KR20020023270A - Removal method of color and COD on dyeing wastewater - Google Patents

Abstract

PURPOSE: Provided is a method for eliminating colors and COD from dyeing wastewater by decolorization and coagulation using the complex of magnesium salts and iron salts. Also polymer is used as coagulant aids for solid-liquid separation. The method can decolorize efficiently without a decolorant and save initial costs for equipment. CONSTITUTION: The method to remove colors and COD proceeds to injecting dyeing wastewater with coagulants composed of magnesium salts and iron salts with the weight ratio of 1:1 and reacting the complex at pH 10-11 and settling solids. Magnesium salts and iron salts are used individually of magnesium chloride and iron chloride(II). The method can reduce from 2500 to 100 of color(96% of removal rate) and from 540 ppm to 250 ppm of COD(54% of removal rate).

Description

Removal method of color and COD on dyeing wastewater

The present invention relates to contaminants in wastewater, and in particular, to process colorants and organic pollutants (COD) in dyeing wastewater generated at a dyeing plant economically by chemical input. Is about

Synthetic dyes are widely used in fields related to electronic devices, such as textiles, paper, stationery cosmetics, foods, and recently, pigments for liquid crystal color films. At present, domestic dye production is about 70,000 tons per year, accounting for about 10% of the world production, and only 1 million tons of primary wastewater discharged during the production process is estimated.

Of these dyes, azo dyes account for the largest proportion, accounting for more than 50% of the total dyes. In recent years, in addition to removing the color of wastewater, each company involved in the dyeing industry has made great efforts to recycle and reuse wastewater after various treatments through wastewater treatment technology.

As a result of changes in the awareness of environmental conservation, strengthening environmental regulations, and voluntary participation of companies, the treatment status of dyeing wastewater has improved significantly compared to the past, but the amount of wastewater discharged, the limitation of existing treatment facilities, and the small size of dyeing wastewater companies. Due to this, the wastewater treatment problem of the Korea Dyeing Corporation is still a serious situation. In terms of wastewater generation and wastewater characteristics, the dyeing industry-related companies, which are classified as Korea's representative polluting industries, account for about 6% of the total wastewater dischargers and about 4.5% of the wastewater discharges. As it accounts for about 24% of the country, the impact on public waters is very large.

In addition, due to the strengthening of emission standards, in addition to satisfying the water quality standards, the removal of color of wastewater, which is the biggest problem of dyeing wastewater, has attracted great attention recently.

At present, the treatment of dye wastewater consists mainly of the first flocculation process and the second activated sludge process. However, organic contaminants can be removed to some extent by the coagulant currently used, but dyes strongly ionized in water, such as acid dyes or reactive dyes, do not aggregate and are almost impossible to discolor. In addition, the addition of excessive coagulant for decolorization has a great effect on the secondary activated sludge process, which is the main cause of bulking of activated sludge, and also causes high chromaticity due to oxidation of unreacted flocculant. Therefore, in order to remove the chromaticity, the situation is using a bleaching agent again. These organic bleaching agents are very expensive products, and there is a waste stage which increases the cost of wastewater treatment. Other methods using adsorption include activated carbon adsorption and the ability to remove chromaticity and residual COD is good, but it is a method that many companies avoid because of the trouble and cost of periodically replacing activated carbon.

Therefore, the object of the present invention was to develop the results of intensive research to solve the above drawbacks, in order to treat the dye that is strongly ionized in the dye wastewater and not removed by the existing inorganic flocculant, first contains a magnesium ion-containing material and iron salt It is to remove the chromaticity and COD excellently by incorporating the prepared material after mixing to cause aggregation.

The existing method of using ferric polysulfate has a pH of about 11 inflow dyeing wastewater, and the sulfuric acid is excessively used by lowering it back to pH 4 or lower for aggregation, but the aggregation ability of magnesium salt and iron salt of this method is mainly alkali. It is possible to maintain optimal pH naturally while reducing the use of sulfuric acid. In addition, the two coagulants having the above cohesive capacity complement each other to cause coagulation, thereby decolorizing and removing COD.

Therefore, the present invention is intended to achieve the reduction of the initial installation cost of wastewater treatment facilities, reduction of site area, convenience of on-site management, prevention of excessive coagulant use, etc. while simultaneously discoloring dyeing wastewater and removing COD.

1 is a process chart of dyeing wastewater using the present invention

Figure 2 is a diagram showing the optimal dose affecting the COD and chromaticity removal rate of the dyeing wastewater according to the present invention.

3 is a diagram showing the effect of the initial pH affecting the COD and chromaticity removal rate of the dyeing wastewater according to the present invention.

4 is a diagram showing the effect of the properties of the dyeing wastewater according to the present invention on the COD and chromaticity removal rate.

The present invention for achieving the technical problem as described above relates to a method for removing the color and COD by using a compound of magnesium salt and iron salt as a flocculant and a bleaching agent in a dyeing wastewater containing a color and high COD-induced dye The invention is economical and efficient.

Dyeing wastewater flowing into the raw water tank undergoes the first chemical treatment step and biological treatment in two steps.

The present invention relates to a first chemical treatment step to adjust the pH to 10 to 11 by adding a neutralizing agent to the amount of wastewater flowing in the dyeing wastewater introduced into the sump tank in the first chemical coagulation reaction tank.

Caustic soda or sulfuric acid is used as the neutralizing agent. In general, the pH of the dyeing waste water is about 11 so it is not necessary to adjust the pH separately. When the pH adjustment by the addition of the neutralization tank is completed, the compound mixed with magnesium salt and iron salt is added.

The compound in which the magnesium salt and the iron salt are mixed serves as a coagulation oxidant. In other words, magnesium salts and iron salts having a polyvalent cation lower the zeta potential of the colloid surface charged with anions in the waste water, causing aggregation, and causing the chemical reaction to agglomerate after oxidative decomposition.

When the solution is stirred with the dyeing waste water for several minutes and then the stirring is stopped, aggregation occurs and precipitation occurs, and in general, the immersion and dehydration rate is high, but a polymer material may be used as a precipitation aid to increase the rate.

In order to measure the treatment efficiency of the actual wastewater according to the present invention, the actual synthetic dye wastewater discharged from the industrial site was used. Samples such as chemical oxygen demand (COD) and chromaticity were measured according to the pollution process test method currently in Korea.

Hereinafter, the processing method of the present invention will be described by the process sequence.

① All experiments use a jar tester with six pedals, taking 500 mL of the same synthetic dye wastewater in a 1 L beaker.

② First, adjust the pH of the wastewater between 10 and 11. The pH of the dyeing wastewater is strongly alkaline (pH10.5-11) and needs little control.

③ After adjusting the pH, add a chemical coagulant mixed with magnesium salt and iron salt, and then stir for several minutes.

④ If it stops after stirring for a few minutes, agglomeration occurs and precipitates.

⑤ After that, settle completely for 20 minutes and use the supernatant as an analysis sample.

⑥ In general, the settling speed is high, but in order to increase the settling speed, the polymer coagulant is injected to perform slow stirring for several minutes.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and embodiments.

Example 1 Investigation of Optimal Dose of Chemical Coagulant Mixed with Magnesium and Iron Salts

As an example of the wastewater treatment of the dyeing wastewater, the raw water of the dyeing wastewater of the test subject was 540 ppm COD of 2500 and pH of 10.5. By the above experimental method, pH was experimented as it is, without adjusting separately. The chemical coagulant mixed with magnesium salt and iron salt was first prepared by using magnesium chloride to produce an aqueous solution containing 4% magnesium salt, and then mixed with ferrous chloride in a volume ratio of 1: 1 to prepare a product. Therefore, the result of performing a jar-test without using any other chemicals other than the flocculant is shown in FIG. 2. The concentration of chemical flocculant mixed with magnesium salt and iron salt was adjusted to 3000, 4000, 5000, 6000, and 7000 mg / L in raw water collected from the integrated dye wastewater treatment plant. The flocculation efficiency at high concentration was very good than at low concentration. COD and color removal were increased when the initial dose of chemical coagulant mixed with magnesium salt and iron salt was increased to 3000, 4000, 5000, mg / L. However, the concentration of the chemical coagulant mixed with magnesium salt and iron salt was increased to over 6000 mg / L, but the removal rate of COD and color did not increase. Therefore, the optimum injection amount of the chemical coagulant mixed with magnesium salt and iron salt was 5000mg / L, and it was found that the optimal amount of injection contributes to the optimal COB and color removal and economics through chemical reduction. At the optimum dose of 5000 mg / L, the treated water was treated well with 250 ppm COD and 100 chromaticity. The COD removal rate was 54% and the chromaticity removal rate was 96%.

Comparative Example 1 Comparison with Existing Methods

Ferric polysulfate, which is currently used as a chemical coagulant for dyeing wastewater, was tested under the same conditions as in Example 1. The raw water of the dyeing wastewater was 540 ppm COD and 2500 and pH 10.5. Table 1 shows a comparison between the case where the chemical coagulant mixed with the magnesium salt and the iron salt of the present invention is injected, and the case where the ferric polysulfate is added. As shown in Table 1, the method of the present invention was found to be very excellent in terms of removal of chromaticity compared to the existing method. In addition, in the case of ferric polysulfate, the pH should be used below 4, so the sulfuric acid is excessively input, which may corrode the existing apparatus, and it is economically considerably lost. Therefore, in consideration of various aspects, it can be seen that the present invention is superior to the conventional method.

[Table 1] Comparison of treatment results of dyeing wastewater by the present invention and the existing method

[Example 2] Optimum pH investigation of chemical flocculant mixed with magnesium salt and iron salt

As an example of the wastewater treatment of the dyeing wastewater, the raw water of the dyeing wastewater of the test subject was 540 ppm COD of 2500 and pH of 10.5. It carried out in the same conditions as [Example 1] by the said experiment method. In order to investigate the optimum pH for using a chemical coagulant mixed with magnesium salts and iron salts, the coagulation experiment was performed by adjusting the coagulation pH conditions to 8.5, 9.5, 10.5, 11.5, and 12.5 step by step. As shown in the results, when the flocculation was performed under alkaline conditions of pH 9.5 or more, the flocculation treatment efficiency was excellent and the optimum pH condition was 10.5. In general, the wastewater discharged from the dyeing plant is similar to the optimum pH condition of the flocculant used in the present invention because the pH is strongly alkaline. Therefore, it can be an economical method for the treatment of dyeing wastewater because aggregation is possible without a separate pH adjustment agent.

Example 3 Treatment According to Dyeing Wastewater Properties

The wastewater discharged from the dyeing plant varies greatly depending on the dye mix of the day. Therefore, the dyeing wastewater discharged daily was collected for 1 month and tested under the same conditions as in Example 1. The chromaticity of the dyeing wastewater was found to be a very severe wastewater change from 2000 to 4500, and the results of the experiment with the present invention are as shown in FIG. Treatment with the present invention showed a very good treatment efficiency of about 85 to 200.

As described above, in the chemical coagulation step, a technique capable of efficiently treating dyeing wastewater containing various dyes which are hardly decomposable substances by using a chemical coagulant mixed with magnesium salt and iron salt according to the present invention has been established. It is well worth it in a very efficient way compared to conventional processes. In addition, the conventional method may cause corrosion of the device due to the addition of excessive sulfuric acid, and there is a considerable economic loss due to the addition of a bleaching agent to treat untreated color. Therefore, in the process of discoloring the dyeing wastewater and removing the COD at the same time, it is possible to reduce the initial installation cost of the wastewater, convenience of field management, excellent treatment effect, and economic benefits.

Claims (2)

A mixed compound containing magnesium salt and iron salt in a dyeing wastewater in a weight ratio of 1: 1 is added as a flocculant and reacted in a pH range of 10-11 to precipitate solids, thereby simultaneously removing color and COD. Dyeing Wastewater Treatment Method The method of treating dyeing wastewater according to claim 1, wherein ferrous chloride is used as a material containing iron salt, and magnesium chloride is used as a material containing magnesium salt.