Chemical Oxygen Demand Measurements Research Articles

Sonochemical degradation of a pharmaceutical waste, atenolol, in aqueous medium

Atenolol is a β-blocker drug and an identified emerging pollutant. Advanced oxidation processes (AOPs) utilise the reaction of a highly oxidising species (hydroxyl radicals, (•)OH) for the mineralisation of emerging pollutants since conventional treatment methodologies generally fail to degrade these compounds. In the present work, degradation of atenolol was carried out using ultrasound with frequencies ranging from 200 kHz to 1 MHz as a source of hydroxyl radical. The degradation was monitored by HPLC, total organic carbon (TOC) and chemical oxygen demand (COD) reduction and ion chromatography (IC). Nearly 90 % of degradation of atenolol was observed with ultrasound having 350 kHz. Both frequency and power of ultrasound affect the efficiency of degradation. Nearly 100 % degradation was obtained at a pH of 4. Presence of various additives such as sodium dodecyl sulphate, chloride, sulphate, nitrate, phosphate and bicarbonate was found to reduce the efficiency of degradation. Although nearly 100 % degradation of atenolol was observed under various experimental conditions, only about 62 % mineralisation (from TOC and COD measurements) was obtained. Nearly eight intermediate products were identified using high-resolution mass spectrometry (LC-Q-TOF). These products were understood as the results of hydroxyl radical addition to atenolol. The degradation studies were also carried out in river water which also showed a similar degradation profile. A mechanism of degradation and mineralisation is presented.

WO3-Enhanced TiO2 Nanotube Photoanodes for Solar Water Splitting with Simultaneous Wastewater Treatment

Composite WO3/TiO2 nanostructures with optimal properties that enhance solar photoconversion reactions were developed, characterized, and tested. The TiO2 nanotubes were prepared by anodization of Ti foil and used as substrates for WO3 electrodeposition. The WO3 electrodeposition parameters were controlled to develop unique WO3 nanostructures with enhanced photoelectrochemical properties. Scanning electron microscopy (SEM) images showed that the nanomaterials with optimal photocurrent density have the same ordered structure as TiO2 nanotubes, with an external tubular nanostructured WO3 layer. Diffuse reflectance spectra showed an increase in the visible absorption relative to bare TiO2 nanotubes and in the UV absorption relative to bare WO3 films. Incident simulated solar photon-to-current efficiency (IPCE) increased from 30% (for bare WO3) to 50% (for tubular WO3/TiO2 composites). With the addition of diverse organic pollutants, the photocurrent densities exhibited more than a 5-fold increase. Chemical oxygen demand measurements showed the simultaneous photodegradation of organic pollutants. The results of this work showed that the unique structure and composition of these composite WO3/TiO2 materials enhance the IPCE efficiencies, optical properties, and photodegradation performance compared with the parent materials.

Influence of Operational Parameters in the Heterogeneous Photo-Fenton Discoloration of Wastewaters in the Presence of an Iron-Pillared Clay

An iron-pillared Tunisian clay (Fe-PILC) was prepared and used as the catalyst in the heterogeneous photo-Fenton oxidation of Red Congo and Malachite Green in aqueous solution. The catalyst Fe-PILC was characterized by XRF, XRD, BET, and FTIR methods. This physicochemical characterization pointed to successful iron pillaring of the clay. The influence of several operational parameters such as the pH, H2O2 concentration, catalyst dosage, and initial dye concentration was evaluated. A solution pH in the range 2.5–3, the addition of 8 mL of 200 mg/L H2O2, and a catalyst dosage of 0.3 g/L appeared as the most favorable reaction conditions for achieving complete discoloration, either for Red Congo or Malachite Green, although oxidation was found to be slower and more complicated in the former case. The kinetics of discoloration of both dyes followed a pseudo-first-order rate law. In general, 20 min of UV irradiation was enough to achieve 100% discoloration of the aqueous solution. UV–vis and chemical oxygen demand measurements indicated, however, that longer reaction times of around 1 h were required for achieving dye mineralization. Leaching tests confirmed a very low amount of dissolved iron and good stability of the catalyst, with almost unaltered discoloration efficiency upon three cycles. Hence, taking into account the favorable photocatalytic properties and low leaching of iron ions, such iron-pillared clay can be considered a promising catalyst for dye wastewater treatment.

Electrochemical oxidation of herbicide bifenox acid in aqueous medium using diamond thin film electrode

The electrochemical oxidation of bifenox acid was studied at a boron-doped diamond thin film by cyclic voltammetry and galvanostatic electrolysis. The course of the electrolysis was monitored by measurement of chemical oxygen demand (COD) and by gas chromatography/mass spectrometry (GC / MS) analysis. It was found that exhaustive electrolysis leads to degradation and, ultimately, to mineralization of the starting herbicide. The degradation intermediates were identified showing that the oxidation process begins with the fragmentation of the molecule followed by reactions involving the hydroxyl radical, which is generated by the discharge of water. The study of the effect of current density and concentration showed that the degradation efficiency increases with decreasing current densities and increasing concentrations. The whole results were interpreted in a mechanistic scheme involving two oxidation pathways, the first is a direct oxidation at the electrode and the second uses hydroxyl radical as mediator of the oxidation. Finally, a kinetic study based on spectrophotometric measurements showed that the degradation process is pseudo first order.

A novel and quick method to avoid H2O2 interference on COD measurement in Fenton system by Na2SO3 reduction and O2 oxidation

Hydrogen peroxide interference on chemical oxygen demand (COD) measurement has been a big problem in the application of the Fenton process. However, there is no simple and effective method available to address this problem, although several methods have been reported in the literature. In this study, a new method has been developed based on Na(2)SO(3) reduction and O(2) oxidation, which has easy operation and short time requirement. Na(2)SO(3) reduction was used to remove H(2)O(2) in water samples, which was independent of pH in the investigated range of 2.50-11.95. Residual Na(2)SO(3) was removed by subsequent O(2) oxidation, and effects of initial solution pH, ferric ion dosage, and stirring speed were explored. Solution pH below 3.0 and stirring speed of 700 rev min(-1) could ensure a sufficiently high oxidation rate for Na(2)SO(3) with ferric ion higher than 0.469 mM. This new method was proven to be effective in the matrix of Fenton treating real landfill leachate. Meanwhile, the procedure for this method in other applications was proposed in detail. To the best of our knowledge, this newly developed method is the most simple and effective way to avoid H(2)O(2) interference on COD analysis.

Photocatalytic mineralization of a water pollutant, Sunset Yellow dye by an advanced oxidation process using a modified catalyst

ZnS-loaded TiO2 (ZnS–TiO2) was synthesized by a sol–gel method. The catalyst was characterized by using different techniques (XRD, HR-SEM, EDS, DRS, PL, XPS, and BET methods). The photocatalytic activity of ZnS–TiO2 was investigated for the degradation of Sunset Yellow FCF (SY) dye in an aqueous solution using ultraviolet light. ZnS–TiO2 is found to be more efficient than prepared TiO2, TiO2–P25, TiO2 (Merck), and ZnS at pH 7 for the mineralization of SY. The effects of operational parameters such as the amount of photocatalyst, dye concentration, and initial pH on photo mineralization of SY have been analyzed. The mineralization of SY has been confirmed by chemical oxygen demand measurements. The catalyst is found to be reusable.

Effects of Biomass Types and Carbonization Conditions on the Chemical Characteristics of Hydrochars

Effects of biomass types (bark mulch versus sugar beet pulp) and carbonization processing conditions (temperature, residence time, and phase of reaction medium) on the chemical characteristics of hydrochars were examined by elemental analysis, solid-state ¹³C NMR, and chemical and biochemical oxygen demand measurements. Bark hydrochars were more aromatic than sugar beet hydrochars produced under the same processing conditions. The presence of lignin in bark led to a much lower biochemical oxygen demand (BOD) of bark than sugar beet and increasing trends of BOD after carbonization. Compared with those prepared at 200 °C, 250 °C hydrochars were more aromatic and depleted of carbohydrates. Longer residence time (20 versus 3 h) at 250 °C resulted in the enrichment of nonprotonated aromatic carbons. Both bark and sugar beet pulp underwent deeper carbonization during water hydrothermal carbonization than during steam hydrothermal carbonization (200 °C, 3 h) in terms of more abundant aromatic C but less carbohydrate C in water hydrochars.

Advanced oxidation (UV-ozone) and cyclodextrin sorption: Effects of individual and combined action on the chemical abatement of organic pollutants in industrial effluents

Among organic pollutants, four families have been listed as priority substances by the European Agency, namely polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), chlorophenols (CPs) and alkylphenols (APs). In this study, sorption onto a non-conventional cyclodextrin-based material alone as well as in combination with advanced oxidation using a UV-ozone process as pre-treatment was applied for the removal of PAHs, VOCs, CPs and APs from industrial effluents. After the various treatments proposed, we present the abatements obtained in the levels of chemical pollution monitored by a complete chemical analysis, and total organic carbon (TOC) and chemical oxygen demand (COD) measurements. High levels of pollutant removal were attained with the combined use of oxidation and sorption. The treatment led to the almost total elimination of organics such as chloroform, 1,2-dichlorobenzene, 2,4,6-trichlorophenol, nonylphenol and phenanthrene. The treatment also lowered TOC and COD by more than 84% and 93%, respectively. This combined lab-scale process using a non-conventional material could constitute an advantageous technology for removing organic pollutants when scaled up to treat polycontaminated industrial effluent.

Simple and large scale one-pot method for preparation of AgBr–ZnO nanocomposites as highly efficient visible light photocatalyst

Nanocomposites of AgBr–ZnO were successfully prepared in water by refluxing about at 90°C for 3h. In this method, zinc nitrate, silver nitrate, sodium bromide and sodium hydroxide were used as starting materials without using any additive and post preparation treatment. The nanocomposites were investigated by XRD, SEM, EDX, UV–vis DRS, and FT-IR techniques. In the nanocomposites, the ZnO has wurtzite hexagonal crystalline phase and loading of AgBr does not change its structure. The SEM images show that with increasing mole fraction of AgBr, surface morphology of the samples is changing to nanorods with smaller diameter. Photocatalytic activity of the nanocomposites was evaluated by degradation of methylene blue (MB) under visible light irradiation. The nanocomposites exhibit higher activity relative to the pure ZnO and AgBr. Among the prepared nanocomposites, the sample with 0.2372 mole fraction of AgBr exhibits highest photocatalytic activity. Moreover, influence of various operational parameters on the degradation reaction was studied and a possible degradation mechanism proposed. Chemical oxygen demand (COD) measurements were applied to check mineralization of MB on the nanocomposite under visible light irradiation.

Investigating wastewater modelling as a tool to predict anaerobic decomposition and biogas yield of abattoir effluent

Due to the high strength nature of abattoir wastewater, the accumulation of crusts on anaerobic ponds is a systemic problem in the red meat processing industry in Australia and can limit the ability to accurately obtain biogas measurements. In this study, BioWin was used to simulate chemical oxygen demand (COD) removal rates and subsequent biogas production rate based on field data from two abattoirs where crust accumulation was an issue. BioWin is a Microsoft Windows-based simulator developed by EnviroSim Associates Ltd, which has seen use in the design and optimisation of wastewater treatment plants. In assessing overall anaerobic decomposition efficiency it was hypothesised that a large percentage of influent COD was present as a surface crust which remained largely unbiodegradable. Field data effluent COD removal rates were matched to simulated rates predicted by BioWin when measured influent COD was reduced to 30% (absolute relative error of 11–14%), thus supporting the notion that a significant portion of COD is not taking part in the anaerobic digestion process. The simulation provides a preliminary assessment of pond performance in terms of COD removal rates and also subsequent biogas production rates. BioWin was able to predict approximate biogas production rates ranging between 113 to 173m3/d and 52m3/d for the two abattoirs investigated. Further work to validate simulation using BioWin includes obtaining actual biogas measurements and performing COD measurement of crust.

Synthesis, characterization and photocatalytic properties of SnO2–ZnO composite under UV-A light

The SnO2 loaded ZnO (SnO2–ZnO) was successfully synthesized by precipitation–decomposition method. The catalyst was characterized by X-ray diffraction (XRD), high resolution scanning electron microscope (HR-SEM) images, energy dispersive spectrum (EDS), diffuse reflectance spectra (DRS), photoluminescence spectra (PL) and BET surface area measurements. The photocatalytic activity of SnO2–ZnO was investigated for the degradation of Acid Orange 10 (AO 10) in aqueous solution using UV-A light. SnO2–ZnO is found to be more efficient than commercial ZnO, bare ZnO, TiO2-P25 and TiO2 (Merck) at pH 12 for the mineralization of AO 10 dye. The effects of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo mineralization of AO 10 dye have been analyzed. The mineralization of AO 10 has been confirmed by chemical oxygen demand (COD) measurements. A degradation mechanism is proposed for the degradation of AO 10 with SnO2–ZnO under UV-A light. This catalyst is found to be reusable.

Visible light assisted photocatalytic activity of TiO2–metal vanadate (M=Sr, Ag and Cd) nanocomposites

TiO2–metal vanadate nanocomposites (TiO2–MV) were synthesized by the precipitation method and successfully characterized using UV–visible diffuse reflectance spectroscopy (UV–vis-DRS), powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The photocatalytic activity of TiO2–MV was investigated for the degradation of fast green (FG) dye under visible light irradiation. The photocatalytic activity of TiO2–silver vanadate [TiO2–Ag3VO4] was found to be much higher than that of TiO2–cadmium vanadate [TiO2–CdV2O6], TiO2–strontium vanadate [TiO2–Sr3(VO4)2] and TiO2. The effect of operational parameters such as pH, photocatalyst concentration and initial dye concentration on the photodegradation of FG was examined in detail. The mineralization of FG was confirmed by chemical oxygen demand (COD) and total organic carbon (TOC) measurements. Moreover, TiO2–Ag3VO4 was found to be a reusable photocatalyst.

Electrochemical treatment of oil refinery effluent using boron-doped diamond anodes

This work describes the electrochemical oxidation of a real oil refinery effluent containing phenolic compounds. The electrooxidation was performed using a flow electrochemical reactor equipped with a boron-doped diamond (BDD) anode. The effects of flow rate and current density on the oxidation kinetics, current efficiency (CE), and energy consumption (EC) were studied using measurements of solution turbidity and chemical oxygen demand. The results showed that the BDD anode could be successfully used to treat effluents containing organic compounds, but that CE and EC were highly dependent on the current density and flow velocity. Although 100% CE could be achieved in some cases, the process must still be optimized to obtain low values of EC and make the technique economically feasible for the treatment of large volumes of effluents. Another point that must be considered concerns the stability of the electrode. Here, the BDD anode (which was deposited onto a niobium substrate) was not stable and showed intense pitting corrosion after 300h of use.

Electrochemical oxidation of dichlorvos on SnO2[sbnd]Sb2O5 electrodes

The effects of electrode potential and the initial concentration of 2,2-dichlorovinyl dimethyl phosphate (dichlorvos, DDVP) on its oxidation/mineralization reaction kinetics, using an electrochemical oxidation system based on SnO2Sb2O5 anodes, have been studied. Electrochemical degradation followed the Langmuir–Hinshelwood mechanism, with adsorption equilibrium constant K=0.082Lmg−1 of dichlorvos on the electrode material surface, and reaction rate constant k=0.021mgL−1s−1 of the organic compound-electrocatalyst adduct. Chemical oxygen demand and CO2 measurements in neutral media suggest that the rate limiting step for mineralization is the same as for the electrochemical oxidation. The results show that the electrochemical mineralization of dichlorvos was readily possible at potentials more positive than 2.5V vs. SCE, with lower reaction half-lives than obtained with other advanced oxidation process. The fastest overall degradation rate constants were obtained at limiting low concentrations of dichlorvos in aqueous solution, kobs=kK=0.0017s−1.

Preparation and characterization of PbO2 electrode and its application in electro-catalytic degradation of o-aminophenol in aqueous solution assisted by CuO–Ce2O3/γ-Al2O3 catalyst

The electrochemical degradation of o-aminophenol (OAP) in aqueous solution was investigated by galvanostatic electrolysis using PbO2 electrode as anode. The Ti/SnO2–Sb2O3/PbO2 anode was prepared by thermal decomposition and electro-deposition method, and was characterized by X-ray diffraction (XRD). The hydroxyl radicals electro-generated on anode were detected by fluorescence spectroscopy. The effects of initial pH and current density on the efficiency of the electrochemical degradation process were also studied. UV spectroscopy and chemical oxygen demand (COD) measurements were conducted to evaluate the removal effects of organic pollutants. The experimental results showed that the refractory organics in wastewater can be removed by pure electrochemical process, COD removal efficiency of 91.6% was obtained in 70min at initial pH 11.0 and current density was equal to 50mAcm−2. In order to improve the efficiency of degradation and accelerate the reaction rate, a novel catalyst, γ-Al2O3 supported Ce-doped CuO, was synthesized by impregnating process and was characterized by X-ray photoelectron spectroscopy (XPS). The catalyst exhibited excellent catalytic activity in the electro-catalytic degradation of OAP wastewater and the COD removal efficiency of 91.7% was obtained in 20min under mild conditions. Finally, a hypothetical mechanism of electro-catalytic degradation was proposed.

Efficient removal of Rhodamine B using a rice hull-based silica supported iron catalyst by Fenton-like process

The objective of this study is to evaluate the catalytic performance of a rice hull-based silica supported iron catalyst on heterogeneous Fenton-like degradation of a xanthene dye, Rhodamine B. The catalyst was found to consist of aggregated silica nanospheres with about 3wt.% of iron loaded. The effects of various reaction parameters such as initial dye concentration, catalyst dosage, H2O2 concentration, pH and temperature on the catalytic degradation of Rhodamine B were studied. Almost 100% decolorization was achieved within 10min at an initial pH of 3.0. Chemical oxygen demand measurement shows that considerably high degree of mineralization could be achieved along with the decolorization of Rhodamine B. The degree of mineralization was further enhanced by using stepwise addition strategy in which the impact of adverse reactions could be minimized. In addition, the effects of foreign ions and ionic strength were investigated and both promoting and inhibiting effects on the degradation rate were observed. In particular, common salts found in textile wastewater such as Na2SO4 and NaCl could even enhance the degradation rate in this catalyst system. FTIR and ICP-MS analysis shows that the catalyst exhibits low iron leaching, good structural stability and no loss of performance in at least three times of repeated use.

Ultrasound‐assisted bioscouring of cotton

In this study, the effects of ultrasound on the bioscouring of cotton by alkaline pectinase were examined. Conventional alkaline scouring was considered as the control treatment, and two different sources of ultrasound, an ultrasonic bath and an ultrasonic homogeniser, were tested, along with the enzymatic scouring process. Results indicated a clear increase in the efficiency of the enzymatic scouring process when the ultrasonic homogeniser was used: wettability time and wicking distance after ultrasonic homogeniser‐assisted bioscouring were much better than for enzymatic scouring without the use of ultrasound energy and almost the same as when conventional alkaline scouring was employed. Ultrasonic bath‐assisted enzymatic bioscouring gave slightly better results than enzymatic scouring without sonication. Reasons for the difference in efficacy of the ultrasound sources were postulated. Weight loss was increased by the use of ultrasonic equipment during enzymatic scouring. Fabric thickness and fabric strength was not significantly affected by the scouring processes. The environmental impact of the processes was also monitored by chemical oxygen demand measurement of the treatment liquors. Conventional alkaline scouring resulted in the highest environmental impact. Ultrasonic homogeniser‐assisted bioscouring also led to slightly higher chemical oxygen demand loads than other enzymatic processes owing to the more efficient removal of impurities.

Enhanced photocatalytic activity of titanium dioxide by β-cyclodextrin in decoloration of Acid Yellow 99 dye

Photocatalytic decoloration of Acid Yellow 99 dye by TiO2 has been investigated under different experimental conditions. Addition of β-Cyclodextrin on TiO2 enhanced the photoactivity of TiO2 in AY99 degradation. Optimal experimental conditions on catalyst amount, pH value, illumination time, and dye concentration have been determined. The mineralization of AY99 has been confirmed by Chemical Oxygen Demand measurements. The higher photoactivity of TiO2-β-CD/visible light system than TiO2/visible light system can be ascribed due to the ligand to metal charge transfer from β-CD to TiIV located in an octahedral coordination environment. The complexation patterns have been confirmed with UV–Visible and FT-IR spectral data. The interactions between TiO2 and β-CD have been characterized by Field Emission Scanning Electron Microscopy, X-ray powder diffraction analysis, and UV–Visible diffuse reflectance spectroscopy.

A novel approach for textile dye degradation by zinc, iron–doped tin oxide/titanium moving anode

The present contribution reports a moving iron (Fe), zinc (Zn)–doped tin oxide/titanium (SnO2/Ti) anode-based system designed and operated for the electro-oxidation of methyl orange dye effluent. Electrochemical oxidation of the dye was carried out at a current density of 1.8 A/dm2 for 120 min. Similar experiments were repeated with pure SnO2-based static and moving anode-based systems and the Fe, Zn-doped SnO2 static anode-based electro-oxidation system. Post oxidation, the surface of the electrodes was critically examined by scanning electron microscopy. Dye samples were analysed at regular intervals during the electro-oxidation process by chemical oxygen demand and colour removal measurements and characterized by UV–Vis spectroscopy and Fourier transform infrared spectroscopy at the end of the oxidation process. The obtained results elucidate the superiority of Fe, Zn-doped SnO2/Ti moving anode-based system for methyl orange dye effluent electro-oxidation. The moving anode prevents passive layer formation and decreases polarization resistance. Doping of Fe and Zn provides the anode-enhanced mechanical strength and electrocatalytic activity. The combined effects of axial anode movement and doping are responsible for improved performance of the moving anode system reported in this contribution.

Solar photocatalytic degradation of Naphthol Blue Black

The solar photocatalytic activity of AgBr–ZnO was investigated for the degradation of Naphthol Blue Black (NBB) in aqueous solution. Removal of azo dyes from wastewater is a challenging process, since these dyes are nonbiodegradable. Presence of a visible light absorbing component, AgBr, makes this catalyst solar active. AgBr–ZnO is found to be more efficient than commercial ZnO and prepared ZnO for solar degradation of NBB azo dye. The effects of operational parameters, such as the amount of photocatalyst, dye concentration, and initial pH on photo mineralization have been analyzed. The optimum pH and catalyst amount for the efficient removal of dye are found to be 11 and 3 g L−1, respectively. Increase of initial dye concentration decreased the degradation rate. The mineralization of NBB has also been confirmed by chemical oxygen demand measurements. The higher photocatalytic activity of AgBr–ZnO towards NBB degradation in solar light is explained by a mechanism involving band energy levels of AgBr and ZnO. The catalyst was found to be reusable.