A temperature controllable magnetic stirrer ensures perfect mixing at a constant rate of 300 rpm during all experiments. The effect of Fe2+ concentration on COD removal varied in the range of 0.5–10 mM (these factors were kept constant: H2O2 = 30 mM; pH = 3; min; COD = 2741 mg/L). The selected H2O2 concentration was in the range of 10–100 mM while pH = 3 and Fe2+ = 10 mM at 30 min. The tested pH values ranged between 2 and 5.
Synthetic acid dye baths (SADB) consist of three different acid dyestuffs (C.I. Acid Yellow 242, C.I. Acid Red 360, and C.I. Acid Blue 264) and two dye auxiliaries (a levelling agent and an acid donor)
Optimum experimental conditions for the simulated acid dye bath effluent were established as follows: Fe2+ = 10 mM, H2O2 = 30 mM, and pH = 3 at room temperature (°C), which yielded an overall COD removal efficiency of 23%. The corresponding colour removal efficiency was 92% and the first-order COD abatement rate constant increased from 0.02 min−1 to 0.03 min−1 by increasing the temperature from 20 to 50°C. The first-order reaction rate constant for H2O2 consumption increased from 0.15 min−1 to 0.34 min−1 by increasing the temperature from 20 to 50°C. Further increases in temperature did not improve oxidation and oxidant consumption rates. H2O2 consumption ran parallel to COD removal at a rate approximately 10 times faster than COD abatement.
The Fenton reactor was stirred at room temperature in an open-batch system with a magnetic stirring bar and was treated for 2 h. The Fe+2 : H2O2 ratio was varied in the range of 1 : 5, 1 : 10, 1 : 20, 1 : 30, 1 : 40, and 1 : 50, pH in the range of 2–4, and Fe2+ in the range 0.5 and 1 mM.
RB49 Reactive Blue 49 RB137 Reactive Blue 137
The Fenton process was decolourized more than 90% in all cases. The best mineralization extent, that is, maximal TOC removal, 72.1%, was obtained for degradation of RB49 by Fenton process, Fe2+ : H2O2 = 1 : 20, Fe2+ = 0.5 mM at pH = 3. The molecular structure of the dyes studied plays a significant role in oxidation by Fenton type processes.
The oxidation studies were conducted in brown 500 mL glass bottles. The pH of wastewater and bleach was first adjusted to 3 with H2SO4. Degradation of EDTA in distilled water was conducted by Fenton’s reagent with Fe concentrations 0–0.9 mM and a maximum reaction time of 15 min. The temperature reaction and pH were fixed at 60°C and 3, respectively.
Fenton’s process proved highly effective in the degradation of EDTA in spiked integrated wastewater. With an initial molar ratio of 70 : 1 (H2O2 and EDTA) or higher, EDTA degradation was nearly complete within 3 min of reaction time. Lower EDTA degradation levels at pH 4 and low temperature in bleaching effluent are a major drawback in this study.
The initial concentrations of Fe(II) used in this study were 8.37, 13.95, 19.53, 25.11, and 33.40 mg/L, the Fe2+ : H2O2 ratios were set at 0.016, 0.028, 0.039, 0.05, and 0.067, and the concentration of H2O2 was kept constant at 500 mg/L. The initial concentrations of H2O2 used in this study were 50, 100, 200, 500, and 700 mg/L, the Fe2+ : H2O2 ratios were set at 0.0199, 0.0279, 0.06975, 0.1395, and 0.279, and the concentration of Fe(II) was fixed at 13.95 mg/L.
Azo dye C.I. Acid Yellow 23 (AY 23)
The decolourization rate is strongly dependent on the initial concentrations of Fe2+ and H2O2. The optimum operational conditions were obtained at pH 3. The results show that as much as 98% of AY 23 can be decolourized by 13.95 mg/L ferrous ions and 500 mg/L H2O2.
All tests were conducted in a 200 mL double glass cylindrical jacketed reactor, which allows cycle water to maintain the reaction mixture at a constant temperature. Temperature control was realized through a thermostat and a magnetic stirrer was used to stir reaction solutions. Operating pH was in the range of 2.5–6.0 and decolouration time was 60 min. Hydrogen peroxide in the range of to M and the Fe2+ dosage on the decolourization of OG with different initial concentrations from to M. Reaction temperature was varied in the range of 20–50°C. The effect of the presence of chloride ion ( to M) on the decolourization of OG was investigated. The decolourization of different concentrations of OG was studied in the range of to M.
Azo dye Orange G (OG)
The results showed a suitable decolourization condition of initial pH 4.0, H2O2 dosage M, and molar ratio of H2O2/Fe2+ 286 : 1. The decolourization efficiencies within 60 min were more than 94.6%. It was found that the decolourization efficiency of OG enhanced with increased reaction temperature but the presence of chloride ion had a negative impact on the decolourization of OG. The decolourization kinetics of OG by Fenton oxidation process followed the second-order reaction kinetics, and the apparent activation energy was detected to be 34.84 kJ/mol.
Chemical oxidation of the red dye solutions with Fenton’s reagent was carried out in a closed jacketed batch reactor (1 L capacity). The reactor was provided with constant stirring, accomplished through a magnetic bar and a Falc magnetic stirrer. The temperature of the reaction mixture was kept constant by coupling the reactor to a Huber thermostatic bath. Operating pH and H2O2 concentration were varied in the range of 2–5 and 5.9–8.8 mM, respectively. The effect of the Fe2+ concentration and reaction temperature was investigated in the range of 0.13–1.1 mM and 20–70°C, respectively.
Azo dye (Procion Deep Red H-EXL gran)
Total organic carbon (TOC) reduction occurred after 120 min of reaction; however, the reaction time required to achieve colour removal levels above 95% is around 15 min. Four operating variables must be considered, namely, the pH, the concentration of hydrogen peroxide, the temperature, and the concentration of ferrous ion, between 3-4, 5.9 mM, 20 min, and 0.27 mM, respectively. It was concluded that temperature and ferrous ion concentration are the only-variables that affect TOC removal, and, due to cross interactions, the effect of each variable depends on the value of the other one, thus affecting the process response positively or negatively.
Fenton’s reagent experiments were carried out at room temperature (°C) using different H2O2 and Fe(II) doses at pH 3.5. The percentage variation of simazine removal was investigated with H2O2 concentration at different simazine doses between 0.5 and 5.0 mg/L and at different Fe(II) doses between 5 and 30 mg/L at the end of a 6 min reaction time.
Simazine
At a constant simazine concentration, the percentage of TOC removal increased with increasing H2O2 and Fe(II) concentrations up to 15 mg/L Fe(II) and 50 mg/L peroxide above which mineralization decreased due to the scavenging effects of H2O2 on hydroxyl radicals. Maximum pesticide (100%) and TOC removals (32%) were obtained with H2O2/Fe(II)/simazine ratio of 55 : 15 : 3 (mg/L). Simazine degradation was incomplete, yielding the formation of intermediates which were not completely mineralized to CO2 and H2O.
The experiments were performed in an insulated vessel with a capacity of 1 L mounted on a steel frame and stirred at 130 rpm. The pH of initial solutions was set at 3. Gradation efficiencies were compared by varying Fenton’s reagent concentration and ratios. The parallel monitoring of Fenton’s reagent concentrations allowed the evidencing hydrogen peroxide or ferrous ion contents as limiting factors for TNT removal. The H2O20/Fe(II)0 ratio was varied in the range of 0.1–2 mM.
TNT
Fenton oxidation is an effective method to transform TNT totally in contaminated aqueous solution. This is feasible by the efficient generation of hydroxyl radicals during H2O2 catalytic decomposition with Fe(II) ions. TNT degradation kinetics and efficiency are largely influenced by H2O2 and Fe2+ concentrations. Using [H2O2]0 : [Fe(II)]0 molar ratios equal to or lower than 0.5 leads to the formation of the maximum number of intermediates. The absolute rate constant of the reaction between hydroxyl radicals and TNT is 9.6– M−1 s−1.
The Fenton reactor was a 0.5 L beaker placed in a thermostat water bath with constant temperature and stirred by a magnetic stirrer, with operating pH values of 2.50, 3.00, 3.50, 4.00, and 5.00, initial H2O2 concentration in the range of 0.10 mM to 4.00 mM, initial concentration of Fe2+ from 0.01 mM to 0.10 mM, and initial Amido Black 10B concentration on its degradation in the range of 10–100 mg/L. A series of experiments were conducted by varying the temperature from 15°C to 45°C.
Azo dye Amido Black 10B
The optimal operation parameters for the Fenton oxidation of Amido Black 10B were 0.50 mM H2O20 and 0.025 mM Fe2+0 for 50 mg/L [dye]0 at an initial pH of 3.50 at a temperature of 25°C. Under these conditions, 99.25% dye degradation efficiency in aqueous solution was achieved after 60 min of reaction. The Fenton treatment process showed that it was easier to destruct the –N = N-group than to destruct the aromatic rings of Amido Black 10B.
Fenton oxidation was performed in a batch reactor under initially anaerobic conditions to determine the effect of [MTBE]0 on the degradation of MTBE with FR: MTBE degradation at different [MTBE]0 in the range of 1, 2, and 5 mg/L when treated with the same amount of FR. This study was performed using solutions containing [MTBE]0 of 11.4 and 22.7 mM, each one in individual experiments at pH values of 3.0, 3.6, 5.0, 6.3, and 7.0. The FR to MTBE molar ratio varied in the range of 0.5 : 1 and 200 : 1. The initial concentration of pollutant was 22.7 M and FR was used in a 1 : 1 molar ratio of ferrous iron (Fe2+) and hydrogen peroxide (H2O2) at pH = 3.
Methyl tert-butyl ether (MTBE)
FR partially degraded low MTBE0 in water (11.4 and 22.7 M). Experiments at acidic pH yielded the best results of MTBE degradation (>90%), and small differences were observed between the results at pH 3.0 and 5.0. The majority of MTBE degradation and generation of intermediates occurred during the initial phase and followed pseudo first-order kinetics.
The experiments were conducted in batch mode. 4L borosilicate reactors were filled with 3.6 L of deionized (DI) water at pH = 3.0 and purged with high-purity nitrogen until the dissolved oxygen (DO) reading was below 0.01 mg/L and the oxygen concentration in the head space was negligible ( 0.01%).
Methyl tert-butyl ether (MTBE)
The added amount of FR proved to be an important controlling parameter for the overall MTBE degradation mineralization efficiency. An FR to MTBE molar ratio of 20 : 1 was the minimum required to achieve complete MTBE degradation. Kinetic analysis is reported to be pseudo first-order given the good linear correlation found between and FMMR. Other intermediates not identified in this study are generated in significant concentrations at these conditions.
A series of experiments were conducted at pH 3 for 5, 15, or 60 min of mixing followed by 30 min clarification. The studied H2O2/Fe2+ stoichiometric molar ratios were 1, 2, 3, 4, 5, and 10 with H2O2 dose of 1000 mgL−1, and the H2O2/Fe2+ stoichiometric molar ratios were 0.5, 2, 3, 5, and 10 with H2O2 dose of 500 mgL−1. A further series of experiments were conducted at an initial pH of 3, 4, 5, 6, or 7 with 5 min mixing followed by 30 min clarification. Comparisons between the Fenton process and Fe3+ coagulation were carried out at an initial pH of 3 and 7.
Nuclear laundry water
The experimental data generally indicated decreased removal efficiencies of organic compounds with an increasing H2O2/Fe2+ ratio. Yet taking into account all factors, thermostat cost-effective degradation conditions were at H2O2/Fe2+ stoichiometric molar ratio of 2 with 5 min mixing and an H2O2 dose of 1000 mgL−1. The initial pH of the laundry water can be as high as 7. Fe3+ coagulation experiments were conducted in order to interpret the nature of the Fenton process. Since the removal efficiency of organic compounds in the Fenton process was slightly higher than in coagulation, the treatment of the nuclear laundry water can be called Fenton-based Fe3+ coagulation.
