Initial 4-chlorophenol Concentration Research Articles

Optimization of 4-chlorophenol decomposition by H2O2 activate catalytic magnetic iron oxide an activated carbon carrier

Wastewater from chemical plants that produce pesticides always carries a large amount of organic matter that is difficult to decompose. One of them is the compound 4-chlorophenol, which has difficult-to-decompose properties, is durable in the environment, and is also listed in the group of substances that are likely to cause cancer in humans. In this study, the 4-chlorophenol compound was treated with heterogeneous Fenton by H2O2 activated by magnetic iron oxide nanoparticles on activated carbon. Magnetic iron oxide nanoparticles were successfully synthesized and mounted on activated carbon 10-15 nm in size with material surface morphological parameters such as specific surface area 330.28 cm2/g; total pore volume 0.16 cm3/g; magnetization 8.19 emu/g. The optimization of the 4-chlorophenols decomposition reaction with pH parameters, the content of catalytic materials, and the initial concentration of 4-chlorophenol is carried out using the Box-Behnken Design. The results showed that the removal efficiency of 4-chlorophenol was 96.5% achieved with optimum parameters pH 2.9; catalytic concentration 0.32 g/L; initial concentration of 4-chlorophenol 92.3 mg/L. The results of the study show the efficiency of the decomposition of an organic compound using magnetic activated carbon.

4-Chlorophenol adsorption from water solutions by activated carbon functionalized with amine groups: response surface method and artificial neural networks

4-Chlorophenol pollution is a significant environmental concern. In this study, powdered activated carbon modified with amine groups is synthesized and investigated its efficiency in removing 4-chlorophenols from aqueous environments. Response surface methodology (RSM) and central composite design (CCD) were used to investigate the effect of different parameters, including pH, contact time, adsorbent dosage, and initial 4-chlorophenol concentration, on 4-chlorophenol removal efficiency. The RSM-CCD approach was implemented in R software to design and analyze the experiments. The statistical analysis of variance (ANOVA) was used to describe the roles of effecting parameters on response. Isotherm and kinetic studies were done with three Langmuir, Freundlich, and Temkin isotherm models and four pseudo-first-order, pseudo-second-order, Elovich, and intraparticle kinetic models in both linear and non-linear forms. The synthesized adsorbent was characterized using X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses. The results showed that the synthesized modified activated carbon had a maximum adsorption capacity of 316.1 mg/g and exhibited high efficiency in removing 4-chlorophenols. The optimal conditions for the highest removal efficiency were an adsorbent dosage of 0.55 g/L, contact time of 35 min, initial concentration of 4-chlorophenol of 110 mg/L, and pH of 3. The thermodynamic study indicated that the adsorption process was exothermic and spontaneous. The synthesized adsorbent also showed excellent reusability even after five successive cycles. These findings demonstrate the potential of modified activated carbon as an effective method for removing 4-chlorophenols from aqueous environments and contributing to developing sustainable and efficient water treatment technologies.

Degradation of 4-chlorophenol from aqueous solution using ultrasound/persulphate: prediction by RSM

ABSTRACT Chlorophenol compounds are considered as toxic and harmful effects caused by them have been proven for human and living organisms. This study is aimed to reduce 4-chlorophenol from aquatic solution using ultrasound/persulphate technique. Response surface method (RSM) is applied to find out the optimum conditions for 4-chlorophenol removal. The independent variables are pH, contact time, 4-chlorophenol concentration, persulphate concentration and ultrasound power. A statistical analysis of variance (ANOVA) is conducted to optimise factors obtained from the experimental data. A second-order model is developed as a great model to predict of 4-chlorophenol reduction efficiency. The optimum conditions is found at pH = 3, reaction time of 65 min, 4-chlorophenol concentration of 15 mg/l, persulphate concentration of 125 mg/L and ultrasound power of 150 W. In terms of 4-chlorophenol removal efficiency R2, Adj. R2 and coefficient of variance (CV) are found to be 0.95, 0.85 and 8.9, respectively. According to the results pH (A), reaction time (B), initial 4-chlorophenol concentration (C), persulphate concentration (D), ultrasound power (E), square terms of pH (A2), reaction time (B2), initial 4-chlorophenol concentration (C2), persulphate concentration (D2), ultrasound power (E2) and interaction terms of AB, AC, AD, BC, BD, CD, AE,and DE are found as effective factors. The results obtained from the extra experiments at optimal conditions indicates 88.92% removal rate of 4-chlorophenol which confirms a great agreement between the predicted (90.88%) and experimental data.

Study of the Efficiency of Proxone Method as Advanced Oxidation Process to Remove 4-Chlorophenol from Aqueous Solution

Introduction: 4-chlorophenol is one of the common contaminants in wastewater resulted from chemical and petrochemical industries. This matter is resistant to biodegradation due to presence of chlorine and benzene ring in its structure. Various methods have been used to remove this contaminant from environment but the advanced oxidation techniques are more capable. In this study, proxone method (hydrogen peroxide plus ozone) was investigated to remove, 4-chlorophenol. Materials & methods: This study is experimental and some parameters including pH, 4-chlorophenol initial concentrations, contact time, and the concentrations of oxidant (H2O2) during proxone process were investigated to remove 4-chlorophenol. All tests were conducted on actual solution (effluent of coal cleaning plant). Microsoft Office Excel 2013 software and SPSS 15 were used for data analysis. Findings: The maximum removal efficiency of 4-chlorophenol at optimum condition (including pH=9, contact time=30 minutes, ozone concentration=0.09 g/hr, the initial concentration of 4-chlorophenol=100 ppm, the optimum concentration of H2O2=0.001 molar) were achieved 96.8% and 92.65% for synthetic and actual solution, respectively. Discussion & conclusions: Advanced oxidation, according to Peroxone method is a suitable way to remove 4-chlorophenol and is able to remove this material from actual wastewater with efficiency of 92.65%. So, this method can be used for water purification and contaminated wastewater with this pollutant.

Preparation and characterizations of CuO doped ZnO nano-structure for the photocatalytic degradation of 4-chlorophenol under visible light

In the present investigation, a ZnO nanostructure was synthesized by means of precipitation and sonochemical methods. The X-ray diffraction (XRD) pattern indicated that the wurtzite structure of ZnO had a hexagonal symmetry and there was no impurity. The average ZnO particles crystallite size was calculated at about 41 nm. The SEM and TEM images revealed nanostructure ZnO particles with a cauliflower-like and rod morphology with dimensions of 85, 79 and 117 nm. In order to investigate the increment of ZnO photoactivity under visible light, the CuO doped ZnO nanostructures were fabricated by a wet impregnation method using copper oxide as the copper source and ZnO as the precursor. The XRD analysis confirmed that the CuO phase was present in the as-prepared sample and the average size of nano crystalline decreased to about 36 nm. The DRS spectra indicated the extended absorption of CuO-ZnO to the visible range as a result of band gap reduction to 2.9 eV (in comparison of 3.2 eV in ZnO). In order to investigate the photocatalytic activity of the synthesized photocatalyst, the degradation of 4-Chlorophenol under visible light was performed. Sixteen experiments using full factorial were executed by adjusting four parameters (amount of catalyst, initial concentration of 4-Chlorophenol, pH, and time of irradiation). An empirical expression was proposed and successfully used to model the photocatalytic process with a high correlation, and an optimal experimental region was also obtained. According to the developed model for degradation and the subsequent ANOVA test using Design Expert software, the time of irradiation with a 46.57% effect played the most important role in the photocatalytic activity, while the influences of parameters on each other were negligible. Optimal experimental conditions for 4-Chlorophenol concentration (0.01 g/L) were found at an initial pH =8 and a catalyst loading of 0.07 g/L. The results indicated that CuO-ZnO can remove 95% of 4-chlorophenol from water under optimal conditions.

Comparable Study of 4-chlorophenol Removal from Petrochemical Wastewater Using Mesoporous and Microporous Carbons: Equilibrium and Kinetics Investigations

In this study, an ordered mesoporous carbon structure with excellent adsorption properties towards chlorophenol compounds was synthesized using a hard template. The physico-chemical properties of the synthesized samples were studied using Small Angle X-ray Diffraction (SAXRD), Transmission electron microscopy (TEM), Scanning Electron Microscopy (SEM) and nitrogen adsorption–desorption analysis. The capability of adsorption of 4-chlorophenol on mesoporous carbon has been investigated by varying the reaction time, initial concentration of 4-chlorophenol, adsorbents loading and the pH of the solution; and the results compared with commercial activated carbon as a microporous carbon. Freundlich, Langmuir, Tempkin and dubinin-radushkevich adsorption isotherms were used to model the equilibrium adsorption data for 4-chlorophenol compound. The kinetic analysis showed that the adsorption process was fitted with the pseudo-second-order kinetic model. The equilibrium data were investigated by the main adsorption isotherm models on the mesoporous and microporous carbons as adsorbents, which revealed that the Freundlich model was better to describe the 4-chlorophenol adsorption than other models. Also, the obtained results indicated that the adsorption capacity and equilibrium time for mesoporous carbon were better than microporous carbon, 90 mg/g after 25 minute compare to 60 mg/g after 60 minute, respectively.

The Photocatalytic Oxidation of 4-Chlorophenol Using Bi2WO6 under Solar Light Irradiation

This report discusses the effects of the initial concentration of 4-chlorophenol (4-CP) on its solar light photoinduced oxidation/mineralization kinetics on Bi2WO6 catalyst. Photocatalytic degradation followed the Langmuir-Hinshelwood (L-H) mechanism. From the kinetic data the Langmuir adsorption equilibrium constant of 4-CP on the Bi2WO6 surface and the L-H maximum reaction rate for 4-CP oxidation have been evaluated. Chromatographic and spectroscopy studies show the presence of p-benzoquinone and maleic acid as the main reaction products; these compounds first increase and then decay until they disappear. Chemical oxygen demand (COD) and produced CO2 measurement show that photocatalytic mineralization of the phenolic compound was readily possible in a wide concentration range.

Sono-catalytic degradation and fast mineralization of p-chlorophenol: La0.7Sr0.3MnO3 as a nano-magnetic green catalyst

La0.7Sr0.3MnO3 (LSMO) nanoparticles with a perovskite structure were prepared by a combination of ultrasound and co-precipitation method. The synthesized catalyst was characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy. The catalytic performance of the catalyst was evaluated for the degradation of 4-chlorophenol in the presence and in the absence of ultrasound. The degradation has been studied at different temperatures, pH, catalyst dosage, and initial concentration of 4-chlorophenol. The results have shown that the degradation efficiency was higher in the presence of ultrasound than its absence under the mild conditions. More than 88% decrease in the concentration and 85% decrease in the TOC for 4-chlorophenol could be achieved in a short time of sonication with respect to the conventional method. This behavior could be attributed to the cavitation process which followed by a high mass transfer on the catalyst with high surface area. These conditions led to facilitate the removal of pollutant from aqueous solution. The results also indicated that the catalyst without recalcination can be used successfully up to five consecutive cycles without any significant loss in activity in the presence and in the absence of ultrasound. In addition, the most important is the magnetic property of the nanoparticles which separated easily from aqueous solution by an external magnetic field.

Electrocatalytic degradation kinetic of 4-chlorophenol by the Pd/C gas-diffusion electrode system

A Pd/C gas-diffusion cathode which generated H2O2 through a two-electron reduction process of fed oxygen molecule was used to degrade 4-chlorophenol in an undivided electrolysis device. The kinetics of 4-chlorophenol degradation has been investigated by the electrochemical oxidation processes. By inspecting the relationship between the rate constants (k) and influencing factors, using first-order kinetics to describe the electrochemical oxidation process of 4-chlorophenol, a kinetic model of 4-chlorophenol degradation process was proposed to calculate the 4-chlorophenol effluent concentration: C = C0 exp( -3:76 × 10(-6) C(-0.5)0 J(2) M(-0.7) Q(0.17) Dt). It was found that the electrocatalytic degradation rate of 4-chlorophenol was affected by current density, electrode distance, air-feeding rate, electrolyte concentration and initial 4-chlorophenol concentration. The kinetics obtained from the experiments under corresponding electrochemical conditions could provide an accurate estimation of 4-chlorophenol effluent concentration and lead to better design of the electrochemical reactor.

Photocatalytic degradation of 4-chlorophenol by UV/H2O2/NiO process in aqueous solution

The removal of 4-chlorophenol from aqueous phase continues to be an important environmental issue. In this work, the photochemical oxidation of 4-chlorophenol in aqueous solutions in a batch reactor using ultraviolet irradiation, hydrogen peroxide and nickel oxide was studied. The efficiency of the system was evaluated with respect to reaction time, pH, feed concentration of reactants, catalyst load, light intensity, and the reaction rate constant. The concentrations of 4-chlorophenol and chloride ions were determined by high performance liquid chromatography and ion chromatography, respectively. Pure nanosized nickel oxide was characterized by X-ray diffraction and scanning electron microscopy. The results showed that the optimum conditions (the complete 4-chlorophenol removal (100%) at 60 min) were obtained at a neutral pH, with 0.2 mol/L H2O2, and 0.05 g/L of nickel oxide. However, no pH effects were observed in the range of 4–10. Analytical profiles on 4-chlorophenol transformation were consistent with the best line fit of the first-order kinetics. Moreover, the degradation rate constant increased with both UV light intensity and decreasing initial concentration of 4-chlorophenol. Finally, the results of mineralization and chloride ions studies indicated that dechlorination was better accomplished but more time was required to completely mineralize 4-chlorophenol into water and carbon dioxide.

4-Chlorophenol degradation with modified domestic microwave and hydrogen peroxide in aqueous solution

Aims: This study was conducted for degradation of 4-chlorophenol by microwave (MW) radiations alone and in combination with hydrogen peroxide from aqueous solution. Materials and Methods: A modified domestic microwave oven was used alone and in combination with hydrogen peroxide for removing 4-chlorophenol. Furthermore, the influences of pH value, irradiation time, the power of MW radiations, and the initial concentration of 4-chlorophenol were studied. Results: It was shown that 4-chlorophenol removal efficiency extremely depend on the concentration of hydrogen peroxide, pH value, MW irradiation power and initial 4-chlorophenol concentration. The optimum conditions obtained for the best degradation rate were pH = 10.5, H 2 O 2 concentration of about 0.1 mol/l, and MW irradiation power of about 600 W. Other result shows that the best degradation rate of 4-chlorophenol was obtained when initial 4-chlorophenol concentration was 50 mg/l. Also the amount of the specific energy consumption in this method was 17460 kwh/kg of the removed organic compound. Conclusion: This result shows that MW irradiation in the presence of hydrogen peroxide can greatly enhance the degradation of 4-chlorophenol. However, the high consumption of energy for this method must be taken into consideration.

Photocatalytic Degradation of 4-Chlorophenol with a Novel α-Ga<sub>2</sub>O<sub>3</sub>

Chlorophenols is a kind of environmental endocrine disrupting chemicals (EDCs) and it is hard for the common methods to degrade or remove them, so how to decompose these pollutants has attracted researches’ attention. In this paper, a novel α-Ga2O3 was used to degrade 4-chlorophenol via photocatalytic reaction and degradation kinetics was investigated. The effects of main factors, such as dosage of α-Ga2O3 and pH of aqueous solution, on degradation were studied, and degradation kinetics was also established. Experimental results displayed that the optimal pH of aqueous solution was about 7.8 and almost 98% 4-chlorophenol was decomposed after 2 h, when the dosage of α-Ga2O3 was 0.4 g and the initial concentration of 4-chlorophenol was 20 mg/L (V=200 ml). Photocatalytic degradation of 4-chlorophenol with α-Ga2O3abided by first-order kinetics and half-life time was 20.4 min.

Photodegradation of 4-chlorophenol using XeBr, KrCl and Cl2 barrier-discharge excilamps: A comparative study

Abstract A study on 4-chlorophenol (4CP) photodegradation has been carried out using UV radiation delivered from three different excimer lamps: XeBr, KrCl and Cl 2 , with maximum emission wavelengths of 283, 222 and 259 nm, respectively. The influence of initial 4-chlorophenol concentration on the photodegradation process was examined with pollutant concentrations ranging from 50 to 500 mg L −1 , and degradation progress was followed by determining the residual 4-chlorophenol, as well as that of the main photoproducts, hydroquinone (HQ) and benzoquinone (BQ). All excilamps were able to degrade 4CP. XeBr and the KrCl excilamps achieved almost total 4-chlorophenol degradation, with the removal efficiency of the Cl 2 excilamp being considerably lower. The KrCl excilamp, in spite of requiring longer exposure times compared with the XeBr, needed a much lower UV dose and, consequently, a lower energy consumption for degradation and, as a result, has been considered the most effective and efficient in 4CP removal. Additionally, and by defining the limit of 4-chlorophenol degradation, a modified pseudo-first order kinetic model was used to fit the kinetics of the 4-chlorophenol degradation process where good agreement between experimental data and those predicted by the model was found. Shielding effects are considered to have an influence on 4-chlorophenol degradation as there is a decrease in the pseudo-first order rate constant with increasing 4-chlorophenol concentrations for the three excilamps. In addition, there is a noticeable decrease in the maximum removal of 4-chlorophenol for the Cl 2 excilamp due to the same effect.

Testing a KrCl excilamp as new enhanced UV source for 4-chlorophenol degradation: Experimental results and kinetic model

Excilamps are new UV sources with great potential for application in wastewater treatment. In the present work, a KrCl excilamp emitting radiation at 222 nm has been used for the photodegradation of 4-chlorophenol within a range of concentrations from 50 to 500 mg L −1. The photodegradation process has been shown to form two main photoproduct intermediates, benzoquinone and hydroquinone. Total removal of 4-chlorophenol was shown for all concentrations assayed, and, for both main intermediates, residual concentrations of 20–30% of the initial concentration of 4-chlorophenol remained. Their increasing presence with increasing initial concentrations of 4-chlorophenol had the effect of decreasing the removal efficiency of the photoproducts. In order to simulate the process and scale-up a simplified kinetic model has been developed and validated from the experimental data.

Photocatalytic treatment of 4-chlorophenol in aqueous ZnO suspensions: Intermediates, influence of dosage and inorganic anions

The photocatalytically driven removal of eco-persistent 4-chlorophenol from water using ZnO is reported here. Kinetic dependence of transformation rate on operating variables such as initial 4-chlorophenol concentration and photocatalyst doses was investigated. A complete degradation of 4-chlorophenol at 50 mg L −1 levels was realised in 3 h. Analytical profiles on 4-chlorophenol transformation were consistent with the best-line fit of the pseudo zero-order kinetics. The addition of small amounts of inorganic anions as SO 4 2−, HPO 4 −, S 2O 8 2− and Cl − revealed two anion types: active site blockers and rate enhancers. Fortunately, Cl − and SO 4 2− commonly encountered in contaminated waters enhanced the rate of 4-chlorophenol degradation. The reaction intermediates and route to 4-chlorophenol mineralisation were elucidated by combined RP-HPLC and GC–MS methods. In addition to previously reported pathway products of 4-chlorophenol photo-oxidation catechol was detected. A radical mechanism involving o-hydroxylation is proposed to account for the formation of catechol.

Photocatalysis of 4-chlorophenol mediated by TiO 2 fixed to concrete surfaces

Titanium dioxide (TiO 2) powder was mixed with varying concrete sealer formulations and applied to prepared concrete surfaces within PVC batch reactors. A solution of 4-chlorophenol in de-ionized water, with an initial 4-chlorophenol concentration of 4 mg/L, was added to each open reactor. The photocatalytic efficiency of each TiO 2-sealer was determined through bulk solution sampling while a reactor was exposed to continuous UV light. Through analysis of mean 4-chlorophenol concentrations, the disappearance of 4-chlorophenol from solution was attributed solely to the presence of TiO 2 in the sealed concrete surface of a UV exposed reactor. The rate of disappearance increased when the mass percent of TiO 2 in the sealer was increased. The zero-order reaction rate constants ranged from 0.135 to 0.2873 mg L −1 h −1.

Sol–gel preparation and characterization of alkaline earth metal doped nano TiO 2: Efficient photocatalytic degradation of 4-chlorophenol

Magnesium and barium doped TiO 2 nanoparticles were synthesized by sol–gel method. The materials were characterized by XRD, BET, FT-IR, TGA, UV–vis, SEM and TEM techniques. The pure TiO 2 nanoparticles contained both anatase and rutile phases together, but Mg 2+ or Ba 2+ metal ion doped nano TiO 2 gave only anatase phase. The framework substitution of Mg 2+ in nano TiO 2 was established by XRD and FT-IR techniques. However, Ba 2+ was retained only on the surface of nano TiO 2 as BaCO 3 and the absence of framework substitution of Ba 2+ in nano TiO 2 was evident from XRD and FT-IR analysis . The band gap values of Mg 2+ and Ba 2+ doped nano TiO 2 were higher than the pure nano TiO 2. The presence of anatase type structure in nano TiO 2 with high crystallinity and high phase stability even after annealing at 800 °C substantially indicates that the dopants might inhibit densification and crystallite growth in nano TiO 2 by providing dissimilar boundaries. The photocatalytic activity in the degradation of 4-chlorophenol was found to be higher for Mg 2+ and Ba 2+ doped nano TiO 2 than both pure nano TiO 2 and commercial TiO 2 (Degussa P-25). The influence of various parameters such as initial concentration of 4-chlorophenol, catalyst loading, pH and light intensity were optimized to obtain maximum degradation.

RETRACTED: Enhanced photocatalytic degradation of 4-chlorophenol by Zr4+ doped nano TiO2

Abstract Zr 4+ doped nano titania was prepared by sol–gel method using titanium(IV) isopropoxide and zirconium nitrate as precursors. The materials were characterized by XRD, BET, UV–vis, FT-IR, SEM-EDX and TEM techniques. The nanoparticles of pure TiO 2 contained both anatase and rutile phases together but Zr 4+ doped TiO 2 gave anatase phase only. The framework substitution of Zr 4+ in TiO 2 was established by XRD, SEM-EDX and FT-IR techniques. The band gap value of Zr 4+ doped TiO 2 was higher than the parent nano TiO 2 . TEM observations confirmed the nanocrystalline nature of Zr 4+ doped TiO 2 . The presence of dopants therefore could suppress the growth of TiO 2 grains, increase the surface area, decrease the anatase–rutile phase transformation and accelerate the surface hydroxylation. These properties resulted higher photocatalytic activity for Zr 4+ doped nano TiO 2 than undoped nano TiO 2 . The presence of anatase type structure in TiO 2 with high crystallinity and high phase stability, even after annealing at 800 °C substantially indicated that the dopants might inhibit densification and crystallite growth by providing dissimilar boundaries. The photocatalytic activity in the degradation of 4-chlorophenol was found to be higher for Zr 4+ doped TiO 2 than both nano TiO 2 and commercial TiO 2 (Degussa P25). The experimental parameters such as initial concentration of 4-chlorophenol, catalyst loading, pH and light intensity were optimized for maximum degradation efficiency.

Photochemical degradation and mineralization of 4-chlorophenol.

Since the intermediate products of some compounds can be more toxic and/or refractory than the original compund itself, the development of innovative oxidation technologies which are capable of transforming such compounds into harmless end products, is gaining more importance every day. Advanced oxidation processes are one of these technologies. However, it is necessary to optimize the reaction conditions for these technologies in order to be cost-effective. The main objectives of this study were to see if complete mineralization of 4-chlorophenol with AOPs was possible using low pressure mercury vapour lamps, to make a comparison of different AOPs, to observe the effect of the existence of other ions on degradation efficiency and to optimize reaction conditions. In this study, photochemical advanced oxidation processes (AOPs) utilizing the combinations of UV, UV/H2O2 and UV/H2O2/Fe2+ (photo-Fenton process) were investigated in labscale experiments for the degradation and mineralization of 4-chlorophenol. Evaluations were based on the reduction of 4-chlorophenol and total organic carbon. The major parameters investigated were the initial 4-chlorophenol concentration, pH, hydrogen peroxide and iron doses and the effect of the presence of radical scavengers. It was observed that the 4-chlorophenol degradation efficiency decreased with increasing concentration and was independent of the initial solution pH in the UV process. 4-chlorophenol oxidation efficiency for an initial concentration of 100 mgl(-1) was around 89% after 300 min of irradiation in the UV process and no mineralization was achieved. The efficiency increased to > 99% with the UV/H2O2 process in 60 min of irradiation, although mineralization efficiency was still around 75% after 300 min of reaction time. Although the H2O2/4-CP molar ratio was kept constant, increasing initial 4-chlorophenol concentration decreased the treatment efficiency. It was observed that basic pHs were favourable in the UV/H2O2 process. The results showed that the photo-Fenton process was the most effective treatment process under acidic conditions. Complete disappearance of 100 mgl(-1) of 4-chlorophenol was achieved in 2.5 min and almost complete mineralization (96%) was also possible after only 45 min of irradiation. The efficiency was negatively affected from H2O2 in the UV/H2O2 process and Fe2+ in the photo-Fenton process over a certain concentration. The highest negative effect was observed with solutions containing PO4 triple ions. Required reaction times for complete disappearance of 100 mgl(-1) 4-chlorophenol increased from 2.5 min for an ion-free solution to 30 min for solutions containing 100 mgl(-1) PO4 triple ion and from 45 min to more than 240 min for complete mineralization. The photodegradation of 4-chlorophenol was found to follow the first-order law. The results of this study showed that UV irradiation alone can degrade 4-CP, although at very slow rates, but cannot mineralize the compound. The addition of hydrogen peroxide to the system, the so-called UV/H2O2 process, significantly enhances the 4-CP degradation rate, but still requires relatively long reaction periods for complete mineralization. The photo-Fenton process, the combination of homogeneous systems of UV/H2O2/Fe2+ compounds, produces the highest photochemical elimination rate of 4-CP and complete mineralization is possible to achieve in quite shorter reaction periods when compared with the UV/H2O2 process. It is more cost effective to use these processes for only purposes such as toxicity reduction, enhancement of biodegradability, decolorization and micropollutant removal. However the most important point is the optimization of the reaction conditions for the process of concern. In such a case, AOPs can be used in combination with a biological treatment systems as a pre- or post treatment unit providing the cheapest treatment option. The AOP applied, for instance, can be used for toxicity reduction and the biological unit for chemical oxygen demand (COD) removal.

Anodic destruction of 4-chlorophenol solution

The electrochemical oxidation of 4-chlorophenol solutions was studied using a dimensional stable anode (DSA), made of pure titanium sheet mesh coated with Ti/TiO 2 and RuO 2 film. An electrochemical cell with one working electrode and two counter-electrodes was designed. A gas collecting system to collect the electrolysis gaseous products was also designed. The influence of current density (6.51–21.58 mA/cm 2), pH (2.0–12.6) and initial 4-chlorophenol concentration (25–100 mg/l) on the destruction was investigated. Complete elimination was successfully achieved within 2 h for most investigated conditions. Highest rates of elimination were achieved at a pH of 12.6. A new approach to calculate the current efficiency (CE) of the cell was proposed. The volumes of the gases produced at the anode and at the cathode were the basis for the new CE calculations. It was observed that the worst CE was approximately 20% and the best CE was approximately 89%. The most efficient pH was at 12.6 and the most efficient current density was at 11.39 mA/cm 2.