Advanced Oxidation of Diuron by Photo-Fenton Treatment as a Function of Operating Parameters

Advanced oxidation of diuron in aqueous solution by photo-Fenton treatment was investigated by batch experiments. Effects of operating parameters, namely, the concentrations of pesticide (diuron), hydrogen peroxide (H2O2), and ferrous ion [Fe (II)] on oxidation of diuron were investigated by using Box-Behnken statistical experiment design and the response surface methodology. Diuron oxidation by photo-Fenton treatment was evaluated by determining the total organic carbon (TOC), diuron, and adsorbable organic halogen (AOX) removals. Concentration ranges of the reagents resulting in the highest level of diuron oxidation were determined. Diuron removal increased with increasing H2O2 and Fe (II) concentrations, up to a certain level. H2O2 concentration had a more profound effect than diuron and Fe (II) on removal of diuron, TOC, and AOX from the aqueous solution. Complete (100%) disappearance of diuron was achieved after a 15?min reaction period. However, 85% of diuron was mineralized after 240?min, indicating a low level of intermediate formation. Optimal H2O2/Fe (II)/diuron ratio resulting in maximum diuron (100%), TOC (85%), and AOX (100%) removals was found to be 267/36/25?(mg?L?1).     

Degradation of MTBE Intermediates using Fenton’s Reagent

In a previous study, the chemical oxidation of methyl tert-butyl ether (MTBE) at low concentrations in water using Fenton’s reagent (FR) was investigated. At certain reaction conditions the process achieved 99.99% degradation of MTBE but it did not result in complete MTBE mineralization. In the present study, the major intermediate by-products generated during the reaction, such as tert-butyl formate (TBF), tert-butyl alcohol (TBA), methyl acetate, and acetone were separately used as parent contaminants and treated under the same reaction conditions initially used for MTBE (i.e., pH of the water, molar ratio of pollutant to FR) in order to compare their degradability by hydroxyl radicals generated from Fenton’s reaction. The results were compatible with the second order reaction rate constants for the reaction of hydroxyl radicals with each contaminant commonly available in the literature. The comparison of the degradation kinetics for each intermediate by-product provided information that aims at unveiling the limiting step(s) of the entire MTBE degradation pathway. In this context, it was found that (1) TBA was generated by reactions subsequent to those that produced TBF, (2) acetone was originated by at least three independent pathways involving direct hydroxyl radical attack on MTBE, TBF, and TBA, and (3) methyl acetate was formed exclusively from MTBE.     

Degradation and Mineralization of Simazine in Aqueous Solution by Ozone/Hydrogen Peroxide Advanced Oxidation

Advanced oxidation of simazine in aqueous solution by the peroxone (hydrogen peroxide/ozone) treatment was investigated using Box-Behnken statistical experiment design and response surface methodology. Effects of pH, simazine and H2O2 concentrations on percent simazine and total organic carbon (TOC) removals were investigated. Ozone concentration was kept constant at 45?mg?L?1. The optimum conditions yielding the highest simazine and TOC removals were also determined. Both simazine and peroxide doses affected simazine removal while pH and pesticide dose had more pronounced effect on mineralization (TOC removal) of simazine. Nearly 95% removal of simazine was achieved within 5 min for simazine and peroxide concentrations of 2.0 and 75?mg?L?1, respectively at pH = 7. However, mineralization of simazine was not completed even after 60 min at simazine doses above 2?mg?L?1 indicating formation of some intermediate compounds. The optimum H2O2/pH/Simazine ratio resulting in maximum pesticide (94%) and TOC removal (82%) was found to be 75/11/0.5(mg?L?1).     

Stabilization of Arsenite Wastes with Prior Oxidation

The stabilization of arsenite hazardous waste is more difficult than arsenate waste. Oxidation of arsenite was investigated as a pretreatment before stabilization of the resulting arsenate. The effectiveness of air oxidation was limited and depended on the amount of water present. Hydrogen peroxide oxidation was effective but limited by reactions with calcium hydroxide. After oxidation, the resulting arsenate waste was effectively stabilized using ferric sulfate.     

Engineering Aspects of the Integration of Chemical and Biological Oxidation: Simple Mechanistic Models for the Oxidation Treatment

Oxidation processes can oxidize biorecalcitrant compounds into biodegradable intermediates, which in turn can be treated less expensively by a subsequent biological process. To design such a two-step (chemical+biological) process to treat poorly characterized wastewaters, it is useful to model the time evolution of characteristic global variables, chemical oxygen demand (COD) and biochemical oxygen demand (BOD), in order to develop a useful treatment strategy based upon these classical variables. We consider two simple model reaction networks, requiring three- and five-rate constants, respectively. The first model, proposed recently, involves conversion of a nonbiodegradable species, C, into a single biodegradable intermediate S. Here, biodegradable compounds are immediate kinetic products of oxidation. In general, it is not probable that a single recalcitrant compound undergoes a single-step reaction to CO2. However, when working with complex undefined wastewaters streams, single-step reactions may be used to simplify. The second new model corresponds to a lag time in BOD formation due to the necessity of multiple partial oxidations to reach a first biodegradable intermediate. The second network includes two intermediates, I and S, which are, respectively, nonbiodegradable and biodegradable. We then compare model behavior with an unfortunately sparse literature on BOD and COD values versus time in chemical reactors, and demonstrate the convenience of the first model, and the occasional necessity of the second, which reflects the presence of early intermediates which are nonbiodegradable.     

Role of Particle Size and Ammonium Oxidation in Removal of 17α-Ethinyl Estradiol in Bioreactors

Laboratory scale bioreactors were used to investigate sorption and biodegradation of 17α-ethinylestradiol (EE2). EE2 is among many emerging micropollutants that may cause endocrine disruption of aquatic organisms in the environment. Results showed that the sludge taken from the membrane bioreactor (MBR) had a sorption distribution coefficient that was more than twice that of biomass derived from sequencing batch reactors (SBRs). The MBR biomass had smaller particles and was more hydrophobic than the SBR biomass. Experiments with nitrifying sludge showed that sorption was more important when the initial ammonia concentration was 48?mg/L or less, but at higher initial ammonia concentrations the role of biodegradation became more important. The ammonium monooxygenase enzyme extracted from a nitrifying mixed culture removed EE2 in batch experiments. These findings are the first that we are aware of to link biomass particle size, hydrophobicity, and sorption capacity. These results also support the notion that cometabolic biodegradation of EE2 can occur in nitrifying sludge.     

Treatment of Fuel-Oil Contaminated Soils by Biodegradable Surfactant Washing Followed by Fenton-Like Oxidation

Among petroleum-hydrocarbon pollutants, fuel-oil is more difficult to treat compared to gasoline and diesel fuel. The objectives of this bench-scale study were to: (1) develop a two-stage remedial system consisting of surfactant washing followed by Fenton-like oxidation process to remediate fuel-oil contaminated soils; (2) evaluate the effects of residual surfactant and soil organic matter (SOM) on the efficiency of Fenton-like oxidation; (3) evaluate the effect of potassium dihydrogen phosphate (KH2PO4) addition on the stability of H2O2 and oxidation efficiency; and (4) evaluate the possible oxidation products after the oxidation process. In the surfactant washing stage, biodegradable surfactant, Simple Green (SG) (50?g?L?1), was applied to flush fuel-oil contaminated soils with initial total petroleum-hydrocarbons (TPHs) concentration of 50,000?mg?kg?1. Results show that approximately 90% of TPH could be removed after washing with 45 pore volumes (PVs) of SG followed by 25 PVs of deionized water, while the soil TPH concentration dropped from 50,000 to 4,950?mg?kg?1. In the Fenton-like oxidation stage with initial soil TPH concentration was approximately 4,950?mg?kg?1, TPH removal efficiency can be significantly increased with increased H2O2 concentrations. Results also reveal that residual SG and SOM would compete with TPH for oxidants and cause the decrease in oxidation efficiency. An “oxidation-sorption-desorption-oxidation” scheme for soil TPH was observed in this experiment due to the initial sorption of TPH on SOM. Results show that an addition of 2.2 mM of KH2PO4 could increase the stability and half-life of H2O2, but caused the decrease in TPH removal efficiency. The oxidation potential of Fenton-like process was not capable of completely oxidizing fuel-oil to nontoxic end products. The observed by-products after oxidation process contained carboxyl groups with molecular weights similar to their parent compounds. Results from this study indicate that the two-stage remedial system is a promising technology for fuel-oil contaminated soil treatment.     

Impact of Reaction Conditions on MnO2 Genesis during Permanganate Oxidation

To enhance the understanding of the behavior and effects of the precipitation of MnO2 particles in the subsurface generated during in situ chemical oxidation (ISCO) using permanganate, laboratory batch experiments were completed to examine the influence that varied reaction matrix conditions have on the generation and properties of manganese oxides. The conditions examined include organic material type and concentration, permanganate concentration, pH, and the presence of calcium (as a representative divalent cation) in solution. Experimental studies included: (1) spectrophotometric examination of permanganate depletion and manganese oxides generation over time during reactions with trichloroethene; (2) scanning electron microscopy analyses of manganese particle morphology; (3) particle size distribution (filtration) characterization studies; and (4) optical particle sizing and numeration studies. Bench-scale, batch experiments were conducted to focus on fundamental chemical properties affecting particle development under varied potential environmental conditions. The amount of manganese oxides particles that develop, grow, and potentially settle as a result of permanganate ISCO of organic contaminants is a function of the particle size and concentration, the time allowed for particle development, and the impact of matrix conditions on the ability of particles to agglomerate.     

Decolorization and Mineralization of Remazol Red F3B by Fenton and Photo-Fenton Processes

Degradation of aqueous solutions of a commercial azo-reactive textile dye, Remazol Red F3B, by the Fenton and photo-Fenton processes, has been investigated. Fenton-type reaction rates are strongly dependent on pH, temperature, and initial concentrations of the Fe2+, H2O2, and dye. The effects of varying these parameters on the degradation performances of these two processes have been studied, and the optimal operational conditions have been found. The optimal conditions for these processes were obtained at pH = 3. A comparative study of the Fenton and photo-Fenton reactions has also been carried out using a photoreactor. The Fenton process is highly efficient for removal of the color, chemical oxygen demand, and total organic carbon of a Remazol Red F3B solution. The photo-Fenton process proved to be more efficient, and proceeds at a much higher oxidation rate than the Fenton process. The photo-Fenton process allows 90% degradation of chemical oxygen demand in about 20 min of reaction time.     

Evaluation of UV LEDs Performance in Photochemical Oxidation of Phenol in the Presence of H2O2

A novel application of ultraviolet (UV) light emitting diodes (LEDs) as a light source for the degradation of organic contaminant has been investigated. Photocleaving of hydrogen peroxide (H2O2) via UV LEDs photolysis resulted in the generation of hydroxyl radicals. It was found that phenol removal was insignificant in the absence of hydrogen peroxide, therefore oxidation of phenol was attributed to the formed radicals. Two criteria were selected to provide detailed information on the performance of UV LEDs in phenol oxidation: (1) the reaction quantum efficiency and (2) the energy consumption. Statistical tools such as the response surface methodology and the ANOVA were applied to estimate the influence of various process parameters such as the wavelength (255, 269, and 276 nm) and H2O2 to phenol molar ratio (5, 50, and 100) on phenol degradation reaction quantum efficiency. The decay of phenol (initial concentration of 1.06 mM) was the most pronounced at 255 nm and H2O2 to phenol molar ratio of 50. Finally, the “figure-of-merit” was used to estimate the specific energy consumption of the UV LED-based process.     

Cadmium Release from Four Sorbents during Treatment of Contaminated Soils by Catalyzed H2O2 Propagations (Modified Fenton’s Reagent)

The release of heavy metals from soils and subsurface solids is a significant concern during in situ chemical oxidation treatment. The release of cadmium sorbed on four solids of varied properties was investigated in slurries treated by catalyzed H2O2 propagations (CHP—modified Fenton’s reagent). Cadmium was released in all four solids in CHP reactions conducted at pH 3; however, aqueous cadmium concentrations decreased in CHP reactions conducted at pH 7. Cadmium release at pH 3 was directly proportional to the soil organic carbon (SOC) content of the four solids (R2 = 0.99), and may have been due to destruction of the SOC by hydroxyl radical in the reactions at pH 3. Scavenging of hydroxyl radical minimized the release of cadmium in CHP systems at pH 3, which is consistent with cadmium release resulting from destruction of SOC by hydroxyl radical. Scavenging of hydroxyl radical in CHP systems at pH 7 resulted in increased cadmium release, compared to pH 7 reactions without the hydroxyl radical scavenger isopropanol. Superoxide, the conjugate base of perhydroxyl radical (pKa = 4.8), was proposed as the desorbing species in the scavenged CHP reactions at pH 7. The results of this research demonstrate that cadmium release will likely be minimal in CHP reactions conducted at pH 7 if compounds that increase the activity of superoxide are not present at significant concentrations.     

Fenton试剂去除聚丙烯酰胺的实验研究

阐述了PAM废水的成因和特点,以Fenton试剂为氧化剂通过氧化的方法去除水体中的过量PAM。探讨在去除PAM过程中H2O2与COD比值,pH值,H2O2与Fe2＋比值以及反应时间对去除效果的影响。通过实验,最佳的配比为：pH=4,H2O2/COD=2.5,Fe2＋/H2O2=1/10,在转速为250 r/min条件下,最佳反应时间为90 min。     

Liquid Sodium Ferrate and Fenton’s Reagent for Treatment of Mature Landfill Leachate

As landfills mature, biodegradable matter in leachate is consumed and remaining compounds are increasingly recalcitrant. In this work, ferrate was compared to Fenton’s reagent for the purpose of removing nonbiodegradable organic compounds from mature leachate. Oxidation conditions (time, pH, and dose) were optimized to yield maximum organic removal using two leachate samples from 20- and 12-year-old solid waste cells. Results from this study demonstrated that Ferrate and Fenton’s reagent had similar optimum pH ranges (3–5), but different organic removal capacities, ranging from 54 to 79% of initial leachate organic contents. An advantage of ferrate was that it was effective over a wide pH range. Advantages associated with Fenton’s reagent include that it had higher organic removal capacity, produced more oxidized organic compounds (measured as chemical oxygen demand/dissolved organic carbon), and produced more biodegradable byproducts (measured as chemical oxygen demand/5-day biochemical oxygen demand). Finally, both treatments were found to attack larger molecules (>1,000?Dalton), as indicated by an increase in smaller molecule contribution to organic carbon.     

电化学法深度处理低浓度贵金属贫液的研究

以自制的煤基材料为电极,采用电化学法深度处理贵金属贫液,研究了电压、时间、pH值及温度等因素对各离子去除率的影响规律,采用扫描电镜及能谱（SEM-EDS）对反应后极板的表面形貌及负载物组成进行表征分析。实验结果表明,随着处理时间的延长,温度的增加,溶液中各离子的去除率逐渐增大,随着电压增大离子去除率表现为先升后降的趋势,在1.6 V时达到最佳,而pH值的升高不利于反应进行。选用原液pH值,在电压为1.6 V、溶液温度为50 ℃、处理时间为6 h的条件下,钯离子去除率为99.32%,铂离子去除率为97.13%,金与钌离子可视为完全去除。研究证实,采用电化学法可以对低浓度贵金属贫液进行深度处理并实现回收贵金属的目的,该电化学反应由电沉积和电吸附两方面共同作用,且前者占主导作用。     

Novel Hybrid Filter for the Treatment of Septic Tank Effluent

Intermittent sand filtration is a common and effective method for treating septic tank effluent. However, if the loading rate is too high, clogging and ponding of the sand filter surface layer can occur due to the accumulation of excessive biomass and the deposition of suspended solids. This ponding limits the practicality of sand filtration as it makes it necessary to take the filter out of service for maintenance. The objective of this study was to develop and test, on-site, a new hybrid filter system that would reduce the risk of clogging at an organic loading rate substantially greater than the maximum recommended loading rate for intermittent sand filters. The system comprised a 0.6?m deep horizontal flow biofilm reactor (HFBR) over a 0.85?m deep stratified sand filter. The HFBR consisted of a stack of 20 horizontal corrugated polyvinyl chloride sheets, at 32?mm vertical spacings. The sheets were arranged so that the wastewater flowed over and back along alternate sheets down through the stack. The main biofilm growth formed on these sheets. The hybrid filter was loaded with septic tank effluent from an office/garage complex at the rate of 206?L/m2?day for a period of 400 days in two phases. During the first phase, the effluent volume of 600?L/day was applied in 24 doses/day for 10?min/dose, and during the second phase in 6 doses/day for 40?min/dose. Biofilms in the HFBR substantially reduced the organic and suspended solids loads that reached the sand filter surface and allowed an average total biochemical oxygen demand (BODT) loading rate, based on HFBR plan area, of 37?g?BODT/m2?day to be applied to the system without clogging. This rate was substantially greater than the maximum recommended loading rate of 24?g?BODT/m2?day for intermittent sand filters. During both loading phases a BODT removal of 94% was achieved and nitrification was nearly complete. The average effluent BODT was 12±4?mg/L during both phases. The hybrid filter system appeared to perform better in terms of suspended solids handling and nitrification during the more frequent dosing phase. The hybrid filtration system offers a more compact alternative to intermittent sand filtration on its own with little risk of clogging.     

Industrial Plant for Olive Mill Wastewater from Two-Phase Treatment by Chemical Oxidation

Olive-oil production generates high and variable amounts of wastewaters from the olives and olive-oil washing (OMW), resulting to great environmental impact. These waters are normally stored in large holding ponds for evaporation during the summer. The present study examines the chemical-oxidation process using ferric chloride catalyst for the activation of H2O2 (Fenton reaction). Tests have been made on an industrial scale. The final average value of chemical oxygen demand (COD) was close to 371?mg?O2?L?1 (%CODremoval = 86%, CODinitial = 2684?mg?O2?L?1), and the water produced can be used for irrigation or can be discharged directly into the municipal wastewater system for tertiary treatment.     

过硫酸盐深度催化氧化垃圾渗滤液膜浓缩液

反渗透膜浓缩液的产生成为渗滤液处理的二次污染问题。本试验采用过硫酸根深度氧化处理膜浓缩液,筛选最佳催化剂,并探讨催化剂投加量、pH和温度等因素对膜浓缩液有机物去除效果的影响。结果表明:相比Fe2+、Ag+和Mn2+,Fe0作为过硫酸钾氧化过程的催化剂在降解有机物和处理经济成本方面具有显著优势;反应条件最佳范围为pH3,温度45℃,K2S2O8:Fe010,可稳定保持COD去除率在80%以上。     

Fenton Process for Landfill Leachate Treatment: Evaluation of Biodegradability and Toxicity

The single Fenton or the Fenton process implemented in combined scheme as a posttreatment after the ferric chloride coagulation was applied for leachate collected from a real waste disposal site. Depending on the ratios of H2O2/chemical oxygen demand, H2O2/Fe2+, and pH, the Fenton oxidation or both the Fenton oxidation and the Fenton coagulation were involved in chemical oxygen demand reduction. The implementation of ferric chloride coagulation as a pretreatment stage or acidification of raw leachate did not result in the improvement of chemical oxygen demand reduction efficacy of the following Fenton process comparing with that obtained by the direct Fenton treatment of raw leachate. The direct Fenton treatment with a higher (3/1) H2O2/chemical oxygen demand ratio applied to raw leachate without pH preadjustment (H2O2/Fe2+ = 10/1), produced more oxidized organic compounds (measured as dissolved organic carbon/chemical oxygen demand ratio), more biodegradable by-products (measured as a 7-day biological oxygen demand/chemical oxygen demand ratio), and required a considerably lower dosage of NaOH for neutralization, making it preferable for the leachate treatment. Although up to a twofold reduction in the toxicity was observed after the overall Fenton process application, the treated leachate remained extremely toxic to Daphnia magna.     

Modeling the Oxidation of Sulfide in Pulp and Paper Wastewaters

Reactor experiments were conducted to study aerobic sulfide oxidation in pulp and paper wastewaters under typical operating conditions. Data produced from these experiments were used to develop a set of sequential rate equations that describe the significant sulfide and oxygen processes in the reactors. Model parameters were estimated for three different pulp and paper wastewaters using a multiresponse procedure. The sulfide oxidation rate coefficients for the wastewaters ranged from 0.108 to 0.155?min?1 at 35°C and approximately neutral pH. The reaction order with respect to oxygen could not be precisely estimated but appeared to be near the lower boundary for the fitting procedure (essentially zero order). Modeling of the oxygen depletion data provided evidence that the first sulfide oxidation reaction product consumed 0.5 mg of oxygen per mg of sulfide oxidized, suggesting polysulfides and elemental sulfur as the initial reaction products. The oxygen depletion modeling also suggested oxidation of the initial reaction product to a more stable intermediate which is postulated to be thiosulfate.     

Destruction of a Carbon Tetrachloride Dense Nonaqueous Phase Liquid by Modified Fenton’s Reagent

Destruction of a dense nonaqueous phase liquid (DNAPL) by soluble iron (III)-catalyzed and pyrolusite (β-MnO2)-catalyzed Fenton’s reactions (hydrogen peroxide and transition metal catalysts) was investigated using carbon tetrachloride (CT) as a model contaminant. In the system amended with 5 mM soluble iron (III), 24% of the CT DNAPL was destroyed after 3 h while CT dissolution in parallel fill-and-draw systems was minimal, indicating that CT was degraded more rapidly than it dissolved into the aqueous phase. Fenton’s reactions catalyzed by the naturally occurring manganese oxide pyrolusite were even more effective in destroying CT DNAPLs, with 53% degradation after 3 h. Although Fenton’s reactions are characterized by hydroxyl radical generation, carbon tetrachloride is unreactive with hydroxyl radicals; therefore, a transient oxygen species other than hydroxyl radicals formed through Fenton’s propagation reactions was likely responsible for CT destruction. These results demonstrate that Fenton-like reactions in which nonhydroxyl radical species are generated may provide an effective method for the in situ treatment of DNAPLs.