Method for treating chlorine-containing wastewater

Abstract

The invention relates to the technical field of wastewater treatment, and discloses a method for treating chlorine-containing wastewater, which comprises the steps of pretreatment, acidification, reductive dechlorination reaction, pH value regulation and recycling, and comprises the following steps: firstly adding hydrochloric acid into the chlorine-containing wastewater for acidification, then adding sodium thiosulfate for reduction, collecting chlorine released from the wastewater, and recycling the chlorine-containing wastewater. The residual chlorine can be prevented from volatilizing to an operation environment, so that the odor can be removed, the air quality of a workshop can be improved, and occupational health and safety standards are met; after reductive dechlorination treatment, the content of residual chlorine in the wastewater is reduced, and when the wastewater is fed into an MVR evaporation system, corrosion to metal equipment can be greatly reduced, the service life of the equipment is prolonged, the frequency of maintenance and shutdown is reduced, the maintenance cost is reduced, and the production continuity is guaranteed; meanwhile, the treated reclaimed water can reach the standard and be recycled to reduce the consumption of fresh water resources, and the captured chlorine can be reused for chlorination reaction, so that waste recycling is realized, and the concept of environmental protection and sustainable development is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a method for treating wastewater containing chlorine. BACKGROUND

[0002] With the rapid development of industry, the problem of discharge of wastewater containing chlorine is becoming increasingly serious, which has become one of the key factors restricting the sustainable development of the environment. Wastewater containing chlorine is widely sourced from multiple industries such as chemical industry, pharmaceutical industry, printing and dyeing industry, and electronics industry. The chloride ions in the wastewater not only have strong corrosive properties, but also can accelerate the damage of metal equipment and concrete structures, increasing maintenance costs and safety hazards. If the wastewater is directly discharged into water bodies without effective treatment, it will change the salinity and osmotic pressure of the water body, causing serious threats to the living environment of aquatic organisms, inhibiting the growth and metabolism of microorganisms, and further affecting the balance of the entire ecological system.

[0003] Currently, the industry generally uses MVR (mechanical vapor recompression) evaporation systems to treat wastewater containing chlorine. Although this technology can achieve the concentration and reduction of wastewater, it has two major defects that are difficult to avoid in actual application.

[0004] 1. The residual chlorine in wastewater containing chlorine has a strong irritating odor. The residual chlorine will volatilize into the operating environment with steam, leading to deterioration of the air quality in the workshop. Long-term exposure can cause damage to the respiratory tract and skin mucosa of the operators, causing air pollution in the operating environment, which does not meet the occupational health and safety standards.

[0005] 2. Wastewater containing chlorine can cause serious corrosion of metal equipment in the MVR evaporation system, especially in a high-temperature and high-humidity operating environment, the corrosion rate will further increase, shortening the service life of the equipment. Each maintenance requires several days of downtime, which not only increases the maintenance cost, but also affects the production continuity, causing economic losses.

[0006] In view of the above problems, the present application is proposed after in-depth research. SUMMARY

[0007] The present application aims to provide a method for treating wastewater containing chlorine to solve the problems of air pollution in the operating environment and serious equipment corrosion existing in the existing wastewater treatment.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical solution: a method for treating wastewater containing chlorine, comprising the following steps:

[0009] Step 1, pretreatment: introducing wastewater containing chlorine into a reaction tank, starting the stirring device for stirring, and controlling the temperature of the wastewater containing chlorine.

[0010] Step 2, acidification: adding hydrochloric acid solution to the temperature-adjusted wastewater containing chlorine, and performing acidification reaction during stirring to reduce the pH value.

[0011] Step three, reduction dechlorination reaction: add sodium thiosulfate solution to the acidified chlorine-containing wastewater, stir the reaction to reduce the residual chlorine and release chlorine gas;

[0012] Step four, pH value adjustment: add caustic soda to the chlorine-containing wastewater after reaction, stir to adjust the pH value of the chlorine-containing wastewater, and complete the neutralization of the water quality;

[0013] Step five, reuse: after the pH value of the chlorine-containing wastewater after step four is adjusted, the residual chlorine content is detected to meet the standard, and then it is directly sent to the MVR evaporation system for treatment, and the treated water meets the standard for reuse.

[0014] By adopting the above technical scheme, the residual chlorine content in the chlorine-containing wastewater can be systematically reduced, which not only meets the water inlet requirement of the subsequent MVR evaporation system, but also realizes water reuse and chlorine gas resource utilization, which is in line with the green environmental protection and sustainable development concept.

[0015] As a preferred technical scheme of the present application, the stirring speed in step one is controlled to be 200-300 r / min, and the temperature of the chlorine-containing wastewater is controlled to be 25-40°C.

[0016] By adopting the above technical scheme, the components of the chlorine-containing wastewater can be uniformly distributed, creating a stable reaction environment for subsequent acidification and reduction reactions, and improving the efficiency and effect of subsequent treatment steps.

[0017] As a preferred technical scheme of the present application, the hydrochloric acid solution added in step two is 3% of the chlorine-containing wastewater, and the addition speed of the hydrochloric acid solution is 0.6-0.8 L / (min·m³).

[0018] By adopting the above technical scheme, it can be avoided that excessive or too fast addition of hydrochloric acid leads to sudden increase of local acidity, ensuring that the acidification process is stable and controllable, and providing suitable acidic conditions for residual chlorine reduction reaction.

[0019] As a preferred technical scheme of the present application, the acidification reaction time in step two is controlled to be 15-30 min, and the pH value is reduced to 2-4.

[0020] By adopting the above technical scheme, the acid range can maximize the activation of the reduction activity of the subsequent sodium thiosulfate, laying a foundation for efficient conversion of residual chlorine, and avoiding low processing efficiency caused by too long reaction time.

[0021] As a preferred technical scheme of the present application, the sodium thiosulfate solution added in step three is 5% of the chlorine-containing wastewater, and the molar ratio of sodium thiosulfate to residual chlorine in the wastewater is controlled to be 1:4-5.

[0022] By adopting the above technical scheme, it can be ensured that the sodium thiosulfate is sufficient and not excessive, which can not only reduce the residual chlorine in the wastewater to chlorine gas, but also avoid waste of reagents and secondary pollution.

[0023] As a preferred technical scheme of the present application, the stirring speed in step three is controlled to be 100-200 r / min, and the stirring reaction is performed for 20-40 min.

[0024] By using the above technical scheme, the sodium thiosulfate can be fully contacted and reacted with the chlorine-containing wastewater, and the complete reduction of residual chlorine can be ensured.

[0025] As a preferred technical scheme of the present application, the chlorine gas released in step three is captured by airtight collection devices at the top of the reaction tank, and is delivered to a chlorination reaction kettle after being pressurized by a chlorine gas pump for recycling.

[0026] By using the above technical scheme, the chlorine gas released in the reduction reaction can be captured and reused in the chlorination reaction through airtight collection and pressurized delivery, which not only avoids the pollution of the working environment and the harm to the health of personnel caused by the volatilization of chlorine gas, but also realizes the recycling of waste and reduces the raw material procurement cost.

[0027] As a preferred technical scheme of the present application, the caustic soda in step four is flaky sodium hydroxide or a 30% sodium hydroxide solution, and the pH value is adjusted to 7-8, and the change rate of the pH value during the adjustment process is controlled to be ≤0.5 pH / min.

[0028] By using the above technical scheme, the wastewater can be smoothly neutralized to the neutral range, the damage to the subsequent MVR equipment caused by the sudden change of the pH value can be avoided, and the water quality safety of the reclaimed water can be ensured.

[0029] As a preferred technical scheme of the present application, the residual chlorine content is detected to be ≤0.5 ppm in step five.

[0030] By using the above technical scheme, the corrosion rate of the wastewater on the metal equipment of the MVR evaporation system can be greatly reduced, the service life of the equipment can be prolonged, the number of maintenance shutdowns can be reduced, the production continuity can be ensured, and the environmental protection standard of the reclaimed water can be met.

[0031] Compared with the prior art, the present application has the following beneficial effects: the method for treating chlorine-containing wastewater;

[0032] 1. Solve the problem of air pollution in the working environment: by adding hydrochloric acid to the chlorine-containing wastewater for acidification, and then adding sodium thiosulfate for reduction, the residual chlorine in the wastewater is converted into harmless chloride ions, and the chlorine gas released by the reaction is captured by airtight collection devices for recycling, thereby avoiding the volatilization of residual chlorine into the working environment, removing the odor, improving the air quality in the workshop, and meeting the occupational health and safety standards.

[0033] 2. Reduce equipment corrosion: after reduction dechlorination treatment, the residual chlorine content of wastewater is ≤0.5ppm, which can greatly reduce the corrosion of metal equipment when sent into the MVR evaporation system, prolong the service life of the equipment, reduce the maintenance downtime, reduce the maintenance cost, and ensure the continuity of production;

[0034] 3. Realize resource recycling: on the one hand, the treated reclaimed water meets the standard for reuse, reducing the consumption of fresh water resources; on the other hand, the captured chlorine gas is reused for chlorination reaction, realizing waste resource utilization, and meeting the green environmental protection and sustainable development concept. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The flowchart of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] Embodiment one

[0038] Please refer to Figure 1 The technical solution of the present application: a method for treating wastewater containing chlorine, comprising the following steps:

[0039] Step one, pretreatment: introduce the wastewater containing chlorine into the reaction tank, start the stirring device, control the stirring speed to be 200r / min, and control the temperature of the wastewater containing chlorine to be 25℃;

[0040] Step two, acidification: add 3% of hydrochloric acid solution based on the total amount of wastewater containing chlorine to the temperature-adjusted wastewater containing chlorine at a speed of 0.6L / (min·m³), stir for 15min, and reduce the pH value to 2;

[0041] Step three, reduction dechlorination reaction: add 5% of sodium thiosulfate solution based on the total amount of wastewater containing chlorine to the acidified wastewater containing chlorine, control the molar ratio of sodium thiosulfate to residual chlorine in the wastewater to be 1:4, control the stirring speed to be 100r / min, and stir for 40min to reduce the residual chlorine and release chlorine gas. The released chlorine gas is captured by the sealed collection device at the top of the reaction tank, pressurized by a chlorine gas pump, and then transported to the chlorination reaction kettle for resource recycling;

[0042] Step four, pH value adjustment: add flaky sodium hydroxide to the reacted wastewater containing chlorine, stir to adjust the pH value of the wastewater containing chlorine to 7, control the pH value change rate to be ≤0.5pH / min during the adjustment process, and complete the neutralization of water quality;

[0043] Step five, reuse: the chlorine-containing wastewater after adjusting the pH value in step four is directly sent into the MVR evaporation system for treatment after detecting that the residual chlorine content is less than or equal to 0.5 ppm, and the treated reclaimed water meets the standard for reuse.

[0044] Example two

[0045] Please refer to Figure 1 The technical scheme of the present application: a method for treating chlorine-containing wastewater, comprising the following steps:

[0046] Step one, pretreatment: introduce the chlorine-containing wastewater into the reaction tank, start the stirring device, control the stirring speed to be 250 r / min, and control the temperature of the chlorine-containing wastewater to be 30 DEG C;

[0047] Step two, acidification: add 3% of hydrochloric acid solution based on the total amount of chlorine-containing wastewater to the temperature-adjusted chlorine-containing wastewater at a speed of 0.6 L / (min.m3), stir for 20 min, and reduce the pH value to 2.5;

[0048] Step three, reduction and dechlorination reaction: add 5% of sodium thiosulfate solution based on the total amount of chlorine-containing wastewater to the acidified chlorine-containing wastewater, control the molar ratio of sodium thiosulfate to residual chlorine in the wastewater to be 1:4, control the stirring speed to be 130 r / min, and stir for 35 min to reduce the residual chlorine and release chlorine gas, which is captured by the closed collection device at the top of the reaction tank, and then transported to the chlorination reaction kettle after being pressurized by a chlorine gas pump for resource recycling;

[0049] Step four, pH value adjustment: add flaky sodium hydroxide to the reacted chlorine-containing wastewater, stir to adjust the pH value of the chlorine-containing wastewater to 7.5, control the pH value change rate to be less than or equal to 0.5 pH / min during the adjustment process, and complete the neutralization of the water quality;

[0050] Step five, reuse: the chlorine-containing wastewater after adjusting the pH value in step four is directly sent into the MVR evaporation system for treatment after detecting that the residual chlorine content is less than or equal to 0.5 ppm, and the treated reclaimed water meets the standard for reuse.

[0051] Example three

[0052] Please refer to Figure 1 The technical scheme of the present application: a method for treating chlorine-containing wastewater, comprising the following steps:

[0053] Step one, pretreatment: introduce the chlorine-containing wastewater into the reaction tank, start the stirring device, control the stirring speed to be 280 r / min, and control the temperature of the chlorine-containing wastewater to be 35 DEG C;

[0054] Step two, acidification: add 3% of hydrochloric acid solution based on the total amount of chlorine-containing wastewater to the temperature-adjusted chlorine-containing wastewater at a speed of 0.7 L / (min.m3), stir for 25 min, and reduce the pH value to 3;

[0055] Step three, reduction dechlorination reaction: add 5% sodium thiosulfate solution to the acidified chlorinated wastewater, control the molar ratio of sodium thiosulfate to residual chlorine in the wastewater to be 1:4.5, control the stirring speed to be 180r / min, stir for 25min, so that the residual chlorine is reduced and chlorine gas is released, the released chlorine gas is captured by the closed collection device at the top of the reaction tank, and then transported to the chlorination reaction kettle after pressurization by a chlorine gas pump for recycling;

[0056] Step four, pH value adjustment: add 30% sodium hydroxide solution to the reacted chlorinated wastewater, stir to adjust the pH value of the chlorinated wastewater to 8, control the pH value change rate to be ≤0.5pH / min during the adjustment process, and complete the water quality neutralization;

[0057] Step five, reuse: after the chlorinated wastewater after adjusting the pH value in step four is detected to have a residual chlorine content of ≤0.5ppm, it is directly sent to the MVR evaporation system for treatment, and the treated reclaimed water meets the standard for reuse.

[0058] Example four

[0059] Please refer to Figure 1 The technical scheme of the present application: a method for treating chlorinated wastewater, comprising the following steps:

[0060] Step one, pretreatment: introduce the chlorinated wastewater into the reaction tank, start the stirring device, control the stirring speed to be 300r / min, and control the temperature of the chlorinated wastewater to be 40℃;

[0061] Step two, acidification: add 3% hydrochloric acid solution to the temperature-adjusted chlorinated wastewater at a speed of 0.8L / (min·m³), stir for 30min, and reduce the pH value to 4;

[0062] Step three, reduction dechlorination reaction: add 5% sodium thiosulfate solution to the acidified chlorinated wastewater, control the molar ratio of sodium thiosulfate to residual chlorine in the wastewater to be 1:5, control the stirring speed to be 200r / min, stir for 20min, so that the residual chlorine is reduced and chlorine gas is released, the released chlorine gas is captured by the closed collection device at the top of the reaction tank, and then transported to the chlorination reaction kettle after pressurization by a chlorine gas pump for recycling;

[0063] Step four, pH value adjustment: add 30% sodium hydroxide solution to the reacted chlorinated wastewater, stir to adjust the pH value of the chlorinated wastewater to 8, control the pH value change rate to be ≤0.5pH / min during the adjustment process, and complete the water quality neutralization;

[0064] Step five, reuse: the chlorine-containing wastewater after pH adjustment in step four is directly sent to the MVR evaporation system for treatment after the residual chlorine content is detected to be less than or equal to 0.5 ppm, and the treated reclaimed water meets the standard for reuse.

[0065] Comparative Example One

[0066] The present scheme is the same as Example One except that hydrochloric acid solution is not added.

[0067] Comparative Example Two

[0068] The present scheme is the same as Example One except that sodium thiosulfate solution is not added.

[0069] The residual chlorine content of the chlorine-containing wastewater in the above examples and comparative examples is detected, and the corrosion degree of the metal equipment of the MVR evaporation system is detected, and the specific results are shown in the following table:

[0070] Final residual chlorine content (ppm) Corrosion rate of MVR equipment (mm / year) Example One 0.24 0.07 Example Two 0.21 0.06 Example Three 0.25 0.08 Example Four 0.18 0.05 Comparative Example One 5.8 0.55 Comparative Example Two 6.2 0.60

[0071] From the above results, it can be seen that the method of the present application can effectively reduce the residual chlorine content (all less than or equal to 0.5 ppm) in the chlorine-containing wastewater, and significantly reduce the corrosion rate of the MVR equipment (all less than or equal to 0.08 mm / year); and the residual chlorine content and the equipment corrosion rate of the comparative examples without adding hydrochloric acid or sodium thiosulfate are significantly increased, which proves that the technical scheme of the present application has significant advantages.

[0072] The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

[0073] Although embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A process for treating wastewater containing chlorine, characterized by, It comprises the following steps: Step one, pretreatment: the chlorine-containing wastewater is introduced into the reaction tank, the stirring device is started to stir, and the temperature of the chlorine-containing wastewater is controlled; Step two, acidification: add hydrochloric acid solution to the temperature-adjusted chlorine-containing wastewater, and perform acidification reaction during stirring to reduce the pH value; Step three, reduction and dechlorination reaction: add sodium thiosulfate solution to the acidified chlorine-containing wastewater, and stir to reduce residual chlorine and release chlorine gas; Step four, pH value adjustment: add caustic soda to the reacted chlorine-containing wastewater, stir to adjust the pH value of the chlorine-containing wastewater, and complete water quality neutralization; Step five, reuse: after the pH value of the chlorine-containing wastewater after step four is adjusted, the residual chlorine content is detected to meet the standard, and then it is directly sent to the MVR evaporation system for treatment, and the treated water meets the standard for reuse.

2. A process for treating wastewater containing chlorine according to claim 1, characterized in that, The stirring speed in step one is controlled at 200-300 r / min, and the wastewater temperature is controlled at 25-40℃.

3. A process for treating wastewater containing chlorine according to claim 1, wherein The hydrochloric acid solution added in step two is 3% of the chlorine-containing wastewater, and the addition rate of the hydrochloric acid solution is 0.6-0.8 L / (min·m³).

4. The method for treating wastewater containing chlorine according to claim 1, wherein The acidification reaction time in step two is controlled at 15-30 min, and the pH value is reduced to 2-4.

5. The method for treating wastewater containing chlorine according to claim 1, wherein The sodium thiosulfate solution added in step three is 5% of the chlorine-containing wastewater, and the molar ratio of sodium thiosulfate to residual chlorine in the wastewater is controlled at 1:4-5.

6. A process for treating wastewater containing chlorine according to claim 1, wherein The stirring speed in step three is controlled at 100-200 r / min, and the stirring reaction time is 20-40 min.

7. A process for treating wastewater containing chlorine according to claim 1, wherein The chlorine gas released in step three is captured by airtight collection device at the top of the reaction tank, pressurized by a chlorine gas pump, and then transported to a chlorination reaction kettle for resource recycling.

8. The method for treating wastewater containing chlorine according to claim 1, wherein The caustic soda in step four is flaky sodium hydroxide or 30% sodium hydroxide solution, the pH value is adjusted to 7-8, and the pH value change rate during adjustment is controlled at ≤0.5 pH / min.

9. The method for treating wastewater containing chlorine according to claim 1, wherein The residual chlorine content in step five is ≤0.5 ppm.

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