TWI583634B - A method for reducing chemical oxygen demand of the waste water - Google Patents

Description

Method for reducing chemical oxygen demand in wastewater

The present invention relates to a method for treating wastewater, and more particularly to a method for reducing chemical oxygen demand in wastewater.

Epichlorohydrin (ECH) is commonly used in the manufacture of glycerin, plastics, elastomers and resins (eg, epoxy resins) and is an important chemical raw material. In general, epichlorohydrin can be obtained by three processes of high-temperature chlorination of propylene, chlorination of propylene chloride and chlorination of glycerol; in the process of chlorination of propylene alcohol, propylene chloride and chlorine are first chlorinated to obtain dichloroethylene. Dichloropropanol (DCH), and then alkalized the dichloropropanol with sodium hydroxide or calcium hydroxide (lime milk), and finally separated and purified to obtain epichlorohydrin. Regardless of the process used to produce the dichloropropanol, an alkalization reaction is required to obtain epichlorohydrin.

However, the amount of wastewater generated by the alkalization reaction is extremely large, and the chemical Oxygen Demand (COD) cannot be directly discharged. It must be treated with sewage to reduce the COD in the wastewater to below the standard value.

For the wastewater generated in the chemical process, the organic matter is mostly degraded by the activated sludge method. However, unlike general sewage treatment procedures, the alkalization waste Because of the high chloride salt nature of water, in order to avoid inhibiting the growth of microorganisms capable of digesting organic matter, a large amount of dilution water must be added, resulting in a significant increase in equipment and costs.

Therefore, how to effectively reduce COD in alkalized wastewater is an urgent issue for the industry.

In order to overcome the above disadvantages, the present invention provides a method for reducing chemical oxygen demand in wastewater, comprising: introducing 1 to 7 weights based on the total weight of the wastewater in a wastewater having a chemical oxygen demand (COD) of more than 3000 ppm. % chlorine gas to cause the wastewater to undergo chlorine oxidation; and to add alkali to the chlorine-containing wastewater.

The invention oxidizes and degrades the organic matter in the waste water through the chlorine gas in the waste water, the gas mixture is mixed and the chlorine gas has high oxidizing power, thereby effectively reducing the chemical oxygen demand in the waste water.

The method of the invention can reduce the COD in the wastewater by the control of chlorine gas and alkali, and can formulate the removal target according to the COD in the wastewater to be treated, and carry out the proportional degradation reaction according to the degree of degradation desired. The method of the invention has a wide operating range and can be operated under normal or low temperature (ie, below 100 ° C, such as 30 ° C to 100 ° C) environment, and finally the alkaline wastewater generated in the epichlorohydrin process can be used. COD fell to environmental standards.

The method of the present invention is not limited to, for example, a step of being subjected to degradation by a microorganism, is limited by the growth environment of the strain, and must be domesticated or diluted with water; and is different from the conventional chemical treatment method (such as the Fenton method). The catalyst can have a good removal effect and a wide operating range.

The embodiments of the present invention are described by way of specific examples, and those skilled in the art can readily understand the advantages and functions of the present invention from the disclosure. The present invention may be embodied or applied by other different embodiments, and the various details of the present invention may be variously modified and changed without departing from the spirit and scope of the invention.

As used herein, the term "chemical oxygen demand" means the equivalent amount of oxygen consumed to oxidize organic matter in wastewater.

In the present invention, the test methods for chemical oxygen demand and alkaline salts are as follows: chemical oxygen demand: firstly tested according to the inspection method announced by the Environmental Protection Agency (NIEA W407.51C chloride salt detection method - silver nitrate titration method) The chloride ion concentration of the water sample was used, whereby the alkaline wastewaters of Comparative Examples 1 to 2 and Examples 1 to 2 were diluted to a chloride ion concentration of less than 2,000 mg/L.

According to the NIEA W515.54A (Inorganic Chemical Oxygen Determination Method, Potassium Chromate Reflow Method), the amount of potassium dichromate solution is added to the water sample at about 50% sulfuric acid. The solution is refluxed, and the remaining potassium dichromate is titrated with ammonium ferrous sulfate solution. The amount of potassium dichromate consumed is used to obtain the chemical oxygen demand (COD) in the water sample. In the sample The amount of organic matter that can be oxidized.

Alkaline salts:

The calcium hydroxide concentration was determined according to the CNS1625 K7125 standard, and the calcium carbonate was measured by HCL and AgNO ₃ as a titration sample, and the concentration of calcium carbonate was measured by a titration method.

The method for reducing the chemical oxygen demand in the waste water comprises: introducing, in the waste water having a chemical oxygen demand of more than 3000 ppm, 1 to 7 wt% of chlorine gas based on the total weight of the waste water to cause the wastewater to undergo chlorine oxidation. Reaction; and adding a base to the chlorine-laden wastewater.

In the present invention, the chemical oxygen demand of the wastewater may be in the range of 3000 ppm, 9000 ppm, 10000 ppm, 20000 ppm, and any two concentrations. Further, in one aspect, the wastewater has a chemical oxygen demand of 3000 ppm to 20,000 ppm of wastewater. Specifically, the method of the present invention is applicable to the wastewater of different chemical oxygen demand mentioned above, that is, the wastewater may be subjected to a general sewage treatment process, subjected to pretreatment (for example, preliminary sedimentation separation or pH adjustment) or untreated. Waste water.

In one aspect of the invention, the wastewater is subjected to an epichlorohydrin process (eg, a saponification reaction (alkalinization reaction) of dichlorohydrin (wherein the dichlorohydrin includes, but is not limited to, Waste water produced by high-temperature propylene, propylene chloride chlorination and glycerol chlorination processes, which have high chemical oxygen demand and high chloride salt characteristics.

In one aspect of the invention, the wastewater is pretreated wastewater, for example, the wastewater is subjected to preliminary sedimentation separation, pH adjustment, and dilution. For example, the wastewater that has undergone preliminary sedimentation separation, pH adjustment, and dilution The COD value is from 3000 ppm to 9000 ppm, and the acidity and alkalinity is weak base, neutral or weakly acidic. For example, the pH of the wastewater after preliminary sedimentation separation, pH adjustment and dilution is 6 to 7.

In one aspect of the invention, the wastewater is an alkaline wastewater produced in a saponification reaction of an epichlorohydrin process. For example, the saponification reaction is an alkalization reaction of dichloropropanol, and the pH of the alkaline wastewater produced by the saponification reaction is usually greater than 10, for example, a pH of 10 to 13.

In the above aspect, the wastewater is alkaline wastewater, which contains dichloropropanol, a chlorine salt, and a base remaining in the alkalization reaction, and has a high chemical oxygen demand; wherein, the waste liquid The chemical oxygen demand is greater than 3000 ppm. In addition, the alkaline wastewater contains glycerin. In the foregoing aspect, the residual base includes calcium hydroxide or calcium carbonate, and the residual alkali content is from 1 to 3% by weight based on the total weight of the wastewater.

In one aspect, the glycerin is present in an amount of from 0.5 to 0.8% by weight based on the total weight of the alkaline wastewater, and the dichlorohydrin is present in an amount of from 0.02 to 0.06% by weight.

In one aspect of the invention, the chlorine gas is passed into the wastewater at a flow rate of from 1 to 7% by weight per hour based on the total weight of the wastewater. For example, the chlorine gas is introduced into the wastewater at a flow rate of 19 kilograms per hour. In the foregoing aspect, the purity of the chlorine gas is greater than 99%.

In one aspect of the invention, the chlorine oxidation reaction is carried out for 1 to 2 hours.

In one aspect of the present invention, the step of adding a base to the chlorine-containing wastewater is to add a base in a solid or liquid form to the chlorine-containing wastewater, for example, dissolving the alkali in water to a liquid state. Form added to the chlorine In the waste water of gas. In this aspect, the base is added in an amount of 5 to 10% by weight based on the total weight of the wastewater. Further, the base is a metal hydroxide such as an alkali metal hydroxide or an alkaline earth metal hydroxide, more specifically sodium hydroxide or calcium hydroxide.

In one aspect of the invention, the alkali is simultaneously added to the chlorine-laden wastewater during the passage of the chlorine gas to maintain the pH of the chlorine-laden wastewater to 4 to 10.

In the foregoing aspect, the treated wastewater has a COD reduction rate of greater than 94%, and more preferably the removal rate is 99%. In the preferred embodiment, the treated wastewater has a COD of less than 100 ppm.

In one aspect of the method for reducing chemical oxygen demand in wastewater according to the present invention, the dechlorination reaction is carried out after the chlorine oxidation reaction is carried out. In the present embodiment, the dechlorination reaction is carried out by adding a dechlorination agent to the wastewater subjected to the chlorine oxidation reaction. For example, the dechlorination agent is hydrogen peroxide, sodium sulfite, sulfur dioxide, sodium thiosulfate or activated carbon.

In another aspect of the method for reducing chemical oxygen demand in wastewater according to the present invention, the wastewater is subjected to sedimentation separation treatment before the chlorine gas is introduced, and the pH of the wastewater is adjusted to 6 to 7.

In the following, in the epichlorohydrin process, the alkaline wastewater generated in the saponification step of dichloropropanol is taken as an example. In the exemplary embodiment of the present case described later, in each of the examples, the COD of the alkaline wastewater is used. The contents of calcium hydroxide and calcium carbonate are described in each of the examples.

Comparative example 1

In Comparative Example 1, the pH of the alkaline wastewater to be treated was 11.57. The COD was 13,391 ppm, and the alkaline wastewater contained 0.94% by weight of calcium hydroxide and 1.22% by weight of calcium carbonate.

The alkaline waste water is introduced into a 500-liter reaction tank having a circulating absorption stirrer, and chlorine gas (purity of 99% or more, manufactured by Yifang Chemical Industry Co., Ltd.) is introduced at a flow rate of 7.9 kg per hour, and the alkalinity is introduced. The chlorine content in the wastewater was 31,600 ppm. After standing for 2 hours at 75 ± 5 ° C, the pH, COD, calcium hydroxide and calcium carbonate in the water were measured and recorded in Table 1.

Comparative example 2

In Comparative Example 2, the pH of the alkaline wastewater to be treated was 11.63, and the COD was 12,500 ppm, and the alkaline wastewater contained 0.16% by weight of calcium hydroxide and 1.75% by weight of calcium carbonate.

The alkaline waste water is introduced into a 500-liter reaction tank having a circulating absorption stirrer, and chlorine gas (purity of 99% or more, manufactured by Yifang Chemical Industry Co., Ltd.) is introduced at a flow rate of 3.8 kg per hour, and the alkalinity is introduced. The chlorine content of the wastewater was 15,200 ppm. After standing for 2 hours at 75 ± 5 °C, the pH, COD, calcium hydroxide and calcium carbonate in the water were measured and recorded in Table 1.

* ND indicates that the content of calcium hydroxide and calcium carbonate is below the quantitative limit value, so that no calcium hydroxide or calcium carbonate is detected.

In Comparative Examples 1 and 2, the pH of the treated alkaline wastewater was changed to 4.26 and 3.29, respectively.

Although calcium hydroxide and calcium carbonate were not detected in the alkaline wastewater treatment by the methods of Comparative Examples 1 and 2, the removal rate of the alkaline salt was 100%, and the COD in the treated alkaline wastewater was still 8,318 ppm. With 9,843 ppm, the COD removal rate is only 38% and 21%.

Example 1 Method for reducing chemical oxygen demand in wastewater by the present invention

In the present embodiment, the pH of the alkaline wastewater to be treated is 11.34, and the COD is 11,632 ppm, and the alkaline wastewater contains 0.86% by weight of calcium hydroxide and 1.03% by weight of calcium carbonate. In addition, by high performance liquid chromatography (HPLC) analysis, the content of glycerin in the untreated alkaline wastewater accounts for 0.519% by weight of the alkaline wastewater and the content of dichloropropanol is 0.0436. weight%.

The alkaline waste water was introduced into a 500-liter reaction tank having a circulation absorption stirrer, and chlorine gas (purity of 99% or more, manufactured by Yifang Chemical Industry Co., Ltd.) was introduced at a flow rate of 19 kg per hour to 80 per hour. The flow rate of kilograms is passed through sodium hydroxide (concentration: 32% by weight, manufactured by Yifang Chemical Industry Co., Ltd.), and the chlorine gas introduced into the alkaline wastewater accounts for 6.3% by weight of the total weight of the alkaline waste water. And the hydrogen and oxygen in the alkaline wastewater Sodium sulphate accounts for 8.5% by weight of the total weight of the alkaline wastewater. After being retained at 95±5°C for 1.6 hours, the pH, COD, calcium hydroxide and calcium carbonate in the water are measured and recorded in the table. 2.

Example 2 Method for reducing chemical oxygen demand in wastewater by the present invention

In the present embodiment, the pH of the alkaline wastewater to be treated is 11.29, and the COD is 11,862 ppm, and the alkaline wastewater contains 0.63% of calcium hydroxide and 1.69% of calcium carbonate. In addition, by high performance liquid chromatography (HPLC) analysis, the content of glycerin in the untreated alkaline wastewater accounts for 0.510% by weight of the alkaline wastewater and the content of dichloropropanol is 0.0431. weight%.

The alkaline waste water was introduced into a 500-liter reaction tank having a circulation absorption stirrer, and chlorine gas (purity of 99% or more, manufactured by Yifang Chemical Industry Co., Ltd.) was introduced at a flow rate of 19 kg per hour to 60 per hour. The flow rate of kilograms is passed through sodium hydroxide (concentration: 32%, manufactured by Yifang Chemical Industry Co., Ltd.), and the chlorine gas introduced into the alkaline wastewater accounts for 3.8% by weight of the total weight of the alkaline wastewater, and is introduced. The sodium hydroxide in the alkaline wastewater accounts for 4% by weight of the total weight of the alkaline waste water, and after being retained for 1 hour at 95±5 ° C, the pH value, COD, calcium hydroxide and calcium carbonate in the water are measured. The content is shown in Table 2.

Example 3 Method for reducing chemical oxygen demand in wastewater by the present invention

In the present embodiment, the preliminary waste separation, pH adjustment, and dilution of the wastewater are taken as an example, and the alkaline waste liquid produced by the saponification reaction (alkalinization reaction) of dichloropropanol is pretreated (for example, Preliminary sedimentation separation, pH adjustment and dilution), the pH of the pretreated wastewater is 6.59, and the COD is 3,285 ppm, and calcium hydroxide and calcium carbonate were not detected in the wastewater (that is, the content of the calcium hydroxide and calcium carbonate was less than the detection limit, and both were about 0.0% by weight).

The wastewater was introduced into a 500-liter reaction tank equipped with a circulating absorption stirrer, and chlorine gas (purity of 99% or more, manufactured by Yifang Chemical Industry Co., Ltd.) was introduced at a flow rate of 4.8 kg per hour to 57 kg per hour. The flow rate is passed through sodium hydroxide (concentration: 10%, manufactured by Yifang Chemical Industry Co., Ltd.), and the chlorine gas introduced into the wastewater accounts for 1.9% by weight of the total weight of the wastewater, and the hydroxide is introduced into the wastewater. Sodium accounted for 2.3% by weight of the total weight of the wastewater. After being retained for 2 hours at 75 ± 5 ° C, the pH, COD, calcium hydroxide and calcium carbonate contents in the water were measured and recorded in Table 2.

Example 4 Method for reducing chemical oxygen demand in wastewater by the present invention

In the present embodiment, the wastewater after preliminary sedimentation separation, pH adjustment, and dilution is taken as an example. The pH of the pretreated wastewater is 6.82, and the COD is 3,491 ppm, and no hydroxide is detected in the wastewater. Calcium and calcium carbonate (i.e., the content of calcium hydroxide and calcium carbonate is less than the detection limit, both being about 0.0% by weight).

The wastewater was introduced into a 500-liter reaction tank equipped with a circulating absorption stirrer, and chlorine gas (purity of 99% or more, manufactured by Yifang Chemical Industry Co., Ltd.) was introduced at a flow rate of 4.8 kg per hour to 75 kg per hour. The flow rate is passed through sodium hydroxide (concentration: 10%, manufactured by Yifang Chemical Industry Co., Ltd.), and the chlorine gas introduced into the wastewater accounts for 1.9% by weight of the total weight of the alkaline wastewater, and is introduced into the wastewater. Sodium hydroxide accounts for 3.0% by weight of the total weight of the alkaline wastewater. After being retained for 2 hours at 75±5°C, the pH, COD, calcium hydroxide and calcium carbonate in the water are measured and recorded in Table 2.

As can be seen from Table 2, in Examples 1, 2, 3 and 4, the pH of the treated alkaline wastewater was changed to 5.01, 4.9, 5.9 and 5.09, respectively, and the COD of the treated alkaline wastewater was 100 ppm and 339 ppm, respectively. 164ppm and 46ppm, COD removal rate of 99%, 97%, 94% and 98%, and no calcium hydroxide and calcium carbonate were detected in the treated wastewater, and the removal rate of alkaline salts was 100%. .

Moreover, it can be seen from Examples 3 and 4 that even in the case where the wastewater is neutral or acidic (both calcium hydroxide and calcium carbonate are not detected), the method of the present invention has a removal rate of 94% or more.

In addition, from the results of Examples 3 and 4, it can be found that the method used in the present invention still has a good removal rate when the COD is relatively low, and it can be seen that the method of the present invention can continuously degrade organic matter without removing COD due to COD drop. The rate tends to be flat, that is, there is no removal limit of conventional degradation, and the ratio is equal. By way of example, the COD in the wastewater is reduced, and the removal target can be prepared according to the COD in the wastewater to be treated, and the proportional degradation reaction is carried out according to the degree of degradation desired.

Further, by HPLC analysis, after treatment by the method of the present invention, the content of glycerin and dichloropropanol is significantly reduced, for example, the content of glycerin and dichloropropanol in the alkaline wastewater is 0.00% and 0.00%, respectively. Therefore, the method of the invention can effectively reduce the COD in the wastewater and achieve the purpose of degradation of the organic matter.

Example 5 Method for reducing chemical oxygen demand in wastewater

In one aspect of the method for reducing chemical oxygen demand in wastewater according to the present invention, the chlorine dioxide oxidation reaction is subjected to a dechlorination reaction after the chlorine oxidation reaction.

In the present embodiment, the wastewater treated by the method of Example 1 is used as a sample, and is detected by a potassium iodide KI titration method, and the residual chlorine molecules are left in the wastewater subjected to the chlorine oxidation reaction in Example 1. The concentration was 0.033% by weight.

Next, when the dechlorination reaction was carried out, hydrogen peroxide was added to the wastewater subjected to the chlorine oxidation reaction in Example 1 so that the molar ratio of the free chlorine molecule to hydrogen peroxide was 1:1. After dechlorination treatment, the residual concentration of free chlorine molecules in the wastewater is 0.00% by weight, so that the problem of free chlorine odor can be solved.

In summary, the method for reducing the chemical oxygen demand in the wastewater by using the present invention can reduce the COD in the alkaline wastewater by introducing chlorine gas into the wastewater and oxidizing the organic matter in the alkaline wastewater. It does not need to use microorganisms that are difficult to control for degradation, and does not need to dilute the alkaline wastewater to be treated, which can effectively save pollution. Water treatment costs.

Furthermore, the wastewater treated by the method of the present invention can have a COD removal rate of 94% or more, 97% or more, or 98% or more, and can achieve a removal rate of 99%, which is lower than 100 ppm of the environmental standard. .

In addition, the problem of odor caused by the free chlorine molecules in the wastewater treated by the present invention is considered, and the dechlorination reaction of the chlorine-oxidized wastewater can be further removed to reduce the environmental impact.

In addition, the method of the invention has good removal effect on the alkaline waste liquid generated in the epichlorohydrin process, and can effectively reduce COD and excess in the alkaline wastewater generated by the saponification reaction step in the epichlorohydrin process. Alkaline salts.

The above embodiments are intended to illustrate the principles of the invention and its effects, and are not intended to limit the invention. Any of the above-described embodiments may be modified by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be as set forth in the appended claims.

Claims (10)

The invention relates to a method for reducing chemical oxygen demand in waste water, which comprises: introducing 1 to 7 wt% of chlorine gas in a waste water having a chemical oxygen demand (COD) of more than 3000 ppm in neutral or alkaline. The chlorine gas is introduced into the wastewater at a flow rate of 1 to 7% by weight per hour to cause the wastewater to undergo a chlorine oxidation reaction; and a base is added to the chlorine-containing wastewater to obtain a wastewater subjected to chlorine oxidation reaction. The base is added in an amount of from 2.3 to 10% by weight based on the total weight of the wastewater. The method of claim 1, wherein the wastewater is alkaline wastewater produced in a saponification reaction of an epichlorohydrin process. The method of claim 2, wherein the saponification reaction is a dichloropropanol alkalization reaction. The method of claim 2, wherein the alkaline wastewater contains glycerin and dichlorohydrin. The method of claim 1, wherein the base is added in an amount of 5 to 10% by weight based on the total weight of the wastewater. The method of claim 5, wherein the base is an alkali gold or alkaline earth metal hydroxide. The method of claim 5, wherein the base is added to the chlorine-laden wastewater in a solid or liquid form. The method of claim 1, wherein the chlorine oxidation reaction is carried out for 1 to 2 hours. For example, the method of claim 1 is included in the chlorine oxidation After the reaction, the chlorine-oxidized wastewater is subjected to a dechlorination reaction. For example, in the method of claim 1, the wastewater is subjected to sedimentation separation treatment before the chlorine gas is introduced, and the pH of the wastewater is adjusted to 6 to 7.