Chemical Oxygen Demand Measurements Research Articles

Synthesis and characterization of cerium–silver co-doped zinc oxide as a novel sunlight-driven photocatalyst for effective degradation of Reactive Red 120 dye

Cerium–silver (Ce–Ag) co-doped ZnO was synthesized by precipitation–decomposition and tested for the degradation of Reactive Red 120 dye under natural sun light irradiation. Three weight percent Ce co-doped Ag–ZnO was found to be most efficient. Hence, this catalyst (3wt% Ce–Ag–ZnO) has been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and XPS reveal the presence of metallic Ag and tetravalent Ce. Ag and Ce shift the absorption of ZnO to entire visible region. It was found that the Ce–Ag–ZnO exhibited higher degradation efficiency when compared to Ag-ZnO, Ce–ZnO, prepared ZnO, Commercial ZnO, TiO2, and TiO2-P25 at neutral pH (=7). Quantum yields of all processes were calculated and compared. Higher activity of Ce–Ag–ZnO in natural sunlight may be due to higher visible light absorption of Ce–Ag–ZnO when compared to native ZnO. The influences of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo mineralization of RR 120 have been analyzed. The mineralization of RR 120 dye was confirmed by chemical oxygen demand (COD) measurements. A dual mechanism has been proposed for efficient degradation of RR 120 dye by Ce–Ag–ZnO under solar light at neutral pH. This photocatalyst was found to be reusable up to four runs.

NEW DEVELOPMENTS IN THE RADIOLYSIS AND OZONOLYSIS OF LANDFILL LEACHATE

Old and young municipal landfill leachates samples were radiation processed with γ rays at a dose rate of 1 kGy/h. The fate of the soluble organic matter (humic substance) present in the leachates was followed by the chemical oxygen demand (COD) measurements. The radiolysis of old landfill leachate is a not an effective process in comparison to ozonolysis but can be enhanced significantly by the addition of H 2 O 2 to the old leachate prior to radiolysis and by bringing the pH of the leachate to zero. Some radiolyzed sample were further ozonized to reduce to the minimum possible the COD level. Young landfill leachate results instead more prone to radiolysis and less sensitive to ozonolysis than the old landfill leachate.

An efficient nanosized strontium fluoride-loaded titania for azo dye (RY 84) degradation with solar light

Strontium fluoride-loaded titanium dioxide (SrF2-TiO2) was successfully synthesized by a sol–gel method and characterized by Fourier transform infrared and diffuse reflectance spectroscopies, scanning electron and transmission electron microscopies, X-ray diffractometry, cyclic voltammetry and Braunauer–Emmer–Teller surface area measurements. SrF2-TiO2 is found to be more efficient than bare TiO2 in the degradation of Reactive Yellow 84 (RY 84) under solar light at pH 5. SrF2 loading shifts the absorption edge to visible region resulting in the increase of solar photocatalytic activity. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photomineralization by SrF2-TiO2 have been analyzed. The mineralization of RY 84 has been confirmed by chemical oxygen demand (COD) measurements. Mechanism of dye degradation by SrF2-TiO2 is proposed on the basis of hole trapping property of SrF2. The catalyst is found to be stable and reusable. Reusability under solar light makes this process more economical for treatment of industrial effluent.

Degradation of organic molecules in advanced oxidation processes: Relation between chemical structure and degradability

Hydroxyl radical induced degradation of maleic acid, fumaric acid and 20 aromatic molecules was investigated in air saturated aqueous solutions. Hydroxyl radicals were generated by an advanced oxidation process (AOP), water radiolysis. Oxidation was followed by chemical oxygen demand (COD) and total organic carbon content (TOC) measurements. Up to ∼30–50% decrease of COD the dose dependence was linear. By the ratio of the decrease of COD and the amount of reactive radiolysis intermediates introduced into the solution the oxidation efficiencies were calculated. Efficiencies around 0.5–1 (O2 molecule built in products/OH) found for most of the compounds show that the one-electron-oxidant OH induces 2–4 electron oxidations. The high oxidation rates were explained by OH addition to unsaturated bonds and subsequent reactions of dissolved O2 with organic radicals. In amino substituted molecules or in Acid Red 1 azo dye, O2 cannot compete efficiently with unimolecular transformation of organic radicals and the efficiency is lower (0.2–0.5).

Highly Efficient, Solar Active, and Reusable Photocatalyst: Zr-Loaded Ag–ZnO for Reactive Red 120 Dye Degradation with Synergistic Effect and Dye-Sensitized Mechanism

The different wt % of Zr-codoped Ag-ZnO catalysts were prepared by the simple precipitation-thermal decomposition method and used for degradation of anionic azo dye Reactive Red 120 (RR 120) under natural sunlight. Highly efficient 4 wt % of Zr-codoped Ag-ZnO was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HR-TEM) images, field emission scanning electron microscope (FE-SEM) images, energy-dispersive spectra (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and BET surface area measurements. Metal codopants increase the absorbance of ZnO to the entire visible region. XRD and XPS reveal that Ag is in the form of Ag(0) and Zr in the form of Zr(4+). The photocatalytic activity of 4 wt % Zr-codoped Ag-ZnO was compared with other single-metal-doped, undoped, and commercial catalysts. The quantum yields of all processes were determined and analyzed. Zr-Ag-ZnO was found to be more efficient than Ag-ZnO, Zr-ZnO, commercial ZnO, prepared ZnO, TiO(2)-P25, and TiO(2) at neutral pH for mineralization of RR 120 under solar light. To the best of our knowledge, this is the first report on the synthesis of Zr-codoped Ag-ZnO and its use in the degradation of RR 120 dye under natural sunlight illuminatioin. The influences of operational parameters such as the amount of photocatalyst, dye concentration, and initial pH on photomineralization of RR 120 have been analyzed. Mineralization of RR 120 has been confirmed by chemical oxygen demand (COD) measurements. A dual mechanism has been proposed for the higher efficiency of Zr-Ag-ZnO at neutral pH under solar light. This catalyst is found to be reusable.

Mechanistic study of electrochemical treatment of basic green 4 dye with aluminum electrodes through zeta potential, TOC, COD and color measurements, and characterization of residues

Herein we report a study on the changes in zeta potential during the electrochemical (EC) treatment of basic green 4 (BG) dye solutions. BG is a basic acrylic dye with a triphenylmethane group. It is extensively used in the textile and other industries. This study was conducted in a batch electrochemical reactor using a sacrificial aluminum anode. Zeta potentials were measured with changes in operating variables such as current density (j), initial pH (pH0), and initial dye concentration (C0). The process performance was analyzed in terms of the chemical oxygen demand (COD), total organic carbon (TOC) and decolorization efficiency along with important cost-related parameters such as electrode and energy consumption. At the optimum conditions, 82.4% COD, 63.5% TOC and 99.4% color removal efficiencies were observed, when C0 = 100 mg L−1, the treatment time was 45 min, with j = 117.64 A m−2 and the initial pH0 = 6.2. The respective electrode and energy consumptions at the optimum conditions were 0.16 kg Al per kg COD removed and 2.48 kW h per kg COD removed. The magnitude of the zeta potential gave an indication regarding the potential stability of the colloidal suspensions of BG dye and aluminum flocs present in the solution over the pH range of 3.2–12.2. It was found that the removal of the cationic dye was maximum when the zeta potential was least negative and that the removal was due to adsorption on neutral aluminum hydroxide. Finally, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), pore size distribution and thermogravimetric analysis (TGA) techniques were used to characterize the solid residues obtained during the EC treatment of aqueous solutions with and without BG dye.

Electrochemical degradation of phenol in aqueous solution using PbO2 anode

The PbO2 electrode was prepared by electrodeposition method in this paper. The electrode was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV). The electrochemical oxidation of phenol in aqueous solution was studied by galvanostatic electrolysis using PbO2 electrode as anode. UV spectroscopy, total organic carbon (TOC) and chemical oxygen demand (COD) measurements were conducted to study the kinetics of phenol electrochemical degradation and the mineralization efficiency under different current densities. The experimental results showed that the applied current density had a positive influence on the degradation of phenol and removal of TOC, but a higher current density led to lower current efficiency and higher energy consumption. The phenol degradation always followed a pseudo-first-order kinetics. In addition, aromatic intermediates and general carboxylic acids generated in the degradation of phenol have been indentified using high-performance liquid chromatography (HPLC) and a general pathway for the electrochemical degradation of phenol on PbO2 anode was proposed.

Modification of the photocatalytic activity of TiO2 by β-Cyclodextrin in decoloration of ethyl violet dye

The photocatalytic decoloration of an organic dye, ethyl violet (EV), has been studied in the presence of TiO2 and the addition of β-Cyclodextrin (β-CD) with TiO2 (TiO2-β-CD) under UV-A light irradiation. The different operating parameters like initial concentration of dye, illumination time, pH and amount of catalyst used have also been investigated. The photocatalytic decoloration efficiency is more in the TiO2-β-CD/UV-A light system than TiO2/UV-A light system. The mineralization of EV has been confirmed by Chemical Oxygen Demand (COD) measurements. The complexation patterns have been confirmed with UV–Visible and FT-IR spectral data and the interaction between TiO2 and β-CD have been characterized by powder XRD analysis and UV–Visible diffuse reflectance spectroscopy.

Highly active WO3–Ag–ZnO photocatalyst driven by day light illumination

The WO3 loaded Ag–ZnO (WO3–Ag–ZnO) was successfully synthesized by precipitation–decomposition method. The catalyst was characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) images, energy dispersive spectrum (EDS), transmission electron microscope (TEM), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV) and BET surface area measurements. The photocatalytic activity of WO3–Ag–ZnO was investigated for the degradation of Naphthol Blue Black (NBB) in aqueous solution using solar light. WO3–Ag–ZnO is found to be more efficient than Ag–ZnO, WO3–ZnO, Ag–WO3, WO3, commercial ZnO, bare ZnO, TiO2–P25 and TiO2 (Merck) at pH 9 for the mineralization of NBB dye. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo mineralization of NBB dye have been analyzed. The mineralization of NBB has been confirmed by Chemical Oxygen Demand (COD) measurements. A degradation mechanism is proposed for the degradation of NBB under solar light. This catalyst is found to be reusable.

Photodegradation of Phenol, 2-Chlorophenol and o-Cresol by Iron Oxide Nanoparticles

Iron oxide nanoparticles were prepared by mixing either aged iron(II) or aged iron(III) hydrated chlorides with hydrogen peroxide at pH 4.2±0.1. Iron oxide nanoparticles were identified in the mixtures of iron(II/III) chlorides with hydrogen peroxide by transmission electron microscopy (TEM) analyses. TEM analyses showed irregular sizes and the formation of different phases of iron oxide (α-Fe2O3, β-Fe2O3, γ-Fe2O3, -Fe2O3…). The variety of iron(III) oxide phases was a consequence of interactions of hydrogen peroxide with different ferric oligomers and iron oxohydroxides formed during the aging of iron(II/III) chloride mixtures. In order to decompose phenol or 2-chlorophenol or o-cresol a photocatalytic reaction was carried out in a “reactor” with iron oxide nanoparticles, visible radiation and hydrogen peroxide. Each reaction was kept at room temperature and pH 3.8±0.1. The photocatalytic processes were analyzed through UV spectrophotometry, chemical oxygen demand (COD) and total organic carbon (TOC) measurements. Iron oxide nanoparticles, in the photodegradation of phenol, 2-chlorophenol and o-cresol, presented bifunctional catalytic properties, such as a semiconductor photocatalyst and probably as Lewis acid catalyst.

Synthesis and characterization of novel WO3 loaded Ag–ZnO and its photocatalytic activity

A novel WO3 loaded Ag–ZnO photocatalyst was successfully synthesized by a simple solvothermal method and characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) images, energy dispersive spectrum (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL), cyclic voltammetry (CV) and Brunauer–Emmett–Teller (BET) surface area measurements. The photocatalytic activity of WO3–Ag–ZnO was investigated for the degradation of RR 120 and RO 4 dyes in aqueous solution using UV-A light. WO3–Ag–ZnO is found to be more efficient than Ag–ZnO, WO3–ZnO, Ag–WO3, commercial ZnO, prepared ZnO, TiO2-P25 and TiO2 (Merck) at neutral pH for the mineralization of dyes. First time we have reported that novel WO3 loaded Ag–ZnO has been found to be very efficient for two azo dyes removal when compared to commercially available catalyst (Degussa P25, ZnO (Merck) and TiO2 (Merck)). The mineralization of dyes has been confirmed by chemical oxygen demand (COD) measurements. A mechanism of degradation has been proposed for the higher efficiency of WO3–Ag–ZnO.

Solar-light-assisted photocatalytic degradation of NBB dye on Zr-codoped Ag–ZnO catalyst

Zr-codoped Ag–ZnO (Zr–Ag–ZnO) was successfully synthesized by the precipitation–decomposition method. The catalyst was characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive spectra (EDS), diffuse reflectance spectra, photoluminescence spectra, cyclic voltammetry, and Brunauer–Emmett–Teller (BET) surface area measurements. The photocatalytic activity of Zr–Ag–ZnO was investigated for the degradation of Naphthol Blue Black (NBB) in aqueous solution using solar light. Codoping shifted the absorbance of ZnO to the entire visible region. Zr–Ag–ZnO is found to be more efficient than Ag–ZnO, Zr–ZnO, commercial ZnO, prepared ZnO, TiO2-P25, and TiO2 (Merck) at pH 9 for mineralization of NBB under solar light. The influence of operational parameters such as the amount of photocatalyst, dye concentration, and initial pH on photomineralization of NBB has been analyzed. Mineralization of NBB was confirmed by chemical oxygen demand (COD) measurements. A mechanism is proposed for the degradation of NBB under solar light. The catalyst is found to be reusable.

Kinetic Modeling of Photocatalytic Degradation of an Azo Dye Using Nano-TiO2/Polyester

Photocatalytic degradation of Reactive Orange 16 (RO16) was investigated using immobilized TiO2 nanoparticles on polyester support in exposure of UV irradiation in recirculated tubular photoreactors. Utilization of the polyester as a support has several advantages, such as low price, remarkable surface area, flexibility, and durability. Moreover, the prepared TiO2/polyester was successfully applied for the photocatalytic degradation of RO16 in aqueous media for several times without any discernible diminution in its activity. Applied TiO2 nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Experimental results indicate that the degradation rate of RO16 follows pseudo-first-order kinetics. With nonlinear regression, a model was developed for prediction of pseudo-first-order rate constants (kapp) as a function of operational parameters, including temperature (295–328K), flow rate (5–15 L·min−1), and initial concentration of RO16 (5–25 mg·L−1) as $$k_{\rm app} = 2.20 ( \exp { [- 7427 / \rm RT} ]) ( FR ) ^{0.5034} [ {0.112 / (1 + 0.112 [ \rm RO16 ] _0} )] .$$ Calculated data from the model are in good agreement with the experimental results. Electrical energies per order (EEO) were estimated from the calculated and experimental data show that EEO depends on the operational parameters, considerably. To monitor the mineralization of RO16, chemical oxygen demand (COD) measurements were carried out during the UV/TiO2 process. COD measurement results indicated that all organic substances were completely mineralized after 5 h of UV irradiation.

Photodegradation of an azo dye with reusable SrF2–TiO2 under UV light and influence of operational parameters

SrF2 loaded TiO2 (SrF2–TiO2), prepared by sol–gel method, was characterized by Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), atomic force microscopy (AFM) and BET surface area measurements. TEM images reveal that the sizes of SrF2–TiO2 particles are in the range of 3–20nm. Presence of metal halide (SrF2) in the catalyst was confirmed by FT-IR, XRD, XPS and CV measurements. SrF2 loading increases the absorption of UV and visible light. AFM images show a cavity which increases the surface area and photocatalytic activity of the catalyst. 3wt% SrF2 loaded TiO2 was found to be more photoactive than bare TiO2 in Reactive Yellow 84 (RY 84) dye degradation. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photomineralization by SrF2–TiO2 have been analyzed. The optimum pH and catalyst amount for efficient removal of dye are found to be 5 and 4gL−1, respectively. The intermediates identified by GC–MS analysis during photodegradation, are 2-amino-4-[(4-amino-6-chloro-1,3,5-triazin-2-yl)amino]phenol (1), 6-chloro-N-phenyl-1,3,5-triazin-2,4-diamine (2), 2,4-diaminophenol (3) and 1,3,5-triazin-2,4-diamine (4) based on their molecular ion and mass spectrometric fragmentation peaks. The mineralization of RY 84 has also been confirmed by CV and chemical oxygen demand (COD) measurements. Mechanism of dye degradation by SrF2–TiO2 is proposed on the basis of hole trapping property of SrF2. The catalyst was found to be stable and reusable.

Fenton and solar photo-Fenton processes for the removal of chlorpyrifos insecticide in wastewater

The degradation of chlorpyrifos in water by Fenton (H2O2/Fe2+) and solar photo-Fenton (H2O2/Fe2+/solar light) processes was investigated. A laboratory-scale reactor was designed to evaluate and select the optimal oxidation condition. The degradation rate is strongly dependent on pH, temperature, H2O2 dosing rate, and initial concentrations of the insecticide and Fe2+. The kinetics of organic matter decay was evaluated by means of chemical oxygen demand (COD) measurement. Overall kinetics can be described by a pseudo-second-order rate equation with respect to COD. The optimum conditions were obtained at pH 3, H2O2 dosing rate 120 mg·min–1, [Fe2+]0 5.0 mM, initial COD 1 330 mg·l–1 and 35°C for the Fenton process. However, in the solar photo-Fenton process, the degradation rate increased significantly. To achieve 90% of COD removal, the solar photo-Fenton process needs 50% less time than that used in the Fenton process which translates to a 50% gain of H2O2.

Comparison of different ultrasound support methods during colour and chemical oxygen demand removal of disperse and reactive dyebath solutions by ozonation

In this study, the effects of ozonation, ozonation with ultrasonic bath and ozonation with ultrasonic homogeniser processes on colour and chemical oxygen demand removal properties of disperse (CI Disperse Red 60, CI Disperse Blue 337) and reactive (CI Reactive Blue 171 and CI Reactive Blue 19) dyebath solutions with and without dyeing auxiliaries were investigated. Chemical oxygen demand (in mg/l) and colour (in Hazen) measurements of the studied dyebath solutions were determined. The ozonation process caused simultaneous chemical oxygen demand removal during decolorisation. However, the improvement in chemical oxygen demand reduction was less than of that on decolorisation. The application of the combination of ozonation with ultrasonic homogeniser is the most efficient process and creates a great time advantage over the other process types studied (ozonation alone and ozonation with ultrasonic bath) to reach the same colour and levels of chemical oxygen demand removal.

Electrochemical degradation of buprofezin insecticide in aqueous solutions by anodic oxidation at boron-doped diamond electrode

Buprofezin (2-tert-butylimino-3-isopropyl-5-phenyl-1,3,5-thiadiazinan-4-one) is identified as a commonly used chemical with satisfactory biological activities against sucking insect pests, but its disposal causes serious environmental problems. This pesticide was treated by an electrolysis system using a boron-doped diamond (BDD) as anode and platinum as cathode. A number of experiments were run on a laboratory scale and the results are presented. The chemical oxygen demand (COD) measurement during the processing permitted the evaluation of the kinetic of organic matter decay and the instantaneous current efficiency. Different operating conditions and factors affecting the treatment process including current density, conductive electrolyte, pH, concentration of buprofezin, and time of electrolysis were studied and optimized. The best obtained conditions for COD removal on the BDD anode to degrade buprofezin solutions (COD0 = 1,200 mg L−1) include operating at 60 mA cm−2 and 25 ± 3 °C. The high efficiency of this technology can be explained in terms of the direct electrooxidation at the BDD surface and the oxidation carried out by hydroxyl radicals (OH•) and other electro-generated oxidants (Cl−, ClO−).

Microbiological and Performance Evaluation of Sequencing Batch Reactor for Textile Wastewater Treatment

This study focused on laboratory‐scaled and real‐scaled treatment plant performances and microbiological investigations for the optimum treatment of textile industry wastewater performed with sequencing batch reactor (SBR). As a result of experimental studies of laboratory‐scaled SBR treatment unit, optimum treatment efficiency was taken from 0.5 h filling to 1.5 h. reaction to 1.5 h. settlement to 0.5 h. discharge‐idle periods. Average chemical oxygen demand (COD) removal efficiency of SBR of laboratory‐scaled textile industry was 75%, whereas average turbidity and color removal (coloration number [RES, m−1] 586 nm) efficiencies were 90% and 75%, respectively. Optimum reaction and settlement periods were used in a real‐scaled plant, and plant efficiency was examined for parameters such as COD, phenol, pH, mixed liquor suspended solids (MLSS) and sludge volume index (SVI). In this study, optimum reaction and settlement periods for treatment of textile industry wastewater were determined within a SBR in a laboratory‐scaled plant. These reaction and settlement periods were verified with the measurement of COD, color, and turbidity parameters. Floc structure and protozoa‐metazoa species of activated sludge in a SBR were also determined. Optimum reaction and settlement times were used in a real‐scaled plant, and plant efficiency was examined for COD, Phenol, pH, MLSS, and SVI parameters. The corresponding values were found as appropriate, acceptable, and meaningful because of variance value of statistical analysis. Protozoa and metazoan in the activated sludge in the laboratory‐scaled plant were investigated. Peranema sp., Epistylis sp., Didinium sp., Chilodonella sp., Opercularia sp., Vorticella sp. as protozoa species and Habrotrocha sp., Philodina sp. as metazoa species were determined.

Measurement of COD for Sugar Refinery Wastewater Using FTIR/ATR Spectroscopy with Stability

Fourier transform infrared spectroscopy (FTIR) and attenuated total reflection (ATR) technology combined with the partial least squares (PLS) regression were successfully applied for the rapid no-reagent determination of chemical oxygen demand (COD) for sugar refinery wastewater. Among 105 samples, 45 samples were randomly selected as the validation set. The remaining 60 samples were divided into the calibration set (40 samples) and the prediction set (20 samples) for a total of 30 times with certain similarities. The appropriate model with stability was established on the waveband of 4500 cm-1to 600 cm-1. The optimal PLS factor was 4, the modeling effect M-SEPAve, M-RP,Ave, M-SEPStd, and M-RP,Stdwere 38.1 mg/L, 0.944, 3.2 mg/L, and 0.013, respectively, the validation effect V-SEP and V-RPwere 38.2 mg/L and 0.949, respectively, which has good prediction effect and stability. The results provide a reliable analytical model for the monitoring of COD in sugar refinery wastewater.

An easy uncertainty evaluation of the COD titrimetric analysis in correlation with quality control and validation data. Method applicability region

Chemical Oxygen Demand (COD) estimates the amount of organic oxidizable matter in wastewaters. It is a critical parameter for assessing the quality of effluents prior to discharge, in the design and operation of wastewater treatment plants, and in environmental modelling and monitoring. In this study COD was determined by a closed reflux titrimetric method according to 5220C, APHA, 21st edn, 2005. This method is applicable to COD values between 40 and 400 mg L−1 and chloride concentrations up to 2000 mg L−1. Chloride interference is a serious problem in COD measurement for wastewaters containing low organic matter concentrations. The reliability of the results depends on a proper validation of the measurement procedure that includes the calculation and evaluation of the measurement uncertainty. This study develops a practical, understandable and simple way for calculating and assessing the Combined Standard Uncertainty (CSU) of COD measurement, mainly based on already existing quality control and validation data. The CSU assessment is based on the existing literature trueness and precision target limits, without any additional assumptions. Diagrams correlating the trueness of the COD measurement mean values with different chloride concentrations and the laboratory control charts' limits offer a tool for improving the performance of the determination and define the method application area. The validation data that were obtained in our laboratory (accredited according to ISO 17025) and the proposed methodology for CSU calculation were verified in the frame of intra and inter-laboratory measurements.