Determination Of Chemical Oxygen Demand Research Articles

Photochemiresistor Sensor Development Based on a Bismuth Vanadate Type Semiconductor for Determination of Chemical Oxygen Demand.

The present paper describes the development of a novel photochemiresistor sensor for the determination of chemical oxygen demand (COD). A chemiresistive device was produced by a thin film of the monoclinic phase of bismuth vanadate deposited on an FTO glass surface. The resistive properties of the photosensor were carried out by electrochemical impedance spectroscopy (EIS). The electrical resistance of the platform was dependent on the presence of organic material in aqueous solution and the incidence of light. The decrease in resistance can be explained by considering that by increasing the amount of organic material, the amount of charge transferred to BiVO4 increases, as does the amount of the photogenerated conduction band on the film. This behavior is not observed when carrying out the same measurements in the absence of light. Under the optimal experimental conditions, the linear response of the chemiresistor sensor is between 0.20 and 19.9 mg L-1 COD at a fixed AC frequency of 0.1 Hz. There is a good correlation between the charge transfer resistance and COD concentration in the electrolyte solution. Quantification of COD in waste and lake waters was successfully performed using the novel photochemiresistor sensor. The results achieved in the analysis with the sensor are in accordance with the conventional method.

Kernel functions embedded in support vector machine learning models for rapid water pollution assessment via near-infrared spectroscopy

Water pollution is a challenging problem encountered in total environmental development. Near-infrared (NIR) spectroscopy is a well-refined technology for rapid water pollution detection. Calibration models are established and optimized to search for chemometric algorithms with considerably improved prediction effects. Machine learning improves the prediction capability of NIR spectroscopy for the accurate assessment of water pollution. Least squares support vector machine (LSSVM) algorithm fits parameters to target problems in a data-driven manner. The modeling capability of this algorithm mainly depends on its kernel functions. In this study, the LSSVM method was used to establish NIR calibration models for the quantitative determination of chemical oxygen demand, which is a critical indicator of water pollution level. The effects of different kernels embedded in LSSVM were investigated. A novel kernel was proposed by using a logistic-based neural network. In contrast to common kernels, this novel kernel can utilize a deep learning approach for parameter optimization. The proposed kernel also strengthens model resistance to over-fitting such that cross-validation can be reasonably utilized. The proposed novel kernel is applicable for the quantitative determination of water pollution and is a prospective solution to other problems in the field of water resource management.

Application feasibility of chromophoric dissolved organic matter (CDOM) absorption coefficient as the substitute for chemical oxygen demand concentration in lakes and reservoirs

化学需氧量是衡量水体中有机物量及污染程度的综合性指标，也是我国《地表水环境质量标准（GB 3838—2002）》的重要评价指标.然而，由于测定过程缓慢和使用了有毒有害试剂易于形成二次污染，现行标准的高锰酸钾和重铬酸钾化学需氧量测定方法无法做到环境友好，也不能反映当前快速和实时监测的技术需求.因此，迫切需要发展操作简便、快速高效、灵敏可靠、环境友好和环保绿色的化学需氧量替代检测方法.本文首先从文献计量学视角比较我国与世界上发达国家化学需氧量研究主题论文发文量，剖析了我国发展化学需氧量替代检测方法的迫切性.基于全国大范围65个湖库706个样本有色可溶性有机物吸收系数、化学需氧量和其他水质参数同步调查数据，构建广覆盖范围的有色可溶性有机物特征波长吸收系数和化学需氧量间高精度线性关系模型，确定了地表水环境质量评价的吸收系数阈值，模型可以广泛应用于不同类型（深水、浅水、大型、中型、小型）和不同营养状态（贫、中、富营养）湖库水体有机物浓度的定量表征，具有一定普适性.通过对比有色可溶性有机物吸收系数和传统的高锰酸钾、重铬酸钾法优势和不足，明确了有色可溶性有机物吸收系数替代化学需氧量用于湖库水体开展有机物表征和污染程度评价的可行性和应用前景.;Chemical oxygen demand (COD) is a comprehensive index to measure the amount of organic matter and reflect pollution degree of organic matter in water. Meanwhile, COD is also an important assessment index of environmental quality standard for surface water (GB 3838-2002). However, due to time consuming, the use of toxic and harmful reagents in the determination process and the easiness to produce secondary pollution, the current potassium permanganate and potassium dichromate COD determination methods are not environmentally friendly and cannot reflect the current rapid and real-time technical requirements. Therefore, there is an urgent need to develop a simple, rapid and efficient, sensitive and reliable, environmentally friendly and pollution-free green alternative detection method of COD. Firstly, from the perspective of bibliometrics by comparing total publication number of COD subject in China and the developed countries in the world, this study analyzes the urgency of developing alternative methods of COD in China. Based on the dataset of 706 samples covering a large range of COD concentration from 65 lakes and reservoirs in China, the high-precision linear relationship models between chromophoric dissolved organic matter (CDOM) absorption coefficient at 350 nm and 254 nm and COD concentration are constructed. In addition, the threshold and standard of CDOM absorption coefficient used to assess the surface water environmental quality was determined. Our linear models can be widely used to accurately and quantitatively characterize organic matter concentration and assess pollution degree in different types (deep and shallow water, large, medium and small area) and different trophic states (oligotrophic, mesotrophic, and eutrophic) of lake and reservoir waters with certain universality. By comparing the advantages and disadvantages of CDOM absorption coefficient and traditional COD measurement methods of potassium permanganate and potassium dichromate, this study demonstrates the feasibility and application prospect using CDOM absorption coefficient to substitute COD concentration for characterizing organic matter quantity and assess the pollution degree in lakes and reservoirs.

Comparative study on ozone oxidation chemiluminescence method and classical alkaline potassium permanganate method for determination of chemical oxygen demand in seawater

Seawater in the coastal waters of Qingdao, China was collected, and COD was measured by ozone oxidation chemiluminescence method and alkaline potassium permanganate method which was adopted in China as the standard method for measuring COD in seawater, respectively. The results show that when COD was less than 1 mg/L, the absolute error of ozone oxidation chemiluminescence method was less than 0.1 mg/L, and when COD was more than 1 mg/L, the relative error was less than 10%. The relative standard deviation of ozone oxidation chemiluminescence method was lower than 5%, and the detection limit was 0.0022 mg/L. The results of ozone oxidation chemiluminescence method were close to those of alkaline potassium permanganate method. With higher precision, lower detection limit, faster measurement, and online measurement, ozone oxidation chemiluminescence method is an ideal monitoring method for COD in seawater in the field.

A Simple Flow Injection Sensing System for the Real-Time On-Line Determination of Chemical Oxygen Demand Based on 3D Au-NPs/TiO2 Nanotube Arrays

3D TiO2 nanotube arrays loaded with Au nanoparticles (3D Au-NPs/TNTAs) were prepared to effectively enhance the photoelectrocatalytic properties. A simple flow injection sensing system was proposed for the real-time on-line determination of chemical oxygen demand using the 3D Au-NPs/TNTAs electrode. The proposed photoelectrochemical oxidative degradation principle of the sensing system was analyzed and validated by the representative organic compounds with known COD values at a potential bias 1.5 V under UV illumination. A practical detection limit of the sensing system is 0.18 mg/L and the linear range is 1.92 - 3360 mg/L under the optimum conditions. In the experimental process, the sensing system exhibits good long-term stability and reproducibility.

Determination of chemical oxygen demand of agricultural wastes by combining acid hydrolysis and commercial COD kit analysis

Chemical oxygen demand (COD) is an essential parameter in waste management, particularly for monitoring bioprocess such as anaerobic digestion. Indeed, chemical oxygen demand (COD) is a key parameter that can prove useful for the evaluation of waste biodegradability and to evaluate mass and energetic balances of the overall process. In this study, an adapted method to determine the COD of solid agricultural wastes was developed. This method combined a double acid hydrolysis of the solid waste materials followed by commercial COD tubes analysis. This method was compared to direct sampling after a standard dilution (3.5 g TS.L-1) and analysis in commercial COD tubes. The method developed in this study allowed the COD of nine agricultural wastes to be accurately predicted, with an absolute error of 7% compared to the theoretical COD. In comparison, the method with only a prior water dilution resulted in higher absolute errors of 36% and 31% when sampling was performed with pipette tips and cut pipette tips, respectively.

A method to eliminate bromide interference on standard COD test for bromide-rich industrial wastewater

Chemical oxygen demand (COD) is one of the most important water quality parameters that quantifies the amount of oxygen needed to oxidize oxidizable pollutants (mainly organics) in water samples. However, erroneous COD results were commonly observed for bromide-rich industrial wastewater samples using standard COD test. Bromide in water sample is known to seriously interfere with COD test. However, there is no satisfactory approach to effectively eliminate bromide interference thus far. In this study, two strategies, namely masking and correction, were investigated for their effectiveness to suppress bromide interference. For the masking strategy, silver ion was assessed for its effectiveness to neutralize bromide in water samples through precipitation and complex formation reactions. Silver ion offered only partial masking effect on bromide, while the residue bromide can still cause significant interference on COD determination. For the correction strategy, an equivalent redox reaction reflecting bromide interference mechanism was proposed, and a theoretical correction factor of 0.1 g COD/g Br− was found based on stoichiometry. The effectiveness of the proposed correction factor for bromide interference under different wastewater pollutant matrix was evaluated using different types of wastewater samples (synthetic wastewater, domestic wastewater and bromide-rich industrial wastewater) with varying amounts of bromide (from 0 to 2000 mg L−1) added to the samples. The findings showed that with bromide concentration up to 600 mg L−1, the correction factor of 0.1 g COD/g Br− was applicable to all the tested wastewater samples, suggesting that this correction strategy could be practically used to eliminate bromide interference in standard COD test.

Electrochemical determination of chemical oxygen demand on functionalized pseudo-graphite electrode

Graphite-like carbon electrodes produced from the University of Idaho thermolyzed asphalt reaction (GUITAR) were examined for anodic sensing of chemical oxygen demand (COD). For maximum sensitivity the surfaces were modified with quinone functionality (q-GUITAR). Analysis by FT-IR indicated C-OH and CO groups on the surface which was verified by and X-ray photoelectron spectroscopies (XPS). The capacitance as measured by cyclic voltammetry (CV) of q-GUITAR is 170 times greater in 1.0 M H2SO4 than the pristine material indicating a more hydrophilic surface. This enhances the anodic oxidations of the COD surrogates consisting of glucose, potassium hydrogen phthalate (KHP), lactic acid, and sodium dodecyl benzenesulfonate (SDBS). At a constant potential of 1.6 V vs. Ag/AgCl q-GUITAR anodes have the largest linear range of 0 to 10,000 ppm (as glucose) reported in literature. The limit of detection (40 ppm) and sensitivity are competitive with other electrode systems.

A Self-Supported CuO/Cu Nanowire Electrode as Highly Efficient Sensor for COD Measurement.

A self-supported CuO/Cu nanowire electrode (CuO/CuNWE), which was prepared by annealing Cu nanowires to form a porous Cu nanowire electrode (CuNWE) and then anodizing the as-prepared CuNWE in alkaline medium to generate Cu(OH)2 nanowires followed by calcination, was employed for chemical oxygen demand (COD) determination using cyclic voltammetry (CV). The structure and electrochemical behavior of the CuO/CuNWE were investigated by scanning electron microscopy, X-ray diffraction, and CV. The results indicated that the as-synthesized CuO/CuNWE, in which CuO nanowires with a length of several micrometers and a diameter of 100 to 300 nm could be found, was stable in alkaline medium and more electrocatalytically active for oxidizing a wide range of organic compounds in comparison with the CuNWE. Under optimized alkaline concentration and scan rate, the CuO/CuNWE exhibited a good performance for COD measurement, with a linear range of 5 to 1153 mg L−1, a sensitivity of 2.46× 10−2 mA /(mg L−1), and a detection limit of about 2.3 mg L−1. In addition, an excellent correlation was observed in COD values obtained by our method and the classic dichromate method (r = 0.9995, p < 0.01, n = 11). Finally, our method was successfully used to measure the COD values in real water samples, showing great potential for practical application in water pollution control.

Direct determination of chemical oxygen demand by anodic oxidative degradation of organics at a composite 3-D electrode

Two layers of α-PbO2- and CeO2-doped β-PbO2 were anodically deposited on Ni foam substrate successively, and the prepared Ni/α-PbO2/CeO2-β-PbO2 electrode was used as a sensor to determine chemical oxygen demand (COD) by coulometric method. SEM and EDS disclose that the layers of α-PbO2 and β-PbO2 are compactly attached to the surface of the 3D structure substrate, and CeO2 is uniformly co-deposited with β-PbO2 onto the anode. Results show that when the prepared Ni/α-PbO2/CeO2-β-PbO2 is used to oxidize the organic compounds at a constant potential of + 1.45 V (vs. Ag/AgCl) in aqueous solution, the anodic charge quantity is directly proportional to the amount of the organic compounds in the range of 15–1000 mg L−1, equivalent to the quantity of COD, no matter what species of the organic compounds is detected. This means that the universal coulometric method is only decided by the total amount of COD but unrelated to the species of COD. It takes only 10~20 min to detect one sample by the well-designed electrode–cell system in this study due to the high generation rate of ·OH on β-PbO2, good electrical conductivity of CeO2-doped PbO2 layer, and the great ratio of area-to-volume (S/V) through elaborative cell–electrode system design. These properties enable the Ni/α-PbO2/CeO2-β-PbO2 electrode to be a promising sensor for coulometric determination of COD in industrial application.

Environmental Applications of Boron‐Doped Diamond Electrodes: 2. Soil Remediation and Sensing Applications

AbstractThe chemical stability and electrocatalytic properties of boron‐doped diamond (BDD) electrodes give rise to various applications. While wastewater treatment is the most widely studied field, the use of BDD for soil remediation and environmental sensing is currently investigated more and more. With regards to soil remediation, promising results have been reported for the treatment of soil washing solutions. Anodic oxidation using BDD at high current density allows high mineralization rates of biorefractory soil pollutants and extracting agents to be reached. At low current density, selective degradation of target pollutants has been achieved, thus allowing the reuse of extracting agents for further soil washing steps. BDD‐based electrochemical sensors have been studied for chemical oxygen demand determination, pesticide/pharmaceutical detection as well as other applications such as pH, O2 and analysis of various organic and inorganic compounds. Low detection limits, wide linear ranges and low standard deviations have been achieved. The main reasons behind the superiority of BDD sensors are the chemical stability, wide applicability and resistance of BDD towards biofouling. The beauty of BDD sensing is that it can work for a variety of organic and inorganic compounds under many physicochemical parameters.

A real-time on-line photoelectrochemical sensor toward chemical oxygen demand determination based on field-effect transistor using an extended gate with 3D TiO2 nanotube arrays

Chemical oxygen demand (COD) is one of the most widely used parameters for water quality assessment. Quantification and detection of COD slight fluctuations is crucial for an early detection of abnormal change in the water environment. Here we report a real-time on-line photoelectrochemical method for sensitive COD detection using an extended-gate field-effect transistor (EGFET) sensor. The FET gate consists of a Ti mesh electrode with 3D TiO2 nanotube arrays modified by Pt nanoparticles. The device shows a COD detection limit down to 0.12 mg/L and a wide dynamic linear range from 1.44 mg/L to 672 mg/L at a continuous flow rate of 1.0 mL/s. The method reported also displays excellent stability, accuracy and reproducibility. More importantly, real water samples analyses with the proposed method are in a good agreement with the standard dichromate method. The results suggest that the EGFET-based photoelectrochemical sensors are potential candidates for practical COD onsite measurement.

The Utilization of Pineapples Waste Enzyme for the Improvement of Hydrolysis Solubility in Aquaculture Sludge

High volumes of sludge discharge from the aquaculture industry have relatively high pollutant content that may lead to severe local environmental problems. Anaerobic digestion is one of the technologies for sludge treatment that might be an efficient method to reduce salty aquaculture sludge production load. However, hydrolysis solubility is becoming a limitation step during the anaerobic digestion process when the occurrence of intermediate accumulation resulted from the conversion of non-soluble biopolymers to soluble organic compounds. Thus, pretreatment is required to increase the solubilization of pollutant parameters from aquaculture sludge before it is further treated in the anaerobic treatment. Therefore, this study focuses on the production of biocatalytic enzyme from the fermentation of pre-consumer supermarket waste such as pineapple dregs to increase the solubility of aquaculture sludge. The fermentation of the pineapples waste was produced via a three-month fermentation of the mixture of molasses, pineapple dregs and water, with the ratio of 1:3:10 in a tight plastic container. Apart from that, analyses showed that the enzyme possessed lipase, amylase and protease activity. The sludge solubilization pretreatment was performed at different pH values, with treatment time for 120 hours and the solubilization was evaluated by determination of Chemical Oxygen Demand (COD) and Total Ammonia Nitrogen (TAN) solubilization; the solubilization of COD and TAN increased by 80% and 50%, respectively. This finding showed that the pineapple enzyme has the capability to solubilize organic compound, which has the potential to improve hydrolysis in further anaerobic digestion process.

A Nafion Film Cover to Enhance the Analytical Performance of the CuO/Cu Electrochemical Sensor for Determination of Chemical Oxygen Demand.

We modified and evaluated the performance of a CuO/Cu electrochemical electrode for chemical oxygen demand (COD) determination by covering it with a Nafion (Nf) film. The resulting modified CuONf/Cu electrode sensor was used for the electrochemical determination of COD in river, slaughterhouse and estuarine water samples in order to evaluate its performance for this particular task. It was compared with the CuO/Cu sensor with no Nafion. The main electrochemical characteristics of interest, resistance, sensitivity, accuracy and reproducibility, were assessed by means of Linear Sweep Voltammetry using glucose as a standard. Results of these essays indicate that the procedure used produced smooth and firmly attached Nf films covering the whole copper surface. This sensor was shown to be resistant to interferences and effective in electro-oxidation of a wide range of organic compounds and therefore very useful for COD determination. Using the newly developed CuONf/Cu electrode an analytical linear range of 50 to 1000 mg·L−1 COD, with a detection limit of 2.11 mg·L−1 (n = 6) COD was achieved. The comparison shows that the CuONf/Cu sensor is more appropriate for COD determination than its counterpart with no Nafion.

Quantification of recalcitrant organic compounds during their removal test by a novel and economical method based on chemical oxygen demand analysis

This article proposes the use of mathematical models obtained by the Pearson correlation between the concentration of various recalcitrant organic compounds (ROCs) measured by chromatographic analysis (ChrA) and experimental chemical oxygen demand (COD). The aim is to reduce the number of samples processed by the ChrA, diminishing the economic costs of analysis. Ten ROCs, including pesticides, colorants, aromatic hydrocarbons and pharmaceuticals compounds, were introduced into four advanced oxidation processes operated at different residence times. Every ROC was tested at each residence time by COD determination and by quantification of concentrations with ChrA. Furthermore, chemical equations for the COD reaction of every ROC were formulated. A linear model was obtained for all the ROCs, after corroborating that the correlation between theoretical and experimental COD was >0.99, which established the ROC concentration from the experimental COD, omitting the ChrA. Results indicated that it is possible to know concentrations in most of the ROCs by means of the experimental COD with a >99±0.01% of accuracy, which leads to a cost decrease and even to evaluate methods in developing countries, which often do not have chromatographs and where pollution issues are meaningful.

Study on the influence and mechanism of sodium chlorate on COD reduction of minerals processing wastewater

In current COD measurement method, we found that sodium chlorate (NaClO3) can effectively reduce the chemical oxygen demand (COD) of minerals processing wastewater (MPW). However, the reduction in COD via the present COD method was only achieved through the interference of NaClO3 with COD measurement. A series of laboratory-scale experiments demonstrated that the COD reduction is independent of NaClO3 reaction time, reaction pH and reaction temperature, but only related to NaClO3 dosage, and a higher NaClO3 dosage leads to a lower COD. Results further showed that the addition of NaClO3 didn’t affect the initial concentration of the total organic carbon, chloride ions and the benzohydroxamic acid (BHA); their concentration remained unchanged after the addition of NaClO3. Moreover, the residual concentration of NaClO3 also remained same as the initial value. However, COD in both MPW and BHA solution decreased. Furthermore, when added reducing agent to consume the residual NaClO3 before COD measurement, and then the COD was determined to return to its initial value. All these observations clearly shown that NaClO3 doesn’t react with the reducing substances in wastewater under the experimental conditions; it only reacts with reducing substances under the COD measurement conditions. From all these evidences, we concluded that NaClO3 can interfere with the determination of COD. In fact, the interference of NaClO3 is not specified in the standard method, which is a defect of the present COD measurement method. Residual NaClO3 remains in wastewater may cause secondary pollution to the environment. This study, therefore, suggest the government revise and improve the COD measurement method in order to avoid the interference of NaClO3 and prevent the industrial use of NaClO3 for COD reduction of wastewater.

Oxidation of Organics using Mn(H2PO4)2 as a Catalyst for Rapid Determination of COD of Industrial Saline Effluents

Abstract Chemical Oxygen Demand (COD) is a water quality parameter which indicates concentration of organic compounds as oxygen equivalents in aqueous effluent samples. Determination of COD is frequently done using APHA Standard Method which requires 2 h digestion time. There is need for improving the method to reduce analysis time. In this paper, we report the comparative study for determination of COD by Standard Method using Ag2SO4 and a rapid method using Mn(H2PO4)2 as a catalyst for different industrial effluent samples having different chloride concentration. A kinetic study has been carried out by varying time interval, HgSO4 dose and catalyst dose in different concentrated H3PO4:H2SO4 acid mixture ratio. The optimum conditions for industrial sample having low chloride concentration are 0.3g Mn(H2PO4)2, per 15 ml of 1:6 H3PO4: H2SO4, 0.2gm HgSO4 and digestion time of 5 min., whereas the sample having high chloride concentration requires 0.4 g of HgSO4 and digestion time of 20 min. The results obtained from the rapid COD determination method in this study and conventional method is found to be comparable. A water quality analyst would be able to save on digestion time by >90 %, if he chooses to perform the COD test as per the rapid method described herein.

An environment-friendly device for rapid determination of chemical oxygen demand in waters based on ozone-induced chemiluminescence technology

An environment-friendly device was developed and optimized for the rapid measurement of chemical oxygen demand (COD) in waters.

Oxidative degradation of cyan flexo dye with Heterogeneous Fenton reagent - Fe2(MoO4)3 particle

Heterogeneous Fenton catalyst Fe2(MoO4)3 was prepared and the process efficiency was evaluated for oxidation of water-based Cyan flexo dye in synthetic aqueous solution and printing wastewater. The removal process of printing dye was analyzed by UV/VIS spectrophotometry, while dye mineralization was evaluated by the determination of total organic carbon content and chemical oxygen demand. Four determinants of the heterogeneous Fenton system, including initial dye concentration, iron concentration, pH and hydrogen peroxide concentration were investigated. Statistical method, definitive screening design was applied to generate optimal operational conditions of the four variables, which maximizes the process of dye removal. The initial dye concentration of 20 mgL-1, catalyst dosage of 0.75 mgL-1, pH of 2 and H2O2 concentration of 11 mM were chosen as the best operational conditions, contributing to 82% of the process efficiency. The Fenton process efficiency of 79% was achieved within the treatment of printing wastewater under optimal conditions for a 90 minute reaction time. The maximum COD removal efficiency was 61.1%, while 67% mineralization was achieved. The obtained results confirmed synergistic effect of Fe3+ and MoO4 2? which contributed to high catalytic activity and high heterogeneous Fenton efficiency.

Optimization of COD determination by UV–vis spectroscopy using PLS chemometrics algorithms

Ultraviolet–visible (UV–vis) spectroscopy combined with chemometrics tools were used to determine chemical oxygen demand (COD) content in the water. 144 samples needed for the research were collected from the Qian Lake in Nanjing. UV–vis spectra (193.91–1121.69 nm) were collected and processed by various preprocessing methods. The samples were divided into calibration set and prediction set by sample set portioning based on joint x–y distance (SPXY) method. Then the spectra were optimized and modeled by interval partial least squares (iPLS), synergy interval partial least squares (siPLS) and moving windows partial least squares (mwPLS). Optimized COD prediction models were established and compared with full-spectrum partial least squares (PLS) models. Model performance was evaluated by the correlation coefficient of the prediction set (Rpred) and the root mean square error of prediction (RMSEP). The results demonstrate that the prediction results of PLS models established by the three spectral interval selection methods are superior to the full-spectrum PLS model. Furthermore, the siPLS model has the best performance (Rpred = 0.8334; RMSEP = 2.63). Therefore, the siPLS is the best COD prediction model obtained in this research, which can effectively select optimal spectral intervals and improve the prediction performance of the model.