PVA production process low concentration wastewater treatment device

Abstract

This invention relates to the technical field of polyvinyl alcohol (PVA) wastewater degradation treatment devices, and discloses a low-concentration wastewater treatment device for the PVA production process. The device includes a controller, a PVA production tank, and a wastewater reaction tank. An inlet pipe connects the PVA production tank and the wastewater reaction tank, and the inlet pipe is equipped with an acid inlet, a baffle plate, and a pH meter. The acid inlet is connected to an acid inlet pipe, which is equipped with an acid regulating valve. The wastewater reaction tank is connected to a reagent inlet pipe and a drain pipe, and the reagent inlet pipe is equipped with a reagent regulating valve. The pH meter, acid regulating valve, and reagent regulating valve are all electrically connected to the controller. This solution treats a batch of low-concentration PVA wastewater (approximately 30 t / h) with a total residence time of only 20–40 minutes in the pipeline and reaction tank, effectively improving the PVA wastewater treatment efficiency. Furthermore, the PVA content in the treated wastewater is below 10 ppm, effectively solving the technical problem of low-concentration PVA in wastewater increasing the difficulty of biodegradability.

Description

Technical Field

[0001] This invention relates to the technical field of polyvinyl alcohol wastewater degradation treatment devices, specifically to a low-concentration wastewater treatment device for the PVA production process. Background Technology

[0002] Polyvinyl alcohol (PVA) is the only water-active organic polymer compound discovered to date. Due to its strong adhesive properties, gas barrier properties, abrasion resistance, and excellent chemical and physical properties, including high compatibility with other sizing agents, it has been used as a sizing agent in the textile, paper, and chemical industries since the 1940s. It is widely used as a sizing agent in the textile industry, a coating and binder in the construction industry, an emulsifier and dispersant in the chemical industry, a lubricant in the pharmaceutical industry, an adhesive in the paper industry, and a soil conditioner.

[0003] However, industrial wastewater containing PVA has characteristics such as high COD value and poor biodegradability. If it is discharged into water bodies, its high surface activity will cause the receiving water to produce a large amount of foam, which is not conducive to water reoxygenation. Moreover, it will promote the migration and release of heavy metals in water sediments, damaging the aquatic environment.

[0004] Currently, conventional methods for treating PVA wastewater include extraction, adsorption, salting-out gelation, membrane separation, foam separation, and strong oxidation. However, existing technologies are mostly designed for high-concentration PVA wastewater, with significantly reduced effectiveness for low-concentration PVA wastewater. These processes are not only costly, but the PVA content in the treated wastewater still exceeds discharge standards, impacting subsequent biological treatment and causing environmental pollution. Furthermore, there are no specific devices or systems for treating low-concentration PVA wastewater. Currently, a combination of biological treatment and MBR membrane concentration is used, but trace amounts of PVA in the wastewater accumulate in downstream wastewater treatment plants, affecting sludge activity in aeration tanks and easily clogging MBR membranes, significantly impacting the continuous and stable operation of wastewater treatment plants.

[0005] Therefore, the development of a low-concentration wastewater treatment device for PVA production not only effectively compensates for the shortcomings of existing technologies, but also effectively reduces the PVA content in wastewater to less than 10 ppm, improves the biodegradability of wastewater, and accelerates its biochemical treatment efficiency. Summary of the Invention

[0006] The present invention aims to provide a device for treating low-concentration wastewater from the PVA production process, in order to solve the technical problem that existing devices are ineffective in treating low-concentration PVA wastewater, resulting in a still high PVA content in the treated wastewater, which increases the difficulty of biodegradability of the wastewater.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a low-concentration wastewater treatment device for PVA production process, comprising a controller, a PVA production tank, and a wastewater reaction tank. An inlet pipe connects the PVA production tank and the wastewater reaction tank. The inlet pipe is equipped with an acid inlet, a baffle plate, and a pH meter. The acid inlet is connected to an acid inlet pipe, which is equipped with an acid regulating valve. The wastewater reaction tank is connected to a reagent inlet pipe and a drain pipe. The reagent inlet pipe is equipped with a reagent regulating valve. The pH meter, acid regulating valve, and reagent regulating valve are all electrically connected to the controller.

[0008] Preferably, as an improvement, the pH meter is used to detect the pH of the wastewater in the inlet pipe, generate a pH signal, and transmit the pH signal to the controller. The controller is used to receive the pH signal and adjust the valve opening of the acid regulating valve according to the pH signal. The controller is also used to match the amount of reagent added according to the real-time input of the PVA concentration in the wastewater before treatment, and to control the valve opening of the reagent regulating valve in stages according to the amount of reagent added. The reagent is sodium hypochlorite.

[0009] Preferably, as an improvement, the wastewater reaction tank is equipped with a stirring device.

[0010] Preferably, as an improvement, the baffle includes several baffles spaced apart on both sides of the inner wall of the inlet pipe.

[0011] Preferably, as an improvement, a return pipe is connected between the drain pipe and the wastewater reaction tank.

[0012] Preferably, as an improvement, the return pipe is equipped with a return valve, which is electrically connected to a controller. The controller is used to adjust the valve opening of the return valve according to the real-time input of the PVA concentration in the treated wastewater.

[0013] Preferably, as an improvement, the bottom of the PVA production tank is connected to a reboiler, the reboiler is connected to a hot water pipe, a hot water valve is installed on the hot water pipe, and a thermometer is installed on the wastewater reaction tank. Both the thermometer and the reboiler are electrically connected to the controller. The thermometer is used to detect the temperature of the wastewater in the wastewater reaction tank, generate a temperature signal, and transmit the temperature signal to the controller. The controller is used to receive the temperature signal and adjust the valve opening of the hot water valve according to the temperature signal.

[0014] Preferably, as an improvement, the graded control is as follows: when the PVA concentration in the wastewater before treatment is below 50 ppm, the sodium hypochlorite dosage is 3-5‰ of the PVA concentration; when the PVA concentration in the wastewater before treatment is between 50 ppm and 100 ppm, the sodium hypochlorite dosage is 2-4‰ of the PVA concentration; when the PVA concentration in the wastewater before treatment is above 100 ppm, the sodium hypochlorite dosage is 1-3‰ of the PVA concentration.

[0015] Preferably, as an improvement, the stirring device is a stirrer with a stirring speed of 60-120 rpm. The stirrer is electrically connected to a controller, which controls the start-up, shutdown, and rotation speed of the stirrer.

[0016] The principle and advantages of this scheme are:

[0017] 1. Compared to existing technologies for treating PVA wastewater, which have limited efficiency and effectiveness and are costly, this solution adjusts the temperature and pH of low-concentration PVA wastewater to a suitable environment for PVA removal before using chemicals to remove PVA. Then, chemicals are added in stages according to the PVA concentration in the wastewater to oxidize and remove PVA. This not only effectively improves the efficiency and effectiveness of chemical oxidation in removing PVA from wastewater but also reduces the amount of chemicals used, thus lowering costs. Specifically, through long-term experiments, the inventors found that this solution treats a batch of low-concentration PVA wastewater (approximately 30 t / h) with a total residence time of only 20–40 minutes in the pipelines and reaction tanks, effectively improving the PVA wastewater treatment efficiency. Furthermore, the PVA content in the treated wastewater is below 10 ppm, effectively avoiding excessive PVA residue that would increase the difficulty of biological treatment, making it easier to discharge after biological treatment and improving environmental benefits.

[0018] 2. Compared with existing technologies that treat high-concentration PVA wastewater, this solution treats low-concentration PVA wastewater. Compared with high-concentration PVA wastewater, the PVA content in low-concentration wastewater is lower, which leads to lower treatment efficiency. Furthermore, PVA in low-concentration PVA wastewater is more difficult to be captured and reacted by oxidants (i.e., reagents). Therefore, the treatment of low-concentration PVA wastewater is more difficult. This solution enables real-time pH adjustment of the wastewater before treatment by setting up an electrically connected controller, pH meter, and acid regulating valve. The controller and reagent regulating valve also allow for real-time adjustment of reagent dosage based on the PVA concentration in the wastewater before treatment, preventing reagent waste. Furthermore, the controller and reflux valve allow for real-time adjustment of the wastewater's discharge into subsequent treatment processes or recirculation for further treatment based on the PVA concentration after treatment, effectively ensuring that the PVA content in the discharged wastewater is below 10 ppm. Finally, the controller, thermometer, and hot water valve allow for real-time temperature adjustment of the PVA wastewater in the PVA production tank based on the temperature of the wastewater in the wastewater reaction tank. This ensures that the wastewater reaches the optimal temperature range for PVA oxidation when transported to the wastewater reaction tank, thereby effectively improving PVA removal efficiency and effectiveness.

[0019] 3. Due to the recalcitrant nature of low-concentration PVA, it cannot be removed during conventional anaerobic fermentation. Instead, it reduces the effectiveness of anaerobic fermentation by affecting wastewater viscosity. This solution effectively enhances the selectivity of the oxidant for PVA by adjusting the temperature and pH of the PVA wastewater in real time before the reaction. This prioritizes the oxidation of PVA while having minimal impact on other organic waste, achieving targeted degradation of PVA in the wastewater. Specifically, by adjusting the temperature and pH of the PVA wastewater before the reaction and adding only a small amount of oxidant, this solution can reduce the PVA content in the wastewater to below 10 ppm, meeting the minimum standard for PVA in wastewater discharge. This allows for direct discharge to the wastewater treatment plant for further treatment, effectively protecting the environment. Although the wastewater treated with this solution still has relatively high COD levels, the absence of PVA's thickening and foaming effects allows it to be treated to discharge standards through anaerobic fermentation, oxidant treatment, and other methods. Furthermore, the absence of PVA significantly reduces the difficulty of wastewater treatment, resulting in a significant improvement in treatment efficiency.

[0020] 4. This solution effectively slows down the flow rate of low-concentration PVA wastewater in the inlet pipe by installing a baffle in the inlet pipe. This allows the acid added from the acid inlet pipe to mix fully with the wastewater in the baffle area, enabling the pH meter to accurately measure the pH of the mixed wastewater. This improves the accuracy of acid adjustment and avoids acid waste. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the low-concentration wastewater treatment device used in the PVA production process in this embodiment of the invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well known to those skilled in the art, and the materials and reagents used can all be obtained commercially.

[0023] The attached diagram is labeled as follows: PVA production tank 1, reboiler 11, hot water valve 111, wastewater reaction tank 2, reagent feed pipe 21, reagent regulating valve 211, drain pipe 22, reflux pipe 221, reflux valve 222, stirrer 23, thermometer 24, water inlet pipe 3, acid inlet pipe 31, acid regulating valve 32, pH meter 33, baffle 34, acid tank 4, reagent tank 5, controller 6.

[0024] Overview of the Plan

[0025] This solution provides a low-concentration wastewater treatment device for the PVA production process, such as... Figure 1As shown, the system includes a controller 6, a PVA production tank 1, and a wastewater reaction tank 2. An inlet pipe 3 connects the PVA production tank 1 and the wastewater reaction tank 2. The inlet pipe 3 is equipped with an acid inlet, a baffle 34, and a pH meter 33. The acid inlet is connected to an acid inlet pipe 31, which is equipped with an acid regulating valve 32. The acid inlet pipe 31 is also connected to an acid tank 4. Both the pH meter 33 and the acid regulating valve 32 are electrically connected to the controller 6. The pH meter 33 is used to detect the pH of the wastewater in the inlet pipe 3, generating a pH signal and transmitting it to the controller 6. The controller 6 receives the pH signal and adjusts the opening of the acid regulating valve 32 according to the pH signal.

[0026] The baffle 34 includes several baffles spaced apart on both sides of the inner wall of the inlet pipe 3, which facilitates the thorough mixing of acid added from the acid inlet pipe 31 with the wastewater in the area of ​​the baffle 34, so that the pH meter can accurately measure the pH of the mixed wastewater, thereby improving the accuracy of acid adjustment and avoiding acid waste.

[0027] Wastewater reaction tank 2 is connected to a reagent inlet pipe 21 and a drain pipe 22. The reagent inlet pipe 21 is equipped with a reagent regulating valve 211, which is connected to a reagent tank 5. The reagent regulating valve 211 is electrically connected to a controller 6. The controller 6 is used to match the reagent addition amount according to the real-time input of the PVA concentration in the wastewater before treatment, and to control the valve opening of the reagent regulating valve 211 in stages according to the reagent addition amount, thereby regulating the reagent addition amount in real time. Specifically, the reagent used in this solution is sodium hypochlorite. An information storage module is installed within the controller 6, pre-entering reagent dosage tiered control information (specifically, three-level threshold control information) as follows: Level 1 threshold: When the PVA concentration in the wastewater before treatment is below 50 ppm, the sodium hypochlorite dosage is 3-5‰ of the PVA concentration; Level 2 threshold: When the PVA concentration in the wastewater before treatment is between 50 ppm and 100 ppm, the sodium hypochlorite dosage is 2-4‰ of the PVA concentration; Level 3 threshold: When the PVA concentration in the wastewater before treatment is above 100 ppm, the sodium hypochlorite dosage is 1-3‰ of the PVA concentration. Furthermore, the information storage module pre-sets the valve opening of the reagent regulating valve 211 corresponding to each level of sodium hypochlorite dosage, facilitating the matching of the valve opening of the reagent regulating valve 211 to the real-time input of the PVA concentration in the wastewater before treatment, thus achieving tiered control of the reagent regulating valve 211.

[0028] Wastewater reaction tank 2 is equipped with a thermometer 24. A reboiler 11 is connected to the bottom of PVA production tank 1, and a hot water pipe is connected to the reboiler 11. A hot water valve 111 is installed on the hot water pipe. Both the reboiler 11 and the thermometer 24 are electrically connected to the controller 6. The thermometer 24 is used to detect the temperature of the wastewater in wastewater reaction tank 2, generate a temperature signal, and transmit the temperature signal to the controller 6. The controller 6 receives the temperature signal and adjusts the opening of the hot water valve 111 according to the temperature signal, thereby regulating the hot water flow rate in the reboiler 11 and thus regulating the wastewater temperature in PVA production tank 1.

[0029] As an improvement, the wastewater reaction tank 2 is equipped with a stirring device. For reference, the stirring device is a stirrer 23. The stirring speed of the stirrer 23 is controlled at 60-120 rpm. The stirrer 23 is electrically connected to the controller 6. The controller 6 is used to control the start and stop of the stirrer 23 and its rotation speed.

[0030] As an improvement, a return pipe 221 is connected between the drain pipe 22 and the wastewater reaction tank 2. A return valve 222 is provided on the return pipe 221. The return valve 222 is electrically connected to the controller 6. The controller 6 is used to adjust the valve opening of the return valve 222 according to the real-time input of the PVA concentration in the treated wastewater.

[0031] In this solution, controller 6 is a PLC controller 6. The PLC controller 6, pH meter 33, thermometer 24, reflux valve 222, stirrer 23, hot water valve 111, acid regulating valve 32 and reagent regulating valve 211 are all existing electrical equipment, and appropriate models are selected according to the usage requirements. They will not be described in detail here.

[0032] The specific implementation method is as follows:

[0033] The information storage module of controller 6 is pre-set with pH threshold, temperature threshold, reagent addition level control information, and reflux information.

[0034] The PVA wastewater generated by PVA production tank 1 is kept at a certain temperature by the reboiler 11. The wastewater flows through the inlet pipe 3 at the bottom of PVA production tank 1 and through the baffle 34 into wastewater reaction tank 2. During this process, the pH meter 33 detects the pH of the wastewater in the inlet pipe 3, generates a pH signal, and transmits the pH signal to the controller 6. After receiving the pH signal, the controller 6 compares the pH signal with the pH threshold preset in the controller 6 to adjust the valve opening of the acid regulating valve 32. Specifically, if the pH signal is lower than the pH threshold, the valve opening of the acid regulating valve 32 is reduced; if the pH signal is higher than the pH threshold, the valve opening of the acid regulating valve 32 is increased. The acid that enters the inlet pipe 3 through the acid inlet pipe 31 is fully mixed in the area of ​​the baffle 34 and is detected by the pH meter 33 to generate a pH signal, which is transmitted to the controller 6 for real-time adjustment of the valve opening of the acid regulating valve 32.

[0035] After the wastewater enters the wastewater reaction tank 2, the controller 6 adjusts the valve opening of the reagent regulating valve 211 according to the real-time input PVA concentration and the corresponding reagent addition amount. After the reagent is added, it is thoroughly mixed and reacted with the wastewater under the stirring action of the stirrer 23. During the reaction, the thermometer 24 detects the wastewater temperature in the wastewater reaction tank 2 in real time, generates a temperature signal, and transmits the temperature signal to the controller 6. After receiving the temperature signal, the controller 6 compares the temperature signal with the temperature threshold preset in the controller 6 and adjusts the valve opening of the hot water valve 111, thereby regulating the hot water flow rate in the reboiler 11 and thus regulating the wastewater temperature in the PVA production tank 1.

[0036] During the reaction, it is also necessary to periodically test the PVA content in the wastewater before and after the reaction, and input both data into the controller 6. This allows the controller 6 to control the opening of the reagent regulating valve 211 in real time based on the PVA content in the wastewater before the reaction, and to adjust the opening and closing of the reflux valve 222 and its opening degree in real time based on the PVA content in the wastewater after the reaction. This facilitates the recirculation of wastewater with a PVA content higher than 10 ppm for further reagent oxidation treatment, avoiding excessively high PVA content from increasing the difficulty of biodegradability of the wastewater.

[0037] This solution also provides a method for treating low-concentration wastewater from the PVA production process, which relies on the aforementioned low-concentration wastewater treatment device for the PVA production process. The PVA content in the wastewater before treatment is less than 300 ppm, and the method specifically includes the following steps:

[0038] In the S1 adjustment stage, the pH and temperature of the wastewater are adjusted.

[0039] As a reference, a reboiler is used to adjust the temperature of the PVA wastewater in the PVA production tank to 80–95°C. In the connecting pipeline that transports the PVA wastewater to the wastewater reaction tank, acid is added to adjust the pH of the wastewater to 5–6. The acid used to adjust the pH of the wastewater is one of concentrated sulfuric acid, concentrated hydrochloric acid, or concentrated nitric acid. As a reference, this scheme uses concentrated hydrochloric acid to adjust the pH of the wastewater.

[0040] In the S2 reaction stage, an oxidant is added to the wastewater to complete the reaction;

[0041] For reference, the oxidant in this scheme is sodium hypochlorite, and the dosage of sodium hypochlorite is 1‰ to 5‰ of the PVA concentration in the wastewater. For further reference, the dosage of sodium hypochlorite is determined based on the PVA concentration in the wastewater: when the PVA concentration in the wastewater is below 50 ppm, the dosage of sodium hypochlorite is 3‰ to 5‰ of the PVA concentration; when the PVA concentration in the wastewater is between 50 ppm and 100 ppm, the dosage of sodium hypochlorite is 2‰ to 4‰ of the PVA concentration; when the PVA concentration in the wastewater is above 100 ppm, the dosage of sodium hypochlorite is 1‰ to 3‰ of the PVA concentration.

[0042] When adding oxidant to the wastewater reaction tank, the stirring device is activated to agitate the wastewater within the tank at a speed of 60–120 rpm. Stirring continues throughout the entire reaction process; for reference, the reaction time in this scheme is 20–40 minutes. Specifically, this scheme treats a batch of PVA wastewater (approximately 30 t / h), with the PVA wastewater residing in the pipelines and reaction tank for only 20–40 minutes, effectively improving the PVA wastewater treatment efficiency.

[0043] In the S3 post-treatment stage, the PVA concentration in the wastewater after the reaction is detected, and the PVA wastewater after the reaction is discharged.

[0044] In the S4 biological treatment stage, wastewater with PVA concentration below 10 ppm undergoes further biological treatment before being discharged in compliance with standards.

[0045] As a reference, the PVA concentration in the wastewater after the reaction is tested. If the PVA concentration in the wastewater after the reaction drops to 10 ppm or below, the wastewater is discharged into the wastewater treatment plant. If the PVA concentration in the wastewater after the reaction is higher than 10 ppm, it needs to be recycled back to the front end for further treatment.

[0046] Example 1

[0047] In this embodiment, the PVA concentration in the low-concentration PVA wastewater was 37 ppm. The reaction temperature was adjusted to 90℃, the pH of the wastewater was 5.3, the amount of sodium hypochlorite added was 4‰ of the PVA content, and the reaction time was 20 min.

[0048] Example 2

[0049] In this embodiment, the PVA concentration in the low-concentration PVA wastewater was 51 ppm, the pH of the wastewater was adjusted to 5.5, the reaction temperature was 95℃, the amount of sodium hypochlorite added was 3‰ of the PVA content, and the reaction time was 20 min.

[0050] Example 3

[0051] In this embodiment, the PVA concentration in the low-concentration PVA wastewater was 110 ppm, the pH of the wastewater was adjusted to 6, the reaction temperature was 90℃, the amount of sodium hypochlorite added was 2‰ of the PVA content, and the reaction time was 30 min.

[0052] Example 4

[0053] In this embodiment, the PVA concentration in the low-concentration PVA wastewater was 216 ppm, the pH of the wastewater was adjusted to 5, the reaction temperature was 80℃, the amount of sodium hypochlorite added was 2‰ of the PVA content, and the reaction time was 40 min.

[0054] Table 1 shows the process conditions and implementation effects of treating low-concentration PVA wastewater in Examples 1-4. Comparative Examples 1-11 are also included in Table 1 to illustrate the treatment effects of this scheme on low-concentration PVA wastewater when the parameters are taken outside the range specified in this scheme.

[0055] The PVA removal rate in Table 1 is calculated using the following formula:

[0056] PVA removal rate (%) = (PVA concentration before treatment - PVA concentration after treatment) / PVA concentration before treatment * 100%

[0057] Table 1 Implementation Conditions and Results

[0058]

[0059]

[0060] Experimental data show that this scheme, by limiting the sequence of steps such as temperature adjustment, pH adjustment, and oxidant addition for PVA wastewater, allows for pre-conditioning of the PVA wastewater temperature in the PVA production tank and pH adjustment in the delivery pipeline connected to the reaction tank. Once the wastewater enters the reaction tank, the oxidant can be directly added to degrade the PVA. This effectively increases the reaction rate while further reducing energy loss in high-temperature PVA wastewater, saving energy and lowering treatment costs.

[0061] Furthermore, the applicant's long-term experiments revealed that adjusting the temperature and pH of the PVA wastewater, as well as the order and parameters of adding oxidants, significantly reduces the treatment effect of PVA wastewater. Specifically, if the pH is too low (as in Comparative Example 1), it not only fails to significantly improve the reaction rate and PVA degradation efficiency but also wastes reagents, resulting in more harm than good. Conversely, failing to adjust the wastewater pH before the reaction (as in Comparative Example 11, where the oxidant was added first, followed by temperature and pH adjustment) or having an excessively high pH after adjustment (as in Comparative Example 2) both prevent the oxidant from rapidly acidifying and generating free radicals, thus reducing the oxidative degradation effect and affecting the removal of PVA, especially in the case of not adjusting the wastewater pH. Specifically, in Comparative Example 11, the wastewater contained 110 ppm of PVA with a pH of approximately 7-8. If the pH of the wastewater was not adjusted before the reaction, and instead 2‰ sodium hypochlorite was added before adjusting the temperature and pH, 76 ppm of PVA remained in the wastewater after 30 minutes of reaction. The PVA removal rate was only 30.9%, which not only failed to meet the PVA discharge standards and required further treatment, but also necessitated increasing the sodium hypochlorite dosage to 3‰ during the re-treatment process, resulting in wasted oxidant and reduced PVA treatment efficiency. This clearly demonstrates that the pH of PVA wastewater must be adjusted to the optimal reaction range before the oxidation reaction to effectively improve the PVA removal efficiency.

[0062] If the wastewater temperature is set too low (as in Comparative Example 3), the PVA wastewater temperature will be too low due to energy loss during equipment transport, which will significantly reduce the PVA oxidation and degradation effect. If the wastewater temperature is set too high (as in Comparative Example 4), not only will energy be wasted, but the PVA modification at high temperature will also make it more difficult to oxidize and degrade. Therefore, it can be seen that both excessively high and excessively low temperatures will reduce the PVA oxidation and degradation effect.

[0063] Regarding reaction time, if the reaction time is too short (e.g., Comparative Example 5), the PVA in the wastewater will not react completely, wasting oxidant and increasing the difficulty of subsequent wastewater treatment, potentially even causing environmental pollution due to excessive PVA levels during discharge. Conversely, if the reaction time is too long (e.g., Comparative Example 6), it will not significantly improve the final PVA removal rate but will actually reduce production efficiency. Regarding the amount of sodium hypochlorite added, if the amount is too small (e.g., Comparative Examples 7 and 8), although the PVA content in the wastewater before treatment is low, the reaction rate with the oxidant will be too slow due to the low PVA concentration, affecting the PVA removal efficiency and results. If the amount is too large (e.g., Comparative Examples 9 and 10), it will not only not significantly improve the final PVA removal rate but will also increase oxidant costs and reduce production efficiency.

[0064] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A low-concentration wastewater treatment device for PVA production process, characterized in that: The system includes a controller, a PVA production tank, and a wastewater reaction tank. The PVA production tank and the wastewater reaction tank are connected by an inlet pipe, which is equipped with an acid inlet, a baffle, and a pH meter. The acid inlet is connected to an acid inlet pipe, which is equipped with an acid regulating valve. The wastewater reaction tank is connected to a reagent inlet pipe and a drain pipe, which is equipped with a reagent regulating valve. The pH meter, acid regulating valve, and reagent regulating valve are all electrically connected to the controller.

2. The low-concentration wastewater treatment device for PVA production process according to claim 1, characterized in that: The pH meter is used to detect the pH of the wastewater in the inlet pipe, generate a pH signal, and transmit the pH signal to the controller. The controller receives the pH signal and adjusts the opening of the acid regulating valve according to the pH signal. The controller is also used to match the amount of reagent added according to the real-time input of the PVA concentration in the wastewater before treatment, and to control the opening of the reagent regulating valve in stages according to the amount of reagent added. The reagent is sodium hypochlorite.

3. The low-concentration wastewater treatment device for PVA production process according to claim 1, characterized in that: The wastewater reaction tank is equipped with a stirring device.

4. The low-concentration wastewater treatment device for PVA production process according to claim 1, characterized in that: The baffle plate includes several baffles spaced apart on both sides of the inner wall of the inlet pipe.

5. The low-concentration wastewater treatment device for PVA production process according to claim 1, characterized in that: A return pipe connects the drain pipe and the wastewater reaction tank.

6. The low-concentration wastewater treatment device for PVA production process according to claim 5, characterized in that: The return pipe is equipped with a return valve, which is electrically connected to the controller. The controller is used to adjust the valve opening of the return valve according to the real-time input of the PVA concentration in the treated wastewater.

7. The low-concentration wastewater treatment device for PVA production process according to claim 1, characterized in that: The bottom of the PVA production tank is connected to a reboiler, which is connected to a hot water pipe. A hot water valve is installed on the hot water pipe. A thermometer is installed on the wastewater reaction tank. Both the thermometer and the reboiler are electrically connected to the controller. The thermometer is used to detect the temperature of the wastewater in the wastewater reaction tank, generate a temperature signal, and transmit the temperature signal to the controller. The controller is used to receive the temperature signal and adjust the opening of the hot water valve according to the temperature signal.

8. The low-concentration wastewater treatment device for PVA production process according to claim 2, characterized in that: The graded control is as follows: when the PVA concentration in the wastewater before treatment is below 50 ppm, the sodium hypochlorite dosage is 3-5‰ of the PVA concentration; when the PVA concentration in the wastewater before treatment is between 50 ppm and 100 ppm, the sodium hypochlorite dosage is 2-4‰ of the PVA concentration; when the PVA concentration in the wastewater before treatment is above 100 ppm, the sodium hypochlorite dosage is 1-3‰ of the PVA concentration.

9. The low-concentration wastewater treatment device for PVA production process according to claim 3, characterized in that: The stirring device is a stirrer with a stirring speed of 60-120 rpm. The stirrer is electrically connected to a controller, which controls the start-up, shutdown, and rotation speed of the stirrer.

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