System and method for neutralizing high-sulfate acidic wastewater and cleaning pH meter underwater online

Abstract

The invention belongs to the technical field of viscose acid bath production, and particularly relates to a system and a method for neutralizing high-sulfate acid wastewater and cleaning a pH meter underwater online. The method comprises the following steps: 1) adding carbide slag slurry into the high-sulfate acidic wastewater for neutralization, and controlling the pH value to be 8-10; 2) filtering the neutralized waste liquid to obtain a filtrate; 3) leading the filtrate to an area where an on-line pH detection device is located; and 4) taking compressed air as a power source, spraying and washing the online pH detection device by using a mixed solution of a cleaning agent and the filtrate, and forming a positive pressure cleaning space on the pH sensor glass film ball. The problems of short service cycle and high replacement cost of the pH sensor when the carbide slag slurry is adopted for high-sulfate sewage are fundamentally solved, the addition amount of the carbide slag slurry is accurately controlled to reduce the cost, and meanwhile, scaling of follow-up equipment and pipelines of a neutralization reaction sedimentation tank is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of viscose acid bath production, and particularly relates to a system and method for neutralizing high-sulfate acid wastewater and cleaning a pH meter online underwater. BACKGROUND

[0002] At present, viscose enterprises have adopted calcium carbide slurry to remove sulfate radicals in high-salt acid wastewater. However, during the process of online pH measurement, calcium hydroxide in the calcium carbide slurry can form calcium sulfate precipitate, which adheres to the surface of the pH electrode, causing inaccurate pH control, short replacement cycle of the pH electrode, high cost, and the problem that the addition amount of the calcium carbide slurry cannot be accurately controlled due to the calcium sulfate scaling and blocking of the pH detection channel, which has become the biggest constraint for the development of high-sulfate wastewater treatment. In addition, high-sulfate acid wastewater contains large-particle solid impurities such as calcium sulfate and calcium carbonate, which also have an adverse effect on pH measurement.

[0003] The application provides a system and method for neutralizing high-sulfate acid wastewater and cleaning a pH meter online underwater, which realizes online pH cleaning, has a simple cleaning process, and low running cost. The addition of a pH electrode measurement sample pretreatment link not only prolongs the service life of the pH electrode, but also realizes accurate addition of calcium carbide slurry, and promotes the progress of high-sulfate wastewater treatment technology in the viscose fiber industry. SUMMARY

[0004] To solve the problems in the prior art, the application provides a system and method for neutralizing high-sulfate acid wastewater and cleaning a pH meter online underwater. The application not only fundamentally solves the problem of short service life and high replacement cost of the pH sensor in high-sulfate wastewater treatment using calcium carbide slurry, but also accurately controls the addition amount of the calcium carbide slurry to reduce cost, reduces scaling of subsequent equipment and pipelines after the neutralization reaction precipitate tank, and has a positive promoting effect on the development of acid wastewater treatment technology in viscose enterprises.

[0005] The technical scheme provided by the application is as follows:

[0006] A system for neutralizing high-sulfate acid wastewater and cleaning a pH meter online underwater comprises, in sequence, a calcium carbide slurry inlet pipe, an adjusting tank, a filtering device, and a sampling buffer tank. An online pH detection device is arranged in the sampling buffer tank. The filtering device is also connected to a spray cleaning device for spraying and cleaning the online pH detection device.

[0007] Based on the above technical scheme:

[0008] High sulfate wastewater is added into carbide slag slurry, and after mixing and precipitation, the mixture is pretreated by quartz sand and waste sodium type cation chelating resin, the pretreatment device uses compressed air as power, and the flow direction is online cleaning pH device, so as to be measured. The electrode cleaning of the online pH detection device uses water jet as power, the cleaning method is chemical cleaning combined with physical flushing, and an acidic environment is formed in the cleaning process to form an acidic positive pressure cavity, which can effectively remove various scales on the glass film ball of the pH sensor.

[0009] Specifically, the filter device comprises one filter unit, or comprises a plurality of filter units arranged in parallel, and each filter unit comprises a quartz sand filter and a waste resin filter arranged in sequence.

[0010] Based on the above technical scheme, the large particle solid impurities such as calcium sulfate and calcium carbonate in the wastewater can be effectively removed, and the small particle impurities such as calcium sulfate and calcium carbonate can be intercepted.

[0011] Specifically, in the waste resin filter, the saturation degree of the resin is greater than or equal to 10 kg of calcium, magnesium and iron ions per cubic resin.

[0012] Specifically, the waste resin is waste sodium type cation chelating resin, and the particle size is 0.3-1.2 mm.

[0013] Specifically, the loading height of the waste resin is 200-300 mm.

[0014] The inventor finds that the saturated and discarded resin, such as waste sodium type cation chelating resin, can continue to intercept small particle impurities such as calcium sulfate and calcium carbonate in the wastewater after saturation, thereby achieving the effect of waste utilization.

[0015] Specifically, the particle size of the quartz sand is 2-8 mm, and the particle size gradually increases from top to bottom.

[0016] Specifically, the loading height of the quartz sand filter is 150-300 mm.

[0017] In the above technical scheme, the pH online continuous measurement solution is pretreated by quartz sand and waste sodium type cation chelating resin, the quartz sand mainly removes large particle solid impurities such as calcium sulfate and calcium carbonate in the water, and the waste chelating resin mainly intercepts small particle impurities such as calcium sulfate and calcium carbonate.

[0018] Specifically, the spraying device comprises a spraying pump connected with the filter device, a compressed air machine and a cleaning agent machine are arranged on the pipeline connected between the filter device and the spraying pump, and the cleaning agent in the cleaning agent machine comprises the following weight percentage of each solute: 4-10% of ethylenediaminetetraacetic acid disodium, and 4-8% of sodium citrate.

[0019] Based on the above technical scheme:

[0020] The disodium ethylenediaminetetraacetate reacts with calcium ions in the wastewater to form chelated calcium, so that the calcium sulfate is dissolved to achieve the cleaning purpose, and the sodium citrate plays a buffering solution role to maintain an acidic environment system, and the pH of the cleaning cavity is 2-3 during the cleaning process;

[0021] During the cleaning process, compressed air of the Venturi jet device is used as a power source to spray the cleaning liquid into the cleaning cavity to clean the pH sensor glass membrane ball and form a positive pressure cleaning cavity.

[0022] The application also provides a method for neutralizing high-sulfate acidic wastewater and online underwater cleaning of a pH meter, comprising the following steps:

[0023] 1) Adding carbide slag slurry to the high-sulfate acidic wastewater for neutralization, and controlling the pH to be 8-10;

[0024] 2) Filtering the neutralized wastewater to obtain a filtrate;

[0025] 3) Leading the filtrate to an area where an online pH detection device is located;

[0026] 4) Using compressed air as a power source, spraying a mixture of a cleaning agent and the filtrate to the online pH detection device, and forming a positive pressure cleaning space on the pH sensor glass membrane ball.

[0027] In the above technical scheme, during the cleaning process, compressed air of the Venturi jet device is used as a power source to spray the cleaning liquid into the cleaning cavity to clean the pH sensor glass membrane ball and form a positive pressure cleaning cavity, without mechanical power, so that the calcium sulfate cannot deposit on the pH glass membrane, and the calcium sulfate is dissolved layer by layer.

[0028] Specifically, in step 1), the amount of carbide slag slurry added can be controlled by interlocking the pH meter and the carbide slag slurry pump frequency conversion.

[0029] Specifically, in step 2), the wastewater is sequentially filtered by quartz sand and waste resin.

[0030] In the above technical scheme, the pH online continuous measurement solution is pretreated by quartz sand + waste sodium type cation chelating resin, the particle size of the quartz sand is 2-8 mm, the particle size increases from top to bottom, the filling height is 150-300 mm, the particle size of the waste sodium type cation chelating resin is 0.3-1.2 mm, and the broken resin particles are removed by flotation

[0031] Specifically, in step 4), the cleaning agent comprises the following weight percentage of solutes: 4%-10% of disodium ethylenediaminetetraacetate, and 4%-8% of buffer solution sodium citrate.

[0032] In the technical solution, the disodium ethylenediaminetetraacetate plays a descaling role, and the sodium citrate plays a role of creating an acidic measuring environment.The disodium ethylenediaminetetraacetate reacts with calcium ions in the wastewater to generate chelated calcium, compressed air is used to separate the dissolved chelated calcium from calcium sulfate to achieve the cleaning purpose, and the sodium citrate plays a role of buffer solution to maintain an acidic environment system and promote the dissolution of calcium sulfate.

[0033] Specifically, in step 4):

[0034] The online pH detection device is cleaned for 1-3 minutes every 1-2 hours of operation;

[0035] During the cleaning process, the pH in the positive pressure cleaning space is 2-3;

[0036] During the cleaning process, the pressure in the positive pressure cleaning space is 1.5-2 MPa.

[0037] Specifically, the high-sulfate acidic wastewater is sulfate wastewater generated in the production process of viscose fibers, and the sulfate content in the wastewater is 10000 mg / l-12000 mg / l, which can be adapted to up to 250,000 tons / year of ordinary viscose fiber production.

[0038] Specifically, the addition amount of the calcium carbide slag slurry is 80 m 3 / h-100 m 3 / h.

[0039] Further, the sampling buffer tank is connected to the adjusting tank, and the wastewater is circulated until the required wastewater is obtained to avoid the discharge of wastewater that is not adjusted to the required position.

[0040] The beneficial effects of the present application are:

[0041] The present application precisely adds calcium carbide slag slurry to high-sulfate wastewater, reduces the excessive consumption of calcium carbide slag slurry, prolongs the service life of the pH electrode, reduces production costs, improves the biodegradability of the neutralized wastewater, reduces high-salt wastewater discharge, reduces sewage treatment costs, and protects the environment;

[0042] In the production process of ordinary viscose fibers, in order to reduce the consumption of production water, the concentration of the acid wastewater discharged from the spinning and drawing workshop is strictly controlled to result in a sulfate content of 10000 mg / l-12000 mg / l. The purpose of adding calcium carbide slag slurry is to replace the expensive caustic soda to neutralize the sulfuric acid in the high-sulfate wastewater, and to make all zinc ions in the wastewater react to generate zinc hydroxide. Since there are strict requirements for heavy metal ions in wastewater discharge, the pH requirement for the complete reaction of zinc ions to generate zinc hydroxide is pH greater than 10. The calcium hydroxide in the calcium carbide slag slurry is a slow-release process, and it accompanies the entire wastewater treatment process. Therefore, how to accurately control the pH of the adjusting tank between 6-8 and use the slow-release hydroxide in the calcium carbide slag slurry to make the zinc ions completely react is the significance of the pH meter.

[0043] The pretreatment device quartz sand filter is a four-layer quartz sand filter with different particle sizes, and the particle size increases from top to bottom, the liquid inlet mode is top liquid inlet, and the main purpose is to remove large particles of impurities; the waste sodium type resin is used to filter out small molecules of calcium sulfate which cannot be intercepted by the sand filter, and to remove part of calcium ions by using the residual adsorption capacity of the chelating resin to calcium ions to promote the dissolution of calcium sulfate and reduce the generation of calcium sulfate in the pH measurement process, the broken particles of the waste resin are removed by water flotation, and the wet method is used to fill the column and discharge air bubbles;

[0044] Compared with various calcium sulfate cleaning agents, the application does not need to add corrosion and scale inhibitors and surfactants, only needs 4%-10% of ethylenediaminetetraacetic acid disodium, and the buffer solution is 4%-8% of sodium citrate chemical cleaning, the cleaning formula is simple, efficient, and low in cost, calcium sulfate reacts with ethylenediaminetetraacetic acid disodium to generate soluble chelated calcium, and under acidic conditions, calcium carbonate also dissolves, and then in combination with compressed air blowing and flushing, the operation time is 1-3 minutes, which can achieve the purpose of scale layer dissolving and penetrating at the same time, and achieves the purpose of rapid stripping.

[0045] The Venturi tube is used to further improve the flow rate of the cleaning liquid, so that the cleaning liquid can be sprayed to the surface of the pH probe, and has obvious physical flushing effect; in the cleaning process, due to the existence of the cleaning cavity structure on the surface of the pH probe, the pressure in the cleaning cavity is obviously higher than the internal pressure of the solution during the cleaning process by the compressed air carrying the cleaning liquid, the dissolved and scaled components in the cleaning cavity are flushed out of the cleaning cavity, and a relatively independent cleaning positive pressure unit is formed. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is a structural schematic diagram of the system for neutralizing high-sulfate acid wastewater and online underwater cleaning of a pH meter.

[0047] ATTACHMENT Figure 1 In the drawings, the structures represented by the respective reference numerals are listed as follows:

[0048] 1, adjustment tank; 2, quartz sand filter; 3, waste resin filter; 4, sampling buffer tank; 5, online pH detection device; 6, jet pump; 7, compressed air supply machine; 8, cleaning agent supply machine; 9, carbide slag slurry inlet pipe. DETAILED DESCRIPTION

[0049] The principles and characteristics of the application are described below, and the examples are only used to explain the application and are not used to limit the scope of the application.

[0050] In the examples, the test methods are conventional methods unless otherwise specified; and the materials, reagents, etc. are commercially available reagents and materials unless otherwise specified.

[0051] In a specific embodiment, Figure 1 As shown, the system for online underwater cleaning of the pH meter includes a carbide slag slurry pipe 9, an adjustment tank 1, a filter device and a sampling buffer tank 4 which are connected in sequence. An online pH detection device 5 is arranged in the sampling buffer tank 4. The filter device is also connected to a spraying device for spraying the online pH detection device 5.

[0052] Preferably, the filtering device includes several filtering units arranged in parallel, each filtering unit includes a quartz sand filter 2 and a waste resin filter 3 which are connected in sequence. The processing capacity can be improved by connecting multiple filtering units in parallel.

[0053] Preferably, the quartz sand has a particle size of 2-8 mm, with the particle size gradually increasing from top to bottom. The filling height of the quartz sand filter 2 is 150-300 mm, preferably 200 mm. This can effectively remove large solid impurities such as calcium sulfate and calcium carbonate in the wastewater and is suitable for high-sulfate acidic wastewater.

[0054] The waste resin is a waste sodium type cationic chelating resin having a particle size of 0.3 mm to 1.2 mm. The waste resin is packed at a height of 200 to 300 mm, preferably 250 mm. The waste resin can be obtained from a waste sodium type cationic chelating resin discarded in a process for preparing xylose from hemicellulose (e.g., produced by Jiangsu Suqing Company). The waste resin is discarded when the conductivity of the filtrate from the cation resin column is greater than 15,000 μs / cm or the service life is greater than 14 months.

[0055] The spray cleaning device includes a jet pump 6 connected to the filter. A compressed air supply 7 and a cleaning agent supply 8 are provided in the pipeline between the filter and the jet pump 6. The cleaning agent in the cleaning agent supply 8 includes the following solutes in weight percentages: 4%-10% disodium EDTA and 4%-8% sodium citrate. In one embodiment, a venturi ejector is used to compress the air and provide the power source.

[0056] Example 1

[0057] A method for cleaning a pH meter underwater in high-sulfate acidic wastewater to solve the problem of electrode scaling preventing accurate pH control, comprising the following steps:

[0058] 1) High sulfate acidic wastewater is neutralized with carbide slag slurry. During the neutralization process, the pH control value is set to pH=8 to control the amount of carbide slag slurry added;

[0059] 2) The pH online continuous measurement solution is pretreated with quartz sand + waste sodium type cationic chelating resin. The quartz sand mainly filters large particles of solid impurities such as calcium sulfate and calcium carbonate in the water, and the waste chelating resin mainly intercepts small particles of calcium sulfate, calcium carbonate and other particulate impurities;

[0060] 3) pH on-line running time is 1 hour, and the on-line cleaning time under water is 1 minute;

[0061] 4) The pH meter uses on-line 4% ethylenediamine tetraacetic acid disodium under water, and the buffer solution is 4% sodium citrate chemical cleaning combined with compressed air flushing running time is 1 minute;

[0062] 5) The cleaning process uses Venturi jet as a power source to spray cleaning liquid into the cleaning cavity, and the pH sensor glass thin film ball forms a positive pressure cleaning cavity;

[0063] 6) The cleaning process in the cleaning cavity is pH = 2, ethylenediamine tetraacetic acid disodium reacts with calcium ions in the wastewater to generate chelated calcium, so that calcium sulfate is dissolved to achieve the purpose of cleaning, and sodium citrate acts as a buffer solution to maintain an acidic environment system.

[0064] In the initial high sulfate acid wastewater: the content of sulfate is 10000 mg / L.

[0065] Before cleaning, the pH meter directly measures the pH value of the wastewater and sets it to pH = 8, and the pH value deviation before and after cleaning is less than 5%, which meets the process control requirements.

[0066] Before cleaning, the pH meter reading is 8.02.

[0067] After cleaning, the pH meter reading is 8.04.

[0068] It can be seen that the test deviation is (8.04-8.02) / 8.02*100% = 0.24%, and the pH meter after cleaning restores the ability to accurately measure the pH value.

[0069] Example 2

[0070] A method for neutralizing high sulfate acid wastewater and on-line cleaning of pH meter under water, comprising the following steps:

[0071] 1) High sulfate acid wastewater is neutralized by carbide slag slurry, and the pH is set to control the pH = 10 to control the amount of carbide slag slurry added during the neutralization process;

[0072] 2) The pH on-line continuous measurement solution uses quartz sand + waste sodium type cation chelating resin pretreatment, and the quartz sand mainly filters large particles of calcium sulfate, calcium carbonate and other large particle solid impurities in water, and the waste chelating resin mainly intercepts small particles of calcium sulfate, calcium carbonate and other particle impurities;

[0073] 3) pH on-line running time is 2 hours, and the on-line cleaning time under water is 3 minutes;

[0074] 4) pH meter adopts underwater online 10% ethylenediamine tetraacetic acid disodium, buffer solution is 8% sodium citrate chemical cleaning, and compressed air blowing flushing operation time is 3 minutes;

[0075] 5) The cleaning process uses Venturi jet compressed air as power source to spray cleaning liquid into the cleaning cavity to clean the pH sensor glass membrane ball to form a positive pressure cleaning cavity;

[0076] 6) The cleaning process in the cleaning cavity pH = 3, ethylenediamine tetraacetic acid disodium reacts with calcium ions in wastewater to generate chelated calcium, so that calcium sulfate is dissolved to achieve the purpose of cleaning, and sodium citrate acts as a buffer solution to maintain an acidic environment system.

[0077] Before cleaning, the pH meter directly measures the pH value of the wastewater and sets it to pH = 10. The pH value deviation before and after cleaning is less than 5%, which meets the process control requirements.

[0078] Before cleaning, the pH meter reading is 9.98.

[0079] After cleaning, the pH meter reading is 10.02.

[0080] It can be seen that the test deviation is (10.02-9.98) / 9.98*100% = 0.40%, and the cleaned pH meter restores the ability to accurately measure the pH value.

[0081] Example 3

[0082] A method for online underwater cleaning of a pH meter in high sulfate acid wastewater neutralization, comprising the following steps:

[0083] 1) High sulfate acid wastewater is neutralized by carbide slag slurry, and the pH is set to control the pH = 8-10 to control the amount of carbide slag slurry added;

[0084] 2) The pH is measured online and continuously, and the quartz sand + waste sodium cation chelating resin is pretreated. The quartz sand mainly filters large particles of calcium sulfate, calcium carbonate and other large particle impurities in water, and the waste chelating resin mainly intercepts small particles of calcium sulfate, calcium carbonate and other particle impurities;

[0085] 3) The pH online operation time is 1.5 hours, and the underwater online cleaning time is 2 minutes;

[0086] 4) The pH meter adopts underwater online 7% ethylenediamine tetraacetic acid disodium, buffer solution is 6% sodium citrate chemical cleaning, and compressed air blowing flushing operation time is 2 minutes;

[0087] 5) The cleaning process uses Venturi jet compressed air as power source to spray cleaning liquid into the cleaning cavity to clean the pH sensor glass membrane ball to form a positive pressure cleaning cavity;

[0088] 6) The pH in the cleaning cavity is 2.25 during the cleaning process. The calcium ions in the waste water react with the disodium ethylenediaminetetraacetate to form chelated calcium, so that the calcium sulfate is dissolved to achieve the cleaning purpose. Meanwhile, the sodium citrate functions as a buffer solution to maintain the acidic environment system.

[0089] Before cleaning, the pH of the waste water is directly measured by the pH meter and is set to pH=10. The pH value deviation before and after cleaning is less than 5%, which meets the process control requirements.

[0090] Before cleaning, the pH meter reading is 9.98.

[0091] After cleaning, the pH meter reading is 10.02.

[0092] It can be seen that the test deviation is (10.02-9.98) / 9.98*100%=0.40%, and the pH meter after cleaning restores the ability to accurately measure the pH value.

[0093] Example 4

[0094] With reference to Example 1, the difference is that the continuous operation is 2, 4, 8, 16 and 24 hours, and the pH of the waste water is directly measured by the pH meter after 2, 4, 8, 16 and 24 hours, respectively, and is compared with the standard pH meter reading. After testing, the cleaning period is 4 hours, and the online cleaning time under water is 3 minutes. Within 5 periods, the error between the directly measured pH of the waste water and the pH meter reading can be ensured to be within 5%. However, when the cleaning is performed with 4 hours as a period, after 30 periods, it is found that the pH meter surface is scaled, the pH measurement deviation reaches 10%, and the pH value cannot be accurately measured, so that it is difficult to strictly control the calcium carbide slurry addition amount. Therefore, according to the cleaning method of the present application, the pH meter can be ensured to work normally for up to 2-3 hours, and the accurate control of the calcium carbide slurry addition amount is ensured.

[0095] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A system for online underwater cleaning of pH meters in high-sulfate acidic wastewater, characterized by: The invention comprises a carbide slag slurry inlet pipe (9), an adjusting tank (1), a filtering device and a sampling buffer tank (4) which are sequentially connected. An online pH detection device (5) is arranged in the sampling buffer tank (4). The filtering device is also connected to a spraying device for spraying the online pH detection device (5).

2. The system for online underwater cleaning of a pH meter in high-sulfate acidic wastewater according to claim 1, characterized in that: The filtering device comprises a filtering unit, or comprises a plurality of filtering units arranged in parallel, each of the filtering units comprising a quartz sand filter (2) and a waste resin filter (3) which are arranged in series and in communication.

3. The system for online underwater cleaning of a pH meter in high-sulfate acidic wastewater according to claim 2, characterized in that: The saturation of the waste resin in the waste resin filter (3) is greater than or equal to 10 kg of calcium, magnesium and iron ions per cubic meter of resin.

4. The system for online underwater cleaning of a pH meter in high-sulfate acidic wastewater according to claim 2, characterized in that: The particle size of the quartz sand filled in the quartz sand filter (2) is 2-8 mm, the particle size gradually increases from top to bottom, and the filling height of the quartz sand is 150-300 mm; The waste resin in the waste resin filter (3) is a waste sodium type cationic chelating resin with a particle size of 0.3 mm to 1.2 mm. The filling height of the waste resin is 200 to 300 mm.

5. The system for online underwater cleaning of a pH meter in high-sulfate acidic wastewater according to any one of claims 1 to 4, characterized in that: The spray cleaning device comprises a jet pump (6) connected to the filter device, and a compressed air supply machine (7) and a cleaning agent supply machine (8) are provided on a pipeline connecting the filter device and the jet pump (6). The cleaning agent in the cleaning agent supply machine (8) comprises the following solutes in the following weight percentages: 4%-10% of disodium ethylenediaminetetraacetic acid and 4%-8% of sodium citrate.

6. A method for cleaning a pH meter in high-sulfate acidic wastewater, characterized in that: The following steps are involved: 1) Add carbide slag slurry to the high sulfate acid wastewater for neutralization, and control the pH to 8-10; 2) filtering the neutralized waste liquid to obtain a filtrate; 3) directing a portion of the filtrate to an area where an online pH detection device is located; 4) Using compressed air as a power source, a mixed solution formed by mixing the cleaning agent and part of the filtrate is sprayed on the online pH detection device, and a positive pressure cleaning space is formed on the glass film ball of the pH sensor.

7. The method for cleaning a pH meter in high-sulfate acidic wastewater under online water according to claim 6, characterized in that: In step 2), the waste liquid is sequentially filtered through quartz sand and then through waste resin.

8. The method for cleaning a pH meter in high-sulfate acidic wastewater under online water according to claim 6, characterized in that: In step 4), the cleaning agent comprises the following solutes in the following weight percentages: 4%-10% of disodium edetate and 4%-8% of sodium citrate.

9. The method for cleaning a pH meter in high-sulfate acidic wastewater under online water according to claim 6, characterized in that: In step 4): The online pH detection device should be cleaned for 1-3 minutes every 1-2 hours of operation; During the cleaning process, the pH in the positive pressure cleaning space is 2-3; During the cleaning process, the positive pressure cleaning space pressure is 0.15-0.2MPa.

10. The method for cleaning a pH meter in high-sulfate acidic wastewater under online water according to any one of claims 6 to 9, characterized in that: The high-sulfate acidic wastewater is sulfate wastewater from the viscose fiber production process, wherein the sulfate content is 10000mg / l-12000mg / l; The amount of carbide slag slurry added is 80m 3 / h-100m 3 / h.

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