Device for determining end point of sample pretreatment through real-time turbidity measurement

Abstract

Provided is a device for determining the end point of a sample pretreatment through real-time turbidity measurement, the device comprising: a sample holding frame in which sample holders for holding a plurality of sample containers are arranged spaced apart concentrically around a central point and rotate in one direction, either clockwise or counterclockwise, on a plane; a sample holder into which a sample container is inserted; a pretreatment unit for performing a pretreatment process in which a sample supplied to the sample container is subjected to ultrasonic waves and acid or alkaline extraction to measure the total organic carbon (TOC) of the sample; a turbidity sensor unit for measuring the turbidity of the sample; and a control and determination unit which controls the turbidity sensor unit to measure the turbidity of the sample at regular time intervals during a pretreatment, checks a turbidity change rate (NTUn / NTUn-k, 1≤k≤3), which is the ratio of the currently measured turbidity to a previously measured turbidity, and determines that it is the end point of the pretreatment and controls the pretreatment unit to terminate the pretreatment process if the turbidity change rate (NTUn / NTUn-k) is within 30%.

Description

A device that determines the end point of sample pretreatment through real-time turbidity measurement

[0001] The present invention relates to a technology for determining the end point of pretreatment of a sample, and more particularly, to a device for determining the end point of pretreatment of a sample through real-time turbidity measurement.

[0002] The national research and development projects that supported this invention are as follows:

[0003] Assignment ID 1345366159

[0004] Assignment Number 2020R1A6A1A03042742

[0005] Ministry of Education

[0006] Project Management Institution Name: National Research Foundation of Korea

[0007] Research Project Name: Establishment of Academic Research Infrastructure for Engineering (R&D)

[0008] Research Project Name: Environmental Technology Research Institute

[0009] Project implementation organization name: Seoul National University of Science and Technology Industry-Academic Cooperation Foundation

[0010] Research period: June 1, 2020 - May 31, 2029

[0011] No assignment number assigned

[0012] Assignment number YL-EC-pa-10-001

[0013] Ministry of Environment

[0014] Project Management Agency Name: Korea Environmental Industry & Technology Institute

[0015] Research Project Name: Green Convergence Technology Talent Development Specialized Graduate School Project

[0016] Research Project Name: Green Convergence Technology Talent Development Specialized Graduate School Project

[0017] Project implementation organization name: Seoul National University of Science and Technology Industry-Academic Cooperation Foundation

[0018] Research period: December 1, 2023 - November 30, 2024

[0019] The total organic carbon (TOC) analysis method of a sample is a new organic matter measurement index introduced for systematic organic matter management due to the increase in recalcitrant pollutants in aquatic systems and the limitations of organic matter management due to the low oxidation rates of existing organic matter measurement indexes such as COD and BOD. TOC analysis method has been adopted and used in many countries as an organic matter management index for public waters for efficient and accurate organic matter management in aquatic systems due to its high oxidation rate and fast analysis time compared to COD and BOD. It is also recognized as the most appropriate index for the management of civil engineering and industrial waste in most countries.

[0020] In particular, in Korea, TOC was introduced as an effluent standard for new public wastewater treatment facilities starting in 2020 to efficiently manage the total amount of organic matter, not only in public waters, and as of 2023, it is being applied as a water quality regulation item for effluent from all public wastewater treatment facilities. Recently, interest in TOC has been increasing as the detection of microplastic particles and other contaminants in water systems has become more frequent. Furthermore, to evaluate the process efficiency of wastewater treatment facilities and enable immediate process improvement, the importance and demand for accurate TOC measurement of influent and process water samples, which contain various suspended solids from the inflow and process stages of wastewater, as well as effluent, is increasing.

[0021] However, when a large amount of suspended solids and non-biodegradable organic matter is included in TOC analysis, it is known that the precision and accuracy are reduced due to the low oxidation rate of the sample and particle sedimentation during the analysis process, and in particular, large errors in TOC analysis values ​​are reported depending on the sample pretreatment method.

[0022] In other words, the pretreatment process is very important for accurate TOC measurement of a sample, and it is very important to know the exact end point of the pretreatment process of the sample to ensure accuracy and reliability of the analysis results of the sample.

[0023] This is because an inappropriate pretreatment termination point can lead to distortion of analytical results. Excessive or insufficient pretreatment can alter or lose components in the sample, resulting in a failure to reflect the actual contamination status. Furthermore, incomplete pretreatment risks damage to analytical equipment and can make it difficult to obtain consistent results even in repeated experiments under identical conditions.

[0024] Therefore, accurately setting and adhering to the pretreatment end point is essential for obtaining high-quality analysis results, improving the organic oxidation process of the sample, minimizing the conversion to analytical interference substances (volatile organic compounds) due to excessive pretreatment, and preparing samples in a condition suitable for the analytical equipment.

[0025] The purpose of the present invention is to provide a device that measures the turbidity of a sample undergoing pretreatment in real time at regular time intervals, calculates the turbidity change rate, and determines that the pretreatment end point is reached when the turbidity change rate is within a certain level, thereby terminating the pretreatment process of the sample.

[0026] The present invention provides a device for determining the end point of pretreatment of a sample through real-time turbidity measurement, including: a sample holder for holding a plurality of sample containers, which is arranged concentrically with respect to a center point and rotates in one direction, clockwise or counterclockwise, on a plane; a sample holder into which the sample container is inserted; a pretreatment unit for performing a pretreatment process for measuring TOC (Total Organic Carbon) of a sample by performing ultrasonic irradiation and acid or alkaline elution on a sample supplied to the sample container; a turbidity sensor unit for measuring turbidity of the sample; and a control panel unit for controlling the turbidity sensor unit to measure the turbidity of a sample during pretreatment at regular time intervals, and checking the turbidity change rate (NTUn / NTUn-k, 1≤k≤3), which is the ratio of the currently measured turbidity to the previously measured turbidity, and determining that the pretreatment end point has been reached when the turbidity change rate (NTUn / NTUn-k) is within 30%, and controlling the pretreatment unit to end the pretreatment process.

[0027] Here, the control panel section is configured such that the pretreated sample has the maximum expected TOC concentration (TOC) when the turbidity change rate is within 30%. MAX ) can be characterized by being judged to have achieved more than 80% of the target.

[0028] Here, the pretreatment unit may be characterized in that it performs pretreatment of the sample through one or more of ultrasonic pretreatment (UL), combined alkaline and ultrasonic pretreatment (CAUL), and combined ultrasonic and dispersant pretreatment with inorganic dispersant injection (CU&D).

[0029] Here, the turbidity sensor unit can measure the turbidity of the upper, middle, and lower layers of the sample by performing a descending or ascending operation, and the control panel unit can be characterized in that it calculates the variability of the turbidity measurement results of the upper and lower layers of the sample measured by the turbidity sensor unit, and if the variability is below a certain level, it is determined that the sample has a fractional representativeness for homogeneity.

[0030] Here, the method may further include a homogeneity evaluation unit including a second turbidity sensor to evaluate the homogeneity of the pretreated sample, and measuring the turbidity of the pretreated sample through the second turbidity sensor to calculate a turbidity ratio (NTUx / NTU0), which is a ratio of the turbidity after x minutes (NTUx) to the initial turbidity (NTU0), and evaluating the sample as homogeneous if the turbidity ratio (NTUx / NTU0) is 70% or more.

[0031] Here, the homogeneity evaluation unit may be characterized in that it determines whether to perform additional preprocessing of a sample for which preprocessing has been completed by judging the reproducibility (precision) of repeated TOC measurements of the sample using the turbidity ratio (NTUx / NTU0).

[0032] The present invention has the effect of finding a method for optimally terminating a pretreatment process according to the characteristics of a sample.

[0033] In addition, the present invention has the effect of being able to determine whether 80% or more of the maximum TOC concentration (TOCMAX) expected in a sample has been achieved.

[0034] In addition, the present invention has the effect of being able to determine whether a pretreated sample has a fractional representativeness for homogeneity.

[0035] FIG. 1 is a drawing showing the external appearance of a device that determines the end point of sample pretreatment through real-time turbidity measurement according to one embodiment of the present invention.

[0036] FIG. 2 is a simplified drawing illustrating the operation of a device for determining the end point of sample pretreatment through real-time turbidity measurement according to one embodiment of the present invention.

[0037] FIG. 3 is a graph showing the results of monitoring the change in total organic carbon concentration and real-time turbidity change according to the pretreatment time as a result of pretreatment of compost particle samples with alkaline ultrasonic combined pretreatment (CUAL) according to one embodiment of the present invention.

[0038] FIG. 4 is a graph showing the results of monitoring the change in total organic carbon concentration and real-time turbidity change according to the pretreatment time as a result of ultrasonic pretreatment (UL) of a sewage particle sample according to an embodiment of the present invention.

[0039] FIG. 5 is a graph showing the results of monitoring the change in total organic carbon concentration and real-time turbidity change according to the pretreatment time as a result of alkaline ultrasonic combined pretreatment (CUAL) of a sewage particle sample according to an embodiment of the present invention.

[0040] Figure 6 is a graph showing the results of monitoring the change in total organic carbon concentration and real-time turbidity change according to the pretreatment time as a result of dispersant ultrasonic complex pretreatment (CU&D) of a sewage particle sample according to an embodiment of the present invention.

[0041] Figure 7 is a graph showing the correlation between the turbidity change rate and the TOC change rate over time during a sample pretreatment process according to one embodiment of the present invention.

[0042] FIG. 8 is a diagram showing the results of predicting the pretreatment time according to the pretreatment method for environmental particle samples and environmental samples according to one embodiment of the present invention.

[0043] FIG. 9 is a graph showing the correlation between the coefficient of variation of the turbidity measurement results (NTU1) of the upper and lower portions of a sample undergoing pretreatment and the coefficient of variation of the TOC measurement according to one embodiment of the present invention.

[0044] FIG. 10 is a drawing illustrating an embodiment of the present invention in which a turbidity sensor unit can move up and down to measure the turbidity of the upper and lower layers of a sample contained in a sample container.

[0045] FIG. 11 is a graph showing the correlation between the TOC reduction rate ((%)) due to particle sedimentation and the precision of the TOC measurement (TOC precision (%)) when measuring a pretreated sample containing floating particles in a homogeneity evaluation unit according to an embodiment of the present invention.

[0046] FIG. 12 is a graph showing the correlation between the precision of TOC measurement (TOC precision, (%)) of a sample pretreated in a homogeneity evaluation unit and the turbidity ratio (NTUx / NTU0) using turbidity sensor 2 according to one embodiment of the present invention.

[0047] FIG. 13 is a graph showing the correlation between the TOC reduction rate (%) and the turbidity ratio (NTU5 / NTU0) using turbidity sensor 2 when measuring a pretreated sample containing floating particles in a homogeneity evaluation unit according to an embodiment of the present invention.

[0048] Hereinafter, a preferred embodiment of the present invention will be described with reference to the attached drawings.

[0049] FIG. 1 is a drawing showing the external appearance of a device for determining the end point of pretreatment of a sample through real-time turbidity measurement according to an embodiment of the present invention, and FIG. 2 is a drawing showing a simplified version of a device for determining the end point of pretreatment of a sample through real-time turbidity measurement according to an embodiment of the present invention for the purpose of explaining its operation.

[0050] The device (10) for determining the end point of pretreatment of a sample through real-time turbidity measurement of the present invention is configured to include a sample holder (100), a sample holder (210), a pretreatment unit (300), a turbidity sensor unit (310), a homogeneity evaluation unit (400), and a control panel unit (500).

[0051] The sample holder (100) performs the function of rotating in one direction, clockwise or counterclockwise, to preprocess the sample contained in the sample container.

[0052] A sample holder (210) into which the lower part of a sample container (200) can be inserted is placed on the sample holder (100).

[0053] The sample holder (210) is a holder into which a sample container (200) is inserted, and is arranged concentrically spaced apart from the center point of the sample holder (100) as shown in FIGS. 1 and 2.

[0054] The sample holder (210) may have a radius greater than the outer circumference radius of the sample container (200) so that the lower end of the sample container (200) can be easily inserted. The shape is not limited, but may have the same shape as the outer circumference of the sample container (200). The depth may be smaller than the entire length of the sample container (200), and more specifically, may be formed to be less than half the entire length of the sample container (200).

[0055] The sample holder (210) is arranged in a concentric circle at regular intervals based on the center point of the sample holder (100), so that the sample container (200) inserted into the sample holder (210) is sequentially exposed to the preprocessing unit (300) and the homogeneity evaluation unit (400), and when the sample holder (100) rotates in one direction, clockwise or counterclockwise, on a plane, the sample holder (210) can be automatically circulated.

[0056] The sample container (200) is inserted at its lower end into a sample holder (210) placed on a sample holder (100). Here, the lower end is a portion of the entire length of the sample container (200), and more specifically, may be formed to be less than half of the entire length.

[0057] The pretreatment unit (300) performs a function of performing a pretreatment process for measuring TOC (Total Organic Carbon) of a sample by performing ultrasonic irradiation and acid or alkaline elution on the sample supplied to the sample container (200).

[0058] For this purpose, the pretreatment unit (300) may be equipped with an ultrasonic treatment unit (320) and a solution inlet unit (330) that induces acid or alkali dissolution.

[0059] In one embodiment, the pretreatment unit (300) can significantly increase the alkaline elution efficiency of particulate organics by simultaneously performing ultrasonic irradiation and alkaline elution to reduce particle size through ultrasonic crushing of particles, and at the same time, by inducing particle size reduction through organic matter elution, thereby improving the TOC oxidation rate of particles, thereby minimizing the influence of sieve size while improving the total organic carbon (TOC) recovery rate (accuracy). Therefore, performing ultrasonic irradiation or alkaline elution alone, or performing ultrasonic irradiation and alkaline elution sequentially regardless of the order, is not preferable because the intended effect of the present invention cannot be obtained as described in the experimental examples below.

[0060] As shown in Fig. 1, the solution inlet (330) may be configured separately as an alkali inlet (331) for injecting an alkaline solution and an acid inlet (332) for injecting an acid solution.

[0061] The ultrasonic treatment unit (320) is intended to irradiate ultrasonic waves to a sample supplied to a sample container (200) to break up floating substances. One end is fixed and the other end is in the form of a probe that can be lowered or raised to contact or separate from the sample.

[0062] Since one end of the ultrasonic treatment unit (320) is fixed, when the sample holder (100) rotates in one direction, clockwise or counterclockwise, the other end in the form of a probe located at the lower part corresponding to the ultrasonic treatment unit (320) descends and contacts the sample to irradiate ultrasonic waves, and when it rises, it can fall off the sample. As the sample holder (100) rotates, a plurality of sample containers are sequentially exposed to the ultrasonic treatment unit (320), so that a plurality of samples can be easily ultrasonicated.

[0063] Ultrasonic irradiation is performed at 5 to 50 kHz and 400 to 800 W / cm 2 It can be done for 5 to 30 minutes under conditions, specifically 10 to 30 kHz and 500 to 700 W / cm 2 The ultrasonic irradiation can be performed for 5 to 15 minutes under these conditions. The above ultrasonic irradiation conditions are within the optimal range for achieving the effects of the present invention. If the conditions are lower or higher than these, the particle size reduction effect of suspended solids or process efficiency may be reduced, which is not desirable.

[0064] The alkali inlet (331) is intended to induce alkaline dissolution by introducing an alkaline solution into the sample supplied to the sample container (200). One end may be fixed and the other end may be positioned in a non-contact state with the sample.

[0065] Since one end of the alkali inlet (331) is fixed, when the sample holder (100) rotates clockwise or counterclockwise and is positioned corresponding to the upper direction of the sample container, the alkaline solution can be discharged from the other end of the alkali inlet (331) and introduced into the sample. As the sample holder (100) rotates, multiple sample containers are sequentially exposed to the alkali inlet (331), so that alkaline elution can be easily induced in multiple samples.

[0066] Dissolved organic carbon (DOC) can be extracted from suspended particles through the above alkaline extraction. This alkaline extraction can be performed for 5 to 30 minutes under pH conditions of 11 to 13. The above alkaline extraction conditions are within the optimal range for achieving the effects of the present invention. If the conditions are lower or higher than this, the particle size reduction effect of suspended particles or process efficiency may deteriorate, which is not desirable. The above alkaline extraction conditions can be adjusted using an alkaline solution, such as, for example, a 0.01 to 0.1 mol / L NaOH aqueous solution, but are not limited thereto.

[0067] The alkali inlet (331) is connected to an alkali reagent container (not shown) and an electric cylinder (not shown).

[0068] In some cases, an acid solution may be additionally injected for neutralization treatment into a sample that has undergone ultrasonic irradiation and alkaline elution through the acid inlet (332). This is for neutralization treatment by injecting an acid solution, and an acid equivalent to the injected alkali may be injected to adjust the pH to a neutral state of 5.5 to 7.5. If the pH is lower than 5.5, the inorganic carbon component of the sample may be damaged, and if the pH is higher than 7.5, the IC content of the sample may increase, which is not desirable. In order to further improve the total organic carbon (TOC) recovery rate (accuracy) through easy acidic state control (pH < 2), one end of the acid inlet (332) may be fixed and the other end may be positioned in a non-contact state with the sample.

[0069] The acid inlet (332) is connected to an acid reagent container (not shown) and an electric cylinder (not shown).

[0070] Additionally, a turbidity sensor unit (310) is configured in the preprocessing unit (300).

[0071] The turbidity sensor unit (310) performs the function of measuring the turbidity of a sample during and immediately after preprocessing.

[0072] The turbidity sensor unit (310) can move up and down as shown in Fig. 10 to measure the turbidity of the upper and lower portions of the sample.

[0073] The homogeneity evaluation unit (400) includes a second turbidity sensor (401) to evaluate the homogeneity of the pretreated sample, and measures the turbidity of the pretreated sample through the second turbidity sensor (401).

[0074] The homogeneity evaluation unit (400) measures the sedimentation and homogeneity of particles in a pretreated sample using turbidity through a second turbidity sensor (401) to ensure a certain homogeneity after pretreatment for a sample containing suspended solids of various properties (origins).

[0075] The homogeneity evaluation unit (400) is equipped with a second turbidity sensor (401) in the form of a probe, and can preliminarily analyze the degree of sedimentation of suspended matter inside through homogeneity evaluation, thereby improving the homogenization (precision) of the sample and increasing the reliability of the TOC measurement value, while improving the maintenance cost of the device due to suspended matter.

[0076] The homogeneity evaluation unit (400) can be positioned in the upper direction of the sample container adjacent to the sample container on which pretreatment has been performed based on the rotational direction of the sample holder (100).

[0077] One end of the homogeneity evaluation unit (400) is fixed and the other end can be lowered or raised to contact or separate from the pretreated sample, for example, in the form of a probe. Since one end of the homogeneity evaluation unit (400) is fixed, when the sample holder (100) rotates in one direction, clockwise or counterclockwise, and is positioned corresponding to the upper direction of the sample container, the other end of the homogeneity evaluation unit (400) is lowered and contacts the pretreated sample to evaluate the homogeneity.

[0078] In the homogeneity evaluation unit (400), turbidity is measured for a preset reference time for a pre-treated sample to calculate a turbidity ratio. Thereafter, the turbidity ratio is compared with a preset reference value, and if it is greater than the preset reference value, the homogeneity of the sample can be evaluated by checking the correlation with the relative standard deviation (RSD) for TOC replicate measurements (mg-C / L) according to the International Organization for Standardization (ISO): 20236.

[0079] The relative standard deviation (RSD) for TOC replicate measurements (mg-C / L) according to the International Organization for Standardization (ISO): 20236 is an index for evaluating the homogeneity of a sample as defined in the International Organization for Standardization (ISO): 20236. It refers to the mutual deviation rate of TOC replicate measurements, i.e. TOC concentration values ​​(mg-C / L), obtained by repeatedly injecting the same sample. Specifically, for a sample containing suspended solids, the relative standard deviation (RSD) for TOC replicate measurements (mg-C / L) according to the International Organization for Standardization (ISO): 20236 must be less than 10% as a standard for TOC analysis quality control to determine that the sample has adequate homogeneity.

[0080] Accordingly, the present invention can confirm whether a sample containing suspended solids satisfies the TOC analysis quality control standards according to the International Organization for Standardization (ISO) solely based on the turbidity ratio of the sample. This is because it has been proven that suspended solids primarily increase the uncertainty of the measured value through sedimentation within the instrument, and thus the degree of suspended solids sedimentation within the instrument can be analyzed in advance by measuring turbidity changes. In other words, this allows for the easy measurement of sample homogeneity, which satisfies the quality control standards, through turbidity changes.

[0081] The above turbidity ratio means the ratio of the turbidity (NTUx) x minutes later (NTUx / NTU0) to the initial turbidity (NTU0). Here, x is a preset reference time, which may be 1 minute or more and 6 minutes or less, and may be 5 minutes in detail. As can be confirmed in the experimental example below, it has a high correlation with the TOC replicate measurements (mg-C / L) according to the International Organization for Standardization (ISO): 20236.

[0082] Specifically, when the turbidity ratio (NTUx / NTU0) is 70% or more, it is confirmed that the relative standard deviation (RSD) for TOC replicate measurements (mg-C / L) according to the International Organization for Standardization (ISO): 20236 is less than 10%, so the sample can be evaluated as having appropriate homogeneity, and therefore the homogeneity evaluation unit (400) can use the turbidity ratio as an indicator for evaluating the homogeneity of the sample.

[0083] In the present invention, homogeneity can be easily evaluated through a process of automatically circulating a large amount of samples with a minimum number of steps, including ultrasonic irradiation, alkaline dissolution, and acid dissolution processes.

[0084] A driving means for rotating the sample holder (100) can be coupled to the bottom of the sample holder (100). The driving means includes, for example, a motor, a power transmission unit for transmitting power, and a screw that rotates by power, and can automatically rotate the sample holder (100).

[0085] The control panel unit (500) controls the turbidity sensor unit (310) to measure the turbidity of a sample undergoing pretreatment at regular time intervals (here, the time interval (t) is set to 1 minute ≤ t ≤ 3 minutes, and preferably, it can be set to 1 minute ≤ t ≤ 2 minutes), checks the turbidity change rate (NTUn / NTUn-k, 1 ≤ k ≤ 3), which is the ratio of the currently measured turbidity to the previously measured turbidity, and, if the turbidity change rate (NTUn / NTUn-k) is within 30%, determines that the pretreatment end point has been reached and controls the pretreatment unit (300) to terminate the pretreatment process.

[0086] In addition, the control panel (500) can perform a function of controlling the process for analyzing total organic carbon, and is connected to the display unit to allow the pretreatment process to be visually confirmed. Specifically, it is connected to sensors that can appropriately adjust the ultrasonic intensity and time, the amount and time of the alkaline and acid solutions, and the like, to control these processes. In addition, it is connected to a second turbidity sensor (410) for homogeneity evaluation to control and confirm these processes.

[0087] The control panel unit (500) can be configured inside or outside the device (10) that determines the end point of sample pretreatment through real-time turbidity measurement.

[0088] The process of determining the end point of preprocessing at the control panel (500) and ending the preprocessing process is as follows.

[0089] First, when the turbidity of the sample being pretreated is measured n times at regular intervals (in real time) in the turbidity sensor unit (310), the control panel unit (500) stores the real-time measurement results of the turbidity sensor unit (310) and compares them with the previous measurement results of turbidity (i.e., NTU n / NTU n-k ,1≤k≤2) through change (NTU n / NTU n-k ) is within a certain level (preferably within 30%), the preprocessing process is controlled to end in the preprocessing unit (300).

[0090] Figures 3 to 6 are graphs showing the results of monitoring the change in total organic carbon concentration and real-time turbidity change according to the pretreatment method and pretreatment time of environmentally sourced particle samples.

[0091] The method for evaluating the preprocessing time according to the experimental results with reference to FIGS. 3 to 6 is as follows.

[0092] When measuring TOC, the presence of suspended solids and high particle size within the sample lowers the TOC oxidation rate, reducing measurement accuracy. Therefore, appropriate pretreatment, such as ultrasound or ultrasonic alkaline treatment, can improve the oxidation rate by reducing the particle size of suspended solids and converting them to dissolved substances, thereby enhancing the accuracy of TOC measurement. However, the required pretreatment time to enhance the oxidation rate varies significantly depending on the sample's properties and origin. Excessive pretreatment times can actually cause organic matter loss and degrade TOC measurement accuracy (see Figure 3).

[0093] Therefore, optimized pretreatment times are required for each sample. However, currently, no domestic or international standards exist for pretreatment times. Furthermore, suspended solids behavior, including concentration, particle size, and turbidity, vary significantly depending on the pretreatment method and sample properties.

[0094] In order to more accurately determine the end point of pretreatment in all samples and pretreatment technologies in the present invention, experiments were conducted on the concentration of suspended solids, particle size, turbidity, TOC, POC, and DOC changes during sample pretreatment. As a result of the research through experiments, when the turbidity of the sample being pretreated was monitored at regular intervals, the turbidity changed rapidly at the beginning of the pretreatment, but at the point where the turbidity change amount changed within a certain range (section), it was confirmed that the TOC pretreatment reached maximum efficiency and no longer required pretreatment. (See Figs. 4 to 6)

[0095] As shown in Fig. 4, the change in turbidity of the sample being pretreated is constant (i.e., NTU) when the pretreatment time is about 4 to 5 minutes. n / NTU n-k It can be seen that at a certain point, the TOC pretreatment reaches a maximum efficiency of 80% or more, and as shown in Fig. 5, the change in turbidity of the sample being pretreated is constant (i.e., NTU) between 6 and 10 minutes of pretreatment time. n / NTU n-k It can be seen that at a certain point, the TOC pretreatment reaches a maximum efficiency of more than 90%.

[0096] In addition, as shown in Fig. 6, the change in turbidity of the sample being pretreated is constant (i.e., NTU) when the pretreatment time is between 3 and 5 minutes. n / NTU n-k It can be seen that at a certain point, the TOC pretreatment reaches a maximum efficiency of 85% or more.

[0097] The above Fig. 3 is a graph showing the change in total organic carbon concentration and the real-time turbidity change monitoring results according to the pretreatment time as a result of CUAL pretreatment of compost particle samples, Fig. 4 is a graph showing the change in total organic carbon concentration and the real-time turbidity change monitoring results according to the pretreatment time as a result of ultrasonic pretreatment (UL) of sewage particle samples, Fig. 5 is a graph showing the change in total organic carbon concentration and the real-time turbidity change monitoring results according to the pretreatment time as a result of alkaline ultrasonic complex pretreatment (CUAL) of sewage particle samples, and Fig. 6 is a graph showing the change in total organic carbon concentration and the real-time turbidity change monitoring results according to the pretreatment time as a result of dispersant ultrasonic complex pretreatment (CU&D) of sewage particle samples.

[0098] In the experiments of the above Figures 3 to 6, the turbidity change of the sample was measured in real time at 2-minute (120-second) intervals during the preprocessing process, and when measuring n times, the result of the n-2nd measurement was compared with the turbidity change.

[0099] From the above results, it can be confirmed that the increase in total organic carbon also slows down when the real-time turbidity change decreases in most samples. In particular, when the turbidity change decreases by less than 30% in all samples, the maximum TOC concentration (hereinafter referred to as TOC) expected from the pretreatment method is MAX) achieved more than 80% of the results, and more than 90% in most samples, showing reliable results.

[0100] That is, it is judged that by using the above experimental results, it is possible to predict the optimal pretreatment time of the sample based on the turbidity change rate of the sample being pretreated and end the pretreatment at the optimal time, thereby contributing to improving the reliability and efficiency of the analysis procedure through pretreatment.

[0101] Furthermore, ultrasonic pretreatment, a commonly used pretreatment method for total organic carbon analysis, can cause structural destruction of the sample's organic matter and loss of volatile organic compounds if performed over a long period of time, potentially leading to decreased accuracy and precision. Therefore, it is crucial to complete the pretreatment within an appropriate timeframe. For example, the sample in Figure 3 exhibits a tendency for total organic carbon concentration and reproducibility to decline when the pretreatment process is performed for a certain period of time.

[0102] The present invention, which utilizes the above experimental results, has the advantage of being able to complete the pretreatment of a sample at an appropriate time, thereby preventing the loss of organic matter in the sample and obtaining accurate measurement results.

[0103] In particular, the present invention was effective and showed reliable results in all pretreatment methods including ultrasonic pretreatment (UL), combined alkaline and ultrasonic pretreatment (CAUL), and combined ultrasonic and dispersant pretreatment with inorganic dispersant injection (CU&D), as shown in the results of FIGS. 3 to 6.

[0104] That is, the present invention has a feature that can predict the end point of pretreatment of a sample based on turbidity regardless of the type of pretreatment method as well as the properties of the sample.

[0105] Figure 7 is a graph showing the correlation between the turbidity change rate and the TOC change rate over time during a sample pretreatment process according to one embodiment of the present invention.

[0106] When measuring total organic carbon in suspended particles in a sample, pretreatment is performed to enhance the conversion of organic matter to CO2, i.e., the oxidation rate. This oxidation rate can be enhanced by converting the suspended particles themselves into dissolved organic matter, which is generally known to have a higher oxidation rate, or by reducing the particle size of the suspended particles to a form more favorable for oxidation.

[0107] At this time, the commonly used pretreatment technology is ultrasonic pretreatment technology, and at this time, the CUAL pretreatment technology is a composite pretreatment technology that enhances the conversion of organic matter in suspended particles into dissolved organic matter in the ultrasonic pretreatment technology, and the dispersant ultrasonic composite pretreatment (CU&D) is a pretreatment method that enhances the sedimentation inhibition effect through particle size reduction and increased dispersion stability due to separation of coagulated particles by the dispersant in the existing ultrasonic pretreatment technology. At this time, when the particle size of the sample decreases, the turbidity generally increases because the scattering within the sample increases, or when the particulate organic matter itself decreases due to dissolution, the scattering decreases and the turbidity decreases.

[0108] Figure 7 shows the correlation between the turbidity change rate and TOC change rate over time during the sample pretreatment process through the UL, CUAL, and CU&D pretreatment results, including various environmental particle samples such as sewage, compost, etc.

[0109] As shown in Figure 7, when the turbidity change rate of the sample being pretreated is within 30%, it can be seen that the TOC change rate is constant at within 25%.

[0110] As a result of the experiment in Fig. 7, when turbidity was measured n times at regular time intervals (t sec) during the total organic carbon pretreatment process, if the change between the n-1 measurement result and the n-1 measurement result was within 10%, the change rate of TOC was also within approximately 10%, and it could be evaluated that the pretreatment was completed because the efficiency improvement due to the pretreatment slowed down.

[0111] At this time, it is recommended to measure turbidity at intervals of 60 to 180 seconds (preferably at intervals of 60 to 120 seconds), and it is desirable to set the amount of change for determining the end point of pretreatment within 10% to 30% based on the above experimental results.

[0112] Here, in the case where a bath type ultrasonic device other than a probe type is used as the pretreatment method, it is also possible to set the turbidity measurement time interval to between 60 and 300 seconds.

[0113] FIG. 8 is a diagram showing the results of predicting the pretreatment time according to the pretreatment method for environmental particle samples and environmental samples according to one embodiment of the present invention.

[0114] The accuracy of the present invention was evaluated using influent from an actual wastewater treatment plant (WWTP) along with previous environmental particle samples.

[0115] Here, SW-A, SW-B, CP, and WWinflent represent environmental particle samples and real wastewater samples.

[0116] The numbers in the heatmap in Figure 8 represent the accuracy (recovery rate) and standard deviation of the prediction model, while the figures in parentheses indicate the coefficient of variation (CV). The evaluation results showed that out of a total of 12 cases (4 samples, 3 preprocessing methods), 10 samples achieved an accuracy of 80% or higher, and 8 samples achieved an accuracy of 90% or higher.

[0117] In particular, when the CU&D and CUAL pretreatment methods were applied, the end point of pretreatment could be accurately predicted in all samples.

[0118] FIG. 9 is a graph showing the correlation between the coefficient of variation of the turbidity measurement results (NTU1) of the upper and lower portions of a sample that underwent pretreatment according to an embodiment of the present invention and the coefficient of variation of the TOC measurement.

[0119] TOC can be measured through turbidity analysis of a sample, but the TOC analysis results depend on the time at which the sample is injected into the sample container (200) and the properties of the suspended solids at the injection location. That is, due to poor homogeneity of the sample at the time of sample collection, a measurement result different from the TOC of the actual sample can be obtained.

[0120] Therefore, for Germany's TOC measurement standard, separate samples are taken from the top and bottom of the prepared sample to assess the representativeness of the measurement results, thereby determining the TOC measurement results. However, this method incurs the additional requirement of analysis for analysis purposes, and its post-evaluation nature reduces accessibility and efficiency.

[0121] In the present invention, taking into account the fact that the measurement of turbidity can qualitatively and quantitatively determine the distribution and amount of suspended solids for a sample of the same medium, the turbidity of the upper and lower parts of the sample was measured, and the correlation with the coefficient of variation of TOC measurement was evaluated.

[0122] As shown in Fig. 9, there was an excellent correlation between the coefficient of variation of the turbidity measurement results at the top and bottom of the sample and the coefficient of variation of the TOC measurement, and it was found that when the turbidity measurement results at the top and bottom of the sample were within 10%, most of the TOC measurement results were predicted to be within 20% in the future prediction interval.

[0123] Additionally, it can be seen that when the difference between turbidity values ​​in the measurement data is within 5%, the coefficient of variation of the TOC measurement results is also within 10% in most samples.

[0124] In Fig. 9, it can be seen that when the coefficient of variation of the turbidity measurement results at the top and bottom of the sample after the pretreatment process is within 10%, the coefficient of variation of the TOC measurement is within 20%.

[0125] Through the experimental results for the above-described Figure 9, it can be seen that the present invention can evaluate the representativeness of a sample through the variability (coefficient of variation) of the turbidity measurement results of the upper and lower portions of the sample after pretreatment.

[0126] Here, the turbidity sensor unit (310) of the present invention is configured to be able to move up and down as shown in FIG. 10 to measure the turbidity of the upper and lower layers of the sample contained in the sample container (200).

[0127] As described above, the homogeneity evaluation unit (410) of the present invention measures the turbidity of a pretreated sample and calculates a turbidity ratio (NTUx / NTU0), which is the ratio of the turbidity after x minutes (NTUx) to the initial turbidity (NTU0), and when the turbidity ratio (NTUx / NTU0) is at a certain standard (preferably 70% or more), the pretreated sample can be evaluated as homogeneous. In addition, the turbidity ratio (NTUx / NTU0) can be used to determine the reproducibility (precision) of TOC measurement of the sample.

[0128] FIG. 11 is a graph showing the correlation between the TOC reduction rate ((%)) due to particle sedimentation and the precision of the TOC measurement (TOC precision (%)) when measuring a pretreated sample containing floating particles in a homogeneity evaluation unit according to an embodiment of the present invention. It can be seen that the main cause of the precision reduction in TOC measurement is sample particle sedimentation.

[0129] FIG. 12 is a graph showing the correlation between the precision (TOC precision, (%)) of TOC measurement of a sample pretreated in a homogeneity evaluation unit and the turbidity ratio (NTUx / NTU0) using turbidity sensor 2 according to an embodiment of the present invention. It can be seen that there is a certain correlation between the turbidity ratio (NTUx / NTU0) and the precision of TOC measurement. In other words, it can be seen that the precision of TOC measurement can be predicted using the turbidity ratio (NTUx / NTU0).

[0130] FIG. 13 is a graph showing the correlation between the TOC reduction rate ((%)) due to particle sedimentation and the turbidity ratio (NTU5 / NTU0) using turbidity sensor 2 when measuring a pretreated sample containing suspended particles in a homogeneity evaluation unit according to an embodiment of the present invention. It can be seen that the turbidity ratio (NTUx / NTU0) and the measurement reduction rate due to particle sedimentation have a certain correlation. In other words, the turbidity ratio can be used to predict the sample particle sedimentation that occurs during the TOC measurement process.

[0131] In the experiments performed in Figs. 12 and 13, the turbidity ratio (NTU5 / NTU0) was used as the ratio of the turbidity after 5 minutes (NTU5) to the initial turbidity (NTU0).

[0132] Through the results of the experiments of the above-described Figures 11 to 13, the homogeneity evaluation unit (410) of the present invention can use the turbidity ratio (NTUx / NTU0) measured by the second turbidity sensor (410) to determine the reproducibility (precision) of the TOC measurement of the sample, and in the case where the reproducibility (precision) of the TOC measurement is low, it can be decided to perform additional preprocessing of the sample for which preprocessing has been completed.

[0133] The present invention is not limited to the specific preferred embodiments described above, and it is obvious that anyone with ordinary skill in the art to which the invention pertains can make various modifications without departing from the gist of the present invention claimed in the claims, and that such modifications fall within the scope of the claims.

Claims

1. A sample holder for holding multiple sample containers is arranged at a distance from each other on a concentric circle with respect to a center point, and a sample holder that rotates in one direction, clockwise or counterclockwise, on a plane; A sample holder into which the above sample container is inserted; A pretreatment unit that performs a pretreatment process for measuring TOC (Total Organic Carbon) of a sample by performing ultrasonic irradiation and acid or alkaline elution on the sample supplied to the sample container; A turbidity sensor unit for measuring the turbidity of the sample; and A control panel section that controls the above turbidity sensor section to measure the turbidity of a sample undergoing pretreatment at regular time intervals, checks the turbidity change rate (NTUn / NTUn-k, 1≤k≤3), which is the ratio of the currently measured turbidity to the previously measured turbidity, and determines that the pretreatment end point has been reached when the turbidity change rate (NTUn / NTUn-k) is within 30%, and controls the pretreatment section to end the pretreatment process; A device for determining the end point of sample pretreatment through real-time turbidity measurement including .

2. In paragraph 1, The above control panel section, when the turbidity change rate is within 30%, the pretreated sample is expected to have the maximum TOC concentration (TOC MAX ) to determine the end point of sample pretreatment through real-time turbidity measurement.

3. In paragraph 1, The above preprocessing unit A device for determining the end point of sample pretreatment through real-time turbidity measurement, characterized in that the pretreatment of the sample is performed through at least one method among ultrasonic pretreatment (UL: Ultrasonic pretreatment), combined alkaline and ultrasonic pretreatment (CAUL: Combined Alkaline and Ultrasonic pretreatment), and combined inorganic dispersant injection and ultrasonic pretreatment (CU&D: Combined Ultrasonic and Dispersant pretreatment).

4. In paragraph 1, The above turbidity sensor unit can measure the turbidity of the upper, middle and lower layers of the sample by performing a descending or ascending motion. A device for determining the end point of pretreatment of a sample through real-time turbidity measurement, characterized in that the control panel section calculates the variability of the turbidity measurement results of the upper and lower portions of the sample measured by the turbidity sensor section, and determines that the sample has a fractional representativeness for homogeneity when the variability is below a certain level.

5. In paragraph 1, A homogeneity evaluation unit including a second turbidity sensor to evaluate the homogeneity of the pretreated sample, and measuring the turbidity of the pretreated sample through the second turbidity sensor, calculating the turbidity ratio (NTUx / NTU0), which is the ratio of the turbidity after x minutes (NTUx) to the initial turbidity (NTU0), and evaluating the sample as homogeneous if the turbidity ratio (NTUx / NTU0) is 70% or more; A device for determining the end point of sample pretreatment through real-time turbidity measurement, characterized by further including:

6. In paragraph 5, A device for determining the end point of pretreatment of a sample through real-time turbidity measurement, characterized in that the above homogeneity evaluation unit determines the reproducibility (precision) of repeated TOC measurements of the sample using the above turbidity ratio (NTUx / NTU0) and determines whether additional pretreatment of a sample for which pretreatment has been completed is required.

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