A total nitrogen detection limit optimization device and method based on temperature control ultraviolet-membrane degassing cooperation

Abstract

The application discloses a total nitrogen detection limit optimization device and method based on temperature control ultraviolet-membrane degassing cooperation, relates to the technical field of water quality total nitrogen detection, and comprises a temperature control digestion module, an ultraviolet photometer main body, a membrane treatment integrated unit and a control system. The temperature control digestion module is used for ensuring the rapid response and high precision of temperature control. The ultraviolet photometer main body is used for reducing baseline drift. The membrane treatment integrated unit is used for realizing efficient water treatment. The control system is used for dynamically adjusting temperature and microbial activity. The detection sensitivity can be significantly improved, the temperature stability is improved, and the energy consumption and cost are optimized.

Description

Technical Field

[0001] This invention relates to the field of total nitrogen detection technology in water quality, and more specifically, to a device and method for optimizing the total nitrogen detection limit based on temperature-controlled ultraviolet-membrane degassing synergy. Background Technology

[0002] Currently, the determination of total nitrogen in water quality mainly follows the standard "HJ 636-2012 Determination of Total Nitrogen in Water Quality - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometric Method". The detection limit of this method is typically 0.05 mg / L. However, in low-concentration total nitrogen monitoring scenarios, the accurate detection of pollutants at the μg / L level is currently insufficient. Therefore, it is imperative to overcome the detection limit to make this method more suitable for current monitoring scenarios.

[0003] The main limitation of existing technologies lies in the significant impact of temperature fluctuations on the digestion process. Current methods mostly operate at room temperature or a fixed temperature, neglecting the crucial influence of temperature on reaction rate and spectral stability. This leads to incomplete digestion and unstable absorbance readings, thus limiting further reductions in the instrument's detection limit. Specifically, insufficient precision in the temperature control module causes uneven temperature during UV testing. Local overheating or underheating can significantly fluctuate the light beam, introducing significant systematic and random errors. Currently, most commercially available devices use discrete temperature control components and manual operation, lacking integrated and intelligent temperature control systems. This not only makes operation cumbersome and requires high operator skills but also results in poor repeatability due to human error, with relative standard deviations (RSDs) often exceeding 5%. Summary of the Invention

[0004] This invention aims to address the problems in the existing HJ 636-2012 standard method, such as the high detection limit of total nitrogen (0.05 mg / L), insufficient temperature control accuracy (fluctuation > ±1℃), and low detection sensitivity and poor repeatability caused by the dispersed operation process. By constructing a collaborative system of "pretreatment-biochemical-membrane treatment", this invention provides an integrated device and method for optimizing the detection limit of total nitrogen.

[0005] The objective of this invention is achieved through the following technical solution: A total nitrogen detection limit optimization device based on temperature-controlled ultraviolet-membrane degassing synergy includes a temperature-controlled digestion module, an ultraviolet spectrophotometer body, a membrane treatment integration unit, and a control system. The temperature-controlled digestion module is used to ensure rapid response and high accuracy of temperature control; the ultraviolet spectrophotometer body is used to reduce baseline drift; the membrane treatment integration unit is used to achieve efficient water treatment; and the control system is used to dynamically adjust temperature and microbial activity.

[0006] Furthermore, in this invention, the temperature-controlled digestion module adopts a double-jacketed reactor, which is equipped with a platinum resistance temperature sensor and a ceramic heating element, and is further combined with a semiconductor cooling chip to achieve wide-range temperature control.

[0007] Furthermore, in this invention, the ultraviolet spectrophotometer body includes a deuterium lamp light source, a quartz cuvette temperature-controlled sample cell, and a dual-beam detection system. The dual-beam detection system is used for synchronous acquisition of the reference optical path and the measurement optical path to suppress baseline drift.

[0008] Furthermore, in this invention, the membrane treatment integrated unit connects a reverse osmosis membrane module and a homogeneous anion exchange membrane electrodialysis unit in series, and maintains stable membrane flux through temperature-controlled circulating water.

[0009] A method for optimizing the total nitrogen detection limit based on temperature-controlled UV-membrane degassing synergy employs a fuzzy PID algorithm for temperature control and introduces non-high-temperature digestion through biological digestion, comprising the following steps: S1. Ultrapure water preparation and system preheating: Activate the integrated or independent membrane treatment unit to prepare concentrated water with a conductivity ≤500μS / cm, which will serve as blank water and diluent for the entire experiment; turn on the UV spectrophotometer, preheat for at least 30 minutes, and start the temperature-controlled colorimetric cell module, setting the constant temperature to 25.0℃ (temperature control accuracy ±0.1℃) to ensure the stability of the optical system and the constant temperature of the detection environment; S2. Sample pretreatment and reagent addition: Measure 100 mL of homogenized water sample to be tested, and use sulfuric acid or sodium hydroxide solution to precisely adjust its pH to 5.0-9.0; add 5 mL of alkaline potassium persulfate solution and 10 mL of salt-tolerant microbial agent to the sample in sequence, tighten the cap and shake well to fully dissolve and mix; S3. Temperature-controlled digestion and transformation: Place the sample in the temperature-controlled digestion module, program the temperature to 85.0±0.2℃, and react at a constant temperature for 30 min; S4. Cooling and Online Degassing: After digestion, the program automatically cools the sample to 25.0℃; for high-precision detection, the sample is processed by the online membrane degassing unit before injection to eliminate bubble interference. S5. Ultraviolet Spectrophotometric Detection: Transfer the digestion solution cooled to 25℃ to a temperature-controlled quartz cuvette in the spectrophotometer; select dual-wavelength absorbance measurement mode, and set the optical parameters to a spectral bandwidth of 2nm and a scan speed of 300nm / min to improve baseline stability; collect absorbance at 220nm and 275nm for calculating the detection limit. The calculation formula is: in: Corrected absorbance of the digestion solution; : The absorbance of the digestion solution at a wavelength of 220 nm; : The absorbance of the digestion solution at a wavelength of 275 nm; S6. Data Analysis and Result Output: The total ammonia concentration is calculated based on the standard curve and expressed as N, representing the sum of all nitrogen-containing compounds in the water or sample. The detection limit of this method is 0.01 mg / L, and the repeatability RSD is less than 2.3% when the number of tests n is 11.

[0010] The beneficial effects of this invention are: 1. Significantly improved detection sensitivity: Through temperature-controlled-biochemical synergistic digestion technology (85℃ constant temperature + microbial enzymatic reaction), the total nitrogen conversion rate reaches 98.5%. Combined with a dual-beam ultraviolet detection system (baseline drift ≤0.001AU), the detection limit is reduced to 0.01mg / L, meeting the ultra-low concentration detection requirement of 1 / 100 of Class III water bodies (1.0mg / L) in the "Surface Water Environmental Quality Standard". 2. Breakthrough in temperature stability: The dual closed-loop temperature control system (control cycle 100ms) using STM32F407 main controller achieves a temperature control accuracy of ±0.1℃ and a temperature fluctuation of ≤±0.05℃, which reduces temperature interference by 95% compared to traditional water bath heating (fluctuation ±1℃), and improves absorbance measurement stability to ±0.002AU. 3. Energy consumption and cost optimization: The membrane-temperature combined synchronous system recovers waste heat from electrodialysis concentrate (heat recovery rate of 60%). Combined with the gradient temperature rise process, the energy consumption for single sample testing is reduced from 0.8kWh to 0.56kWh, the operating cost is reduced by 0.8 yuan / ton of water, and the membrane fouling rate is reduced by 40% (membrane life is extended from 3 months to 8 months). 4. Intelligent and automated operation: The intelligent control system with integrated fuzzy PID algorithm can automatically identify the water sample type (surface water / groundwater / wastewater) and match the optimal digestion program. It supports remote monitoring via Modbus Ethernet, reducing manual intervention (the operation steps are simplified from 12 to 7), making it suitable for unattended on-site monitoring. 5. Strong method compatibility: Fully compatible with the HJ 636-2012 standard method reagent system, no need to change the existing detection process, technical transformation can be achieved by upgrading only the temperature control module, the transformation cost is less than 30% of the cost of purchasing new equipment, which is convenient for existing laboratories to deploy quickly. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the operation of the ultraviolet spectrophotometer according to an embodiment of the present invention; Figure 2 The temperature control algorithm response curve of this invention embodiment (set to 85℃ step response). Detailed Implementation

[0012] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] Please see Figure 1 and Figure 2 The present invention provides a technical solution: A total nitrogen detection limit optimization device based on temperature-controlled ultraviolet-membrane degassing synergy includes a temperature-controlled digestion module, an ultraviolet spectrophotometer body, a membrane treatment integration unit, and a control system. The temperature-controlled digestion module is used to ensure rapid response and high accuracy of temperature control; the ultraviolet spectrophotometer body is used to reduce baseline drift; the membrane treatment integration unit is used to achieve efficient water treatment; and the control system is used to dynamically adjust temperature and microbial activity.

[0014] Specifically, in this embodiment, a double-jacketed reactor (500mL volume, 316L stainless steel) is used, incorporating a built-in PT1000 platinum resistance temperature sensor (measurement range -50~200℃, accuracy ±0.05℃) and a ceramic heating element (power adjustable from 50-300W), coupled with a semiconductor cooling chip (TEC1-12706, cooling power 60W) to achieve wide-range temperature control. The reactor integrates a salt-tolerant microbial immobilization carrier (porous ceramic packing, specific surface area 120m² / g), loaded with halophilic Bacillus (concentration 1.2×10⁶ CFU / mL), facilitating organic nitrogen conversion through microbial enzymatic reactions.

[0015] In this embodiment, the ultraviolet spectrophotometer uses a deuterium lamp light source (wavelength range 190-400nm, stability ≤0.5% / h), equipped with a 30mm quartz cuvette temperature-controlled sample cell (temperature control accuracy ±0.1℃, temperature fluctuation ≤±0.05℃), and employs a dual-beam detection system (simultaneous acquisition of the reference and measurement optical paths to suppress baseline drift). The data acquisition module uses a 16-bit AD converter (sampling frequency 10Hz, resolution 0.0001AU) to ensure the accuracy of weak signal detection.

[0016] In this embodiment, the membrane treatment integrated unit connects a 4040 type reverse osmosis membrane module (molecular weight cutoff 100 Da, operating pressure 1.2 MPa) and a homogeneous anion exchange membrane electrodialysis unit (membrane area 0.5 m², operating current density 200 A / m²). The membrane flux is kept stable by temperature-controlled circulating water (35 ± 2 °C), the concentrate recovery rate reaches 82%, and the permeate conductivity is ≤500 μS / cm.

[0017] The control system uses an STM32F407IGH6 main control chip (168MHz main frequency, 1MB on-chip Flash), which integrates 4 Pt1000 acquisition channels, 8 analog outputs (for controlling heating / cooling power), an Ethernet communication interface (supporting Modbus protocol) and a 7-inch touch screen (for real-time display of temperature curves and detection data).

[0018] The innovative temperature control method in this embodiment is as follows: 1. A three-stage gradient temperature rise digestion process is adopted: First stage (25→60℃): Heating rate 2℃ / min, activating the oxidizing property of potassium persulfate (the decomposition rate of potassium persulfate reaches 0.021 min at 60℃). -1 ); Second stage (60→85℃): Heating rate 1℃ / min, promoting the hydrolysis of organic nitrogen (the rate of amide bond breaking increases by 3 times at 85℃); The third stage (85℃ constant temperature): keep warm for 30 min, and the synergistic effect of microbial enzymatic reaction and chemical oxidation (total nitrogen conversion rate ≥98.5%).

[0019] It should be noted that, in Figure 2 In the diagram, the solid black line represents the actual temperature change over time; the horizontal dashed line represents the set temperature of 85℃.

[0020] 2. Dual closed-loop temperature control algorithm: Inner loop (hardware layer): Employs PID + feedforward control with a control cycle of 100ms and a proportional coefficient K. p =8.5, integral coefficient K i =0.02, differential coefficient K d =1.2, achieving a temperature control accuracy of ±0.1℃; Outer loop (algorithm layer): Based on fuzzy logic, the PID parameters are dynamically adjusted. When the temperature deviation is >1℃, it automatically switches to Bang-Bang control to shorten the response time (the time to rise from room temperature to 85℃ is ≤20min).

[0021] 3. Key Algorithm Formulas (1) Temperature-conversion rate correlation model: In the determination of total nitrogen (TN), temperature affects the oxidation of organic nitrogen and ammonia nitrogen by alkaline potassium persulfate (K2S2O8) to nitrate nitrogen (NO3). - Key factors of -N): This reaction is an oxidative digestion process, and its kinetics follow the Arrhenius equation: in: : Reaction rate constant (s -1 ); Pre-index factor (approximately 10) 8 s -1 (Experience points); Activation energy (approximately 60 kJ / mol, based on a similar oxidation reaction); R: gas constant (8.314 J / mol·K); T: Absolute temperature (K); Conversion rate Defined as total nitrogen to NO3 - The proportion of -N conversion, assuming a first-order reaction, and time... Conversion rate within: in Set the digestion time (to 1800 seconds, or 30 minutes).

[0022] Temperature-conversion correlation function: Based on experimental data and theoretical derivation, the relationship between temperature and conversion rate is fitted by a sigmoid model, reflecting the nonlinear effect of temperature on the reaction rate. in: Maximum conversion rate (assuming 1, i.e., 100%); Optimal temperature (set to 358K = 85℃); Temperature sensitivity factor (approximately 0.1 K⁻¹, experimental verification required).

[0023] 4. Experimental verification data: Note: Experimental conditions were 0.01-0.5 mg / L total nitrogen standard solution, n=11 parallel experiments, and confidence level of 95%.

[0024] A method for optimizing the total nitrogen detection limit based on temperature-controlled UV-membrane degassing synergy employs a fuzzy PID algorithm for temperature control and introduces non-high-temperature digestion through biological digestion, comprising the following steps: S1. Ultrapure water preparation and system preheating: Activate the integrated or independent membrane treatment unit to prepare concentrated water with a conductivity ≤500μS / cm, which will serve as blank water and diluent for the entire experiment; turn on the UV spectrophotometer, preheat for at least 30 minutes, and start the temperature-controlled colorimetric cell module, setting the constant temperature to 25.0℃ (temperature control accuracy ±0.1℃) to ensure the stability of the optical system and the constant temperature of the detection environment; S2. Sample pretreatment and reagent addition: Measure 100 mL of homogenized water sample to be tested, and use sulfuric acid or sodium hydroxide solution to precisely adjust its pH to 5.0-9.0; add 5 mL of alkaline potassium persulfate solution and 10 mL of salt-tolerant microbial agent to the sample in sequence, tighten the cap and shake well to fully dissolve and mix; S3. Temperature-controlled digestion and transformation: Place the sample in the temperature-controlled digestion module, program the temperature to 85.0±0.2℃, and react at a constant temperature for 30 min; S4. Cooling and Online Degassing: After digestion, the program automatically cools the sample to 25.0℃; for high-precision detection, the sample is processed by the online membrane degassing unit before injection to eliminate bubble interference. S5. Ultraviolet Spectrophotometric Detection: Transfer the digestion solution cooled to 25℃ to a temperature-controlled quartz cuvette in the spectrophotometer; select dual-wavelength absorbance measurement mode, and set the optical parameters to a spectral bandwidth of 2nm and a scan speed of 300nm / min to improve baseline stability; collect absorbance at 220nm and 275nm for calculating the detection limit. The calculation formula is: in: Corrected absorbance of the digestion solution; : The absorbance of the digestion solution at a wavelength of 220 nm; : The absorbance of the digestion solution at a wavelength of 275 nm; S6. Data Analysis and Result Output: The total ammonia concentration is calculated based on the standard curve and expressed as N, representing the sum of all nitrogen-containing compounds in the water or sample. The detection limit of this method is 0.01 mg / L, and the repeatability RSD is less than 2.3% when the number of tests n is 11.

[0025] Working principle: After pretreatment, the sample entered the temperature-controlled digestion module and reacted with alkaline potassium persulfate at a constant temperature of 85℃ (pH=12.5). Salt-tolerant microorganisms assisted in the conversion of total nitrogen to nitrate through extracellular enzymatic reactions (the activation energy of the reaction was reduced to 58kJ / mol). After stabilization in the temperature-controlled sample cell for 10 minutes, the absorbance was measured at 220nm using a UV spectrophotometer (bandwidth 2nm, scan speed 300nm / min). Combined with membrane treatment to recover concentrated water (conductivity ≤500μS / cm), the detection limit was reduced to 0.01mg / L.

[0026] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for optimizing the total nitrogen detection limit based on temperature-controlled ultraviolet-membrane degassing synergy, characterized in that, This is achieved using the following device: The system includes a temperature-controlled digestion module, a UV spectrophotometer, a membrane treatment integration unit, and a control system. The temperature-controlled digestion module ensures rapid response and high accuracy in temperature control; the UV spectrophotometer reduces baseline drift; the membrane treatment integration unit enables efficient water treatment; and the control system dynamically adjusts temperature and microbial activity. The above method uses a fuzzy PID algorithm for temperature control and introduces biological digestion to achieve non-high-temperature digestion, including the following steps: S1. Ultrapure water preparation and system preheating: Activate the integrated or independent membrane treatment unit to prepare concentrated water with a conductivity ≤500μS / cm, which will serve as blank water and diluent for the entire experiment; turn on the UV spectrophotometer, preheat for at least 30 minutes, and start the temperature-controlled colorimetric cell module, setting the constant temperature to 25.0℃ with a temperature control accuracy of ±0.1℃ to ensure the stability of the optical system and the constant temperature of the detection environment; S2. Sample pretreatment and reagent addition: Measure 100 mL of homogenized water sample to be tested, and use sulfuric acid or sodium hydroxide solution to precisely adjust its pH to 5.0-9.0; add 5 mL of alkaline potassium persulfate solution and 10 mL of salt-tolerant microbial agent to the sample in sequence, tighten the cap and shake well to fully dissolve and mix; S3. Temperature-controlled digestion and transformation: Place the sample in the temperature-controlled digestion module, program the temperature to 85.0±0.2℃, and react at a constant temperature for 30 min; S4. Cooling and Online Degassing: After digestion, the program automatically cools the sample to 25.0℃; for high-precision detection, the sample is processed by the online membrane degassing unit before injection to eliminate bubble interference. S5. Ultraviolet Spectrophotometric Detection: Transfer the digestion solution cooled to 25℃ to a temperature-controlled quartz cuvette in the spectrophotometer; select dual-wavelength absorbance measurement mode, and set the optical parameters to a spectral bandwidth of 2nm and a scan speed of 300nm / min to improve baseline stability; collect absorbance at 220nm and 275nm for calculating the detection limit. The calculation formula is: ； in: Corrected absorbance of the digestion solution; : The absorbance of the digestion solution at a wavelength of 220 nm; : The absorbance of the digestion solution at a wavelength of 275 nm; S6. Data Analysis and Result Output: The total nitrogen concentration is calculated based on the standard curve and expressed as N, representing the sum of all nitrogen-containing compounds in the water or sample. The detection limit of this method is 0.01 mg / L, and the repeatability RSD is less than 2.3% when the number of tests n is 11.

2. The method for optimizing the total nitrogen detection limit based on temperature-controlled ultraviolet-membrane degassing synergy as described in claim 1, characterized in that: The temperature-controlled digestion module adopts a double-jacketed reactor, which is equipped with a platinum resistance temperature sensor and a ceramic heating element, and is further combined with a semiconductor cooling chip to achieve wide-range temperature control.

3. The method for optimizing the total nitrogen detection limit based on temperature-controlled ultraviolet-membrane degassing synergy as described in claim 1, characterized in that: The main body of the ultraviolet spectrophotometer includes a deuterium lamp light source, a quartz cuvette temperature-controlled sample cell, and a dual-beam detection system. The dual-beam detection system is used for synchronous acquisition of the reference optical path and the measurement optical path to suppress baseline drift.

4. The method for optimizing the total nitrogen detection limit based on temperature-controlled ultraviolet-membrane degassing synergy as described in claim 1, characterized in that: The membrane treatment integrated unit connects a reverse osmosis membrane module and a homogeneous anion exchange membrane electrodialysis unit in series, and maintains stable membrane flux through temperature-controlled circulating water.

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