction processing wastewater without neutralizing it, separating the calcium terephthalate, and then transferring the supernatant and the filtrate to a neutralization tank;
This method involves adding hydrochloric acid to neutralize it and then discharging it.

As the acid used for neutralization, hydrochloric acid, sulfuric acid, nitric acid, or a mixed acid thereof is used, but nitric acid is not only expensive but also undesirable because the nitrogen content of the effluent water becomes high.

Chlorides or nitrates of alkaline earth metals include calcium chloride, calcium nitrate, barium chloride, barium nitrate, strontium chloride, and strontium nitrate.
These may be used alone or in combination of two or more in the form of powder or solution. However, the most economical and effective one is calcium chloride; the others are generally expensive and, as described below, have insufficient TOC removal rates.

The volume of the precipitate in the precipitation tank is extremely small compared to the bulky precipitate of terephthalic acid in the conventional acid precipitation method.
As will be described later, the precipitation rate is less than 10% of that of the acid precipitation method, and the precipitation rate is extremely fast.

Therefore, the amount of liquid passed through a dehydrating device such as a filter is very small, and dehydration is easy.

If the precipitate is generated in alkaline conditions without performing the above-mentioned neutralization treatment, the precipitate is quite bulky and the efficiency of sedimentation and dehydration is poor, so it cannot be said to be a good solution.

In the treated water treated by the method of the present invention, in addition to some sodium terephthalate, there is still 1,000 pl of TOC derived from organic substances such as ethylene glycol and activators)
Since there are about 1,000 ml of sludge, it must be diluted before being discharged, or it must be treated with a small-scale activated sludge treatment device before being discharged.

According to the method of the present invention, there are the following remarkable effects.

(1) Unlike the conventional acid precipitation method, the amount of acid required for pH adjustment is small and no alkali is required, so drug costs can be reduced by about 30%.

(2) Because the precipitate that is formed settles quickly and has little bulk,
It is very easy to separate the supernatant and dehydrate the precipitate.

(3) In order to carry out the treatment in neutral or alkaline conditions, a reaction tank,
There is very little damage to the sedimentation tank, dehydrator, etc.

(4) Effective wastewater treatment can be performed using relatively inexpensive equipment in a small area.

(5) The treated water can be diluted and discharged, or can be discharged by activated sludge treatment using small-scale equipment.

(6) Since dewatered sludge is not acidic, there is no risk of damaging the incinerator.

Next, various embodiments of the present invention will be described in comparison with conventional acid precipitation methods. Experiment Na 1 is the conventional acid precipitation method, Experiment N
α2 to Nα7 are obtained by the method of the present invention.

TOC was measured using a total organic carbon measuring device for the liquid obtained by filtering the treated water using Nα5 filter paper. Regarding the volume of sediment, the treated water is II! Binding, 60
The sedimentation volume when left standing for a minute is measured and displayed as 5V6o, but in this experiment, the treated water 100
The total amount of m/m was measured by the method described above.

Experiment Nα1 (Acid precipitation method) While stirring alkali reduction processing wastewater, 1:1 hydrochloric acid 5
．． 4 ml was added to adjust the pH to 4, and terephthalic acid was precipitated.

Real wkNα2 Add 1:1 hydrochloric acid 3 while stirring the alkali weight loss processing wastewater.
．． After adjusting the pH to 7 by adding 5 m/g, 1.25 g of calcium chloride powder was added and stirring was continued to form a precipitate of calcium terephthalate.

Experiment Nα3 2 g of calcium chloride powder was added to the alkali weight loss processing wastewater while stirring it to form a precipitate of calcium terephthalate.

Experiment Nα4 While stirring the alkaline reduction processing wastewater, add 1:1 hydrochloric acid 3
．． The pH was adjusted to 7 by adding 5 m/g of calcium terephthalate, and 2165 g of calcium nitrate powder was added thereto and stirring was continued to form a precipitate of calcium terephthalate.

Experiment Nα5 While stirring the alkali reduction processing wastewater, 4.25 g of calcium nitrate powder was added to form a precipitate of calcium terephthalate.

Experiment Nα6 While stirring the alkaline reduction processing wastewater, add 1:1 hydrochloric acid 3
．． 5 m/ was added to adjust the pH to 7, and 2.75 g of barium chloride powder was added thereto to form a precipitate of barium terephthalate.

Experiment Nα7 While stirring the alkali weight loss processing wastewater, 4.4 g of barium chloride powder was added to form a precipitate of terephthalic acid/(lium).

The above experimental results are shown in Table 1.

As shown in Table 1, the TOC removal rate of the method of the present invention using calcium chloride is 82% or more, which is equivalent to the acid precipitation method, and the removal rate of TOC using calcium nitrate and barium chloride is slightly lower. ing. However, there is a notable difference in the volume of the precipitate compared to the acid precipitation method.In the acid precipitation method, no sedimentation occurs after 60 minutes of standing, so the entire volume must be filtered to separate the acid precipitate. In the method of the present invention, the lowest amount is 5V6o3-8%, and the highest is 2896, which shows that it is sufficient to dehydrate a very small volume, and one of the remarkable effects of the method of the present invention is understood. Good morning.

In addition, the amount of chemicals used in the acid precipitation method of Experiment Nα1 and the method of the present invention in Experiment Nα2 (as shown in Table 2), in the case of the method of the present invention, the amount of hydrochloric acid is significantly smaller, and the expensive hydroxide method is It can be seen that l-IJum is also unnecessary.

[Brief explanation of drawings]

Figure 1 is a flowchart of the acid precipitation method, and Figure 2 is a flowchart of an example of implementing the present invention. Patent applicant: Kazuo Tsukabayashi

Claims (1)

[Claims] Terephthal, which is characterized in that alkaline earth metal chlorides or nitrates are added to wastewater containing sodium terephthalate in alkaline or neutral conditions to produce alkaline earth metal terephthalates, which are then separated. A method for treating wastewater containing sodium chloride.