Ammonia nitrogen detection pretreatment method and application thereof

Abstract

The invention belongs to the technical field of ammonia nitrogen detection, and relates to an ammonia nitrogen detection pretreatment method which comprises the following steps: taking a wastewater sample, adding a pH regulator while stirring, and regulating the pH value to a set value A to obtain a mixed solution; filtering the mixed solution through a gaseous membrane, converting ammonia nitrogen from ammonia ions into ammonia gas, and absorbing the ammonia gas by an absorption liquid through the gaseous membrane to obtain a to-be-detected liquid; determining the ammonia nitrogen concentration of the to-be-detected liquid by using a colorimetric method; repeating the steps and adjusting the pH value to a set value B during repeating; evaluating whether the ammonia nitrogen transfer efficiency reaches the standard or not, and calculating the error of the ammonia nitrogen measured twice, if the error is gt; according to the standard value, repeating the contrast test until the error of two adjacent ammonia nitrogen measurements is less than or equal to the standard value. Ammonia nitrogen in the wastewater is transferred to the absorption liquid through the gaseous membrane, the influence of impurities in the wastewater on ammonia nitrogen content measurement is avoided, operation is easy, few reagents are used, ammonia nitrogen detection is more accurate, and the pretreatment effect can be detected and adjusted according to different water quality dynamic states on a wastewater treatment site.

Description

Technical Field

[0001] The invention belongs to the technical field of ammonia nitrogen detection and relates to an ammonia nitrogen detection pretreatment method and application thereof. Background Art

[0002] Liquor wastewater mainly includes production wastewater (cellar bottom water, pot bottom water and cleaning water, etc.) and domestic sewage. The ammonia nitrogen concentration of wastewater discharged from different sections is different. Among them, the ammonia nitrogen concentration of cleaning water is only a few milligrams / liter, the ammonia nitrogen concentration of pot bottom water is hundreds of milligrams / liter, and the ammonia nitrogen concentration of cellar bottom water can reach thousands of milligrams / liter. Low-concentration ammonia nitrogen-containing wastewater will lead to eutrophication of water bodies, while high-concentration ammonia nitrogen-containing wastewater is more toxic to organisms, so it is very important to accurately analyze the ammonia nitrogen concentration in this type of wastewater.

[0003] However, in the process of determining ammonia nitrogen concentration, since the wastewater discharged from different production process stages of sauce-flavored liquor contains interfering substances of different types and concentrations, such as calcium and magnesium ions and humus, pretreatment is generally required before determination to eliminate interference as much as possible.

[0004] At present, the methods for ammonia nitrogen detection include pretreatment combined colorimetry and electrode method. The electrode method basically uses a gas-sensitive electrode to detect ammonia nitrogen, and usually does not require pretreatment of water samples. However, the electrode responds slowly after long-term use, and the electrode is easily contaminated, so it is not as reliable as the colorimetric method. The colorimetric method requires appropriate pretreatment to achieve accurate measurement.

[0005] Conventional pretreatment methods for ammonia nitrogen detection include flocculation with drugs, distillation, or a combination of the above methods. The flocculation method mainly uses zinc sulfate-sodium hydroxide or iron aluminum salts to remove the interference of calcium and magnesium ions and some colloids and suspended solids, but cannot remove the interference of color. In addition, as mentioned above, due to the different ammonia nitrogen concentrations and impurity contents of wastewater discharged from different sections of workshop production, during the on-site detection of ammonia nitrogen, the same pretreatment method cannot be applied to wastewater detection at different times. It is necessary to dynamically adjust the types and dosages of multiple reagents, which is cumbersome and inconvenient. Distillation is the best recommended method among all the methods currently available. It can effectively remove the influence of interfering substances, but the operation process such as heating absorption is complicated and is currently used more in laboratories. Summary of the invention

[0006] In view of this, the present invention provides an ammonia nitrogen detection pretreatment method and application thereof, which can solve the above-mentioned technical problems.

[0007] The purpose of the present invention is to provide an ammonia nitrogen detection pretreatment method and its application, which utilizes a gaseous membrane to transfer ammonia nitrogen in wastewater to an absorption liquid, thereby avoiding the influence of impurities in the wastewater on the subsequent colorimetric measurement of ammonia nitrogen content. Only Ph needs to be adjusted, the operation is simple, less reagents are used, and the effect on the ammonia nitrogen detection result is small. The pretreatment method can be dynamically adjusted according to different water qualities, and therefore, it is suitable for wastewater treatment sites.

[0008] An ammonia nitrogen detection pretreatment method comprises the following steps:

[0009] Adjusting pH: taking a wastewater sample and adding a pH adjuster to the wastewater sample under stirring to adjust the pH to a set value A to obtain a mixed solution;

[0010] Transfer ammonia nitrogen: The mixed liquid is filtered through a gaseous membrane, and the ammonia nitrogen is converted from ammonia ions to ammonia gas, which is then absorbed by the absorption liquid through the gaseous membrane to obtain the liquid to be tested;

[0011] Detection: Determine the ammonia nitrogen concentration of the liquid to be tested by colorimetry;

[0012] Control test: Repeat the above steps and adjust the pH to set value B during repetition;

[0013] Evaluation and correction: Evaluate whether the ammonia nitrogen transfer efficiency meets the standard, calculate the error of two ammonia nitrogen measurements, if the error is greater than the standard value, repeat the control test until the error of two consecutive ammonia nitrogen measurements is ≤ the standard value.

[0014] In some embodiments, the set value B ≥ the set value A;

[0015] Preferably, the set value A is 10-13; preferably, the set value A is 10.5-12;

[0016] Preferably, the set value B is 10.5-14; preferably, the set value B is 12-14.

[0017] In some embodiments, the wastewater includes at least one of low-concentration ammonia nitrogen wastewater, medium-concentration ammonia nitrogen wastewater, or high-concentration ammonia nitrogen wastewater;

[0018] Preferably, the ammonia nitrogen content of the low-concentration ammonia nitrogen wastewater is less than or equal to 10 mg / L;

[0019] Preferably, the ammonia nitrogen content of the medium-concentration ammonia nitrogen wastewater is greater than 10 mg / L and less than 1000 mg / L;

[0020] Preferably, the ammonia nitrogen content of the high-concentration ammonia nitrogen wastewater is greater than or equal to 1000 mg / L;

[0021] Preferably, when the wastewater is low-concentration ammonia nitrogen wastewater, the set value A is 10-11, and the set value B is 11-12; preferably, when the wastewater is low-concentration ammonia nitrogen wastewater, the set value A is 10.5-10.8, and the set value B is 11.5-12;

[0022] Preferably, when the wastewater is medium-concentration ammonia nitrogen wastewater, the set value A is 10.5-11.5, and the set value B is 11.5-13.5; preferably, when the wastewater is medium-concentration ammonia nitrogen wastewater, the set value A is 10.8-11.3, and the set value B is 12-13;

[0023] Preferably, when the wastewater is high-concentration ammonia nitrogen wastewater, the set value A is 11-12, and the set value B is 12-14; preferably, when the wastewater is high-concentration ammonia nitrogen wastewater, the set value A is 11.5-12.5, and the set value B is 12.5-13.5.

[0024] In some embodiments, in the evaluation and correction step, the standard value is 5-15%; preferably, the standard value is 10%.

[0025] In some embodiments, a quality control step is further included, wherein the quality control method is: spike recovery and calculation of spike recovery rate, and evaluation of whether the control test step needs to be repeated according to the spike recovery rate;

[0026] Preferably, when the spiked recovery rate is within the range of 90-110%, there is no need to repeat the control test step, otherwise the control test step needs to be repeated; preferably, when the spiked recovery rate is within the range of 95-105%, there is no need to repeat the control test step, otherwise the control test step needs to be repeated.

[0027] In some embodiments, the pH adjuster is alkali solution;

[0028] Preferably, the pH regulator is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium bicarbonate solution, and potassium bicarbonate solution;

[0029] Preferably, the absorption liquid is at least one of sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid;

[0030] Preferably, the absorption liquid is sulfuric acid.

[0031] In some embodiments, before the pH adjustment step, the ammonia nitrogen content of the wastewater is predicted, and the specific method of the prediction is to pre-treat the wastewater tested for the first time by alkali-distillation method to determine the approximate pH range.

[0032] In some embodiments, the gaseous membrane includes at least one of a PP gaseous membrane, a PVDF gaseous membrane, or a PTFE gaseous membrane.

[0033] In a second aspect, the present invention provides an ammonia nitrogen detection method, comprising any one of the pretreatment methods described above.

[0034] In a third aspect, the present invention provides an application of the above-mentioned pretreatment method, wherein the pretreatment method is applied in the detection process of ammonia nitrogen in sauce wine wastewater; preferably, the sauce wine wastewater includes at least one of low-concentration ammonia nitrogen wastewater, medium-concentration ammonia nitrogen wastewater or high-concentration ammonia nitrogen wastewater;

[0035] Preferably, the ammonia nitrogen content of the low-concentration ammonia nitrogen wastewater is less than or equal to 10 mg / L;

[0036] Preferably, the ammonia nitrogen content of the medium-concentration ammonia nitrogen wastewater is greater than 10 mg / L and less than 1000 mg / L;

[0037] Preferably, the ammonia nitrogen content of the high-concentration ammonia nitrogen wastewater is greater than or equal to 1000 mg / L;

[0038] Preferably, the calcium ion content in the sauce wine wastewater is 100-10000 mg / L, and the magnesium ion content is 30-3000 mg / L; the concentrations of calcium and magnesium ions in the sauce wine wastewater from different production stages are quite different, and the interference with ammonia nitrogen detection is also different. The calcium ion content is about 100 mg / L for the bottom water of the pot and about 10000 mg / L for the bottom water of the cellar. The magnesium ion content is about 30 mg / L for the bottom water of the pot and about 3000 mg / L for the bottom water of the cellar.

[0039] Preferably, the pretreatment method is applied in on-site ammonia nitrogen detection.

[0040] In summary, the present application includes at least one of the following beneficial technical effects:

[0041] (1) A gas membrane is used to transfer ammonia nitrogen in the wastewater to the absorption liquid, thereby avoiding the influence of impurities in the wastewater on the subsequent colorimetric method for measuring ammonia nitrogen content. The pretreatment method of the present invention only needs to adjust Ph, which is simple to operate, uses less reagents, and has little effect on the ammonia nitrogen detection results. The pretreatment Ph can be dynamically adjusted according to different water qualities at the wastewater treatment site, and the effect of the pretreatment can be tested and adjusted at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is an operation flow chart of the pretreatment method of the present invention. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below by specific embodiments, which do not limit the protection scope of the present invention. Some non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the protection scope of the present invention.

[0044] Example 1

[0045] An ammonia nitrogen detection pretreatment method comprises the following steps:

[0046] (1) pH adjustment: 100 mL of low-concentration ammonia nitrogen wastewater (ammonia nitrogen content of 2.24 mg / L) of sauce wine is pumped into a reaction container through a water inlet pump, and then 1-2 mL of sodium hydroxide solution is added under stirring until the pH is 10-11 to obtain a mixed solution. Considering the on-site treatment environment and rapid removal of interference, the water sample extracted from the sauce wine wastewater can also be other appropriate volumes. The specific amount of sodium hydroxide solution added is controlled by observing the pH value measured by the pH meter to adjust the pH to 10-11;

[0047] (2) Transferring ammonia nitrogen: Stop stirring and let stand for 1-2 minutes, then start the suction pump. The mixed liquid is filtered through a PP gas membrane and stored in a temporary storage tank. The ammonia nitrogen is converted from ammonia ions to ammonia gas and passes through the gas membrane. It enters 5% (v / v) sulfuric acid and is absorbed by the sulfuric acid to obtain the liquid to be tested;

[0048] (3) Cleaning: After the suction is completed, add ammonia-free water to the reaction container, mix and stir to rinse the reaction container, and then discharge it all through the vent pipe, and ensure that the precipitate is discharged until the reaction container is clean;

[0049] (4) Detection: Determine the ammonia nitrogen concentration of the liquid to be tested by colorimetry;

[0050] (5) Control test: repeat steps (1-4) and increase the amount of sodium hydroxide solution added during the repetition to adjust the pH to 11-12;

[0051] (6) Evaluation and correction: Calculate the error of the two ammonia nitrogen determinations. If the error is >10%, repeat steps (1-4) until the error is ≤10%. The error calculation method is: (second test value - first test value) / second test value * 100%;

[0052] (7) Quality control: On the basis that the error of two determinations of ammonia nitrogen is ≤10%, a set amount of standard sample is simultaneously drawn into the reaction container by a standard sample injection pump, and steps (1-4) are repeated. When the measured ammonia nitrogen spike recovery rate is 95-105%, the ammonia nitrogen result is the final result, wherein the spike recovery rate is calculated as follows: spike recovery rate = difference in ammonia nitrogen before and after spike addition / spike amount*100%.

[0053] Example 2

[0054] An ammonia nitrogen detection pretreatment method comprises the following steps:

[0055] (1) pH adjustment: 100 mL of medium-concentration ammonia nitrogen wastewater (ammonia nitrogen content 37.78 mg / L) of sauce wine is pumped into a reaction container through a water inlet pump, and then 1-2 mL of potassium hydroxide solution is added under stirring until the pH is 10.5-11.5 to obtain a mixed solution. Considering the on-site treatment environment and rapid removal of interference, the water sample extracted from the sauce wine wastewater can also be other appropriate volumes. The specific amount of sodium hydroxide solution added is controlled by observing the pH value measured by the pH meter;

[0056] (2) Transferring ammonia nitrogen: Stop stirring and let stand for about 3 minutes before starting the suction pump. The mixed liquid is filtered through a gas membrane made of PVDF and stored in a temporary storage tank. The ammonia nitrogen is converted from ammonia ions to ammonia gas and then passes through the gas membrane and enters 5% (v / v) sulfuric acid to be absorbed, thereby obtaining a liquid to be tested;

[0057] (3) Cleaning: After the suction is completed, add ammonia-free water to the reaction container, mix and stir to rinse the reaction container, and then discharge it all through the vent pipe, and ensure that the precipitate is discharged until the reaction container is clean;

[0058] (4) Detection: Determine the ammonia nitrogen concentration of the liquid to be tested by colorimetry;

[0059] (5) Control test: repeat steps (1-4) and increase the amount of potassium hydroxide solution added during the repetition to adjust the pH to 11.5-13.5;

[0060] (6) Evaluation and correction: Calculate the error between the two determinations of ammonia nitrogen. If the error is >10%, repeat steps (1-4) until the error is ≤10%.

[0061] (7) Quality control: On the basis that the error of two determinations of ammonia nitrogen is ≤10%, a set amount of standard sample is simultaneously drawn into the reaction container by a standard sample injection pump, and steps (1-4) are repeated. When the measured ammonia nitrogen spike recovery rate is 95-105%, the ammonia nitrogen result is the final result, wherein the spike recovery rate is calculated as follows: spike recovery rate = difference in ammonia nitrogen before and after spike addition / spike amount*100%.

[0062] Example 3

[0063] An ammonia nitrogen detection pretreatment method comprises the following steps:

[0064] (1) pH adjustment: 100 mL of medium-concentration ammonia nitrogen wastewater (ammonia nitrogen content 264.00 mg / L) of sauce wine is pumped into a reaction container through a water inlet pump, and then 1-2 mL of potassium hydroxide solution is added under stirring until the pH is 10.5-11.5 to obtain a mixed solution. Considering the on-site treatment environment and rapid removal of interference, the water sample extracted from the sauce wine wastewater can also be other appropriate volumes. The specific amount of sodium hydroxide solution added is controlled by observing the pH value measured by the pH meter;

[0065] (2) Transferring ammonia nitrogen: Stop stirring and let stand for about 3 minutes before starting the suction pump. The mixed liquid is filtered through a gas membrane made of PVDF and stored in a temporary storage tank. The ammonia nitrogen is converted from ammonia ions to ammonia gas and then passes through the gas membrane and enters 5% (v / v) sulfuric acid to be absorbed, thereby obtaining a liquid to be tested;

[0066] (3) Cleaning: After the suction is completed, add ammonia-free water to the reaction container, mix and stir to rinse the reaction container, and then discharge it all through the vent pipe, and ensure that the precipitate is discharged until the reaction container is clean;

[0067] (4) Detection: Determine the ammonia nitrogen concentration of the liquid to be tested by colorimetry;

[0068] (5) Control test: repeat steps (1-4) and increase the amount of potassium hydroxide solution added during the repetition to adjust the pH to 11.5-13.5;

[0069] (6) Evaluation and correction: Calculate the error between the two determinations of ammonia nitrogen. If the error is >10%, repeat steps (1-4) until the error is ≤10%.

[0070] (7) Quality control: On the basis that the error of two determinations of ammonia nitrogen is ≤10%, a set amount of standard sample is simultaneously drawn into the reaction container by a standard sample injection pump, and steps (1-4) are repeated. When the measured ammonia nitrogen spike recovery rate is 95-105%, the ammonia nitrogen result is the final result, wherein the spike recovery rate is calculated as follows: spike recovery rate = difference in ammonia nitrogen before and after spike addition / spike amount*100%.

[0071] Example 4

[0072] An ammonia nitrogen detection pretreatment method comprises the following steps:

[0073] (1) pH adjustment: 100 mL of high-concentration ammonia nitrogen wastewater (ammonia nitrogen content 1870.65 mg / L) of sauce wine is pumped into a reaction container through a water inlet pump, and then 1-2 mL of sodium hydroxide solution is added under stirring until the pH is 11-12 to obtain a mixed solution. Considering the on-site treatment environment and rapid removal of interference, the water sample extracted from the sauce wine wastewater can also be other appropriate volumes. The specific amount of sodium hydroxide solution added is controlled by observing the pH value measured by the pH meter;

[0074] (2) Transferring ammonia nitrogen: Stop stirring and let stand for 5 minutes before starting the suction pump. The mixed liquid is filtered through a PTFE gas membrane and stored in a temporary storage tank. The ammonia nitrogen is converted from ammonia ions to ammonia gas and then passes through the gas membrane and enters 5% (v / v) sulfuric acid to be absorbed, thereby obtaining a liquid to be tested;

[0075] (3) Cleaning: After the suction is completed, add ammonia-free water to the reaction container, mix and stir to rinse the reaction container, and then discharge it all through the vent pipe, and ensure that the precipitate is discharged until the reaction container is clean;

[0076] (4) Detection: Determine the ammonia nitrogen concentration of the liquid to be tested by colorimetry;

[0077] (5) Control test: repeat steps (1-4) and increase the amount of sodium hydroxide solution added during the repetition to adjust the pH to 12-14;

[0078] (6) Evaluation and correction: Calculate the error between the two determinations of ammonia nitrogen. If the error is >10%, repeat steps (1-4) until the error is ≤10%.

[0079] (7) Quality control: On the basis that the error of two determinations of ammonia nitrogen is ≤10%, a set amount of standard sample is simultaneously drawn into the reaction container by a standard sample injection pump, and steps (1-4) are repeated. When the measured ammonia nitrogen spike recovery rate is 95-105%, the ammonia nitrogen result is the final result, wherein the spike recovery rate is calculated as follows: spike recovery rate = difference in ammonia nitrogen before and after spike addition / spike amount*100%.

[0080] Example 5

[0081] An ammonia nitrogen detection pretreatment method comprises the following steps:

[0082] (1) pH adjustment: First, the ammonia nitrogen content of different sections of the sauce wine wastewater is predicted at the wastewater treatment site. For the wastewater tested for the first time, the approximate pH range is determined by pretreatment with alkali-distillation method. After the approximate pH range of the wastewater to be tested is obtained, 100 mL of the sauce wine wastewater of this period is pumped into the reaction container through the water inlet pump, and then sodium hydroxide solution is added under stirring until the pH is within the predicted range to obtain a mixed solution. Considering the on-site treatment environment and rapid removal of interference, the water sample extracted from the sauce wine wastewater can also be other appropriate volumes. The specific dosage of the sodium hydroxide solution is controlled by observing the pH value measured by the pH meter;

[0083] (2) Transferring ammonia nitrogen: Stop stirring and let it stand for a certain period of time before starting the suction pump. The mixed liquid is filtered through a PP gas membrane and stored in a temporary storage tank. The ammonia nitrogen is converted from ammonia ions to ammonia gas and then passes through the gas membrane and enters 5% (v / v) sulfuric acid to be absorbed, thereby obtaining a liquid to be tested;

[0084] (3) Cleaning: After the suction is completed, add ammonia-free water to the reaction container, mix and stir to rinse the reaction container, and then discharge it all through the vent pipe, and ensure that the precipitate is discharged until the reaction container is clean;

[0085] (4) Detection: Determine the ammonia nitrogen concentration of the liquid to be tested by colorimetry;

[0086] (5) Control test: repeat steps (1-4) and increase the amount of sodium hydroxide solution added during the repetition to adjust the pH to 11-12 for wastewater predicted to have a low concentration of ammonia nitrogen, to 11.5-13.5 for wastewater predicted to have a medium concentration of ammonia nitrogen, and to 12-14 for wastewater predicted to have a high concentration of ammonia nitrogen;

[0087] (6) Evaluation and correction: Calculate the error between the two determinations of ammonia nitrogen. If the error is >10%, repeat steps (1-4) until the error is ≤10%.

[0088] (7) Quality control: On the basis that the error of two determinations of ammonia nitrogen is ≤10%, a set amount of standard sample is simultaneously drawn into the reaction container by a standard sample injection pump, and steps (1-4) are repeated. When the measured ammonia nitrogen spike recovery rate is 95-105%, the ammonia nitrogen result is the final result, wherein the spike recovery rate is calculated as follows: spike recovery rate = difference in ammonia nitrogen before and after spike addition / spike amount*100%.

[0089] Comparative Example 1

[0090] During the ammonia nitrogen detection process of on-site treatment of Maotai liquor wastewater, it was found that the test results of the absorption liquid being sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid were similar. During the test, the above-mentioned different acidic solutions can be replaced as absorbents according to the actual situation. Based on Example 2, the results of using other solutions besides acidic solvents as absorption liquids are further explored.

[0091] A pretreatment method for ammonia nitrogen detection is different from Example 2 in that the absorption liquid is replaced by an equal amount of pure water.

[0092] Effect example

[0093] 1. The first two ammonia nitrogen detection errors and spiked recovery rates of Examples 1-4 and Comparative Example 1 are shown in Table 1 below:

[0094] Table 1 Ammonia nitrogen detection error and recovery results

[0095]

[0096] It can be seen that the absorption efficiency of acidic solutions such as sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid is better than that of ammonia-free water or pure water. It not only ensures that there is no interference from calcium, magnesium ions and humus substances in the absorption liquid, but also sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid can quickly and thoroughly absorb ammonia and quickly achieve reaction equilibrium.

[0097] Generally, calcium and magnesium ions in sauce-flavored liquor wastewater exist in combination with bicarbonate ions, and become precipitates after the addition of sodium hydroxide, in which the sodium hydroxide solution reacts to produce magnesium hydroxide and calcium carbonate. The sodium hydroxide solution can also be replaced by potassium hydroxide solution or other alkaline solutions that do not contain ammonium ions.

[0098] In an alkaline environment of pH ≥ 10.5, calcium and magnesium ions are basically precipitated, and no other agents need to be added to eliminate interference, but the efficient conversion of ammonia nitrogen from ammonium ions to ammonia gas requires further increase in pH. Therefore, the present invention sets the pH value before the initial gaseous membrane filtration to 10.5-12. At this time, it is impossible to determine whether the pretreatment transfers all ammonia nitrogen to the absorption liquid. Therefore, the second gaseous membrane filtration sets the pH value to 12-14. If the efficiency of ammonia nitrogen transfer through the gaseous membrane is low, then increasing the pH value before the second gaseous membrane is conducive to the transfer of ammonia nitrogen that cannot be transferred at the first pH value. There will be a large error between the ammonia nitrogen content of the two tests, indicating that the transfer of the first gaseous membrane filtration is not complete, and the pH value before the first gaseous membrane filtration is set too small. Therefore, the ammonia nitrogen transferred by the second gaseous membrane filtration is evaluated in the same way until the error between the two adjacent times is less than 10%, and the ammonia nitrogen transfer reaches the maximum at this pH value.

[0099] Through such a pretreatment method, the influence of other impurities in the wastewater on the detection of ammonia nitrogen can be reduced without the use of additional reagents to eliminate interference, and the content of ammonia nitrogen can be detected more accurately. The pH value can also be dynamically adjusted at the wastewater treatment site to detect wastewater with different ammonia nitrogen contents, and the ammonia nitrogen content detection of complex wastewater with changing water quality can be realized. This method only needs to adjust the pH and does not require heating. The method is simple, easy to operate, simple in process, and has little interference, which can ensure that the subsequent colorimetric ammonia nitrogen detection is more accurate. However, in order to ensure that the ammonia nitrogen in the wastewater is not interfered by factors such as gaseous membrane pollution and absorption rate, the wastewater needs to be spiked and recovered, and the accuracy of the ammonia nitrogen data can be achieved under the dual control conditions of error ≤10% and spike recovery rate 95-105%. If the spike recovery rate cannot reach 95-105% for the second time, the detection is stopped and the "detection error" message is displayed.

[0100] Although there is currently a pretreatment method that transfers ammonia nitrogen in wastewater to absorption liquid after filtering the wastewater through a selective membrane, it requires combined means such as adding alkali and heating to achieve as much ammonia nitrogen transfer as possible. This is not only inconvenient for on-site wastewater treatment operations, but the membrane distillation phenomenon will cause the ammonia nitrogen concentration in the absorption liquid to be diluted, affecting the detection accuracy. At the same time, it is also impossible to guarantee and evaluate whether the ammonia nitrogen transfer is complete.

[0101] Similarly, although ammonia nitrogen is currently removed from wastewater by filtering wastewater with gaseous membranes, it is also necessary to add alkali and heat to achieve the ammonia nitrogen standard in the treated wastewater as much as possible. The membrane distillation phenomenon that also exists causes the ammonia nitrogen concentration in the absorption liquid to be diluted, and the accuracy of ammonia nitrogen detection on the absorption liquid side is not paid attention to in wastewater treatment projects. Therefore, it cannot be used to accurately detect the ammonia nitrogen content, and it is also impossible to monitor and adjust whether the ammonia nitrogen transfer is thorough.

[0102] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A pretreatment method for ammonia nitrogen detection, characterized in that: The following steps are involved: Adjusting pH: taking a wastewater sample and adding a pH adjuster to the wastewater sample under stirring to adjust the pH to a set value A to obtain a mixed solution; Transfer ammonia nitrogen: The mixed liquid is filtered through a gaseous membrane, and the ammonia nitrogen is converted from ammonia ions to ammonia gas, which is then absorbed by the absorption liquid through the gaseous membrane to obtain the liquid to be tested; Detection: Determine the ammonia nitrogen concentration of the liquid to be tested by colorimetry; Control test: Repeat the above steps and adjust the pH to set value B during repetition; Evaluation and correction: Evaluate whether the ammonia nitrogen transfer efficiency meets the standard, calculate the error of two ammonia nitrogen measurements, if the error is greater than the standard value, repeat the control test until the error of two consecutive ammonia nitrogen measurements is ≤ the standard value.

2. The ammonia nitrogen detection pretreatment method according to claim 1, characterized in that: The set value B ≥ the set value A; Preferably, the set value A is 10-13; preferably, the set value A is 10.5-12; Preferably, the set value B is 10.5-14; preferably, the set value B is 12-14.

3. The ammonia nitrogen detection pretreatment method according to claim 1, characterized in that: The wastewater includes at least one of low-concentration ammonia nitrogen wastewater, medium-concentration ammonia nitrogen wastewater or high-concentration ammonia nitrogen wastewater; Preferably, the ammonia nitrogen content of the low-concentration ammonia nitrogen wastewater is less than or equal to 10 mg / L; Preferably, the ammonia nitrogen content of the medium-concentration ammonia nitrogen wastewater is greater than 10 mg / L and less than 1000 mg / L; Preferably, the ammonia nitrogen content of the high-concentration ammonia nitrogen wastewater is greater than or equal to 1000 mg / L; Preferably, when the wastewater is low-concentration ammonia nitrogen wastewater, the set value A is 10-11, and the set value B is 11-12; preferably, when the wastewater is low-concentration ammonia nitrogen wastewater, the set value A is 10.5-10.8, and the set value B is 11.5-12; Preferably, when the wastewater is medium-concentration ammonia nitrogen wastewater, the set value A is 10.5-11.5, and the set value B is 11.5-13.5; preferably, when the wastewater is medium-concentration ammonia nitrogen wastewater, the set value A is 10.8-11.3, and the set value B is 12-13; Preferably, when the wastewater is high-concentration ammonia nitrogen wastewater, the set value A is 11-12, and the set value B is 12-14; preferably, when the wastewater is high-concentration ammonia nitrogen wastewater, the set value A is 11.5-12.5, and the set value B is 12.5-13.

5.

4. The ammonia nitrogen detection pretreatment method according to claim 1, characterized in that: In the evaluation and correction step, the standard value is 5-15%; preferably, the standard value is 10%.

5. The ammonia nitrogen detection pretreatment method according to claim 1, characterized in that: The step of quality control is also included, wherein the quality control method is: spike recovery and calculation of spike recovery rate, and evaluation of whether the control test step needs to be repeated according to the spike recovery rate; Preferably, when the spiked recovery rate is within the range of 90-110%, there is no need to repeat the control test step, otherwise the control test step needs to be repeated; preferably, when the spiked recovery rate is within the range of 95-105%, there is no need to repeat the control test step, otherwise the control test step needs to be repeated.

6. The ammonia nitrogen detection pretreatment method according to claim 1, characterized in that: The pH regulator is alkali solution; Preferably, the pH regulator is at least one of sodium hydroxide solution, potassium hydroxide solution, sodium bicarbonate solution, and potassium bicarbonate solution; Preferably, the absorption liquid is at least one of sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid; Preferably, the absorption liquid is sulfuric acid.

7. The ammonia nitrogen detection pretreatment method according to claim 1, characterized in that: Before the pH adjustment step, the ammonia nitrogen content of the wastewater is predicted. The specific method of the prediction is to pre-treat the wastewater tested for the first time by adding alkali-distillation method to determine the approximate pH range.

8. The ammonia nitrogen detection pretreatment method according to claim 1, characterized in that: The gaseous membrane includes at least one of a PP gaseous membrane, a PVDF gaseous membrane or a PTFE gaseous membrane.

9. A method for detecting ammonia nitrogen, characterized in that: The method comprises the pretreatment method described in any one of claims 1 to 8.

10. An application of the pretreatment method according to any one of claims 1 to 8, characterized in that: The pretreatment method is applied in the detection process of ammonia nitrogen in sauce wine wastewater; preferably, the sauce wine wastewater includes at least one of low-concentration ammonia nitrogen wastewater, medium-concentration ammonia nitrogen wastewater or high-concentration ammonia nitrogen wastewater; Preferably, the ammonia nitrogen content of the low-concentration ammonia nitrogen wastewater is less than or equal to 10 mg / L; Preferably, the ammonia nitrogen content of the medium-concentration ammonia nitrogen wastewater is greater than 10 mg / L and less than 1000 mg / L; Preferably, the ammonia nitrogen content of the high-concentration ammonia nitrogen wastewater is greater than or equal to 1000 mg / L; Preferably, the calcium ion content in the sauce wine wastewater is 100-10000 mg / L, and the magnesium ion content is 30-3000 mg / L; Preferably, the application scenario of the pretreatment method is on-site ammonia nitrogen detection.

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