Oxidation of enrofloxacin with conductive-diamond electrochemical oxidation, ozonation and Fenton oxidation. A comparison

The treatment of enrofloxacin synthetic wastewaters using conductive-diamond electrochemical oxidation (CDEO), ozonation and Fenton oxidation has been studied. Results show that the three technologies can reduce the organic content of enrofloxacin synthetic wastewaters but with different performances. CDEO was the most efficient technology in terms of mineralization but not on COD removal, which was more efficiently achieved by ozonation. This indicates that ozonation is efficient in the breakage of the complex molecules but not on the removal of final carboxylic acids. The high initial efficiency in terms of oxidant-use obtained by Fenton oxidation evidences that it is very efficient in the removal of the enrofloxacin, although it rapidly leads to the formation of refractory compounds to the treatment. This indicates the significance of other oxidation mechanisms (e.g. coagulation) that enhance the results obtained by the expected hydroxyl-mediated oxidation. Ammonium ions were the primary product species in CDEO and nitrate ions in ozonation, whereas Fenton effluents contained similar amounts of both nitrogen ionic species.     

Treatment of landfill leachate using Fenton process and coagulation/flocculation

Coagulation/flocculation process, Fenton oxidation and combinations between them were studied, aiming to provide an efficient method for the treatment of partially stabilized leachates. Leachates were collected from a municipal landfill site, samples containing around 3800 mg/L COD, BOD₅/COD ratio about 0.11 and pH around 8. The sequence of stages implemented was: (a) coagulation/flocculation; (b) Fenton oxidation; (c) coagulation/flocculation followed by Fenton oxidation which resulted in a best COD removal (63.62%) and (d) Fenton oxidation followed by coagulation/flocculation.     

Optimizing the treatment of landfill leachate by conventional Fenton and photo-Fenton processes

Landfill, a matured and economically appealing technology, is the ultimate approach for the management of municipal solid wastes. However, the inevitable generation of leachate from landfill requires further treatment. Among the various leachate treatment technologies available, advanced oxidation processes (AOPs) are among powerful methods to deal with the refractory organic constituents, and the Fenton reagent has evolved as one promising AOPs for the treatment of leachates. Particularly, the combination of UV-radiation with Fenton's reagent has been reported to be a method that allows both the photo-regeneration of Fe²⁺ and photo-decarboxylation of ferric carboxylates. In this study, Fenton and photo-Fenton processes were fine tuned for the treatment of leachates from the Colmenar Viejo (Madrid, Spain) Landfill. Results showed that it is possible to define a set of conditions under which the same COD and TOC removals (≈ 70%) could be achieved with both the conventional and photo-Fenton processes. But Fenton process generated an important quantity of iron sludge, which will require further disposal, when performed under optimal COD removal conditions. Furthermore conventional Fenton process was able to achieve slightly over an 80% COD removal from a “young” leachate, while for “old” and ”mixed” leachates was close to a 70%. The main advantage showed by the photo-assisted Fenton treatment of landfill leachate was that it consumed 32 times less iron and produced 25 times less sludge volume yielding the same COD removal results than a conventional Fenton treatment.     

Optimization of the landfill leachate treatment by the Fenton process

The Fenton process was used with the objective of improving the biodegradability of the leachate pretreated biologically up to a value compatible with a subsequent biological treatment. The optimum reaction and settlement pH was 3, both for the organic matter removal and for the improvement of the biodegradability. The chemical oxygen demand (COD) removal increased at increasing Fe²⁺ dosages, from 75.6% for 300 mg/L to 89.0% for 1400 mg/L. The most significant enhancement (84.8%) was obtained with 800 mg Fe²⁺/L. However, the biological oxygen demand/chemical oxygen demand ratio (BOD/COD) was almost the same at all the Fe²⁺ dosages, around 0.29. Moreover, varying the H₂O₂ concentration between 600 and 3600 mg/L, COD removal percentages were between 85.9 and 89.0%. However, the BOD/COD ratio increased at increasing H₂O₂ dosage up to 3000 mg/L, from 0.12 at 600 mg/L to 0.29 at 3000 mg/L.     

Treatment of landfill leachate by the Fenton process

In recent years, studies of leachate treatment by conventional Fenton, photo-Fenton and electro-Fenton processes have indicated that these methods can effectively reduce concentrations of organic contaminants and color. In addition, the process can increase the biodegradable fraction of organic constituents in leachate, particularly in mature or biologically recalcitrant leachate. Oxidation and coagulation both play important roles in the removal of organics. Initial pH, dosages of Fenton reagents, aeration, final pH, reagent addition mode, temperature, and UV irradiation may influence final treatment efficiency. In this paper, current knowledge of performance and economics of Fenton processes for treatment of landfill leachate as reported for laboratory, pilot and full-scale studies is reviewed, with the conclusion that the Fenton process is an important and competitive technology for the treatment or pretreatment of landfill leachate.     

Oxone/Co oxidation as an advanced oxidation process: Comparison with traditional Fenton oxidation for treatment of landfill leachate

In this paper, the application of Fenton and Oxone/Co²⁺ oxidation processes for landfill leachate treatment was investigated. The removal of the chemical oxygen demand (COD), suspended substances (SS) and the color of the landfill leachate by Fenton oxidation to that by Oxone/Co²⁺ oxidation were compared under optimal operational conditions. For Fenton oxidation process, the optimal conditions were determined as: [H₂O₂] = 80 mmol L⁻¹, [H₂O₂]/[Fe²⁺] = 2.0, initial pH = 2.5, reaction temperature = 37.5 ± 1 °C, reaction time = 160 min, number of stepwise addition = 3. Under the given conditions, 56.9% of the COD removal efficiency was achieved, but the SS and the color of the treated landfill leachate increased due to the generation of a large quantity of ferric hydroxide sludge. In reference to Oxone/Co²⁺ oxidation process, the optimal conditions were determined as: [Oxone] = 4.5 mmol L⁻¹, [Oxone]/[Co²⁺] = 10⁴, pH = 6.5, reaction temperature = 30 ± 1 °C, reaction time = 300 min, number of stepwise addition = 7, the COD, SS and the color removal efficiencies were 57.5, 53.3 and 83.3%, respectively. From this work, it can be concluded that Oxone/Co²⁺ oxidation process demonstrated higher degradation efficiencies of the COD, SS and color for landfill leachate treatment than that by Fenton oxidation process. It also suggested that Oxone/Co²⁺ oxidation process could be considered as one of the most promising technologies for practical applicability to treat landfill leachate in large scale. For further improving the efficiency of Oxone/Co²⁺ oxidation process, we proposed that combination of it with other technologies in future such as ultraviolet, ultrasound and biological methods.     

Ultrasound-assisted photo-Fenton process for treatment of pulp and paper mill wastewater and reduction of phytotoxicity

The efficiency of classical Fenton (CF) and modified Fenton (MF) as well as photo-Fenton processes in real wastewater treatment of pulp and paper (P&P) mill was investigated in this study. The chemical oxygen demand (COD) was chosen as the reference measurement for evaluating the treatment's efficiency. After determining the optimum parameters for each process, the effect of adding ultrasound (US) on improving treatment efficiency was examined. In addition, kinetic study and phytotoxicity analysis were conducted under optimum conditions for all processes. With pH 4, reaction time 50 min, 1.2 g/L Fe²⁺ and 8 g/L H₂O₂ dosages, the best removal efficiency (RE) of COD was determined to be 82.18% in CF process, and this rate rose to 90.1% when US was added. The best RE in MF process was 84.16% with the application of UV-C, pH 4, reaction time 50 min, 1 g/L Fe⁰ and 8 g/L H₂O₂ doses, although it increased to 93.4% when US was applied. The greatest results in the seed germination test were achieved in US processes with 100% of germination percentage (GP) for spinach and tomato and 90% for cress. In the economic evaluation, when conducting the treatment without US, the estimated relative cost decreased in a 15 and 16%, for CF/UV-C and CF processes respectively, whereas the CF process was 64% cheaper than the MF process in all applications. The US contributed to enhanced water treatment efficiency by having a significant synergistic impact on Fenton applications. Hence, the combination of photo-Fenton and ultrasound to treat effluent from P&P mills proved to be an effective and promising technique.     

泡沫分离—Fenton氧化处理炼油废水

针对炼油厂废水处理工程,分析了表面活性剂成分及运行中产生泡沫的原因。采用泡沫分离—Fenton氧化技术进行处理,实践证明其出水水质优于国家排放标准,解决了废水排放过程中产生泡沫的问题。     

Fenton法在焦化废水处理中的应用及研究进展

介绍了Fenton氧化法及其各种联合技术在焦化废水处理中的应用及研究进展,分析了各种因素对Fenton氧化法处理效果的影响,并对Fenton氧化法在焦化废水处理中的发展前景作了展望.     

The effect of humic acids on nitrobenzene oxidation by ozonation and O3/UV processes

Three types of commercially available humic acids from different sources were used to simulate natural organic matter in water for the investigation of nitrobenzene oxidation by ozonation and O(3)/UV. Despite the structural differences among the Fluka, Aldrich and Suwanee River humic acids as reflected by the UV absorptivity, their effects on nitrobenzene removal rate was observed to be similar for the two processes. Removal rate of nitrobenzene was hindered by the addition of humic acids in ozonation as well as in O(3)/UV processes. However, the hindrance by the humic acids was more pronounced in O(3)/UV as compared to the ozonation process. The effect of humic acid in O(3)/UV was primarily a UV light screening. Addition of humic acids above a certain concentration did not cause any further retardation on nitrobenzene removal rate by ozonation and O(3)/UV.Accumulation of hydrogen peroxide as well as probable formation of peroxy radicals in the solutions might induce chain promoting reactions to produce hydroxyl radical during the nitrobenzene oxidation. For waters containing high levels of humic acid, ozonation alone might be as effective as O(3)/UV process for the removal of nitrobenzene.     

Kinetics of aniline degradation by Fenton and electro-Fenton processes

Aniline degradation at pH 2 by Fenton and electro-Fenton processes was kinetically investigated in this study. Electro-Fenton process was found to be superior to ordinary Fenton process with the current impacts of 1.2 to 3.1 for removal efficiency and 1.2 to 5.8 for degradation rate depending on initial Fe2+ concentration. This is mainly due to the rapid electrochemical regeneration of Fe2+. Overall rate equations for aniline degradation by Fenton and electro-Fenton processes (in units of molar and minute) are: [EQUATION: SEE TEXT]. With current application, aniline degradation rate seems to be autonomous from Fenton's reagent concentrations and approaching a half order with respect to aniline. In addition, for complete removal of 0.01 M aniline, the delay in current supply at the initial stage could save up to one-third of the total energy required by the ordinary electro-Fenton process. As a result, significant reduction in energy consumption and operating cost could be obtained by the current-delay operating mode.     

Calcium enhanced COD removal for the ozonation of phenol solution

In order to improve the chemical oxygen demand (COD) removal rate for the ozonation of phenol solution, ozonation combined with calcium binding was investigated. The results show that the addition of Ca(2+) can effectively enhance the COD removal rate. During the ozonation, calcium ion can bind with some of the intermediate products of phenol, including high molecular weight products, maleic acid and oxalic acid, to form insoluble precipitates. These calcium binding effects are responsible for the enhancement of COD removal. The variations of ADMI value during ozonation are similar for solutions with and without Ca(2+). However, the peak ADMI value in calcium-contained solution is lower than that without Ca(2+). As the phenol was completely decomposed, the ozone gas outlet concentration rapidly increases. The increasing rate of the ozone gas outlet concentration for ozonation with the presence of Ca(2+) is faster than that without Ca(2+). The optimal initial calcium dosage shows linear relationship with the initial phenol concentration, which is useful for practical application.     

Paracetamol oxidation from aqueous solutions by means of ozonation and H2O2/UV system

Paracetamol oxidation from aqueous solutions is studied by means of ozonation and H(2)O(2) photolysis. Both oxidative systems are able to destroy the aromatic ring of the substrate with a partial conversion of the initial carbon content into carbon dioxide. For the adopted experimental conditions mineralization degrees up to 30% and 40% are observed with ozonation and H(2)O(2) photolysis, respectively. Main reaction intermediates and products are identified for both systems by HPLC and GC-MS analyses and a kinetic characterization is achieved.     

Effects of Fenton treatment on the properties of effluent organic matter and their relationships with the degradation of pharmaceuticals and personal care products

This study examined effects of Fenton oxidation on trace level pharmaceuticals and personal care products (PPCPs) commonly occurring in wastewater. The tested PPCPs included acetaminophen, atenolol, atrazine, carbamazepine, metoprolol, dilantin, DEET, diclofenac, pentoxifylline, oxybenzone, caffeine, fluoxetine, gemfibrozil, ibuprofen, iopromide, naproxen, propranolol, sulfamethoxazole, bisphenol-A and trimethoprim. Transformations of effluent organic matter (EfOM) caused by Fenton oxidation were also quantified. All tested PPCPs, except atrazine and iopromide, were completely removed by Fenton treatment carried out using a 20 mg/L Fe (II) concentration and a 2.5 H₂O₂/Fe (II) molar ratio. Up to 30% on the total carbon concentration was removed during Fenton treatment which was accompanied by the oxidation of EfOM molecules and formation of oxidation products such as oxalic, formic and acetic acids and, less prominently, formaldehyde, acetaldehyde, propionaldehyde and glycolaldehyde. The absorbance of EfOM treated with Fenton reagent at varying Fe (II) concentration and contact time underwent a consistent decrease. The relative decrease of EfOM absorbance was strongly and unambiguously correlated with the removal of all tested PPCPs.     

Enhancing Fenton oxidation of TNT and RDX through pretreatment with zero-valent iron

The effect of reductive treatment with elemental iron on the rate and extent of TOC removal by Fenton oxidation was studied for the explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using a completely stirred tank reactor (CSTR). The results support the hypothesis that TNT and RDX are reduced with elemental iron to products that are oxidized more rapidly and completely by Fenton's reagent. Iron pretreatment enhanced the extent of total organic carbon (TOC) removal by approximately 20% and 60% for TNT and RDX, respectively. Complete TOC removal was achieved for TNT and RDX solutions with iron pretreatment under optimal conditions. On the other hand, without iron pretreatment, complete TOC removal of TNT and RDX solutions was not achieved even with much higher H(2)O(2) and Fe(2+) concentrations. Nitrogen was recovered as NH(4)(+) and NO(3)(-) when Fe(0)-treated TNT and RDX solutions were subjected to Fenton oxidation. The bench-scale iron treatment-Fenton oxidation integrated system showed more than 95% TOC removal for TNT and RDX solutions under optimal conditions. These results suggest that the reduction products of TNT and RDX are more rapidly and completely degraded by Fenton oxidation and that a sequential iron treatment-Fenton oxidation process may be a viable technology for pink water treatment.     

Fenton氧化/厌氧/好氧工艺处理苯胺农药废水

硝基苯胺类农药在生产和提纯过程中产生大量COD浓度高、SS高、色度大、含盐量高以及含有生物抑制性的废水,采用Fenton氧化/水解酸化/曝气生物滤池工艺进行处理,出水水质可达到<污水综合排放标准(GB 8978-1996)的一级标准.     

Effect of nonionic surfactants on the oxidation of carbaryl by anodic Fenton treatment

As a potentially promising technology, anodic Fenton treatment (AFT) has been shown to be very successful in pesticide removal. However, the influence of other constituents in the pesticide formulation, such as nonionic surfactants, has not been addressed. In this study, the effect of Triton X (TX) on the degradation kinetics and pathways of carbaryl undergoing AFT was investigated in an effort to facilitate its practical application. The presence of Triton X-100 was found to slow down the carbaryl degradation rate. This result can be attributed to the consumption of hydroxyl radicals ((*)OH) by surfactants and the formation of a carbaryl...TX...Fe(3+) complex, resulting in the unavailability of carbaryl to (*)OH attack. The modified AFT kinetic model previously developed in this laboratory shows an excellent fit to the carbaryl degradation profile (R(2)>0.998), supporting the formation of a carbaryl...TX...Fe(3+) complex. The carbaryl degradation rate decreased as Triton X-100 concentration increased from 20 to 1000 mg L(-1). Both (*)OH consumption by surfactants and complex formation are responsible for the degradation rate reduction below the critical micelle concentration (CMC), whereas the complex and micelle formation becomes a more dominant factor above the CMC. The effect of ethylene oxide (EO) numbers of a given nonionic surfactant mainly lies in the consumption of hydroxyl radicals, which increases with the length of the EO chain, but does not significantly affect the formation of the carbaryl...TX...Fe(3+) complex. Based on the GC-MS and LC-ESI-MS results, no evidence was found that the carbaryl degradation pathway was affected. Carbaryl was typically oxidized to 1-naphthol and 1,4-naphthoquinone similar to what is observed in the absence of surfactants. Triton X-100 was degraded via the breakdown of EO chains and omega-oxidation of the terminal methyl group, which resulted in the production of a series of ethoxylate oligomers.     

Occurrence of emerging pollutants in urban wastewater and their removal through biological treatment followed by ozonation

This work reports a systematic survey of over seventy individual pollutants in a Sewage Treatment Plant (STP) receiving urban wastewater. The compounds include mainly pharmaceuticals and personal care products, as well as some metabolites. The quantification in the ng/L range was performed by Liquid Chromatography-QTRAP-Mass Spectrometry and Gas Chromatography coupled to Mass Spectrometry. The results showed that paraxanthine, caffeine and acetaminophen were the main individual pollutants usually found in concentrations over 20 ppb. N-formyl-4-amino-antipiryne and galaxolide were also detected in the ppb level. A group of compounds including the beta-blockers atenolol, metoprolol and propanolol; the lipid regulators bezafibrate and fenofibric acid; the antibiotics erythromycin, sulfamethoxazole and trimethoprim, the antiinflammatories diclofenac, indomethacin, ketoprofen and mefenamic acid, the antiepileptic carbamazepine and the antiacid omeprazole exhibited removal efficiencies below 20% in the STP treatment. Ozonation with doses lower than 90 μM allowed the removal of many individual pollutants including some of those more refractory to biological treatment. A kinetic model allowed the determination of second order kinetic constants for the ozonation of bezafibrate, cotinine, diuron and metronidazole. The results show that the hydroxyl radical reaction was the major pathway for the oxidative transformation of these compounds.     

Anodic Fenton process assisted by a microbial fuel cell for enhanced degradation of organic pollutants

The electro-Fenton process is efficient for degradation of organic pollutants, but it suffers from the high operating costs due to the need of power investment. Here, a new anodic Fenton system is developed for energy-saving and efficient treatment of organic pollutants by incorporating microbial fuel cell (MFC) into an anodic Fenton process. This system is composed of an anodic Fenton reactor and a two-chamber air-cathode MFC. The power generated from a two-chamber MFC is used to drive the anodic Fenton process for Acid Orange 7 (AO7) degradation through accelerating in situ generation of Fe²⁺ from sacrificial iron. The kinetic results show that the MFC-assisted anodic Fenton process system had a significantly higher pseudo-first-order rate constant than those for the chemical Fenton methods. The electrochemical analysis reveals that AO7 did not hinder the corrosion of iron. The anodic Fenton process was influenced by the MFC performance. It was also found that increasing dissolved oxygen in the cathode improved the MFC power density, which in turn enhanced the AO7 degradation rate. These clearly demonstrate that the anodic Fenton process could be integrated with MFC to develop a self-sustained system for cost-effective and energy-saving electrochemical wastewater treatment.     

天津港油污水处理改造工程工艺的最优化配置

论述了天津港油污水处理改造的必要性,原有污水系统概况,试验情况,根据工程最优化设置选择工艺方案,提出一套能够适应现有含油废水排放特征的工艺流程和综合处理方法,旨在提高出水水质。