Determination Of Chemical Oxygen Demand Research Articles

Influence of Humic Substance in Solids on the Measurement of Oxygen-Consuming Organics of the Yellow River

The Yellow River has a high content of solids. The influence of solids on the measurement of oxygen-consuming organics (OCOs) such as chemical oxygen demand (CODMn) has aroused attentions in recent years. However, no research about effects of humic substance in solids on the determination of CODMn has been reported. Experiments have been carried out to study the influence of humic substance in solids (Loess soil) on CODMn in this research. Several significant results have arisen from the study. (1) The total CODMn of water sample including liquid and solid phases increased significantly with the increase of solid content; the CODMn of liquid phase of water sample under pre-treatment with acid (LPUPA) also increased significantly with the increase of solid content while that without pre-treatment did not increased significantly. (2) With the increasing of solid content, the total BOD5 of water sample increased much slower than the total CODMn and the CODMn of LPUPA. (3) The humic substances in solids contributed greatly to the total CODMn of water sample. When the solid contents were 7.5 and 15.0 g/L, the humic substances in solids accounted for 15.9% and 17.1% of the total CODMn of water sample, respectively; fulvic acid-one of the main compositions of humic substance-contributed to 23.6% and 46.3% of the CODMn of LPUPA, respectively. (4) The humic substances can hardly be biologically oxidized under natural conditions, the CODMn of LPUPA and the total CODMn of water sample exaggerates the oxygen-consuming organic contamination of the Yellow River. Therefore, CODMn was not suitable for being regarded as a parameter reflecting the pollution degree of OCOs in river water with a high solid content.

Amperometric determination of chemical oxygen demand with flow injection analysis using F-PbO 2 modified electrode

An electrochemical detection system with an F-PbO 2 modified electrode for flow injection analysis to determine chemical oxygen demand (COD) was proposed and experimentally validated. The measuring principle was based on the current response on the modified electrode which was proportional to the COD value. Under the optimized experiment condition, the linear range was 100–1200 mg l −1, and the detection limit was 15 mg l −1. This method was successfully applied to determine the COD in samples without pretreatment. It was characterized by short analysis time, simplicity, low environmental impact, a limited reagent consumption and easy automation. Additionally, the COD values obtained from the proposed and conventional methods agreed well as demonstrated by the high significant correlation between the two sets of COD values ( R = 0.9985, n = 25).

Study on photocatalytic oxidation for determination of the low chemical oxygen demand using a nano-TiO 2–Ce(SO 4) 2 coexisted system

A new photocatalytic system, nano-TiO 2–Ce(SO 4) 2 coexisted system, which can be used to determine the low chemical oxygen demand (COD) is described. Nano-TiO 2 powders is used as photocatalyst in this system. The measuring method is based on direct determination of the concentration change of Ce(IV) resulting from photocatalytic oxidation of organic compounds. The mechanism of the photocatalytic oxidation for COD determination was discussed and the optimum experimental conditions were investigated. Under the optimum conditions, a good calibration graph for COD values between 1.0 and 12 mg l −1 was obtained and the LOD value was achieved as low as 0.4 mg l −1. When determining the real samples, the results were in good agreement with those from the conventional methods.

Chemical oxygen demand of seawater determined with a microwave heating method

This paper investigates a microwave heating method for the determination of chemical oxygen demand (COD) in seawater. The influences of microwave-power, heating time and standard substances on the results are studied. Using the proposed method, we analyzed the glucose standard solution, the coefficient of variation being less than 2%. Compared with the traditional electric stove heating method, the results of F-test and T-test showed that there was no significant difference between the two methods, but the microwave method had slightly higher precision and reproducibility than the electric stove method. With the microwave heating method, several seawater samples from Jiaozhou Bay and the South Yellow Sea were also analyzed. The recovery was between 97.5% and 104.3%. This new method has the advantages of shortening the heating time, improving the working efficiency and having simple operation and therefore can be used to analyze the COD in seawater.

Preparation and application of TiO 2 photocatalytic sensor for chemical oxygen demand determination in water research

In this work, a TiO 2 photocatalytic sensor was prepared and utilized into flow injection analysis (FIA) for chemical oxygen demand (COD) determination. With a positive bias potential of 0.4 V (vs. Ag/AgCl) applied to the sensor and a 12-W quartz UV lamp illuminating it, photocurrent, due to the charge transfer at the interface of TiO 2 sensor and the passing solution, was recorded and its change (Δ I Photo) caused by the detected sample was calculated to characterize the COD value of the sample. Under the optimizing conditions, the sensor responded linearly to the COD of d-glucose solution in the range of 0.5–235 mg/L, with a linear correlation coefficient of 0.9998. Its application in artificial wastewater analysis has achieved results in good agreement with those from the conventional dichromate method; meanwhile, the process requires no hypertoxic reagents and less analysis time, suggesting that it would be another appropriate method for COD determination in water assessment.

Determination of chemical oxygen demand in fresh waters using flow injection with on-line UV-photocatalytic oxidation and spectrophotometric detection

A flow injection manifold incorporating UV-photocatalytic oxidation for the determination of chemical oxygen demand (COD) in freshwater is reported. The method utilises the UV-photocatalytic oxidation of organic compounds instead of conventional heating (used in the standard method), with acidified potassium permanganate as the oxidant. Sodium oxalate, d-glucose and potassium hydrogen phthalate were used as COD standards. A 100 microL sample solution was injected into a 0.3 mol L(-1) H2SO4 carrier stream containing 0.1 mol L(-1) (NH4)2SO4, merged with a permanganate solution (8 x 10(-4) mol L(-1)) and passed through a 250 cm FEP (fluoroethylene polymer) photo-reaction coil wound around a 15 W UV lamp. The sample throughput was 30 h(-1), with an LOD (blank plus 3sigma) of 0.5 mg COD L(-1) and a linear range of 0.5-50 mg COD L(-1) (D-glucose, r2 = 0.9966). The method had good precision with relative standard deviations of 2.7% at 5 mg COD L(-1) and 1.2% at 20 mg COD L(-1) (n = 12) for glucose. Results for a COD certified reference material (QC Demand Quality Control Standard) were in good agreement with the certified COD value. Recovery from Tamar River water samples for all three COD standards was 83.0-111.0% and the COD values determined were in good agreement with those of a permanganate index reference method.

FIBROUS-WOOD SORBENT FOR ELIMINATING OIL POLLUTION

Abstract In this paper, we examine the possibility of eliminating oil pollution by using fibrous-wood sorbents on the basis of short wool fibres, technical hydrolysis lignin, wood sawdust and barks. The sorption ability of waste fibrous-wood materials has been investigated by determination of Chemical Oxygen Demand (COD). The special sorption patterns by net cover and fibrous-wood compositions as a nucleus have been prepared. The sorbents on the basis of technical hydrolysis lignin (THL) and wool shoddy have high sorption ability to oil pollution.

Photoelectrochemical determination of chemical oxygen demand based on an exhaustive degradation model in a thin-layer cell

This work focuses on the experimental optimisation of a newly developed photoelectrochemical system for the determination of chemical oxygen demand (PECOD). This method is developed based on a photoelectrochemical degradation principle. Chemical oxygen demand (COD) is directly quantified by measuring the amount of electron transferred at a TiO 2 nanoporous thin-film electrode during an exhaustive photoelectrocatalytic degradation process in a thin-layer photoelectrochemical cell. In this fashion, the COD value of a sample can be determined in a simple, rapid and accurate manner. The PECOD is a direct and absolute method that requires no calibration. The effects of important experimental conditions, such as light intensity, applied potential bias, supporting electrolyte concentration and oxygen concentration, on analytical performance have been investigated and optimum experimental conditions were obtained. Analytical linear range of 0−360 ppm COD with a practical detection limit of 0.2 ppm COD were achieved. Real sample analyses were also carried out. The results demonstrated that the measured COD values using the PECOD and the standard methods were in an excellent agreement.

Photoelectrochemical determination of chemical oxygen demand based on an exhaustive degradation model in a thin-layer cell

This work focuses on the experimental optimisation of a newly developed photoelectrochemical system for the determination of chemical oxygen demand (PECOD). This method is developed based on a photoelectrochemical degradation principle. Chemical oxygen demand (COD) is directly quantified by measuring the amount of electron transferred at a TiO 2 nanoporous thin-film electrode during an exhaustive photoelectrocatalytic degradation process in a thin-layer photoelectrochemical cell. In this fashion, the COD value of a sample can be determined in a simple, rapid and accurate manner. The PECOD is a direct and absolute method that requires no calibration. The effects of important experimental conditions, such as light intensity, applied potential bias, supporting electrolyte concentration and oxygen concentration, on analytical performance have been investigated and optimum experimental conditions were obtained. Analytical linear range of 0−360 ppm COD with a practical detection limit of 0.2 ppm COD were achieved. Real sample analyses were also carried out. The results demonstrated that the measured COD values using the PECOD and the standard methods were in an excellent agreement.

Study on photocatalytic oxidation for determination of chemical oxygen demand using a nano-TiO 2–K 2Cr 2O 7 system

A photocatalytic method for the determination of chemical oxygen demand (COD) using a nano-TiO 2–K 2Cr 2O 7 system is described. The measuring principle is based on direct determination of the change of Cr(III) concentration resulting from photocatalytic oxidation of organic compounds and simultaneous photocatalytic reduction of stoichiometrically involved K 2Cr 2O 7 in the solution. The operation conditions were optimized. The determinative COD value using this method was calculated from the absorbance of Cr(III). The operational characteristics of this method were demonstrated by use of a standard glucose solution as substrate. This method was also applied to the determination of the COD of wastewater samples. The results were in good agreement with those from the conventional (i.e., dichromate) COD methods.

Electrocatalytic Sensor for the Determination of Chemical Oxygen Demand Using a Lead Dioxide Modified Electrode

AbstractAn amperometric method that makes use of a nano‐PbO2 modified electrode as an electrocatalytic sensor for the determination of chemical oxygen demand (COD) is described. The sensor signal was observed as a result of the detection of the oxidation current due to electrocatalytic oxidation of organic compounds in the sample solution. This sensor responded linearly to the CODCr of standard samples in the range of 5–3 000 ppm and the detection limit was 2.5 ppm. When using the sensor to determine real samples, it displays short analysis time, simplicity and no sample pretreatment. The sensor was stable for over 20 days in real wastewater samples and has successfully been applied to the determination of COD in real wastewater samples.

Evaluation of organic load measurement techniques in a sewage and waste stabilisation pond

Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are the major parameters used as routine surrogate tests for measuring the load of organic carbon into the environment. In this context, an evaluation of possible replacement of BOD and COD for Dissolved Organic Carbon (DOC) measurements are presented for different wastewaters. For anaerobic pond effluent, the following correlations were obtained: COD = 1.08 DOC + 79 and BOD = 0.82 DOC + 12. For facultative pond effluent, COD = -0.29DOC + 109 and BOD = 0.14DOC + 26. For raw sewage COD = 4.18DOC - 2 and BOD = 0.46COD + 5. For aerated pond effluent COD = 3.57DOC + 6 and BOD = 0.27COD + 3. For sedimentation pond effluent, COD = -1.34DOC + 138 and BOD = 0.73DOC + 16.5. Determination of COD was not appropriate for substituting classical alternatives in tested samples in despite of the limitations of the samples.

Development of a Direct Photoelectrochemical Method for Determination of Chemical Oxygen Demand

A novel rapid methodology for the determination of chemical oxygen demand (COD) based on photoelectrochemical oxidative degradation principle (PECOD) was proposed and experimentally validated. With this new method, the extent of degradation of dissolved organic matter in a water sample is measured simply by directly quantifying the extent of electron transfer at a TiO2 nanoporous film electrode during an exhaustive photoelectrocatalytic degradation of organic matter in a thin layer photoelectrochemical cell. The PECOD method demonstrated in this work is a direct and absolute method. It does not require the use of standard for calibration. The method, in principle, measures the theoretical COD value due to the extraordinary high oxidation efficiency and accuracy of charge measurement. This new approach overcomes many of the current problems associated with existing oxygen demand techniques (e.g., the matrix effect, one of the serious practical problems that most rapid COD methods suffered because of the insufficient oxidation efficiency). The PECOD method overcomes the matrix effect by employing a highly effective photoelectrochemical system that is capable of fully oxidizing a wide spectrum of organics in the water sample. The method was successfully applied to determine the COD of a range of synthetic and real samples. Excellent agreement with a standard dichromate method was achieved. The practical detection limit of 0.2 mg L-1 COD with the linear range of 0−200 mg L-1 was also achieved. The PECOD method is a method that is environmentally friendly, robust, rapid, and easily automated. It requires only 1−5 min to complete an assay and consumes very limited reagent (electrolyte only).

Semimicro Determination of COD Employing Microwave Digestion

A modified semimicro method is described for determining chemical oxygen demand (COD) employing microwave (MW) digestion (0.5 min exposure at 1,000 W power, and 10 min exposure at 250 W power) with a titration assessment. Composition of reaction mixture was the same as that of the usual reflux method. Determination was performed in glass vessels of original tetrafluoromethoxil containers. Under given conditions dichromate autoreduction was low. A good agreement with the usual reflux method was obtained with selected substances (potassium hydrogen phthalate, glutamic acid, glucose, dodecyl sulphate, where COD-MW/ThOD is 98.9–101.5%). With real samples (municipal sewage, mixed tanning and chemical wastewaters, and treated wastewater from biological treatment plants) the obtained results were also satisfactory (88.0–111.9%).

Rapid determination of chemical oxygen demand using a focused microwave heating system featuring temperature control

This paper demonstrates the use of a microwave heating system, employed in the chemical digestion step, for the determination of chemical oxygen demand in wastewater. The results are first compared with those provided by standard methods using reference substances. The problems arising from abrupt heating of the sample and the potential thermal decomposition of potassium dichromate are examined. Two different approaches to sample digestion involving a gradually increasing irradiation time were tested. First, a constant power strategy is applied, and the second proposes a constant temperature approach by using a temperature control system. By optimising the operating conditions, the digestion time was reduced to 8–60 times with respect to the standard method. The reference digestion time is 5 min. In especially difficult digestions, the proposed approach provides a substantially improved degradation with respect to conventional procedures. The procedure was applied to wastewater from various industries and found to ensure thorough digestion of all samples and to provide favourable results in all cases tested.

Chemiluminescence system for automatic determination of chemical oxygen demand using flow injection analysis

A novel chemiluminescence (CL) system for automatic determination of chemical oxygen demand (COD) combined with flow injection analysis is proposed in this paper. In this system, potassium permanganate is reduced to Mn 2+ which is first adsorbed on a strongly acid cation-exchange resin mini-column to be concentrated during chemical oxidation of the organic compounds at room temperature, while the excessive MnO 4 − passes through the mini-column to be waste, then the concentrated Mn 2+ is eluted reversely and measured by the luminol–H 2O 2 CL system. The calibration graph is linear in the range of 4–4000 mg l −1 and the detection limit is 2 mg l −1. A complete analysis could be performed in 1.5 min including washing and sampling, giving a throughout of about 40 h −1. The relative standard deviation was 4.4% for 10 mg l −1 COD ( n=11), 4.8% for 100 mg l −1 COD ( n=11). This CL flow system for determination of COD is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to the determination of COD of water samples.

Uncertainty of chemical oxygen demand determination in wastewater samples

The measurement uncertainty of the result of chemical oxygen demand determination in wastewater was evaluated. The major sources of uncertainty of the result of measurement were identified as the purity of reagents, volumetric operations, gravimetric operations, bias, and the repeatability of the method. Identification and evaluation of uncertainty sources was followed by combined uncertainty calculations. The combined uncertainty was compared to the experimentally determined variation and good agreement was found, indicating that the major uncertainty sources had been identified. The results show that the major sources of uncertainty arose from repeatability at high concentration level and volumetric steps at low concentration level, thus revealing the target operations for reducing the measurement uncertainty of this determination.

Ultrasound-assisted method for determination of chemical oxygen demand.

A method for determination chemical oxygen demand (COD) assisted by use of ultrasound has been successfully evaluated for the first time. The method uses instrumentation simpler and cheaper and, in some instances, safer than that used by previous methods for the same purpose. The new device used for sonication is an all-glass cylindrical sonotrode that can be introduced directly into the reaction mixture. Use of this device enables more efficient interaction between sample and ultrasonic energy. The optimized experimental conditions are high ultrasonic power (55% amplitude, 0.9-second pulses each second), high sulfuric acid concentration (>60%), and a sonication time of 2 min. Under these conditions the method has limitations similar to those of the official COD method with regard to the type of organic compound. It works adequately with easily oxidized organic matter (potassium hydrogen phthalate and dextrose) and other organic compounds difficult to oxidize by conventional methods (e.g. phenol and acetic acid) but the COD values obtained with volatile compounds and difficult organic matter are poor. Chloride is tolerated up to a concentration of 7000 mg L(-1) without any masking agent. Gasification of the sample is recommended to improve results; use of air and argon resulted in no significant differences - bubbling with air during sonication resulted in COD values for certified materials and real wastewater samples statistically identical with the certified COD values and those obtained by the classic (open reflux) method. The use of ultrasound energy for COD determination thus seems to be an interesting and promising alternative to conventional oxidation methods used for the same purpose.

Bias‐free results in the spectrophotometric determination of chemical oxygen demand in bleached textile mill effluents

AbstractA calibration methodology that enables validation of the analytical procedure used in those cases where no placebo or standard reference material is available is applied here. The total Youden blank is used to eliminate the constant error component, and analytical measurements in the presence of the matrix at two different levels of the test portion, in order to avoid its interactive interference, are made. Moreover, the results obtained in the determination of chemical oxygen demand following a closed reflux spectrophotometric method are compared with those obtained when a definitive analytical method is applied, in order to show the absence of direct interference from the matrix.© 2002 Society of Chemical Industry

A flow method with photocatalytic oxidation of dissolved organic matter using a solid-phase (TiO2) reactor followed by amperometric detection of consumed oxygen.

A photocatalytic sensor for the determination of chemical oxygen demand (COD) using titanium dioxide, based on the use of a pair of oxygen electrodes and flow injection analysis, is described. The measuring principle is based on the direct determination of the oxygen concentration change resulting from photocataltic oxidation of organic compounds. One of the two oxygen electrodes, the reference oxygen electrode, was utilized to measure the reference signal responding only to oxygen present in the injected samples. Oxygen consumption due to the TiO2-catalyzed photochemical oxidation of organic compounds in samples was monitored with the working oxygen electrode. The COD value of this sensor was calculated as the difference of the currents at reference and working oxygen electrodes, respectively. The operation characteristics of the sensor are demonstrated using artificially treated wastewater as a substrate. The sensor was also applied to the determination of COD in real water samples from dam reservoirs (n = 20) all over Japan. The results were in good agreement with those from the conventional COD methods (i.e., permanganate and dichromate methods).