Determination Of Chemical Oxygen Demand Research Articles

Implementation of an automatic and miniature on-line multi-parameter water quality monitoring system and experimental determination of chemical oxygen demand and ammonia-nitrogen.

An automatic, miniature and multi-parameter on-line water quality monitoring system based on a micro-spectrometer is designed and implemented. The system is integrated with the flow-batch analysis and spectrophotometric detection method. The effectiveness of the system is tested by measuring chemical oxygen demand (COD) and ammonia-nitrogen in water. The results show that the modified system provides a cost-effective, sensitive, reproducible and reliable way to measure COD and ammonia-nitrogen in water samples with automatic operation and low toxic chemical consumption. In addition, the experiment results show that the relative error of the system is less than 10%, the limit of detection is 2 mg/L COD and 0.032 mg/L ammonia-nitrogen, respectively, and the relative standard deviation was 6.6% at 15.0 mg/L COD (n = 7) and 5.0% at 0.300 mg/L ammonia-nitrogen (n = 7). Results from the newly designed system are consistent with the data collected through the Chinese national standard analysis methods.

Determination of chemical oxygen demand based on photoelectrocatalysis of nanoporous TiO2 electrodes

Here we report on a novel, rapid, and environmentally friendly methodology for the determination of chemical oxygen demand (COD) using an electrochemically reduced nanoporous TiO2 electrode. A highly ordered nanoporous structure is grown directly onto a Ti plate through a three-step anodic oxidation process. Subsequent to electrochemical reduction, the nanoporous TiO2 electrode demonstrates a significant enhancement in photoelectrocatalytic activity. An advanced photoelectrochemical method based on the reduced nanoporous TiO2 is successfully developed and employed to quantify COD values in both synthetic and actual wastewater samples. Specifically, a typical processing period of 1–2min, a practical detection limit of 8mgL−1, and a linear range of 20–250mgL−1 COD are achieved. More importantly, the proposed method is in excellent agreement with the standard K2Cr2O7 COD determination technique, albeit with a more rapid analysis period. Further merits include the negation of the necessity of any toxic (Cr2O7−) and highly corrosive (H2SO4) reagents, simple and automatic operation, and environmental compatibility.

Development of a Three-Dimensional Structured Carbon Fiber Felt/β-PbO2 Electrode and Its Application in Chemical Oxygen Demand Determination

A three-dimensional (3-D) structured sensor of microcrystalline β-PbO2-coated carbon felt consisting of crisscrossing carbon fibers has been developed to determine chemical oxygen demand in wastewater. Each carbon fiber in the felt is coated by perfect octahedral β-PbO2 microcrystals. The unique structure makes it possess huge surface area and abundant active sites for generating hydroxyl radicals, thus exhibiting excellent performances. Results show a RSD within 5% as compared with the traditional standard method, a high sensitivity of 2.05×10−3 mA cm−2/mg L−1, a wide linear range of 50-5000mg L−1, a correlation coefficient (R) of 0.993 and a detection limit of 3.9mg L−1 (S/N=3). Additionally, this electrode demonstrates excellent reproducibility, low cost and good stability. These properties enable the electrode to be used as a COD sensor for in situ determination in industry, showing a promising application perspective.

Applying electro-Fenton process as an alternative to a slaughterhouse effluent treatment

Electrochemical oxidation of the effluent of a slaughterhouse facility by electrolysis under galvanostatic control was studied using Ti-RuO2/carbon felt (CF), Ti-PdPtOx/CF and BDD/CF cells by electro-Fenton at constant current density. Electrode material and the applied current density are significant parameters on oxidative degradation of pollutants in wastewater. It was found that pollutants of the effluent were oxidized to simple substrates and CO2 with different results, obtaining good removal efficiencies of chemical oxygen demand of 83.5%, 77.9% and 74.3%, for the Ti-RuO2/CF, Ti-PdPtOx/CF and BDD/CF systems, respectively. Trends in degradation depend on the production of hydroxyl radicals (OH) on the anodic materials and coagulation as confirmed by this study. Efficiency of electrochemical oxidation process was tested by carrying out chemical oxygen demand (COD) determinations. Additional operating parameters such as pH, initial ferrous concentration and electrolysis time were also evaluated.

Novel FGMOS based PCS device for low power applications

The spice model for photo catalytic sensor (PCS) proposed by Whig and Ahmad overcomes several drawbacks like complex designing, non-linearity, and long computation time generally found in the flow injection analysis (FIA) technique by Yoon-Chang Kim et al. for the determination of chemical oxygen demand (COD). The FIA technique involves the complete analysis including sampling and washing. The flow injection analysis is an analytical method for the measurement of the chemical oxygen demand by using the photochemical column. This method uses a bulky setup and takes 10 minutes to 15 minutes to get the output result which is a tedious and time consuming job. If the conventional method is continuously used for a long time then it is stable only for 15 days. The purpose of this paper is to propose a new floating gate photo catalytic sensor (FGPCS) approach which has low power consumption and more user-friendly, and it is fast in operation by the modeling and optimization of sensor used for water quality monitoring. The proposed model operates under sub-threshold conditions which are appreciated in large integrated system design. The results of simulation are found to be fairly in agreement with the theoretical predictions. The results exhibit near linear variations of parameters of interest with appreciably reduced response time.

A Mercury Free Method for the Determination of Chemical Oxygen Demand of the Sample with High Salinity and Organic Macromolecule

An improved method for the determination of chemical oxygen demand (COD) is presented. This method is based on the standard method but using silver sulfate as a masking agent for the chloride and using the microwave for the digestion. The method gives tiny errors when the chloride of the samples increases from 606.6 mg/L to more than 30,000 mg/L. The method applies to the samples containing macromolecules and give better results when the sample is prehydrolysed.

Recovery and Recycling of Silver from Residual Solution Derived from Determination of Chemical Oxygen Demand

Analytical methodologies that generate wastewater rich in potentially recoverable silver ions are commonly used to determine chemical oxygen demand (COD). The chemical residue resulting from these assays is classified not only as dangerous, containing high concentrations of heavy metal ions, Ag+, Hg (2+), Cr3+ and Cr(VI), but also is highly acid. The disposal of the crude residue in the environment will result in negative environmental impacts and financial loss, since silver has significant value. Considering the aforementioned, the risk of silver shortage, as well as the fact that silver sulfate is one of the most expensive inputs used in these assays, in this paper we proposed procedures for the recovery of silver present in residual solution from the COD determination and converting the silver recovered in an acid solution of silver sulfate. In order to do so, the silver present in the residual solution was precipitated as AgCl, which, after being separated from the liquid, was converted into metallic silver, using sucrose as reduction agent. The recovered metallic silver has greater than 99 %(w/w) purity, and the acidic solution of silver sulfate prepared from the recovered material was tested in COD determination, providing comparable results to those obtained with acid solution prepared from commercial Ag2SO4.

A fast and environment-friendly method for determination of chemical oxygen demand by using the heterogeneous Fenton-like process (H2O2/Fe3−xCoxO4 nanoparticles) as an oxidant

An easy, fast and environment-friendly method for COD determination in water is proposed. The procedure is based on the oxidation of organic matter by the H2O2/Fe3−xCoxO4 system. The Fe3−xCoxO4 nanoparticles activate the H2O2 molecule to produce hydroxyl radicals, which are highly reactive for oxidizing organic matter in an aqueous medium. After the oxidation step, the organic matter amounts can be quantified by comparing the quantity of H2O2 consumed. Moreover, the proposed COD method has several distinct advantages, since it does not use toxic reagents and the oxidation reaction of organic matter is conducted at room temperature and atmospheric pressure. Method detection limit is 2.0mgL−1 with intra- and inter-day precision lower than 1% (n=5). The calibration graph is linear in the range of 2.0–50mgL−1 with a sample throughput of 25 samples h−1. Data are validated based on the analysis of six contaminated river water samples by the proposed method and by using a comparative method validated and marketed by Merck, with good agreement between the results (t test, 95%).

Direct determination of chemical oxygen demand by anodic decomposition of organic compounds at a diamond electrode.

Chemical oxygen demand (COD) was measured directly with a simple electrochemical method using a boron-doped diamond (BDD) electrode. By applying a highly positive potential (+2.5 V vs Ag/AgCl) to an aqueous electrolyte containing potassium hydrogen phthalate, glucose, and lactic acid or sodium dodecylbenzenesulfonate using a BDD electrode, an anodic current corresponding to the electrolytic decomposition of these organic compounds was observed. No such current was seen on glassy carbon or platinum electrodes due to a significant background current caused by the oxygen evolution reaction. The electric charge for the anodic current observed at the BDD electrode was found to be consistent with the theoretical charge required for the electrolytic decomposition of the organic compounds to CO2 and was used to calculate COD. This analysis was performed by a simple I-t measurement at constant potential using a BDD electrode, and no calibration was needed. This new simple indicator, "ECOD" (electrochemical oxygen demand), will be useful for continuous monitoring of industrial wastewater with low protein concentrations and on-site instant analysis of natural water with a BDD electrode-based portable ECOD meter.

WO₃/W nanopores sensor for chemical oxygen demand (COD) determination under visible light.

A sensor of a WO3 nanopores electrode combined with a thin layer reactor was proposed to develop a Chemical Oxygen Demand (COD) determination method and solve the problem that the COD values are inaccurately determined by the standard method. The visible spectrum, e.g., 420 nm, could be used as light source in the sensor we developed, which represents a breakthrough by limiting of UV light source in the photoelectrocatalysis process. The operation conditions were optimized in this work, and the results showed that taking NaNO3 solution at the concentration of 2.5 mol·L−1 as electrolyte under the light intensity of 214 μW·cm−2 and applied bias of 2.5 V, the proposed method is accurate and well reproducible, even in a wide range of pH values. Furthermore, the COD values obtained by the WO3 sensor were fitted well with the theoretical COD value in the range of 3–60 mg·L−1 with a limit value of 1 mg·L−1, which reveals that the proposed sensor may be a practical device for monitoring and controlling surface water quality as well as slightly polluted water.

TiO2 nanotube sensor for online chemical oxygen demand determination in conjunction with flow injection technique.

A simple, rapid and environmental friendly online chemical oxygen demand (COD) analytical method based on TiO2 nanotube sensor in conjunction with the flow injection technique was proposed to determine the COD of aqueous samples, especially for refractory organics, low-concentration wastewater, and surface water. The new method can overcome the drawbacks of the conventional COD determination methods. The results show that with the new method, each analysis takes only about 1 to 3 min, the linear range is up to 1 to 500 mg x L(-1) of the compound of interest, and the detection limit is 1 mg x L(-1). The COD values obtained by the proposed method are more accurate than those obtained by the conventional method.

Enhanced Photocatalytic Degradation of Aqueous Nitrobenzene Using Graphitic Carbon–TiO2 Composites

Graphitic carbon–TiO2 nanocomposites with different carbon loadings were synthesized by a one-pot hydrothermal method. The prepared catalysts were characterized by X-ray diffractometry (XRD), scanning electron microscopy, UV–vis diffuse reflectance spectrophotometry, and Brunauer–Emmett–Teller surface area analysis. The XRD results confirmed the presence of graphite in the composite without alteration of the TiO2 structure. The photocatalytic efficiencies of the synthesized composites were determined by the degradation of aqueous nitrobenzene (NB) under UV irradiation. Because of the presence of graphitic carbon in the composite, there was an increase in the adsorption of NB (24%) on the composite surface, which led to a higher photocatalytic yield (up to 96% in 4 h at a graphitic carbon content of 1%). NB degradation was corroborated by chemical oxygen demand determinations.

Development of Rapid Chemical Oxygen Demand Analysis Using Ozone as Oxidizing Agent

A new and environmental friendly method for the rapid determination of Chemical Oxygen Demand (COD) as a measure of organic pollution was developed. Ozone was used as an oxidizing agent in the current method. Experiment was setup in 500mL glass bottle containing 390mL distilled water and 10mL wastewater sample at 31°C. The extent of dissolved ozone reacted with the wastewater sample was monitored through an ozone sensor. Reaction time of 60seconds achieved good linear correlation between the extent of ozone degradation and the wastewater concentrations. The results showed that the rate and extent of ozone degradation are linearly proportional to the initial COD concentrations in range of 0-80mg/L for the glucose- containing distilled water and canteen wastewater.

A rapid determination method for chemical oxygen demand in aquaculture wastewater using the ultraviolet absorbance spectrum and chemometrics

The ultraviolet (UV) absorbance spectrum was studied for the fast determination of chemical oxygen demand (COD) in aquaculture wastewater.

Simulation of linear dynamic macro model of photo catalytic sensor in SPICE

Purpose – The flow injection analysis (FIA) technique by Yoon-Chang Kim et al. for the determination of chemical oxygen demand (COD) involves the complete analysis including sampling and washing. FIA is analytical method for the measurement of COD using photochemical column. This method uses a bulky setup and takes 10-15 minutes to get the output result which is a tedious and time-consuming job. If conventional method is continuously used for a long time, then it is stable only for 15 days. The purpose of this paper is to propose an approach which is more users friendly and fast in operation by modeling and optimization of sensor used for water quality monitoring. This is to overcome several drawbacks generally found in the previous work like complex designing, nonlinearity and long computation time. The nonlinearity in conventional device is overcome by increasing the values of coefficient of determination R2 which in turn reduce the standard error. Design/methodology/approach – A simulation program with integrated circuit emphasis (SPICE) model of photo catalytic sensor (PCS) is proposed for easy and fast operation and optimization of power. Findings – The proposed macro model operates under subthreshold conditions that are appreciated in large integrated system design. The results of simulation were found to be fairly in agreement with the theoretical predictions. The results exhibited near linear variations of parameters of interest with appreciably reduced response time. The coefficient of determination (R2) has been found to be more in this technique. Research limitations/implications – As the threshold voltage of different photo catalytic materials will be different, Eref in the setup has to be adjusted accordingly to obtain sufficient quantity of current to operate the device. Originality/value – This approach relies on the SPICE model. The development of SPICE model for photochemical sensor is novel which is fast in operation and more user friendly.

A Rapid Monitoring System for the Determination of COD in Waters Based on Ultrasonic Assisted Digestion and Miniaturized Spectral Analytical System

Chemical Oxygen Demand (COD) is an much important key water quality parameter . In view of the technical defects of existing detection methods and monitoring instruments for measuring COD, a new detection method based on ultrasonic assisted sample digestion and spectrum analysis was put forward in this paper, and the automatic monitoring system prototype based on such detection method had been developped. Aiming at environmental water samples, the spot experiment had been carried out to contrast prototype with Chinas national standard analysis method for measuring COD, and the results showed that the automatic monitoring instrument prototype had good repeatability (10%) and high accuracy (±10%), which met the technical qualifications of Chinas envirormental protection industry standards.

Comparison of spectrophotometric methods using cuvette tests and national standard methods for analysis of wastewater samples

The suitability of spectrophotometric methods using cuvette tests (CT) for determination of ammonia (NH4+-N), nitrates (NO3--N), total phosphates (РО43--Ð ) and chemical oxygen demand (COD) in real wastewater were evaluated by comparison with corresponding Bulgarian national standard methods (BS). The CT methods are based on measuring of ready-to-use cuvettes (bar-coded reagent vials) inwavelength range of 340 to 900 nm. Nine wastewater samples from the inlet of the wastewater treatment plant of Sofia city were collected in the period of three months and the above mentioned quality indicators were measured in parallel both with CT and BS methods. Mean values of ten replicate determinations for each of the samples were compared statistically using Dixon’s t-test and linear regression model. Excellent linear correlation (R2 > 0.99) was found. As another mean of comparison, all the methods (CT and BS) for the determination of all the quality indicators were validated and uncertainties were estimated. Based on this, all data were compared and proved statistically equivalent. Key words: Method comparison, method validation, uncertainty estimation, cuvette tests, linear regression, spectrophotometer, wastewater.

A visible light assisted photocatalytic system for determination of chemical oxygen demand using 5-sulfosalicylic acid in situ surface modified titanium dioxide

Titanium dioxide (TiO2) nanoparticles were in situ surface modified by the chemisorption of 5-sulfosalicylic acid as non-sacrificial organics and then used as a visible light active photocatalyst (5-SA-TiO2). Based on the photodegradation of organic pollutants, a new system, 5-SA-TiO2–KMnO4, was used for the first time for the determination of chemical oxygen demand (COD). A linear correlation was observed between the amount of oxidizable dissolved organic matter and the amount of MnO4− consumed by the coupled reduction process. Thus, COD could be determined by the depletion of MnO4−. After TiO2 was surface modified by 24.82μg/mg of 5-SA, the working calibration range was extended from 2–12mg/L and 50–300mg/L to 0.3–400mg/L and the disadvantages of pure TiO2 for COD detection techniques were overcome, including UV irradiation and low oxidation percentage. Without any sample pretreatment and toxic reagents, the COD values of nature water and real wastewater could be successfully determined by achieved technique. Excellent agreement between our proposed method and conventional dichromate method was achieved.

Miniaturized and green method for determination of chemical oxygen demand using UV-induced oxidation with hydrogen peroxide and single drop microextraction

We report on a green method for the determination of low levels of chemical oxygen demand. It is based on the combination of (a) UV-induced oxidation with hydrogen peroxide, (b) headspace single-drop microextraction with in-drop precipitation, and (c) micro-turbidimetry. The generation of CO2 after photolytic oxidation followed by its sequestration onto a microdrop of barium hydroxide gives rise to a precipitate of barium carbonate which is quantified by turbidimetry. UV-light induced oxidation was studied in the absence and presence of H2O2, ultrasound, and ferrous ion. Determinations of chemical oxygen demand were performed using potassium hydrogen phthalate as a model compound. The optimized method gives a calibration curve that is linear between 3.4 and 20 mg L−1 oxygen. The detection limit was 1.2 mg L−1 of oxygen, and the repeatability (as relative standard deviation) was around 5 %. The method was successfully applied to the determination of chemical oxygen demand in different natural waters and a synthetic wastewater.

Photoelectrocatalytic determination of chemical oxygen demand under visible light using Cu2O-loaded TiO2 nanotube arrays electrode

A novel, visible light responsive chemical oxygen demand (COD) determination method using a Cu2O-loaded TiO2 nanotube arrays (TNTAs) electrode as sensor was proposed. In comparison with the pure TNTAs, the composite electrode showed much enhancement in the photocurrent response in visible region. With a positive bias potential of 0.3V (vs. Ag/AgCl) and visible light illumination, a COD detection limit of 15mgL−1 COD and a linear range of 20–300mgL−1 COD were achieved by the present composite electrode. When the composite electrode was used for the test of real wastewater samples, the obtained values were in good agreement with those determined by the standard K2Cr2O7 COD determination method. This paper would provide a potential outdoor COD determination method utilizing solar energy.