Photochemical degradation and mineralization of 4-chlorophenol

INTENTION, GOAL, SCOPE, BACKGROUND: 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. OBJECTIVE: 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. METHODS: 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. RESULTS AND DISCUSSION: 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. CONCLUSION: 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. RECOMMENDATIONS AND OUTLOOK: 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.     

臭氧洗消化学战剂模拟剂DPCP试验研究

用臭氧对神经性化学战剂的模拟剂氯磷酸二苯酯（DPCP）进行洗消,试验考察了初始酸度、O₂流量、放电功率、放电室压力、反应温度、初始浓度和O₃流量等因素对DPCP降解率的影响。碱性条件下DPCP降解率高于酸性条件下的降解率;反应温度、O₃流量、放电功率的增加,DPCP降解率上升;初始浓度增加,DPCP降解率下降;氧气流量和放电室压力增加,DPCP降解率先上升,后下降。在最佳反应条件下,50 mg/L的DPCP处理16 min降解率达到98%,矿化率40.1%。     

Catalytic decomposition of hydrogen peroxide and 4-chlorophenol in the presence of modified activated carbons

The objective of this research was to examine the heterogeneous catalytic decomposition of H(2)O(2) and 4-chlorophenol (4-CP) in the presence of activated carbons modified with chemical pretreatments. The decomposition of H(2)O(2) was suppressed significantly by the change of surface properties including the decreased pH(pzc) modified with oxidizing agent and the reduced active sites occupied by the adsorption of 4-CP. The apparent reaction rate of H(2)O(2) decomposition was dominated by the intrinsic reaction rates on the surface of activated carbon rather than the mass transfer rate of H(2)O(2) to the solid surface. By the detection of chloride ion in suspension, the reduction of 4-CP was not only attributed to the advanced adsorption but also the degradation of 4-CP. The catalytic activity toward 4-CP for the activated carbon followed the inverse sequence of the activity toward H(2)O(2), suggesting that acidic surface functional group could retard the H(2)O(2) loss and reduce the effect of surface scavenging resulting in the increase of the 4-CP degradation efficiency. Few effective radicals were expected to react with 4-CP for the strong effect of surface scavenging, which could explain why the degradation rate of 4-CP observed in this study was so slow and the dechlorination efficiency was independent of the 4-CP concentration in aqueous phase. Results show that the combination of H(2)O(2) and granular activated carbon (GAC) did increase the total removal of 4-CP than that by single GAC adsorption.     

吸附-电化学氧化耦合处理对氯苯酚废水及动力学

以毡状活性炭纤维为阳极,不锈钢为阴极,吸附-电化学氧化耦合降解对氯苯酚废水进行了研究。考察了吸附或耦合电化学氧化过程、电流密度、支持电解质硫酸钠浓度和活性炭纤维重复使用对废水COD去除率的影响,结果表明,采用吸附-电化学氧化耦合方法,当电流密度7.6 mA/cm2支持电解质（硫酸钠）浓度为1 g/L,处理时间为180 min,4-CP废水COD去除率可达97.09%。毡状活性炭纤维对4-CP的静态吸附过程符合Langmiu吸附等温方程。建立了吸附-电化学氧化COD去除动力学模型,动力学模型参数表明,对于COD的去除,电化学氧化作用比吸附作用大。     

Photoelectrocatalytic degradation of 4-chlorophenol and oxalic acid on titanium dioxide electrodes

Photocatalytically active thin TiO(2) films were produced by spin-coating or dip-coating an alkoxy precursor onto a transparent conducting electrode substrate and by thermal oxidation of titanium metal. The thin films were used to study the photoelectrocatalytic or photoelectrochemical degradation of oxalic acid and 4-chlorophenol (4-CP) under near UV (monochromatic, 365 nm) light irradiation. Degradation was monitored by a variety of methods. In the course of oxalic acid degradation, CO(2) formation accounted for up to 100% of the total organic carbon degradation for medium starting concentrations; for the degradation of 4-CP, less CO(2) was detected due to the higher number of oxidation steps, i.e. intermediates. Incident-photon-to-current conversion efficiency, educt degradation and product formation as well as Faradaic efficiencies were calculated for the degradation experiments. Quantum yields and Faradaic efficiencies were found to be strongly dependent on concentration, with maximum values (quantum yield) around 1 for the highest concentrations of oxalic acid.     

2-Chlorophenol induced hydroxyl radical production in mitochondria in Carassius auratus and oxidative stress--an electron paramagnetic resonance study

In our previous study, electron paramagnetic resonance (EPR) evidence of reactive oxygen species (ROS) production in Carassius auratus following 2-chlorophenol (2-CP) administration was provided. To further investigate the potential pathway of ROS production, liver mitochondria of C. auratus was isolated and incubated with 2-CP for 30 min. An EPR analysis indicated ROS was produced, and intensities of ROS increased with increasing concentrations of 2-CP. The ROS was then assigned OH by comparing with Fenton reaction. Either catalase or superoxide dismutase, extinguished OH completely in the mitochondria mixture. These facts suggested that O2(.-) and H2O2 contributed to the formation of OH in mitochondria in C. auratus stressed by 2-CP. Combining previous references and our own data, it is reasonable to suggest that 2-CP is first oxidized by H2O2 present in vivo to form phenoxyl radical under the catalytic action of cellular peroxidase (1); phenoxyl radical oxidizes mitochondria NADH to NAD in the presence of NADH (2); NAD reacts with oxygen in vivo to produce O2(.-) (3); O2(.-) is spontaneously dismutated by SOD to form H2O2 and O2, which creates a renewable supply of H2O2 as the initiators of the chain reactions until NADH is consumed (4); simultaneously with reaction (4), O2(.-) reacts with H2O2 to form OH radical via the Haber-Weiss reaction (5). A strong negative correlation (r=-0.9278, p<0.01) between glutathione (GSH) pool and OH production was observed after fish were i.p. injected with 2-CP (250 mg kg(-1)), indicating the depletion of GSH caused by OH.     

六氯苯的O3及UV/O3高级氧化降解试验研究

采用O₃、UV/O₃高级氧化法对水中六氯苯（HCB）的降解效果及机理进行了研究，并对结果进行了比较，结果表明，UV本身对HCB的去除率贡献不大，HCB可被O₃、UV/O₃快速降解，即UV＜O₃＜UV/O₃；O₃、UV/O₃作用时，提高体系的初始pH值不利于HCB的降解，在pH＝3，HCB=0.2 mg/L，反应40 min时，HCB的去除可达50%左右，酸性条件下有利于降解反应的进行；无论是O₃单独作用还是UV/O₃联合作用，HCB的降解基本上满足准一级反应动力学规律，如果体系的pH值基本保持恒定，这种规律就更为明显。根据离子色谱(IC)、GC对六氯苯降解中间产物进行了测定，探讨了O₃、UV/O₃降解六氯苯的途径和机理。     

Reductive transformation of 2,4-dichlorophenoxyacetic acid by nanoscale and microscale Fe3O4 particles

Reductive transformation of 2,4-dichlorophenoxyacetic acid (2,4-D) by nanoscale and microscale Fe₃O₄ was investigated and compared. Disappearance of the parent species and formation of reaction intermediates and products were kinetically analyzed. Results suggest that the transformation of 2,4-D followed a primary pathway of its complete reduction to phenol and a secondary pathway of sequential reductive hydrogenolysis to 2,4-dichlorophenol (2,4-DCP), chlorophenol (2-CP, 4-CP) and phenol. About 65% of 2,4-D with initial concentration of 50 μ M was transformed within 48 h in the presence of 300 mg L^?1 nanoscale Fe₃O₄, and the reaction rates increased with increasing dosage of nanoscale Fe₃O₄. The decomposition of 2,4-D proceeded rapidly at optimum pH 3.0. Chloride was identified as a reduction product for 2,4-D in the magnetite–water system. Reductive transformation of 2,4-D by microscale Fe₃O₄ was slower than that by nanoscale Fe₃O₄. The reactions apparently followed pseudo-first-order kinetics with respect to the 2,4-D transformation. The degradation rate of 2,4-D decreased with the increase of initial 2,4-D concentration. In addition, anions had a significant adverse impact on the degradation efficiency of 2,4-D.     

Degradation of chlorophenols in aqueous media using UV XeBr excilamp in a flow-through reactor

2-Chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) at initial concentrations of 10, 20, 50 and 100mg l(-1) were degraded in aqueous media by direct UV photolysis using dielectric barrier discharge XeBr( *) excilamp (283nm) in a flow-through photoreactor. The pseudo-first order rate constants were highest and half-life times were lowest for 4-CP. The rates of photolysis under the experimental conditions increased in the order: 2-CP<2,4-DCP<4-CP. The intermediates of photolysis were identified by GC-MS and HPLC. The evolution of hydroquinone and p-benzoquinone as major intermediates of 4-CP photolysis was monitored.     

Degradation of 2-chlorophenol via a hydrogenotrophic biofilm under different reductive conditions

This research studies the 2-chlorophenol (2-CP) degradation by the hydrogenotrophic biofilm cultivated in three silicone-tube membrane bioreactors under the conditions of denitrification (DN), sulfate-reduction (DS) and dechlorination (DC). Experimental results showed that after acclimation for more than four months with 2-CP, the respective 2-CP removal efficiency was 95% in DN, 94% in DS and 95% in DC reactors, under the condition of influent 2-CP 25 mg/l with hydraulic retention time (HRT) of 15 h. The metabolic pathway of 2-CP was different in different reactors. The 2-CP was thought to be utilized as carbon and energy source in DN and DS reactors, while the dechlorination occurred in the DC reactor in lack of nitrate and sulfate. The pH dramatically affected the 2-CP degradation in all reactors. Experimental results showed that the optimal pH range was around 6+/-0.2 in DN, 7+/-0.2 in DS, and 5.8-7.2 in DC reactors. Both nitrate and sulfate inhibited the 2-CP dechlorination, but the inhibition levels were different. Nitrate completely inhibited the dechlorination at once, while sulfate took a longer time to reach complete inhibition, only after the bacteria were adapted to the sulfate-reducing condition. Both inhibitions were accomplished by taking the place of 2-CP as electron acceptors. H2 served as an electron donor for dechlorination of 2-CP. The dechlorination was apparently stopped when lacking H2 and another pathway was responsible for the 2-CP degradation.     

Degradation of diuron in aqueous solution by ozonation

Degradation of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in aqueous solution and the proposed degradation mechanism of diuron by ozonation were investigated. The factors that affect the degradation efficiency of diuron were examined. The generated inorganic ions and organic acids during the ozonation process were detected. Total organic carbon removal rate and the amount of the released Cl(-) increased with increasing ozonation time, but only 80.0% of the maximum theoretical concentration of Cl(-) at total mineralization was detected when initial diuron concentration was 13.8 mg L(-1). For N species, the final concentrations of NO3(-) and NH4+ after 60 min of reaction time were 0.28 and 0.19 mg L(-1), respectively. The generated acetic acid, formic acid and oxalic acid were detected during the reaction process. The main degradation pathway of diuron by ozonation involved a series of dechlorination-hydroxylation, dealkylation and oxidative opening of the aromatic ring processes, leading to small organic species and inorganic species. The degradation efficiency of diuron increased with decreasing initial diuron concentration. Higher pH value, more ozone dosage, additive Na2CO3, additive NaHCO3 and additive H2O2 were all advantageous to improve the degradation efficiency of diuron.     

Synergistic effects of liquid and gas phase discharges using pulsed high voltage for dyes degradation in the presence of oxygen

The technology of combined liquid and gas phase discharges (LGD) using pulsed high voltage for dyes degradation was developed in this study. Apparent synergistic effects for Acid orange II (AO) degradation in the presence of oxygen were observed. The enhancement of AO degradation rate was around 302%. Furthermore, higher energy efficiency was obtained comparing with individual liquid phase discharge (LD) or gas phase discharge process (GD). The AO degradation in the presence of oxygen by LGD proceeded through the direct ozone oxidation and the ozone decomposition induced by LD. Important operating parameters such as electrode distance, applied voltage, pulse repetition rate, and types of dyes were further investigated.     

Ozonation of Cationic Red X-GRL in aqueous solution: degradation and mechanism

Ozonation of the azo dye Cationic Red X-GRL was investigated in a bubble column reactor at varying operating parameters such as oxygen flow rate, temperature, initial Cationic Red X-GRL concentration, and pH. The conversion of dye increased with the increasing of pH and oxygen flow rate. As the reaction rate constant and the volumetric mass transfer coefficient increase while the ozone equilibrium concentration decreases with the temperature, there is a minimum conversion of dye at 25 degrees C. The increasing of initial dye concentration leads to a decreasing conversion of dye while the ozonation rate increases. The formation of intermediates and the variation of pH, TOC, and nitrate ion during ozonation were investigated by the use of some analytical instruments such as GC/MS, GC, and IC. The intermediates of weak organic acids lower the pH value of the solution. The probable degradation mechanism of the Cationic Red X-GRL in aqueous solution was deliberated with the aid of Molecular Orbital calculations. The N(12)-C(13) site in Cationic Red X-GRL, instead of the N(6)-N(7) site, is found to be the principal site for ozone cycloaddition in the degradation processes. During the degradation process, among the six nitrogen atoms of Cationic Red X-GRL, one is transferred into a nitrate ion, one is converted into an amine compound, and the remaining four are transformed into two molecules of nitrogen.     

Application of response surface methodology to the removal of the antibiotic tetracycline by electrochemical process using carbon-felt cathode and DSA (Ti/RuO2-IrO2) anode

The removal of antibiotic tetracycline (TC) from water by electrochemical advanced oxidation process (EAOP) was performed using a carbon-felt cathode and a DSA (Ti/RuO(2)-IrO(2)) anode. The influence of applied current, initial pH and initial TC concentration on TC removal efficiency was investigated. Response surface methodology (RSM) based on Box-Behnken statistical experiment design (BBD) was applied to analyze the experimental variables. The positive and negative effects of variables and the interaction between variables on TC removal efficiency were determined. The applied current showed positive effect, while the initial pH value and initial tetracycline concentration gave negative effect on TC removal. The interaction between applied current and initial pH value was significant, while the interactions of initial TC concentration with applied current or initial pH were not pronounced. The results of adequacy check confirmed that the proposed models were accurate and reliable to analyze the variables of EAOP. The reaction intermediates were identified by high-performance liquid chromatography-mass spectrometry (LC-MS) technique and a plausible degradation pathway for tetracycline degradation was proposed. The acute toxicity experiments illustrated that the Daphnia magna immobilization rate reached the maximum after 240 min of electrolysis and then decreased with the progress of the reaction.     

Pesticide by-products in the Rhône delta (Southern France). The case of 4-chloro-2-methylphenol and of its nitroderivative

A field monitoring campaign for pesticides and their transformation intermediates was carried out in the Rh?ne delta (Southern France). It was evidenced the following transformation sequence: MCPA-->4-chloro-2-methylphenol (CMP)-->4-chloro-2-methyl-6-nitrophenol (CMNP). Interestingly CMP disappeared about as quickly as MCPA, while CMNP was environmentally more persistent than the parent molecules. This is very relevant to the environmental risk associated with the occurrence of these compounds, because the nitration of chlorophenols reduces their acute toxicity but the nitroderivatives could have more marked long-term effects, associated with their genotoxicity. Irradiation experiments suggested that the photonitration of CMP into CMNP involves nitrogen dioxide, generated from the photolysis of nitrate and from the photooxidation of nitrite by ()OH. The photochemistry of Fe(III) species could also play a significant role, but its contribution is still difficult to be quantified. Another important intermediate of CMP transformation is methylnitrophenol (MNP), produced via a dechlorination/nitration pathway, with ortho-cresol as the most likely reaction intermediate.     

Degradation of 3,4-dichloro- and 3,4-difluoroaniline by Pseudomonas fluorescens 26-K

3,4-Dichloro- and 3,4-difluoroanilines were degraded by Pseudomonas fluorescens 26-K under aerobic conditions. In the presence of glucose strain degraded 170 mg/L of 3,4-dichloroaniline (3,4-DCA) during 2-3 days. Increasing of toxicant concentration up to 250 mg/L led to degradation of 3,4-DCA during 4 days and its intermediates during 5-7 days. Without cosubstrate and nitrogen source degradation of 3,4-DCA took place too, but more slowly--about 40% of toxicant at initial concentration 75 mg/L was degraded during 15 days. 3,4-Difluoroaniline (3,4-DFA) (initial concentration 170 mg/L) was degraded by Pseudomonas fluorescens 26-K during 5-7 days. The strain was able to completely degrade up to 90 mg/L of 3,4-DFA, without addition of cosubstrate and nitrogen during 15 days. Degradation of fluorinated aniline was accompanied by intensive defluorination. Activity of catechol 2,3-dioxygenase (C2,3DO) (0.230 micromol/min/mg of protein) was found in the culture liquid of the strain, grown with 3,4-DCA and glucose. This fact, as well as, the presence of 3-chloro-4-hydroxyaniline as a metabolite suggested that 3,4-DCA degradation pathway includes dehalogenation and hydroxylation of aromatic ring followed by its subsequent cleaving by C2,3DO. On the contrary, activity of catechol 1,2-dioxygenase (C1,2DO) (0.08 micromol/min/mg of protein) was found in the cell-free extract of biomass grown on 3,4-DFA. 3-Fluoro-4-hydroxyaniline as intermediate was found in this cell-free extract.     

Method of removal of volatile organic compounds by using wet scrubber coupled with photo-Fenton reaction - Preventing emission of by-products

The photo-Fenton reaction was applied as a novel method for the removal of volatile organic compounds (VOCs) in the gas phase, and its effectiveness was experimentally examined. In conventional VOCs removal methods using a photocatalyst or ozone, VOCs are oxidized in the gas phase. Therefore, incompletely oxidized intermediates, which may have adverse effects on health, are likely to contaminate the treated air. On the other hand, in the VOCs removal method developed in this study, because the VOCs are oxidized in the liquid phase by the photo-Fenton reaction, any incompletely oxidized intermediates produced are confined to the liquid phase. As a result, the contamination of the treated air by these harmful intermediates can be prevented. Using a semi-batch process, it was found that the removal efficiency for toluene in a one-pass test (residence time of 17 s) was 61%, for an inlet toluene gas concentration of 930 ppbv, an initial iron ion concentration of 20 mg L⁻¹, and an initial hydrogen peroxide concentration of 630 mg L⁻¹. The removal efficiency was almost constant as long as H₂O₂ was present in the solution. Proton transfer reaction mass spectrometry analysis confirmed the absence of any incompletely oxidized intermediates in the treated air.     

Mineralization of C.I. Reactive Yellow 84 in aqueous solution by sonolytic ozonation

The operational parameters and mechanism of mineralization of C.I. Reactive Yellow 84 (RY84), one of the azo dyes, in aqueous solution were investigated using sonolytic ozonation (US/O(3) oxidation). Of the pseudo-first-order degradation rate constants of TOC reduction, 9.0 x 10(-4), 7.3 x 10(-3) and 1.8 x 10(-2)min(-1) were observed with US, O3, and a combination of US and O3, respectively. These results illustrate that ozonation combined with sonolysis for removal of TOC is more efficient than ozonation alone or ultrasonic irradiation alone without considering the operating costs. With the initial pH value at 10.0, the ozone dose at 4.5 g h(-1), the energy density of ultrasound at 176 W l(-1), and the initial concentration of RY84 at 100 mg l(-1), the extent of mineralization measured as TOC loss was maximized. The variation of the concentrations of related ions (oxalate, formate, acetate, NO3(-), NO2(-), NH4(+), Cl(-), and SO4(2-)) during the reaction process was monitored. Other organic intermediates detected by GC/MS were N-methyleneaniline, phthalic acid, 4-hydroxyphthalic acid, isocyanatobenzene, aniline, 4-iminocyclohexa-2,5-dien-1-one, butene diacid and urea. Based on these findings, a tentative degradation pathway was proposed.     

Kinetics and mechanism of TNT degradation in TiO2 photocatalysis

The photocatalytic degradation of TNT in a circular photocatalytic reactor, using a UV lamp as a light source and TiO(2) as a photocatalyst, was investigated. The effects of various parameters such as the initial TNT concentration, and the initial pH on the TNT degradation rate of TiO(2) photocatalysis were examined. In the presence of both UV light illumination and TiO(2) catalyst, TNT was more effectively degraded than with either UV or TiO(2) alone. The reaction rate was found to obey pseudo first-order kinetics represented by the Langmuir-Hinshelwood model. In the mineralization study, TNT (30 mg/l) photocatalytic degradation resulted in an approximately 80% TOC decrease after 150 min, and 10% of acetate and 57% of formate were produced as the organic intermediates, and were further degraded. NO(-)(3) NO(-)(2), and NH(+)(4) were detected as the nitrogen byproducts from photocatalysis and photolysis, and more than 50% of the total nitrogen was converted mainly to NO(-)(3)in the photocatalysis. However, NO(-)(3) did not adsorbed on the TiO(2) surface. TNT showed higher photocatalytic degradation efficiency at neutral and basic pH.     

Characteristics of electrolysis, ozonation, and their combination process on treatment of municipal wastewater.

The characteristics of municipal wastewater treatment by electrolysis, ozonation, and combination processes of electrolysis and aeration using three gaseous species (nitrogen [N2], oxygen [O2], and ozone [O3]) were discussed in this research using ruthenium oxide (RuO2)-coated titanium anodes and stainless-steel (SUS304) cathodes. Electrolysis and electrolysis with nitrogen aeration were characterized by a rapid decrease in 5-day biochemical oxygen demand (BODs) and total nitrogen and a slow decrease in chemical oxygen demand (COD). In contrast, ozonation, electrolysis with oxygen aeration, and electrolysis with ozone aeration were characterized by transformation of persistent organic matter to biodegradable matter and preservation of total nitrogen. The best energy efficiency in removing BOD5 and total nitrogen was demonstrated by electrolysis, as a result of direct anodic oxidation and indirect oxidation with free chlorine produced from the chloride ion (Cl-) at the anodes. However, electrolysis with ozone aeration was found to be superior to the other processes, in terms of its energy efficiency in removing COD and its ability to remove COD completely, as a result of hydroxyl radical (*OH) production via cathodic reduction of ozone.