Chemical Oxygen Demand Measurements Research Articles

Batch Fabrication of Miniaturized Ag/AgCl Reference Electrode With Ion Exchanging Micro-Nano-Pores by Silicon-Base Double-Side Anisotropic Etching Process

To address the demands for the large-scale application of electrochemical sensors in the field of environmental pollution monitoring, a novel silicon-based Ag/AgCl reference electrode (RE) was batch fabricated. The reference electrode consisted of a mini-chamber for saturated KCl solution storage and micro-nano-pores for Cl− exchange. The microstructures were fabricated via a two-step KOH wet etching on double sided oxidized and polished silicon wafer. The size of the micro-nano-pore diameters were precisely controlled by the etching time. The Ag/AgCl electrode was prepared on a Pyrex 7740 glass via silver lift-off process and electrochemical treatment. The silicon and glass substrates were joined by anodic bonding to form the finished Ag/AgCl micro- reference electrode. Compared with a commercial glass tube Ag/AgCl reference electrode, the micro-RE had the advantages of better reference potential stability, a small size, easy integration, and batch fabrication. The micro-RE was combined with a PbO2 working electrode and a Pt counter electrode and applied to measure the glucose concentration in water samples. The results indicate that the novel micro-RE suitable for actual electrochemical detection, such as chemical oxygen demand (COD) measurements in water samples. [2019-0084]

Comparison of the effectiveness electrocoagulation of dye (batik waste water) using iron and zinc as an anodes

This study aims to obtain dye (batik waste water) treatment by electrocoagulation with optimal results. The performance of electrocoagulation process was carried out in batch reactor. Four variables were taken which thought to greatly influence the electrocoagulation process, such as: distance between electrodes, voltage, acidity (pH) and electrolysis time. In this process, samples of 20 mL were taken out from the batch at 5, 10, 15, 20, 25, 30, 35, 40, 45 dan 50 minutes of contact time. Results obtained show that the most effective removal efficiency could be achieved at alkaline condition. Research that has been done shows that the percentage of wastewater treatment results is strongly influenced by the four variable changes. The study demonstrated that the lowest degradation efficiency occours at acid pH, while an increase temperature has only a slight effect on the electrocoagulation process. The maximum results from the electrocoagulation processes was obtained, with determine by measurement of chemical oxygen demand (COD). The results showed that, iron is better used as an anode than zinc. The effectiveness electrocoagulation reached optimal at 96.54% (at Fe anode) and 81.65% (at Zn anode), at alkaline condition (pH > 9), electrolysis time of 30 minutes, electrode distance of 1 cm and temperature at 70°C.

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.

Developing a Strategy to Recover Condensate Water from Air Conditioners in Palestine

As the need for water is increasing in Palestine, and the available water resources are barely sufficient to meet the demands of the current quality of life and the economy, air conditioner condensate water could be explored as an alternative water source. The objective of this study is to better understand the potential for recovery of condensate water from air conditioning systems in two Palestinian cities. In addition, this study aims to evaluate this water source in terms of quality and quantity. Generally, it was found that the condensate water has good quality, which conforms to the Palestinian standards for reused water for irrigation, except for turbidity, biological oxygen demand (BOD) and chemical oxygen demand (COD) measurements. Reflecting the heavy metal occurrence in the collected condensate water, no particular risk was recognized for drinking water or reused irrigation standards, except for manganese occurrence of 0.19 mg/L in one sample. From a single unit capacity, high quantities of water were observed of approximately 259 L and 453 L per month in Ramallah and Jericho cities, respectively. These figures should draw the attention of decision and policy makers to put in place strict technical guidelines to be followed for potential reuse of condensate water at the local level.

High precision wide range online chemical oxygen demand measurement method based on ultraviolet absorption spectroscopy and full-spectrum data analysis

In this paper, a new method for high precision and wide range measurement of chemical oxygen demand (COD) based on ultraviolet absorption spectroscopy without reagent is proposed. The reasons for limiting measurement range and the main factors affecting the measurement accuracy are analyzed. A novel method of selecting different calibration wavelengths according to COD value to expand the measurement range and the turbidity compensation strategy based on full-spectrum data analysis to improve accuracy in wide measurement range are proposed and realized by an automatic wavelength selection calibration algorithm. Experiments were conducted to verify our idea with the self-developed micro UV–vis spectrophotometer (with a spectral range of 200–750 nm and a resolution of 5 nm) with a 10mm-path-length sample cell. By comparing various algorithms, the Savitzky-Golay (SG) convolution smoothing algorithm and the orthogonal signal correction (OSC) algorithm were chosen to compensate the additional absorption owing to turbidity. The experimental results show that the algorithm can automatically select the optimal characteristic wavelengths according to the spectral data and the measurement range of COD is enormously expanded from 10–150 mg/L to 1–1000 mg/L. The linear correlation coefficient (R2) of model is above 0.9995 and the relative error of measurement is less than 5%. This method can be used for in-situ and online COD measurement.

Preparation and characterization of SnO2 doped TiO2 nanoparticles: Effect of phase changes on the photocatalytic and catalytic activity

Abstract The effects of phase changes on the photocatalytic and catalytic activities of SnO2/TiO2 nanoparticles prepared via a surfactant-assisted sol-gel method were investigated. The as-prepared SnO2/TiO2 was calcined at 400°, 500°, 600°, and 700 °C. The prepared samples were studied by XRD, TEM, SEM, FTIR, BET, UV-vis diffuse reflection spectroscopy (DRS) and Photoluminescence (PL) spectra. The results showed that the crystallite size and anatase-to-rutile phase transformation increased greatly with increasing the calcination temperature. The transformation of anatase to rutile phase was found to be between 400° and 600 °C, and then the anatase completely transformed to rutile phase at 700 °C. Also, the specific surface area and pore volume decreased, whereas the mean pore size increased with increasing the calcination temperature. The effect of calcination temperature on the catalytic activity of the samples was tested by different applications: photodegradation of Methylene Blue (MB), Rhodamine B (RhB) dyes and phenol and synthesis of xanthene (14-phenyl-14H-dibenzo [a,j]xanthene). The mineralization of MB and RhB has been confirmed by chemical oxygen demand (COD) measurements. The SnO2/TiO2 nanoparticles calcined at 500 °C are found to exhibit the highest photocatalytic and catalytic activities.

An environmentally friendly surrogate method for measuring the soluble chemical oxygen demand in wastewater: use of three-dimensional excitation and emission matrix fluorescence spectroscopy in wastewater treatment monitoring.

Gaining rapid knowledge of dissolved organic matter (DOM) proves to be decisive for wastewater treatment plant operators in efforts to achieve good treatment efficiency in light of current legislation. DOM can be monitored by application of fluorescence spectroscopy both online and in real time in order to derive an assessment of DOM oxidation potential. This work presents an eco-friendly alternative method for measuring the soluble chemical oxygen demand (COD) in raw sewage by means of three-dimensional fluorescence spectroscopy. A peak-picking approach has been developed based on a previous parallel factor analysis (PARAFAC) model dedicated to Paris raw sewage. Fluorescence spectroscopy parameters were used to obtain a good prediction model of soluble COD (r2 = 0.799; p < 0.0001; n = 80) for raw sewage. The approach employed in this study serves as a guideline for purposes of implementing online wastewater monitoring and conducting environmentally friendly soluble COD measurements in the laboratory.

Study on an Online Detection Method for Ground Water Quality and Instrument Design.

The online measurement of ground water quality, as one important area of water resource protection, can provide real-time measured water quality parameters and send out warning information in a timely manner when the water resource is polluted. Based on ultraviolet (UV) spectrophotometry, a remote online measurement method is proposed and used to measure the ground water quality parameters chemical oxygen demand (COD), total organic carbon (TOC), nitrate nitrogen (NO3–N), and turbidity (TURB). The principle of UV spectrophotometry and the data processing method are discussed in detail, the correlated mathematical modeling of COD and TOC is given, and a confirmatory experiment is carried out. Turbidity-compensated mathematical modeling is proposed to improve the COD measurement accuracy and a confirmatory experiment is finished with turbidity that ranges from 0 to 100 NTU (Nephelometric Turbidity Unit). The development of a measurement instrument to detect the ground water COD, TOC, NO3–N, and TURB is accomplished; the test experiments are completed according to the standard specification of China’s technical requirement for water quality online automatic monitoring of UV, and the absolute measuring errors of COD, TOC, and NO3–N are smaller than 5.0%, while that of TURB is smaller than 5.4%, which meets the requirements for the online measurement of ground water quality.

Enhancement of the photocatalytic activity of ZnO nanoparticles by silver doping for the degradation of AY99 contaminants

Photocatalytic activity of commercial zinc oxide nanoparticles (ZnO) has been investigated and its photocatalytic efficiency improved by loading silver (Ag/ZnO) using UV light. Ag-doping onto ZnO, various mole % (1, 3, 5, 7 and 9) of silver has been investigated for the photoactivity of the doped material in acid yellow 99 (AY99) degradation. The effect of operation parameters such as pH, catalyst dosage, and initial dye concentration was estimated. The optical band gap of the samples was found to be 3.36 eV for ZnO and 3.34 eV for Ag/ZnO (7%), which proves the change in the acceptor level induced by the Ag atoms. Optimal experimental conditions on catalysts amount, pH value, illumination time, and dye concentration have been determined. These catalysts were characterized for surface area, particle size and crystallinity. The mineralization of AY99 has been confirmed by Chemical Oxygen Demand measurements. Furthermore, the kinetics and scavengers of the reactive species during the degradation were also investigated. It was found that the degradation of AY99 fitted the pseudo first-order kinetics and OH radicals were the main species. Formation of OH free radicals during irradiation is established by photoluminescence studies using terephthalic acid as examination molecule.

A turbidity compensation method for COD measurements by UV–vis spectroscopy

In water quality detection by ultraviolet-visible (UV–vis) spectroscopy, the detection equipment faces diverse water bodies. It is easy to be interfered by turbidity caused by suspended solid particles (SSP), resulting in a nonlinear rise of the whole spectrum and a significant decrease in measurement accuracy of chemical oxygen demand (COD). A turbidity compensation algorithm for UV–vis spectroscopy based on Lambert-Beer’s law for fitting the absorbance caused by turbidity in the whole spectrum region is studied. According to the additivity of absorbance, a few absorbance spectra of turbidity were obtained by filtering and difference method. They are then used as base spectra to linearly fit the absorbance spectrum of any turbidity value water. Finally, turbidity compensation of all samples in the whole region is realized by the subtraction method. Compared with 350 nm proportional compensation (350 nm PC) and multiplicative scatter correction (MSC), the compensated spectra of the method proposed in this paper are in the best coincidence with the filtered spectra by a 0.45 um filter membrane. Partial least squares (PLS) method is used to establish the COD prediction model of the raw spectra and compensated spectra of the three methods. The results show that the Rpred of the proposed method is the biggest and the RMSEP is the smallest. The experimental results show that the proposed turbidity compensation method can effectively correct the absorption spectrum without affecting the absorption characteristics of water samples. Furthermore, improving the accuracy of COD measurement by UV–vis spectroscopy.

Immobilization of palladium nanoparticles on thiol-functionalized multi-walled carbon nanotubes with enhanced photocatalytic activity for the degradation of alizarin red

In this article the new heterogeneous photocatalyst based on palladium supported on thiol-functionalized multi-walled carbon nanotubes (MWCNTs) has been introduced. The synthetic process of preparation of mentioned nanocatalyst (MWCNTs/Si-SH/Pd) has been described. The formation of nanocatalyst was analyzed by FTIR, Raman spectroscopy, EDS, TEM, SEM, WDX and ICP. The photocatalytical activity of this photocatalyst material was determined by degradation of organic dye Alizarin red in aqueous solution and in the presence of hydrogen peroxide. The effect of the reaction time, solution pH, and concentration of photocatalyst has been studied. The photocatalytic activity of the heterogeneous photocatalyst were assessed by analyzing the decrease in concentration of the Alizarin red as a colorant after exposure to UV irradiation. The work operated in a photoreactor with less energy consumption about 16 watts. The results clarify that the Alizarin red concentration decreases continuously, concomitant with the UV irradiation time up to 150 min. The mineralization of this dye has been confirmed by Chemical Oxygen Demand (COD) measurements. Finally, this mesoporous material heterojunction nanocatalyst was stable and could be easily recycled several times opening new avenues for potential industrial applications.

Comparative Study of Balancing SRT by Using Modified ASM2d in Control and Operation Strategy at Full-Scale WWTP

Detailed knowledge on the composition of the influent going into the wastewater treatment system is essential for the development of a reliable computer model. In the context of WWTPs (wastewater treatment plants), the wastewater characteristics are not only important for activated sludge system modelling, but also have an impact on the appropriate control of single unit operations. The aim of this study was to evaluate the concepts of COD (chemical oxygen demand) fractionation measurement in municipal wastewater with a respirometric method in control, and modelling the biological treatment processes at WWTP using the modified Activated Sludge Model no. 2d (ASM2d) developed by Drewnowski and Makinia. The batch OUR (oxygen uptake rate) test results and COD measurements obtained at BNR plant (96,000 m3/d) in Gdansk (Poland), were compared and evaluated with the main BNR (biological nutrient removal) WWTP (144,000 m3/d) located in Malaga (Spain). Respirometric tests and COD fractionation provided the experimental database for the comparison of the wastewater characteristics and model predictions at both large WWTPs. Some parameters, such as the heterotrophic growth yield (YH) coefficient, required calibration/validation of the range (YH = 0.64 and 0.74 gCOD/gCOD for Gdańsk and Malaga WWTP, respectively) to fit the modified ASM2d. The crucial issue when dealing with the newly developed model and proposed wastewater characterization for both study plants were extremely low and high values of the XS/XI ratio, which can be used to control full-scale WWTP and balance the solid retention time (SRT) in activated sludge systems.

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.

Highly efficient modified lead oxide electrode using a spin coating/electrodeposition mode on titanium for electrochemical treatment of pharmaceutical pollutant

In this study, Ti/TiO2/PbO2 anodes consisting of a PbO2 coating growth on the TiO2 interlayer deposited on titanium substrates were prepared combining different deposition technics: electrochemical method using anodization (Anod), electrodeposition (EL), and sol gel spin coating (SG). Different kinds of anodes have been tested for the removal of ampicillin, a pharmaceutical pollutant, from water. The structure and the surface morphology of the prepared multiple coatings were characterized by scanning electron microscopy and Energy-Dispersive X-ray spectroscopy respectively. Electrochemical impedance spectroscopy was also investigated in order to study the electrocatalytic activity of the anodes. The performance of the electrodes was evaluated through high performance liquid chromatography and chemical oxygen demand (COD) measurements. It was noticed that ampicillin could be mineralized by anodic oxidation process using Ti/TiO2/PbO2 anodes. The best results were obtained for Ti/TiO2SG/PbO2EL as anode with a 64% of COD removal after 300 min of treatment and a fast decrease in the amount of ampicillin was reached after almost one hour. Experimental results demonstrate that Ti/TiO2SG/PbO2EL anode presents the best ability for the degradation of ampicillin through anodic oxidation compared to the Ti/TiO2SG/PbO2SG and Ti/TiO2Anod/PbO2EL electrodes.

Robust output disturbance rejection control for anaerobic digestion processes

Anaerobic digestion (AD) is a powerful bioprocess used mainly in the treatment of highly polluted wastewaters with a valuable byproduct called biogas. However, the difficulties associated with the AD stable operation have prevented its worldwide application. The intrinsic complexity of the physicochemical and biological characteristics combined with the uncertain feedstock conditions, time lags and the lack of reliable measurements have hindered the application of a number of classical and advanced control strategies to deal with the control problem. On the other hand, robust H∞ theory offers a solid framework to handle feedback regulation of state variables on the plant frequency response in the face of disturbances and model uncertainties. This contribution presents a robust H∞ mixed sensitivity control design and tuning for output disturbances rejection and it is applied to an anaerobic digestion plant. This H∞ control holds the balance between robustness in the Chemical Oxygen Demand (COD) regulation and control effort. Simulation results show the effectiveness and benefits of the proposed design and tuning method. COD can effectively be regulated under: (i) load perturbations; (ii) model uncertainties and (iii) persistent output disturbances induced by COD measurement faults. The controller is applied to anaerobic digestion process but the approach can be implemented in distinct applications for organic matter degradation and other similar bioprocess and biological systems.

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.

Removal of the commercial reactive dye Procion Blue MX-7RX from real textile wastewater using the synthesized Fe2O3 nanoparticles at different particle sizes as a source of Fenton's reagent.

The aim of the present study was to signify the role of the particle size of an iron source in the photo-Fenton system for textile dyeing wastewater oxidation. In this respect, a facile synthesis of Fe2O3 nanoparticles (Fe2O3 NPs) via a simple sol–gel route using FeCl3 with different molarities was investigated. The XRD patterns confirmed the formation of Fe2O3 nanoparticles. Furthermore, different molar concentrations of the FeCl3 precursor significantly influenced the size and shape of the nanoparticles. The treatment of wastewater effluents containing the reactive dye Procion Blue MX-7RX from a real textile dyeing facility, was investigated using the synthesized Fe2O3 NPs as a source of the Fenton's reagent photocatalyst. The reaction was initiated and enhanced using an artificial UV source for increasing the ˙OH radical yield. System parameters such as the initial dye load in wastewater, H2O2 and Fe2O3 NP concentrations, pH and the working temperature were investigated for process optimization. The quality of water in this investigation was examined by making measurements of chemical oxygen demand (COD), total suspended solids (TSS) and dye removal which decreased during the illumination time. The effects of different Fe2O3 NPs based on the varying precursor solution molarities namely F1, F3, F5 and F7 on the wastewater remediation were investigated, and the optimum Fe2O3 NPs were found to be F1, which exhibited the highest dye removal value of 83% and a chemical oxygen demand (COD) reduction of 88%. Furthermore, the oxidation kinetics of the Procion Blue dye were studied, and the data were well fitted with the second order kinetics. Finally, the thermodynamic parameters including the changes in the Gibbs free energy of activation, entropy of activation and enthalpy of activation for the Procion Blue oxidation with different Fenton's reagent sources under ultraviolet light illustrated that the reaction was non-spontaneous and endothermic.

Reduction of BOD and COD of by using stratified filter and constructed wetland for blackwater treatment

Blackwater is a type of domestic wastewater that must be processed before discharge into the river. This study uses gravel, sand, and charcoal as filtration materials which arranged from coarse to fine, and also wetland system using Vetiver grass (Vetiveria zizanioides) and Cattail (Typha angustifolia). The treatment process is obtained by applying different treatments related to the sand thickness and blackwater residence time in the wetland. The focus of observation is emphasized on the measurement of BOD (Biological oxygen demand) and COD (Chemical oxygen demand). Both parameters measured and compared with the standard of water for agricultural purposes (Grade IV) regulated by Indonesian Government. The results showed that stratified filters can reduce the levels of BOD and COD effectively. The final results obtained after blackwater flowed through the wetland tube shows that BOD and COD levels have yet to meet the standard of grade IV water, although the overall result indicated the significant reduction of both parameters. This can be related to the input of organic matter from wetland itself, and it also can be considered an indication that blackwater treatment requires longer residence time.

Significant mineralization of beta blockers Propranolol and Atenolol by TiO2 induced photocatalysis

Abstract Degradation of wastewater containing recalcitrant pharmaceuticals is one of the emerging problems. Photocatalytic degradation and mineralization of two beta blockers Propranolol (PR) and Atenolol (AT) was investigated in TiO2 suspension. Four commercially available TiO2 samples viz. Aeroxide P25, Hombikat UV 100, Kronoclean 7000 and Merck TiO2 were used in which, Aeroxide TiO2 P25 was found to give best photocatalytic activity for both the pollutants studied under UV light as well as simulated solar light irradiation. The key experimental parameters such as effect of concentration of photocatalyst (0.05g/L to 0.4g/L), substrate concentration (1×10-5 Mto 1×10-4 M for PR and 9×10-5 Mto 3×10-4 M for AT), initial pH of the reaction sample (acidic, neutral and basic) and effect of addition of H2O2 (0.02mM-0.12mM H2O2) were studied in detail and optimized. Degradation of pollutants was assessed spectrophotometrically at 214 and 224 nm for PR and AT respectively, while mineralization data was obtained by Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) measurements. Mineralization studies (COD) highlight the dramatic enhancement in mineralization efficiency for PR and AT both under photocatalytic degradation as compared to photolysis alone. Aeroxide TiO2 P25 showed good recyclability and reusability up to three consecutive cycles without hampering its efficiency

Environmental properties of phosphonium, imidazolium and ammonium cation-based ionic liquids as potential lubricant additives

This research compares the environmental properties (bacterial toxicity and biodegradability) of 12 ionic liquids -ILs- (7 phosphonium, 2 imidazolium and 3 ammonium cation-based ones), potentially applicable as lubricant additive, with two types of the traditional lubricant additive ZDDP. Aquatic toxicity was determined by means of Vibrio fischeri and Escherichia coli bacteria, while biodegradability was evaluated through biological oxygen demand (BOD5) and chemical oxygen demand (COD) measurements. Regarding toxicity results, [P4442][DEP] was the least toxic IL (acute 3 according to GHS) for both bacteria, whereas ZDDP fell into the acute 1 category (very toxic). All samples tested turned out to be poorly biodegradable, showing BOD5/COD values below 0.1. Two ILs showed better combined tribological and environmental properties than ZDDP.