KR20230016993A - Total-Organic-Carbon-Based Quantitative Estimation Method of Microplastics in Sewage - Google Patents

Abstract

The present invention relates to a method for analyzing microplastics in sewage based on total organic carbon (TOC) measurement, in which sewage is filtered and organic matter oxidation pretreatment is performed to remove an organic matter, and then a sewage sample from which the organic matter has been removed is introduced into a TOC analyzer to indirectly measure microplastics in the sewage by quantifying carbonaceous components in the microplastics present in the sewage with the TOC analyzer, and to comprehensively evaluate the behavior of the microplastics by including the removal efficiency of contaminants in a sewage treatment process.

Description

Total-Organic-Carbon-Based Quantitative Estimation Method of Microplastics in Sewage}

The present invention relates to a total organic carbon (TOC) measurement-based analysis method for microplastics in sewage, and more particularly, to a method for analyzing microplastics in sewage, rather than a conventional spectroscopic analysis method for counting microplastic particles. It relates to a mass spectrometry method for analyzing microplastics by quantifying with a total organic carbon analyzer and using indirect quantification of the amount of carbon originating from plastics as an indicator.

In the past few years, microplastics have occurred in water, soil and air of land and sea and their behavior has been studied (A.L. Andrady, Mar. Pollut. Bull. 62(2011) 1596-1605; R. Dris et al. al., Environ. Pollut. 221 (2017) 453-458 A. A. Horton et al., Sci. Total. Environ. ). It has been concluded that controlling the pollution of the global water environment by microplastics requires considerable effort and budget and cannot be achieved without changing the industrial paradigm. Disposal of microplastics in sewage is a challenge for sewage treatment plants (STPs) designed to prevent various contaminants in sewage from entering the aquatic environment. Current sewage treatment plants are assessed using existing water quality indicators such as pH, biological or chemical oxygen demand (BOD or COD), total nitrogen or phosphorus (TN or TP) and total organic carbon (TOC); Although trace organic contaminants such as pesticides, per- and polyfluoroalkyl (PFAS) substances, and pharmaceuticals and personal care products (PPCP) are recently known to be present in significant amounts in sewage (L. Joseph et al. , Chem. Eng. J. 369(2019) 928-946; Y. Zhou et al., Environ. Int. 131 (2019), 104982), microplastics are commonly monitored in sewage treatment processes simply because of the complexity involved in measuring them. It doesn't work.

Several analytical techniques have been applied to characterize microplastics. Micro-Fourier transform infrared spectroscopy (μ-FTIR) to quantify microplastics in water environments (S. Primpke et al., Anal. Methods-Uk. 11 (2019) 2138-2147; A.S. Tagg et al., Anal. Chem. 87 (2015) 6032-6040), Raman spectroscopy (Z. Sobhani et al., Anal. Chim. Acta. 1077 (2019) 191-199; S. Wolff et al., Water Res X. 2 (2018), 100014), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) (M. Fischer et al., Environ. Sci. Technol. 51 (2017) 5052-5060; L. Hermabessiere et al., Anal. Bioanal. Chem. 410 (2018) 6663-6676) and thermogravimetric-thermal desorption-GC/MS (TGA-TD-GC/MS) (E. Dumichen et al., Chemosphere 174 ( 2017) 572-584) and the like are used. In particular, spectroscopic methods such as μ-FTIR and Raman techniques are used to investigate the type, properties and number of microplastics. However, these methods give highly uncertain results related to the number of particles. Particularly in samples such as sewage and sludge, the uncertainty can be even greater when there are many or varied overlapping particles that are not uncommon. The microplastics that can detect and count the usefulness of the method are limited by their size. Also, particles smaller than several micrometers cannot be counted. In addition, it takes about 6 to 24 hours to analyze each sample using this spectroscopy method, even excluding the pretreatment step of selectively separating microplastics.

However, these methods can provide an intuitive way to understand the properties of microplastics and, when combined with other quantitative methods, can be synergistic technologies to evaluate the performance of treatment processes (E. Hendrickson et al., Environ. Sci. Technol. Thermal analysis methods such as TGA- and Py-GC/MS can selectively separate and detect plastic monomers. This method can qualitatively and quantitatively measure small amounts of microplastics at the μg level (E. Duemichen et al., J. Chromatogr. A. 1592 (2019) 133-142), and potentially this method can be used as a source of microplastics. can be used to effectively track and control (C. Schwaferts et al., Trac. Trends Anal. Chem. 112 (2019) 52-65).

On the other hand, very extensive sample preparation steps are required for particle separation and concentration before applying these analytical methods to quantification. Reagent, labor-intensive and time-consuming degradation steps are applied to remove organic particles other than microplastics from samples (RR Hurley et al., Environ Sci Technol. 52 (2018) 7409-7417; J. Masura et al., recommendations for quantifying synthetic particles in waters and sediments., (2015) JC Prata et al., Sci. Total Environ. 686 (2019) 131-139). In particular, organic matter such as biomass in natural water or sewage can hinder accurate measurement of microplastics. Thus, H ₂ O ₂ , Fenton's reagent, KOH, HCl or HNO ₃ have sometimes been attempted to destroy organics other than plastics by heat (CB Alvim et al., Chem. Eng. J. 402 (2020), 126293;Z. Zhang et al., Chem. Eng. J. 382 (2020), 122955). Among the aforementioned reagents, Fenton's reagent (H ₂ O ₂ + Fe(II)) at high temperatures (>50 °C) in particular has been reported to decompose organic matter in water within a short decomposition time (1-2 hours), which has led some researchers to (X. Lv et al., J Clean Prod. 225 (2019) 579-586; J. Lin et al., Sci. Total Environ. 760 (2021), 144316). Nonetheless, these sample preparation and disaggregation steps, along with sophisticated instrumentation, often prevent ongoing or routine monitoring programs for microplastics from being established in various water quality environments, including sewage.

As mentioned above, the results of spectroscopic and thermal analysis methods can be used as complementary data when evaluating the removal efficiency of sewage treatment processes for microplastics and improving treatment processes. Recently, Simon et al. calculated the mass of 10-500 μm microplastics by spectroscopic method (M. Simon et al., Water Res. 142 (2018) 1-9), and they evaluated microplastics by mass as well as number. emphasized the importance of doing The method of measuring the mass of plastics, rather than the spectroscopic method of measuring the number of microplastics, has the advantage of being able to evaluate the performance of the sewage treatment process when removing microplastics from sewage even if the mass of microplastics is roughly estimated.

In practice, sewage treatment plant operators or researchers investigating sewage and wastewater want to try an approach for quantitative assessment of microplastics from a technical point of view, how much plastic (in terms of particles or mass) enters and is removed from the sewage treatment plant. do. Because so many types of plastic particles of different sizes and shapes flow into treatment plants, there is great interest in determining the type or shape of plastic particles in routine monitoring. There is also a lack of information on the polymer science and analytical instruments needed to characterize these particles. It is the same as the case of Biochemical Oxygen Demand (BOD) or Chemical Oxygen Demand (COD) determined to quantify the biodegradability or relatively easily decomposed organic matter content of actual sewage. Because various organic chemicals exist in sewage, it is impossible and impractical to analyze individual organic compounds (Y.-Y. Choi et al., Water-Sui. 9 (2017) 409).

Therefore, it is urgently required to develop a fast and accurate analysis method for evaluating the efficiency of a sewage treatment process in which a large amount of microplastics are introduced.

Accordingly, as a result of diligent efforts to solve the above problems, the inventors of the present invention filter sewage, perform organic matter oxidation pretreatment to remove organic matter, and then introduce the sewage sample from which the organic matter is removed to a TOC analyzer for the total amount of carbon present in microplastics. In the case of measuring, carbonaceous components among microplastics present in sewage are quantified with a Total Organic Carbon (TOC) analyzer, and the indirect quantification of the amount of carbon originating from plastics is used as an indicator to indirectly measure microplastics in sewage. It was confirmed that it can be used as a method for measuring and evaluating the removal efficiency of pollutants in the sewage treatment process, and the present invention was completed.

An object of the present invention is to provide a method for analyzing microplastics present in sewage based on total organic carbon measurement.

In order to achieve the above object, the present invention comprises the steps of (a) filtering sewage to obtain a sewage sample; (b) removing organic matter from the sewage sample by subjecting the sewage sample to organic material oxidation pre-treatment; and (c) measuring the total amount of carbon present in the microplastic by introducing the sewage sample from which the organic matter has been removed into a TOC analyzer.

The quantitative method according to the present invention is a method that can quantitatively evaluate microplastics in sewage and wastewater, and can selectively measure microplastics in sewage samples using TOC rather than a difficult approach using spectroscopy or chromatography. , the fraction of microplastics in the organic matter entering the sewage treatment process and its treatment efficiency can be measured.

The total organic carbon measurement method according to the present invention can be used as a very easy and accurate method to comprehensively evaluate the behavior of microplastics in the sewage treatment process, and it is easy and accurate to take a sewage sample, and good decomposition efficiency can be obtained with a small amount of oxidizing agent. Therefore, time, cost, and generation of waste liquid are reduced. This method can flexibly adjust the measurement range by adjusting the particle diameter and filtration volume of the filter to be filtered, and can contribute to standardization for evaluating sewage treatment processes.

1 is a flow chart of a microplastic indirect quantification method using TOC-based pyrolysis according to an embodiment of the present invention.
2 is a schematic diagram showing an indirect microplastic quantification method using TOC-based pyrolysis according to an embodiment of the present invention.
Figure 3 is a graph comparing the concentration profiles of (a) influent and (b) effluent for TOC and TOC _MP in STP according to an embodiment of the present invention and (c) conventional method (FT-IR).

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is one well known and commonly used in the art.

After filtering the sewage at STP and performing organic matter oxidation pretreatment to remove organic matter, and then introducing the sewage sample from which the organic matter has been removed to a TOC analyzer to measure the total amount of carbon present in microplastics, among the microplastics present in the sewage By quantifying the carbonaceous component with a total organic carbon analyzer and using the indirect quantification of the amount of carbon originating from plastic as an indicator, it was confirmed that microplastics in sewage can be indirectly measured and the removal efficiency of pollutants in the sewage treatment process can be evaluated. .

Accordingly, the present invention, in one aspect, (a) obtaining a sewage sample by filtering the sewage; (b) removing organic matter from the sewage sample by subjecting the sewage sample to organic material oxidation pre-treatment; and (c) measuring the total amount of carbon present in the microplastic by introducing the sewage sample from which the organic matter has been removed into a TOC analyzer.

In the present invention, in step (a), the influent and effluent of the sewage process are filtered through a sieve of 450 to 550 μm, and then filtered through a filter of 40 to 50 μm. there is.

In the present invention, the step (a) may further include filtering the sewage using a filter and then washing the filter.

In the present invention, the washing may be performed using a methanol solvent, preferably methanol, but is not limited thereto.

In the quantitative method of the present invention, as a preferred embodiment, (i) using a pre-sieve of 450 to 550 μm and a filter of 40 to 50 μm for the inflow and outflow water obtained from the pipeline of the sewage treatment process vacuum filtration and washing the filter; (ii) placing the filter in a ceramic boat, adding a decomposition reagent containing Fe(II) and H ₂ O ₂ at 50 to 70 °C and leaving it for 1 hour to 3 hours; and (iii) introducing the ceramic boat into a TOC analyzer, burning it at 850 to 950° C., and then measuring the total amount of carbon present in the microplastic.

In the present invention, in step (b), a decomposition reagent containing Fe(II) and H ₂ O ₂ may be added at 50 to 70 °C and left to stand.

In the present invention, the step (c) may further include burning at 850 to 950 ° C. in a TOC analyzer.

Hereinafter, the present invention will be described in detail.

The TOC-based measurement method according to the present invention can check the total organic carbon content by burning organic matter at a high temperature and detecting CO ₂ . Among the samples to be analyzed, if most of the remaining substances, excluding organic matter of particulate matter, are plastics through pretreatment, if the amount of carbon is measured, the concentration of carbon components in microplastics can be indirectly quantified of the total amount of actual microplastics. do. That is, most of the microplastics are carbon (over 85%), and microplastics can be quantified through TOC analysis.

In the present invention, combustion-based TOC analyzers are widely used as tools to evaluate the performance of STP in sewage in removing organic pollutants (D. Dubber et al., J. Environ. Sci. Heal Part. 45 (2010) 1595-1600). By effectively burning all organic compounds, some of which are rarely oxidized by strong oxidizing agents, i.e. insoluble and macromolecular organic compounds such as humic substances and plastic particles, TOC analyzers quantify the carbon content of water samples. (I. Bisutti et al., Trac. Trends Anal. Chem. 23 (2004) 716-726), the use of a TOC analyzer allows analysis of the carbon content of particulate matter down to the microgram level.

In the measurement method according to the present invention using such a TOC analyzer, organic particles other than microplastics in sewage are selectively removed before applying a spectroscopic or thermal analysis method to accurately quantify microplastics. Likewise, when organic substances other than microplastics in the stainless steel filter are dissolved, the TOC measured by the filter in the TOC analyzer indicates the carbon content of the microplastics in the filter.

The TOC measurement method used in the present invention is a method widely used as a method for evaluating the removal efficiency of pollutants in a sewage treatment process. This method burns organic matter including plastics at a high temperature and detects CO ₂ , and can measure the carbon content of solid organic matter to a sub-mg level. Methods for removing organic matter other than plastics contained in sewage have already been reviewed in several studies. However, most of them are used for qualitative purposes, not to determine the amount of microplastics. In this invention, a filter sample obtained by filtering a sewage sample is subjected to simple pretreatment for organic matter oxidation, and then directly introduced into a TOC analyzer to measure the total amount of carbon present in microplastics. There is no report on the amount of generalized microplastics in the environment, including river water, sewage, and wastewater, and the thermal analysis-based total organic carbon measurement method is used as a very easy and accurate method to comprehensively evaluate the behavior of microplastics in the sewage treatment process. It can be.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, and it will be apparent to those skilled in the art that the scope of the present invention is not to be construed as being limited by these examples.

[Example]

Example 1: Reagents and Materials

For the measurement of total organic carbon in sewage influent and effluent, potassium hydrogen phthalate was dissolved in water to prepare a calibration standard solution at 2-100 mg/L. Water of 18.2 M-ohm or higher produced in an ultrapure water device was used. Glucose was used as a standard material for quantification of microplastics, and a calibration curve was prepared by weighing about 0.5-50 mg using a balance. Polystyrene (PS) was purchased from PSS Co., Ltd. for GPC standards, and polyethylene with an average particle diameter of 40-48 ㎛ and 125 ㎛ was purchased from Sigma. Polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and cellulose acetate (CA) were purchased from Sigma. Hydrogen peroxide and iron(II) sulfate heptahydrate were purchased from Sigma as decomposition reagents, and they were prepared according to the experimental method of NOAA (National Oceanic and Atmospheric Administration) and experiments were performed (J. Masura et al., Laboratory methods for the analysis of microplastics in the marine environment: recommendations for quantifying synthetic particles in waters and sediments, (2015)).

Sampling and filtration

Sampling was performed at J sewage treatment plant located in Seoul, and was collected once every day at 6-7 pm for one month. Samples were taken from the influent and effluent of the A2O process (275,000 m ³ /d). 0.2 L of inflow water and 20 L of outflow water were immediately filtered in the field using a self-made filtering device, and the sample was put in a glass petri dish and moved to the laboratory. As shown in FIG. 1, the sample was filtered through a pre-sieve (500 μm grid) and a filter-pack equipped with a filter having a diameter of 25 mm (45 μm grid). , pre-sieve, filter, and filter-pack were all self-manufactured with stainless steel. Although discussions on the particle size and shape of microplastics are very diverse, in general, particles with a size of 20 μm or more capable of microscopic-FT-IR detection are mainly studied. According to the report by Anger et al., the mass of microplastic particles of 45-500 μm is expected to be several to several hundred ng/unit (PM Anger et al., Trac. Trends Anal. Chem. 109 (2018) 214-226). , Carr et al. reported that microplastics larger than 400 μm were rarely detected in the effluent after tertiary treatment of a sewage treatment plant (SA Carr et al., Water Res. 91 (2016) 174-182). In the study of sewage, it is expected that the mass ratio of particles of 45 μm or less is small, and particles of 500 μm or more are very difficult to filter due to clogging of the filter. Therefore, in the present invention, an analysis method capable of evaluating the amount of microplastics having a size of 45 to 500 μm was developed.

To confirm the amount of microplastics in the organic matter of the sewage, the TOC of the raw water before filtering the sample and the filtered water after filtering were measured. Raw water and filtered water for TOC measurement were filtered through a 500 μm sieve, stored in a 1 L amber bottle, and adjusted to pH 2 by adding HCl. Filters and TOC samples were refrigerated at 4 °C until analysis.

Organic matter decomposition and analysis method

Filter samples for measuring the content of microplastics were placed in a ceramic boat to remove organic matter, and Fenton's reagent (H ₂ O ₂ + Fe(II); 30% H ₂ After injecting 0.5 mL of O ₂ 10 mL and 0.05 M Fe(II) solution 10 mL), the mixture was heated on a hotplate at 60 °C for 1 hour, and this process was performed twice. When the heating temperature and time are increased, the decomposition reagent may all evaporate, so 1 mL is divided into two times to decompose the organic matter. The decomposed sample was analyzed by directly putting a ceramic boat into a TOC analyzer and burning at 900 ° C without any other pretreatment process (filter elution, density separation, re-filtration). . The assay was completed within 8 minutes.

The NOAA method or the decomposition methods reported in various literatures require a relatively large amount of decomposition reagents because the filtered sample is eluted and wet oxidation is performed, or the decomposition reagent is added in a liquid state to decompose. . Since the method according to the present invention has a small amount of decomposition reagent and does not require additional pretreatment of the filter, the pretreatment process is simplified, loss is minimized, and analysis is possible within a short time. TOC in sewage samples was measured by catalytic-combustion oxidation at 680 °C after filtering the sample through a 500 μm sieve.

Evaluation of analytical methods

For the quantification of microplastics using TOC, linearity, method detection limit, and recovery rate were evaluated. As a result of comparing the linearity of the calibration curve according to the type of standard material, the coefficient of determination (R2 ) was more than 0.999, and the slopes of the calibration curves between each standard material were similar within 3%. In this example, since the standard material should be weighed with a balance, glucose having a low carbon content (40%, wt.) was selected as the standard material. MDL was tested according to EPA, and the MDL of the measured carbon weight was 0.1 mg. In order to evaluate the recovery rate, it was prepared by adding about 10 mg of each plastic (PS, PE, PP, PVC, PET, CA) powder to 1 L of ultrapure water in the laboratory. After filtration and pretreatment, the carbon content was measured 6 times, and the result was 92.1±4.3%. Although some particles may be lost by adhering to the filtration mechanism, the inner wall of the glass bottle, or passing through the filter, the recovery rate was very good. Additionally, the detection limit for TOC measurement of liquid samples was 0.05 mg/L, and detailed analysis conditions are shown in Table 1.

[Table 1: Analysis conditions of TOC _MP and organic carbon analyzer in liquid (TOC)]

The carbon contents of the liquid sample and the filtered solid sample were measured with a TOC analyzer, and the results are shown in FIG. 3 . During sampling, the TOC and TOC _MP (TOC derived from microplastics) of the influent sample were measured to be 43.1±4.9 mg L ^-1 ( p = 0.05) and 4.8 ± 0.8 mg L ^-1 ( p = 0.05), respectively. Therefore, TOC _MP was calculated to account for 11.4% ± 2.0% ( p = 0.05) of the influent organic matter. Meanwhile, TOC and TOC _MP in the effluent were 4.0±0.1 mg L ^-1 ( p = 0.05) and 0.017 ± 0.004 mg L ^-1 ( p = 0.05), respectively. Approximately 0.4% of the organic matter in the wastewater was estimated as TOC _MP .

Therefore, it is concluded that both TOC and TOC _MP can be effectively removed from STP according to the present invention. Removal efficiencies for TOC and TOC _MP were calculated to be 90.1%±0.8% ( p = 0.05) and 99.6%±0.1% ( p = 0.05), respectively. As mentioned above, some of the organic matter in wastewater is not biodegradable. Some of them are dissolved organic carbon: often more than 10% of the influent organic content (Y.-Y. Choi et al., Water-Sui. 9 (2017) 409). Therefore, since the main organic matter treatment process of STP is biological, it is logical to observe STP's removal efficiency of less than 90% for total organic matter. Dissolved non-biodegradable organics can pass through the STP to the discharge point. On the other hand, microplastics with a size of 45 to 500 μm can be well removed by conventional particle treatment processes such as coagulation and sedimentation. For this reason, the removal efficiency of TOC _MP was observed to be higher than that of total TOC.

On the other hand, the correlation formula between the carbon content (mg C) and the measured value of TOC is as follows:

[Equation 1]

y (TOC measurement area) = 160.4 x (mg C) + 0.7 Carbon content 0.2-10 mg section

or x carbon content mg C = (y; TOC measurement area - 0.7) / 160.4

According to the present invention, a filter sample obtained by filtering a sewage sample is oxidized with a Fenton decomposition reagent and then directly introduced into a TOC analyzer to measure the total amount of organic carbon present in microplastics and to determine the behavior of microplastics in the sewage treatment process. It can provide a very easy and accurate method of comprehensive evaluation.

Moreover, in combination with existing pyrolysis-based GC/MS analysis methods or spectroscopic analysis methods such as Raman and FT-IR, the characteristics of microplastics in the same sample in which TOC quantification was performed are analyzed, and when DB is made, site-specific It is possible to secure microplastic-derived TOC data considering

In addition, in connection with the effluent TOC monitoring of sewage treatment plants, which will be introduced from 2021, it is expected that the amount of microplastics present in the effluent can be checked every hour.

Having described specific parts of the present invention in detail above, it will be clear to those skilled in the art that these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby. will be. Accordingly, the substantial scope of the present invention will be defined by the claims and their equivalents.

Claims (7)

A method for quantification of microplastics in sewage based on total organic carbon (TOC) measurement comprising the following steps:
(a) obtaining a sewage sample by filtering the sewage;
(b) removing organic matter from the sewage sample by subjecting the sewage sample to organic material oxidation pre-treatment; and
(c) measuring the total amount of carbon present in microplastics by introducing the sewage sample from which organic matter has been removed into a TOC analyzer.
The method of claim 1, wherein step (a) filters the influent and effluent of the sewage process through a sieve of 450 to 550 μm and then through a filter of 40 to 50 μm. A method for quantifying microplastics in sewage based on carbon (TOC) measurement.
The method for quantifying microplastics in sewage based on total organic carbon (TOC) measurement according to claim 1, further comprising filtering the sewage using a filter in step (a) and then washing the filter.
The method for quantifying microplastics in sewage based on TOC measurement according to claim 3, wherein the washing is performed using a methanol solvent.
The total organic carbon (TOC) measurement base according to claim 1, wherein in the step (b), a decomposition reagent containing Fe(II) and H ₂ O ₂ is added at 50 to 70 °C and then allowed to stand. A method for quantifying microplastics in sewage.
The method for quantifying microplastics in sewage based on total organic carbon (TOC) measurement according to claim 1, further comprising burning at 850 to 950 ° C in a TOC analyzer in step (c).
The method of claim 1, wherein the quantification method
(i) vacuum filtering influent and effluent obtained from a pipeline of a sewage treatment process using a pre-sieve of 450 to 550 μm and a filter of 40 to 50 μm and washing the filter;
(ii) placing the filter in a ceramic boat, adding a decomposition reagent containing Fe(II) and H ₂ O ₂ at 50 to 70 °C and leaving it for 1 hour to 3 hours; and
(iii) introducing the ceramic boat into a TOC analyzer, burning it at 850-950 ° C, and then measuring the total amount of carbon present in microplastics; A method for quantification of microplastics in heavy metals.

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