A comparative study among different photochemical oxidation processes to enhance the biodegradability of paper mill wastewater

Advanced oxidation processes including UV, UV/H(2)O(2), Fenton reaction (Fe(II)/H(2)O(2)) and photo-Fenton process (Fe(II)/H(2)O(2)/UV) for the treatment of paper mill wastewater will be investigated. A comparison among these techniques is undertaken with respect to the decrease of chemical oxygen demand (COD) and total suspended solids (TSS) and the evolution of chloride ions. Optimum operating conditions for each process under study revealed the effect of the initial amounts of Fe(II) and hydrogen peroxide. Of the tested processes, photo-Fenton process was found to be the fastest one with respect to COD and TSS reduction of the wastewater within 45 min reaction time under low amounts of Fe(II) and hydrogen peroxide of 0.5 and 1.5mg/L, respectively, and amounted to 79.6% and 96.6% COD and TSS removal. The initial biodegradability of the organic matter present in the effluent, estimated as the BOD(5)/COD, was low 0.21. When the effluent was submitted to the different types of AOPs used in this study, the biodegradability increases significantly. Within 45 min of reaction time, the photo-Fenton process appears as the most efficient process in the enhancement of the biodegradability of the organic matter in the effluent and the BOD(5)/COD ratio increased from 0.21 to 0.7.     

Comparison of various advanced oxidation processes for the degradation of 4-chloro-2 nitrophenol

In the present study an attempt is made efficiently to degrade USEPA listed 4-chloro-2-nitrophenol (4C-2-NP), widely available in bulk drug and pesticide wastes using various advanced oxidation processes (AOPs). A comparative assessment using various AOPs (UV, H(2)O(2,) UV/H(2)O(2), Fenton, UV/Fenton and UV/TiO(2)) was attempted after initial optimization studies, viz., varying pH, peroxide concentration, iron concentration, and TiO(2) loading. The degradation of the study compound was estimated using chemical oxygen demand (COD) reduction and compound reduction using spectrophotometric methods and further validated with high performance liquid chromatography (HPLC). The degradation trends followed the order: UV/Fenton > UV/TiO(2) > UV/H(2)O(2) > Fenton > H(2)O(2) > UV(.) It can be inferred from the studies that UV/Fenton was the most effective in partial mineralization of 4C-2-NP. However, lower costs were obtained with H(2)O(2). Kinetic constants were evaluated using first order equations to determine the rate constant K.     

Catalytic oxidation of anionic surfactants by electrochemical oxidation with CuO-Co2O3-PO4(3-) modified kaolin

A new catalytic oxidation of anionic surfactants by electrochemistry method was designed and used to investigate the removal of anionic surfactant from simulated wastewater. Synergetic effect on COD removal was studied when integrating the electrochemical reactor, using porous graphite as anode and cathode, with the effective CuO-Co2O3-PO4(3-) modified kaolin catalyst in a single undivided cell. The result showed that this combined process could effectively remove anionic surfactant. Its COD removal efficiency was much higher than those individual processes and could reach up to 90% in 60 min. The operating parameters such as initial pH, cell voltage, and current intensity were also investigated. Possible theory for COD removal was also proposed to predict the role of modified kaolin, electro-catalysis and oxidation in the combined process. The pollutants in wastewater could be decreased by the high reactive OH* that produced on the surface of catalyst by the decomposition of electrochemical generated H2O2. The result indicates that the catalytic oxidation by electrochemistry method is a promising wastewater treatment technique.     

Advanced oxidation processes applied to tannery wastewater containing Direct Black 38--elimination and degradation kinetics

The application of advanced oxidation processes (H(2)O(2)/UV, TiO(2)/H(2)O(2)/UV and TiO(2)/UV) to treat tannery wastewater was investigated. The experiments were performed in batch and continuous UV reactors, using TiO(2) as a catalyst. The effect of the hydrogen peroxide concentration on the degradation kinetics was evaluated in the concentration range 0-1800 mg L(-1). We observed that the degradation rate increased as the hydrogen peroxide increased, but excessive H(2)O(2) concentration was detrimental because it acted as a hydroxyl radical scavenger since it can compete for the active sites of the TiO(2). In the H(2)O(2)/UV treatment, the COD removal reached around 60% in 4 h of reaction, indicating that the principal pollutants were chemically degraded as demonstrated by the results for BOD, COD, nitrate, ammonium and analysis of the absorbance at 254 nm. Artemia salina toxicity testing performed in parallel showed an increase in toxicity after AOP treatment of the tannery wastewater.     

Purification of storage brines from the preservation of table olives

The chemical oxidation of the wastewaters generated during storage of table olives in NaCl brines, prior to their manufacturing process, was studied. Ozone alone produced COD removals in the range 14-23%, and a higher average removal of 73% of the aromatic compounds. The additional presence of hydrogen peroxide and UV radiation increased these values to 39% for COD and 86% for aromatics. However, UV radiation alone only gave a removal of 9% for COD and 27% for aromatics, and the additional presence of 0.5M H(2)O(2) led to 13% for COD and 38% for aromatics, respectively. The Fenton's reagent oxidation achieved a COD removal of 24% for the higher concentrations of Fe(2+) and H(2)O(2). The most effective process was the combination O(3)/UV/H(2)O(2) with total removals of 65 and 92% for the COD and aromatics, respectively. The aerobic treatment of these effluents gave a 66% removal regardless of the initial biomass concentration used, and a rate constant of 0.19 per day was obtained for the process by using the Contois model. Finally, the aerobic treatment of the wastewaters previously ozonated alone, and ozonated with UV radiation, gave increases in the COD removal and a final rate constant of 0.44 per day. The enhancements were due to the chemical oxidations, these procedures being suitable technologies as pre-treatments to subsequent biological processes for the purification of these residues.     

Use of Fenton oxidation to improve the biodegradability of a pharmaceutical wastewater

The applicability of Fenton's oxidation to improve the biodegradability of a pharmaceutical wastewater to be treated biologically was investigated. The wastewater was originated from a factory producing a variety of pharmaceutical chemicals. Treatability studies were conducted under laboratory conditions with all chemicals (having COD varying from 900 to 7000 mg/L) produced in the factory in order to determine the operational conditions to utilize in the full-scale treatment plant. Optimum pH was determined as 3.5 and 7.0 for the first (oxidation) and second stage (coagulation) of the Fenton process, respectively. For all chemicals, COD removal efficiency was highest when the molar ratio of H(2)O(2)/Fe(2+) was 150-250. At H(2)O(2)/Fe(2+) ratio of 155, 0.3M H(2)O(2) and 0.002 M Fe(2+), provided 45-65% COD removal. The wastewater treatment plant that employs Fenton oxidation followed by aerobic degradation in sequencing batch reactors (SBR), built after these treatability studies provided an overall COD removal efficiency of 98%, and compliance with the discharge limits. The efficiency of the Fenton's oxidation was around 45-50% and the efficiency in the SBR system which has two reactors each having a volume of 8m(3) and operated with a total cycle time of 1 day, was around 98%, regarding the COD removal.     

Ozone and membrane filtration based strategies for the treatment of cork processing wastewaters

The degradation of the pollutant organic matter present in the cork processing wastewater was studied by combining chemical treatments, which used ozone and some Advanced Oxidation Processes, and membrane filtration procedures. Two schemes were conducted: firstly, a single ozonation stage followed by an UF stage; and secondly, a membrane filtration stage, using different MF and UF membranes, followed by a chemical oxidation stage, where ozone, UV radiation, and the AOPs constituted by ozone plus UV radiation and ozone plus hydrogen peroxide, were used. The membrane filtration stages were carried out in tangential filtration laboratory equipment, and the membranes used were two MF membranes with pores sizes of 0.65 and 0.1microm, and three UF membranes with molecular weights cut-off of 300, 10, and 5kDa. The effectiveness of the different stages (conversions in the chemical procedures and rejection coefficients in the membrane processes) were evaluated in terms of several parameters which measure the global pollutant content of the wastewater: COD, absorbance at 254nm, tannins content, color, and ellagic acid. In the ozonation/UF combined process the following removals were achieved: 100% for ellagic acid and color, 90% for absorbance at 254nm, more than 80% for tannins, and 42-57% for COD reduction. In the filtration/chemical oxidation combined process, 100% elimination of ellagic acid, more than 90% elimination in color, absorbance at 254nm and tannins, and removal higher than 80% in COD were reached, which indicates a greater purification power of this combination.     

Photo-assisted Fenton type processes for the degradation of phenol: a kinetic study

In this study the application of advanced oxidation processes (AOPs), dark Fenton and photo-assisted Fenton type processes; Fe(2+)/H(2)O(2), Fe(3+)/H(2)O(2), Fe(0)/H(2)O(2), UV/Fe(2+)/H(2)O(2), UV/Fe(3+)/H(2)O(2) and UV/Fe(0)/H(2)O(2), for degradation of phenol as a model organic pollutant in the wastewater was investigated. A detail kinetic modeling which describes the degradation of phenol was performed. Mathematical models which predict phenol decomposition and formation of primary oxidation by-products: catechol, hydroquinone and benzoquinone, by applied processes were developed. The study also consist the modeling of mineralization kinetic of the phenol solution by applied AOPs. This part, besides well known reactions of Fenton and photo-Fenton chemistry, involves additional reactions which describe removal of iron from catalytic cycle through formation of ferric complexes and its regeneration induced by UV radiation. Phenol decomposition kinetic was monitored by HPLC analysis and total organic carbon content measurements (TOC). Complete phenol removal was obtained by all applied processes. Residual TOC by applied Fenton type processes ranged between 60.2 and 44.7%, while the efficiency of those processes was significantly enhanced in the presence of UV light, where residual TOC ranged between 15.2 and 2.4%.     

Degradation of DMSO by ozone-based advanced oxidation processes

The present study investigates the oxidation of dimethyl sulfoxide (DMSO) by conventional ozonation and the advanced oxidation processes (AOPs). The major degradation products identified were methanesulfinate, methanesulfonate, formaldehyde, and formic acid in ozonation process. The subsequent degradation of intermediates shows that methanesulfonate is more resistance to ozonation, which reduces the mineralization rate of DMSO. The effect of t-butanol addition and ozone gas flow dosage on the degradation rate was evaluated. The rate constant of the reaction of ozone (k(D)) with DMSO was found to be 0.4162 M(-1)S(-1). In the second part of this study, DMSO degradation and TOC mineralization were investigated using O(3)/UV, O(3)/H(2)O(2) and UV/H(2)O(2) processes. In all theses processes the degradation of target organics is more pronounced than TOC removal. The efficiencies of these processes were evaluated and discussed. The formation of sulfate ion in all AOPs have been identified and compared with other processes. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of DMSO in wastewater.     

Effects of reaction conditions on nuclear laundry water treatment in Fenton process

This study presents the efficiency of Fenton process in the degradation of organic compounds of nuclear laundry water. The influence of Fe(2+) and hydrogen peroxide ratio, hydrogen peroxide dose, pH and treatment time were investigated. The degradation of non-ionic surfactant and other organic compounds was analysed as COD, TOC and molecular weight distribution (MWD). The most cost-effective degradation conditions were at H(2)O(2)/Fe(2+) stoichiometric molar ratio of 2 with 5 min mixing and H(2)O(2) dose of 1000 mg l(-1). With the initial pH of 6, the reductions of COD and TOC were 85% and 69%, respectively. However, the removal of the organic compounds was mainly carried out by Fenton-based Fe(3+) coagulation rather than Fenton oxidation. Fenton process proved to be much more efficient than previously performed ozone-based oxidation processes.     

Decomposition of dimethyl phthalate in an aqueous solution by ozonation with high silica zeolites and UV radiation

This study investigates the enhanced ozonation of dimethyl phthalate (DMP), which is a pollutant of concern in water environments, with high silica zeolites and ultraviolet (UV) radiation. Semibatch ozonation experiments are performed under various reaction conditions to examine the effects of inlet gas ozone concentration, high silica zeolite dosage, and UV radiation intensity on the decomposition of DMP. The complete removal of DMP can be efficiently achieved via both O(3) and O(3)/UV treatments. Note that the presence of high silica zeolites accelerates the decomposition rate of DMP in the O(3) process. On the other hand, the removal efficiencies of both chemical oxygen demand (COD) and total organic carbons (TOC) are significantly enhanced by employing the ozonation combined with UV radiation. The O(3)/UV process is also advantageous for the utilization efficiency of fed ozone especially in the late ozonation period. Furthermore, the correlation between the COD removal percentage (%) and the mole ratio of ozone consumed to the DMP treated (mol mol(-1)) is obtained. The clear-cut removal relationship of the TOC with COD during the ozonation of DMP has also been presented. Consequently, the results evaluate the flexibility of ozonation system associated with high silica zeolites and UV radiation for the removal of DMP and provide the useful information in engineering application.     

The decolorization and mineralization of acid orange 6 azo dye in aqueous solution by advanced oxidation processes: a comparative study

The comparison of different advanced oxidation processes (AOPs), i.e. ultraviolet (UV)/TiO(2), O(3), O(3)/UV, O(3)/UV/TiO(2), Fenton and electrocoagulation (EC), is of interest to determine the best removal performance for the destruction of the target compound in an Acid Orange 6 (AO6) solution, exploring the most efficient experimental conditions as well; on the other hand, the results may provide baseline information of the combination of different AOPs in treating industrial wastewater. The following conclusions can be drawn: (1) in the effects of individual and combined ozonation and photocatalytic UV irradiation, both O(3)/UV and O(3)/UV/TiO(2) processes exhibit remarkable TOC removal capability that can achieve a 65% removal efficiency at pH 7 and O(3) dose=45mg/L; (2) the optimum pH and ratio of [H(2)O(2)]/[Fe(2+)] found for the Fenton process, are pH 4 and [H(2)O(2)]/[Fe(2+)]=6.58. The optimum [H(2)O(2)] and [Fe(2+)] under the same HF value are 58.82 and 8.93mM, respectively; (3) the optimum applied voltage found in the EC experiment is 80V, and the initial pH will affect the AO6 and TOC removal rates in that acidic conditions may be favorable for a higher removal rate; (4) the AO6 decolorization rate ranking was obtained in the order of O(3)相似文献   

An integrated technique using zero-valent iron and UV/H2O2 sequential process for complete decolorization and mineralization of C.I. Acid Black 24 wastewater

The zero-valent iron (ZVI) reduction succeeds for decolorization, while UV/H(2)O(2) oxidation process results into mineralization, so that this study proposed an integrated technique by reduction coupling with oxidation process in order to acquire simultaneously complete both decolorization and mineralization of C.I. Acid Black 24. From the experimental data, the zero-valent iron addition alone can decolorize the dye wastewater yet it demanded longer time than ZVI coupled with UV/H(2)O(2) processes (Red-Ox). Moreover, it resulted into only about 30% removal of the total organic carbon (TOC), which was capable to be effectively mineralized by UV/H(2)O(2) process. The proposed sequential ZVI-UV/H(2)O(2) integration system cannot only effectively remove color and TOC in AB 24 wastewater simultaneously but also save irradiation power and time demand. Furthermore, the decolorization rate constants were about 3.77-4.0 times magnitude comparing with that by UV/H(2)O(2) process alone.     

Pretreatment of wastewater from triazine manufacturing by coagulation, electrolysis, and internal microelectrolysis

We studied the pretreatment of concentrated wastewater from triazine manufacturing by coagulation, electrolysis, and internal microelectrolysis. Results show that coagulation by polyaluminum chloride at dosage of 0.5 g/L could remove up to 17.2% chemical oxygen demand (COD) from the wastewater. Electrolysis using iron electrode achieved 33.2% COD removal at current of 2A in 180 min, which was attributed to coagulation and oxidation of the organic contaminants in the wastewater by the radicals (OH and O) and oxidants (O2, O3, and H2O2) produced in electrochemical reactions. Internal microelectrolysis using iron chips and granular activated carbon (GAC) showed that up to 60.5% COD could be removed under the conditions of iron/GAC/wastewater volumetric ratio of 3:2:490, sparge ratio (ratio of air flow rate to volume of wastewater) of 2:490 min(-1), and reaction time of 132 h. COD reduction in internal microelectrolysis was attributed to a combination of chemical and physical processes, mainly oxidation by radicals and oxidants formed in electrochemical reactions, adsorption on, co-precipitation with, and enmeshment in ferrous and ferric hydroxides resulted from Fe2+ released during anode oxidation. The results suggest that internal microelectrolysis using iron chips and GAC is a promising, low-cost alternative for pretreating concentrated wastewater from pesticide manufacturing.     

Granular activated carbon promoted ozonation of a food-processing secondary effluent

This paper reports on the application of a simultaneous combination of ozone and a granular activated carbon (O(3)/GAC) as a tertiary treatment of a wastewater generated from the activity of various food-processing industries. Prior to the O(3)/GAC treatment, the wastewater was subjected to conventional primary and secondary treatments in a full-scale wastewater treatment plant (WWTP). The effluent from the WWTP presented high organic load (COD>500 mg/l and TOC>150 mg/l), which could be much reduced by the O(3)/GAC treatment. Results from the O(3)/GAC experiments were compared with those obtained in single ozonation, single adsorption onto GAC and sequential O(3)-GAC adsorption experiments. While single processes and the sequential one showed limited capacity to remove organic matter for the food-processing effluent (COD removal <40%), the simultaneous O(3)/GAC process led to decreases of COD up to 82% at the conditions here applied. The combined process also improved the ozone consumption, which decreased from about 19 g O(3)/g TOC (single ozonation process) to 8.2-10.7 g O(3)/g TOC (O(3)/GAC process). The reusability of the GAC throughout a series of consecutive O(3)/GAC experiments was studied with no apparent loss of activity for a neutral GAC (PZC = 6.7) but for a basic GAC (PZC = 9.1).     

Treatment of pesticide wastewater by moving-bed biofilm reactor combined with Fenton-coagulation pretreatment

In order to treat pesticide wastewater having high chemical oxygen demand (COD) value and poor biodegradability, Fenton-coagulation process was first used to reduce COD and improve biodegradability and then was followed by biological treatment. Optimal experimental conditions for the Fenton process were determined to be Fe(2+) concentration of 40 mmol/L and H(2)O(2) dose of 97 mmol/L at initial pH 3. The interaction mechanism of organophosphorous pesticide and hydroxyl radicals was suggested to be the breakage of the P=S double bond and formation of sulfate ions and various organic intermediates, followed by formation of phosphate and consequent oxidation of intermediates. For the subsequent biological treatment, 3.2g/L Ca(OH)(2) was added to adjust the pH and further coagulate the pollutants. The COD value could be evidently decreased from 33,700 to 9300 mg/L and the ratio of biological oxygen demand (BOD(5)) to COD of the wastewater was enhanced to over 0.47 by Fenton oxidation and coagulation. The pre-treated wastewater was then subjected to biological oxidation by using moving-bed biofilm reactor (MBBR) inside which tube chip type bio-carriers were fluidized upon air bubbling. Higher than 85% of COD removal efficiency could be achieved when the bio-carrier volume fraction was kept more than 20% by feeding the pretreated wastewater containing 3000 mg/L of inlet COD at one day of hydraulic retention time (HRT), but a noticeable decrease in the COD removal efficiency when the carrier volume was decreased down to 10%, only 72% was observed. With the improvement of biodegradability by using Fenton pretreatment, also due to the high concentration of biomass and high biofilm activity using the fluidizing bio-carriers, high removal efficiency and stable operation could be achieved in the biological process even at a high COD loading of 37.5 gCOD/(m(2)carrierday).     

Studies on degradation of Methyl Orange wastewater by combined electrochemical process

The combined process of electro-catalytic oxidation and de-colorization of wastewater contained Methyl Orange (MO) in a double-anode system, with iron plate and graphite plate as anodes and graphite plate as cathode assisted by Co2O3-CuO-PO4(3-) modified kaolin, was investigated systematically. The effects of pH, current density and electrolyte on de-colorization efficiency were also studied. Chemical oxygen demand (COD) was selected as another parameter to evaluate the efficiency of this combined degradation method on treatment of MO wastewater and the results revealed that when initial pH was 5.0, current density was 30 mA cm(-2), NaCl as electrolyte and its concentration was 2.5 g dm(-3), the color removal efficiency and COD removal can reach 100% and 89.7%, respectively. Meanwhile, the kinetics and the possible mechanism were also discussed.     

Catalysis of advanced oxidation reactions by ultrasound: a case study with phenol

The present study is about the enhancement in ozone-mediated degradation and UV (254nm) photolysis of phenol in aqueous solutions by 300kHz acustic cavitation and the selection of operating parameters for optimum phenol removal efficiency. The method was based on monitoring of the concentration of phenol during 90min exposure to ozonation, sonication, UV photolysis, O(3)/ultrasound, UV/ultrasound and O(3)/UV/ultrasound operations. It was found that ozonation at alkaline pH was an effective method of phenol destruction, but it was considerably more effective when applied simultaneously with ultrasonic irradiation. The observed synergy particularly at alkaline pH was attributed to combined effects of: (i) increased ozone mass transfer (upon hydrodynamic shear forces created by ultrasonic bubbles) and (ii) excess hydroxyl radical formation (upon thermal decomposition of ozone in the gaseous cavity bubbles). Degradation of phenol by photolysis alone was negligible, while combination of UV-irradiation and ultrasound rendered considerable degrees of decay. The synergy here was explained by excess hydroxyl radicals that are formed by photolysis of ultrasound-generated H(2)O(2). Maximum rate of phenol degradation was observed in case of combined application of ozone, UV and ultrasound at basic pH.     

Electrochemical treatment of anionic surfactants in synthetic wastewater with three-dimensional electrodes

The electrochemical oxidation of anionic surfactants (sodium dodecyl benzene sulfonate, DBS) contained in simulated wastewater treated by three-dimensional electrode system with combined modified kaolin served as packed bed particle electrodes and Ti/Co/SnO(2)-Sb(2)O(3) anode was studied, the chemical oxygen demand (COD) removal of pollutants in the solutions was also investigated. The results showed that the three-dimensional electrodes in combined process could effectively decompose anionic surfactants. The COD removal efficiency can reach 86%, much higher than that of Ti/Co/SnO(2)-Sb(2)O(3) electrodes used singly or modified kaolin employed singly (graphite as anode and cathode) on the same condition of pH 3 and 38.1 mA/cm(2) current density. The current efficiency and kinetic constant were calculated and energy consumption was studied. At the same time the influence of pH and current density on COD removal efficiency with combined three-dimensional electrodes was also investigated, respectively. The optimal initial pH value of degradation is 3 (acid condition), and a minor COD removal increase follows higher current density.     

Decontamination of soil washing wastewater using solar driven advanced oxidation processes

Decontamination of soil washing wastewater was performed using two different solar driven advanced oxidation processes (AOPs): the photo-Fenton reaction and the cobalt/peroxymonosulfate/ultraviolet (Co/PMS/UV) process. Complete sodium dodecyl sulphate (SDS), the surfactant agent used to enhance soil washing process, degradation was achieved when the Co/PMS/UV process was used. In the case of photo-Fenton reaction, almost complete SDS degradation was achieved after the use of almost four times the actual energy amount required by the Co/PMS/UV process. Initial reaction rate in the first 15 min (IR₁₅) was determined for each process in order to compare them. Highest IR₁₅ value was determined for the Co/PMS/UV process (0.011 mmol/min) followed by the photo-Fenton reaction (0.0072 mmol/min) and the dark Co/PMS and Fenton processes (IR₁₅ = 0.002 mmol/min in both cases). Organic matter depletion in the wastewater, as the sum of surfactant and total petroleum hydrocarbons present (measured as chemical oxygen demand, COD), was also determined for both solar driven processes. It was found that, for the case of COD, the highest removal (69%) was achieved when photo-Fenton reaction was used whereas Co/PMS/UV process yielded a slightly lower removal (51%). In both cases, organic matter removal achieved was over 50%, which can be consider proper for the coupling of the tested AOPs with conventional wastewater treatment processes such as biodegradation.