A method for determining ultraviolet dose based on direct photolysis of chloramine

Abstract

This invention discloses a method for determining ultraviolet dosimetry based on the direct photolysis of chloramine, belonging to the field of water supply and drainage treatment technology. This method addresses the problems of existing biological dosimetry methods being unable to determine high ultraviolet doses and the incompatibility of chemical tracers with water supply systems. It selects monochloramine (NH₂Cl), a commonly used disinfectant in water treatment processes, as the tracer, and adds a certain amount of chloride ions (Cl₂Cl₃) as an auxiliary agent. ‑ This invention eliminates interference from the direct photolysis of chloramine to generate free radicals. By measuring the tracer curves under both UV lamp on and off conditions, and calculating the NH2Cl concentration difference at the same moment, the UV dose of the photoreactor can be calculated using a formula. This invention is highly compatible with water treatment processes, produces no secondary pollution, and can accurately measure 400 mJ / cm³. 2 The above high UV dose is simple to operate and uses conventional equipment, making it suitable for on-site determination of UV dose in advanced UV oxidation processes.

Description

Technical Field

[0001] This invention belongs to the field of advanced ultraviolet oxidation technology in water supply and drainage treatment, specifically relating to a method for measuring ultraviolet dose in an ultraviolet photoreactor, particularly suitable for high ultraviolet dose (400 mJ / cm²) processes in advanced ultraviolet oxidation. 2 The above) precise measurements. Background Technology

[0002] Advanced ultraviolet (UV) oxidation technologies (such as UV-H2O2) are widely used in the advanced treatment of drinking water and industrial wastewater due to their ability to efficiently degrade and even mineralize recalcitrant organic pollutants, and their advantages of safety, environmental friendliness, and lack of secondary pollution. UV dose is a core indicator for evaluating the performance of UV photoreactors and a key reference for selecting equipment power in engineering design.

[0003] Among existing methods for ultraviolet (UV) dosimetry, the bio-dosimetry method is an internationally recognized approach. Its principle involves adding target microorganisms (such as T1, MS2, fecal coliforms, and Bacillus subtilis) to a UV photoreactor, measuring the inactivation rate of these microorganisms, and then calculating the UV dose-inactivation rate curve of the target microorganisms by irradiating a known concentration of the target microorganism sample with a UV parallel light reactor in the laboratory. This allows for the inverse estimation of the UV dose in the photoreactor. However, this method has significant drawbacks: firstly, it has a narrow applicable dose range. The Chinese standard "Test Method for Ultraviolet Dosimetry of Ultraviolet Water Disinfection Equipment" (GB / T 32091—2015) stipulates that the verified UV dose should not exceed 120 mJ / cm². 2 For low UV doses (dose validation of drinking water and reclaimed water disinfection equipment, the applicable dose range for MS2 is 10-120 mJ / cm²), the recommended dose range is 10-120 mJ / cm². 2 For dosage validation of wastewater disinfection equipment, the applicable dosage range for T1 or fecal coliform is 2.5-25 mJ / cm³. 2 This cannot meet the 400 mJ / cm requirement in advanced UV oxidation processes. 2 The above-mentioned high dosage requirements; secondly, the harsh operating conditions, the microbial preparations need to be stored at a low temperature of 4°C, and laboratory verification needs to be completed within 24 hours after on-site sampling, which places extremely high demands on the testing site and time; thirdly, poor compatibility, the microorganisms have low compatibility with complex systems such as industrial wastewater and high salinity, which can easily lead to measurement errors.

[0004] To address the issue of high ultraviolet dose measurement, some studies have employed chemical tracer methods. However, existing chemical tracers (such as sulfamethoxazole and potassium iodate) are mostly non-conventional water treatment agents, which pose problems such as toxicity, incompatibility with water treatment systems, and potential secondary pollution, thus limiting their application in practical engineering.

[0005] To address the aforementioned issues, developing a method that is compatible with water supply processes, non-toxic and harmless, and allows for precise on-site measurement of high UV doses has become a key requirement for the promotion and application of advanced UV oxidation technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for measuring ultraviolet dosimetry based on the direct photolysis of chloramine, which solves the technical problems of existing biological dosimetry methods being unable to measure high ultraviolet doses, difficult to verify on-site, and incompatible with water supply systems.

[0007] 1. Technical Solution

[0008] This invention leverages the properties of monochloramine (NH2Cl) as a commonly used disinfectant in water treatment, using it as a tracer, combined with the auxiliary agent Cl... - The free radical scavenging effect was assessed, and the ultraviolet dose was calculated using a dual tracer curve comparison method. The specific technical solution is as follows:

[0009] (1) Selection and concentration determination of tracers and auxiliary agents

[0010] NH₂Cl was chosen as the tracer because it is non-toxic, has no impact on reactor operation, and is highly compatible with the water treatment process. An auxiliary agent, Cl, was added to the system. - ([NH2Cl]:[Cl) - ]≤1:100), Cl - It can react rapidly with Cl· and derived free radicals generated by the photolysis of NH2Cl (k=8.5×10). 9 M -1 s -1 With a scavenging effect of ≥99%, it avoids the indirect photolysis of NH2Cl initiated by free radicals, ensuring that the degradation of NH2Cl is contributed only by direct ultraviolet photolysis;

[0011] The concentration of NH2Cl was verified to meet the requirement that the concentration change of NH2Cl after turning on the UV lamp is 20%~50% relative to the time when the UV lamp is turned off, ensuring the accuracy of the concentration measurement;

[0012] The tracer NH2Cl is prepared by mixing hypochlorous acid or sodium hypochlorite with ammonium chloride or ammonium sulfate in a molar ratio of 1:1.5~2.

[0013] auxiliary agent Cl - For chlorides that have no impact on the water treatment process, such as sodium chloride (or potassium chloride); based on competition kinetics calculations, the selected auxiliary agent Cl... - molar concentration ([NH2Cl]: [Cl]) - The scavenging effect of NH2Cl in the system is ≥99% (≤1:100), ensuring that the degradation of NH2Cl is contributed by direct ultraviolet photolysis.

[0014] (2) Determination of dual-state tracer curves

[0015] Turn off the UV lamp: At the inlet of the photoreactor (consistent with the oxidant addition location during actual operation of the photoreactor), instantaneously add the tracer NH2Cl and the auxiliary agent Cl. - The mixed stock solution was thoroughly mixed with the influent using a mixer, and samples were continuously taken at the outlet to determine the NH2Cl concentration over a continuous period of time. A time-concentration tracer curve was plotted under UV-off conditions.

[0016] Turn on the UV lamp: After the UV lamp is running stably, repeat the above addition, sampling and measurement operations, and plot the time-concentration tracer curve under UV conditions.

[0017] (3) Calculation of ultraviolet dose

[0018] Based on the ultraviolet photolysis kinetics formula of NH2Cl: The transformation yields the formula for calculating the ultraviolet dose I: .

[0019] Based on the same sampling time t i The concentration difference a of the tracer NH2Cl between UV off and UV on i -b i Then calculate the ultraviolet dose at that moment. Finally, regarding I i The UV dose of the UV reactor can be obtained by taking the average value. .

[0020] Among them, a i With b i (b) i ≥0) represents the sampling time t. i The concentration of NH2Cl (M, as Cl2) under both UV-off and UV-on states, t0 is the moment (s) before the first detection of NH2Cl during the UV-off tracer curve measurement, i.e., a0=0, a1>0, Ф is the quantum yield of NH2Cl at the corresponding wavelength (mol / Einstein), f i The proportion of ultraviolet light absorbed by NH2Cl ( ), ε is the molar absorptivity of NH2Cl at the corresponding wavelength (M -1 cm -1 A i For the corresponding time t i Total absorbance in the system (cm) -1 ), that is, A i =ε×a i +A matrix A matrix Absorbs light to the water background (cm) -1 ), Fs i For the corresponding time t i The light absorption ratio of the system, l represents the effective optical path (cm) of the ultraviolet reactor.

[0021] In steps (2) and (3), the location for adding the tracer and auxiliary agent mixed stock solution is consistent with the location for adding the oxidant during the actual operation of the photoreactor, and a mixing stirrer is required to ensure thorough mixing in order to meet the actual operating conditions.

[0022] 2. Technical Principles

[0023] The core design concept of this invention is as follows: Figure 1 As shown, NH2Cl undergoes direct photolysis under ultraviolet light to produce NH2· and Cl· (reaction 1). NH2· has low reactivity, but Cl· further reacts with water and OH-. - The reaction generates ·OH and other derived free radicals (reactions 2-5). These free radicals undergo secondary reactions with NH2Cl (reactions 6-7), leading to additional consumption of NH2Cl and interfering with the determination of UV dosimetry. By adding a specific concentration of Cl... - It can rapidly consume Cl· and its derived free radicals, generating Cl2· which has extremely low reactivity with NH2Cl. - (As in reaction 8), thereby blocking the indirect photolysis pathway of NH2Cl and ensuring that the degradation of NH2Cl is contributed solely by direct ultraviolet photolysis. By measuring the amount of NH2Cl degradation at the same time, the ultraviolet dose of the photoreactor can be calculated.

[0024] Reaction 1: NH₂Cl + hv → NH₂· + Cl·

[0025] Reaction 2: Cl· + OH- - →ClOH· - k=1.8E10 M -1 s -1

[0026] Reaction 3: Cl· + H₂O → ClOH· - +H + k=4.5E3 s -1

[0027] Reaction 4: ClOH· - →Cl - +OH· k=6.1E9 s -1

[0028] Reaction 5: ClOH· - +H + → Cl·+H2O k=2.1E10 M -1 s -1

[0029] Reaction 6: Cl· + NH₂Cl → NH₄Cl· + Cl - +H + k=1.0E9 M -1 s -1

[0030] Reaction 7: OH· + NH₂Cl → NH₃· + H₂O k = 5.1E⁸ M -1 s -1

[0031] Reaction 8: Cl· + Cl - →Cl2· - k=8.5E9 M -1 s -1

[0032] Beneficial effects:

[0033] This invention provides a method for determining high ultraviolet dose in photoreactors used in advanced ultraviolet oxidation processes:

[0034] (1) Highly compatible with water treatment processes: NH2Cl is a commonly used disinfectant in water treatment processes, which is non-toxic and harmless, and the auxiliary agent Cl - It is a common ion in water treatment, and has high water solubility, so it will not cause secondary pollution, thus solving the toxicity and compatibility problems of existing chemical tracers.

[0035] (2) Suitable for high-dose measurement: can accurately measure 400 mJ / cm 2 The above high UV dose compensates for the dose range deficiency of the biological dosimetry method and meets the needs of UV dose determination in advanced UV oxidation processes.

[0036] (3) High measurement accuracy: by adding Cl - By blocking the indirect photolysis pathway of NH2Cl, the interference of free radicals generated by the photolysis of NH2Cl is eliminated, ensuring that the degradation of NH2Cl is contributed only by direct ultraviolet photolysis, thus reducing measurement errors.

[0037] (4) It can be directly measured on site: the amount of NH2Cl degradation can be measured on site by spectrophotometer or portable chloramine analyzer. The ultraviolet dose of the photoreactor can be calculated according to the formula. No laboratory linkage measurement is required. It is simple to operate and low in cost.

[0038] (5) It helps in reactor flow field diagnosis and structural optimization: By using the instantaneous (pulse) dosing method, parameters such as HRT distribution and actual hydraulic residence time of the reactor can be calculated by the tracer curve (curve A) with the UV lamp turned off. This can help diagnose reactor flow field defects and guide structural optimization. Attached Figure Description

[0039] Figure 1 This is a schematic diagram illustrating the principle of an ultraviolet dosimetry method based on the direct photolysis of chloramine according to the present invention.

[0040] Figure 2 This is a schematic diagram of the tracer curve for a UV dosimetry method based on the direct photolysis of chloramine according to the present invention.

[0041] Figure 3 This is a graph showing the change in tracer concentration over time under conditions of UV lamp off and on in Example 1 of the present invention. Detailed Implementation

[0042] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific implementation methods, in conjunction with its accompanying drawings and tables.

[0043] This invention provides a method for ultraviolet dosimetry based on the direct photolysis of chloramine. The experimental scheme proposed to solve the technical problems mentioned in the prior art mainly includes the following steps:

[0044] (1) Measurement of water quality parameters and equipment parameters: background absorbance A at the corresponding ultraviolet wavelength for water quality matrix The effective optical path length l (cm) of the ultraviolet reactor;

[0045] (2) Preparation of tracer mixed stock solution: Preparation of tracer NH2Cl and auxiliary agent Cl - Mixed stock solution;

[0046] (3) Measurement of UV lamp off curve: Turn off the UV lamp of the photoreactor, add the tracer mixed stock solution instantaneously at the inlet of the photoreactor, mix it evenly with the influent through a stirrer, and continuously sample at the outlet of the photoreactor. Use a spectrophotometer or portable water quality analyzer to measure the chloramine concentration (i.e., the total chlorine index in the water quality) and plot the time-concentration tracer curve after turning off the UV lamp (see Figure 2 Curve A);

[0047] (4) UV lamp activation curve determination: Turn on the UV lamp of the photoreactor. After the lamp has been running stably for 30 minutes, repeat the addition, sampling and determination operations in step (3) to plot the time-concentration tracer curve of UV activation (see Figure 2 Curve B);

[0048] (5) Data processing and UV dose calculation: Organize the data (as shown in Table 1):

[0049] Table 1. Calculation table for a UV dosimetry method based on direct photolysis of chloramine.

[0050] Based on the UV tracer-off curve, indicators such as HRT distribution can be calculated, and the concentration difference of tracer NH2Cl at the same sampling time can be calculated (a i -b i (1≤i≤n-1), and then calculate the ultraviolet dose at that moment. Finally, regarding I i The UV dose of the UV reactor can be obtained by taking the average value. .

[0051] Note: 1) t0 is the moment before the first detection of NH2Cl during the UV tracer curve measurement process with the UV tracer off, i.e., a0=0, a1>0; t1 is the moment before the first detection of NH2Cl during the UV tracer curve measurement process with the UV tracer on, i.e., b1=0, b2>0; t n-1 To initiate the final detection of NH2Cl during the UV tracer curve determination process, i.e., b n-2 >0, b n-1 =0; t n To turn off the moment after the final detection of NH2Cl during the UV tracer curve determination process, i.e., a n-1 >0, a n =0;

[0052] 2) f i This represents the absorbance ratio of NH2Cl at the corresponding time. Where ε is the molar absorptivity of NH2Cl (M -1 cm -1 A i The total absorbance of the system at the corresponding time (cm) -1 ), that is, A i = ε×a i +A matrix A matrix Absorbs light to the water background (cm) -1 );

[0053] 3) F s i This corresponds to the light absorption of the system at that time. , where l is the effective optical path (cm) of the ultraviolet reactor;

[0054] 4) The formula for calculating HRT distribution is: The actual hydraulic residence time tactual of the UV reactor can be calculated based on the tracer curve A with UV off and the trapezoidal integration method. This allows for the calculation of the reactor's dead volume. ;

[0055] The parameters are defined as described above.

[0056] The present invention will be further described below with reference to specific embodiments and accompanying drawings. The following embodiments are based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. For those skilled in the art, any obvious modifications made without departing from the technical solution of the present invention are within the scope of protection of the claims of the present invention.

[0057] Example 1

[0058] An ultraviolet dosing assay was conducted using a ring-shaped central sleeve ultraviolet reactor. The reactor had an effective reaction volume of 1 L, and a low-pressure mercury lamp (254 nm) was used as the ultraviolet light source. The effective length of the central quartz sleeve was 50 cm, and the radial optical path between the outer wall of the quartz sleeve and the inner stainless steel wall of the reactor was 2 cm. During the experiment, the influent flow rate was controlled at 100 mL / min, corresponding to a theoretical hydraulic retention time (HRT) of 10 min.

[0059] Prepare a monochloramine (NH₂Cl) tracer solution of a certain concentration and add Cl₂. - The auxiliary agent was used to inhibit the indirect degradation caused by the free radical chain reaction during the photolysis of chloramine. The change in tracer concentration was measured under both UV-off and UV-on conditions.

[0060] With the UV lamp off, NH2Cl tracer solution was instantaneously added at the reactor inlet. After the system was fully mixed, samples were continuously taken at the reactor outlet to measure the NH2Cl concentration at different time points, thus obtaining the tracer concentration-time curve under UV-free conditions.

[0061] The UV lamp was then turned on, and after the UV light source stabilized, the experiment was repeated under the same operating conditions to obtain the NH2Cl concentration-time change curve under UV irradiation (see...). Figure 3 The calculated UV dose for this reactor is 3.65 × 10⁻⁶. - 6 Einstein L -1 s -1 Based on the actual working conditions, the calculated UV dose is 978 mJ / cm². 2 .

[0062] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for ultraviolet dosimetry based on the direct photolysis of chloramine, characterized in that, Includes the following steps: 1) Preparation of a mixed stock solution of tracer and auxiliary agent: using NH2Cl as the tracer, Cl... - As an auxiliary agent, to eliminate the interference of free radicals generated by the direct photolysis of the tracer NH2Cl; 2) Tracer curve determination with UV lamp off: Turn off the UV lamp in the UV reactor, and add tracer NH2Cl and auxiliary agent Cl at the inlet of the photoreactor instantaneously. - The mixed stock solution was continuously sampled at the outlet to determine the NH2Cl concentration, and a time-concentration tracer curve was plotted under UV-off conditions. 3) Determination of tracer curve with UV lamp on: After turning on the UV lamp and waiting for the system to stabilize, repeat the addition, sampling and measurement operations in step 2) and plot the time-concentration tracer curve under UV light conditions. 4) Calculation of ultraviolet dose: according to the formula Calculate the ultraviolet dose at the same time point, and finally apply it to I. i The UV dose of the UV reactor can be obtained by taking the average value. .

2. The ultraviolet dosimetry method based on the direct photolysis of chloramine according to claim 1, characterized in that, In step 1), the concentration of NH2Cl is such that after the UV lamp is turned on, the concentration of NH2Cl changes by 20% to 50% relative to the time when the UV lamp is turned off, ensuring the accuracy of the concentration measurement. The tracer NH2Cl is prepared by mixing hypochlorous acid or sodium hypochlorite with ammonium chloride or ammonium sulfate in a molar ratio of 1:1.5~2; auxiliary agent Cl - Chlorides that have no impact on water treatment processes; Based on competition dynamics calculations, the selected auxiliary agent Cl - The molar concentration of NH2Cl is: Cl - ≤1:

100.

3. The ultraviolet dosimetry method based on the direct photolysis of chloramine according to claim 1, characterized in that, In steps 2) and 3), the location for adding the tracer and auxiliary agent mixed stock solution is consistent with the location for adding the oxidant during the actual operation of the photoreactor, and a mixing stirrer is required to ensure thorough mixing.

4. The ultraviolet dosimetry method based on the direct photolysis of chloramine according to claim 1, characterized in that, In step 4), the formula for calculating the ultraviolet dose of the photoreactor is: , where a i With b i b i ≥0 represents the sampling time t i The concentration of NH2Cl in the off and on UV states, expressed as Cl2, t0 is the moment s before the first detection of NH2Cl during the measurement of the off UV tracer curve, i.e., a0=0, a1>0, Ф is the quantum yield of NH2Cl at the corresponding wavelength, and f is the concentration of NH2Cl in the off and on UV states. i The proportion of ultraviolet light absorbed by NH2Cl. ε is the molar absorptivity of NH₂Cl at the corresponding wavelength, and A i For the corresponding time t i The total absorbance of the system, i.e., A i =ε×a i +A matrix A matrix For absorbing light from the water background, F s i For the corresponding time t i The light absorption ratio of the system, , where l is the effective optical path of the ultraviolet reactor.

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