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Wastewater Treatment with Green Chemical Ferrate: An Eco-Sustainable Option
Published in Prabhat Kumar Rai, Phytoremediation of Emerging Contaminants in Wetlands, 2018
The ferrate(VI) ion, with the molecular formula, FeO42−, is a very strong oxidant. Under acidic conditions, the redox potential of ferrate(VI) ions (2.2 V) is the strongest of all the oxidants/disinfectants practically used for water and wastewater treatment (Table 8.1); note that it is greater than that of ozone (2.0 V). Moreover, during the oxidation/disinfection process, ferrate(VI) ions will be reduced to Fe(III) ions or ferric hydroxide. As such, this simultaneously generates a coagulant in a single dosing and mixing unit process (Jiang and Lloyd, 2002). The FeO42− ion has a tetrahedral structure similar to its geometry in the solid state; these four Fe–O bonds are equivalent with covalent characteristics (Jiang and Lloyd, 2002; Hoppe et al., 1982). The thermodynamic constants of potassium ferrate were first measured/calculated by Wood (1958). There are two major methods for characterizing ferrate(VI) salts in practice, such as the volumetric titration method and spectroscopy method (Jiang and Lloyd, 2002).
Treatment of bypass wastewater using potassium ferrate(VI): assessing the role of mixing
Published in Environmental Technology, 2020
Ferrate(VI) is considered one of the promising multi-purpose chemical enhancement alternatives for primary wastewater treatment [7] as it has shown the versatility to act as an oxidant, disinfectant and coagulant [7–11]. The standard half-cell reduction potential of ferrate(VI) ions () at E° = 2.20 ± 0.03 V under acidic pH conditions is among the highest of all oxidants and disinfectants (Reaction 1), whereas under alkaline conditions, ferrate(VI) is a mild oxidant with E° = 0.72 ± 0.03 V (Reaction 2) [12].The speciation and decomposition of ferrate(VI) have been studied previously using phosphate/acetate buffer, and the pKa values are shown in Reactions 3–5 [13]. The reaction rates of different pollutants with ferrate(VI) increase with decreasing pH due to the faster reaction rates of the protonated form of ferrate(VI) () as compared to the unprotonated form () [9,14]. Pre-acidification or alkalisation of the flow to be treated followed by pH adjustment may be effective for the removal of certain contaminants [10,15,16]. However, such change in the pH of the wastewater adds extra cost to the treatment.
Oxidation of propyl paraben by ferrate(VI): Kinetics, products, and toxicity assessment
Published in Journal of Environmental Science and Health, Part A, 2018
Jibin An, Chunqiu Xia, Jiahong He, Huixia Feng
At present, ferrate(VI) () has emerged as a potential environmentally friendly chemical in wastewater treatment process due to its strong oxidation, which has a oxidation-reduction potential of 2.2–0.7 V at acidic and 0.57 V at basic condition.[15,16] Ferrate(VI) can also perform dual functions oxidation and coagulation/precipitant as ferric hydroxide (Fe(III)) simultaneously.[17] Generally, H2FeO4, HFeO4−, FeO42− are the predominant species at different pH solution. The oxidizing power of these species increase in the order < < H2FeO4, and ferrate work well in a broader pH range.[18,19] On the contrary, as the oxidatant of iron series, the low pH (<3) operation requirement limits the application of the traditional Fenton oxidation system.[18] Presently, Fe(VI) has been demonstrated to effectively destroy the electron-rich and recalcitrant contaminants such as EOCs.[20–23] Nevertheless, considerable research efforts have been devoted to understanding of aqueous Fe(VI) chemistry;[22,24] further studies are still needed to study Fe(VI) reactions with structurally complex organic micropollutants and the biological activity (e.g., toxicity) change during the oxidation process of these EOCs such as PPB. Furthermore, the removal of various micropollutants by Fe(VI) treatment may be influenced by water constituents, such as metal and inorganic ions, chromatograph-dissolved organic matter,[25] and the water constituents could be an important factor in the removal of micropollutants.
Analytical and ecotoxicological studies on degradation of fluoxetine and fluvoxamine by potassium ferrate
Published in Environmental Technology, 2019
Przemysław Drzewicz, Agata Drobniewska, Katarzyna Sikorska, Grzegorz Nałęcz-Jawecki
The ferrate can be successfully applied for removal of FLX and FLU from natural water. Both for FLX and FLU, treatment with 50 mg/L FeO42− reduced toxicity of investigated solutions by 50%. Therefore, a small amount of ferrate may be used for removal of toxicity caused by the antidepressant, whose average concentration in municipal effluents is at μg/L (three orders of magnitude lower than concentration of investigated solution of the pharmaceuticals). Because of good coagulation properties, iron hydroxide formation is an advantage of the process. Iron hydroxide may be used for removal of metals and other organic compounds as well as suspended solid particles (minerals, humic acids) [31,32]. It may be assumed that ferrate oxidation process is very fast for most of the compounds [24]. The main disadvantage is high cost of ferrate and its stability both in solid form and in the solution. It may cause some problem in application in water and wastewater treatment. However, ferrate(VI) can be encapsulated in water-soluble and biodegradable material in order to protect against decomposition caused by moisture. Ferrate can be also adsorbed on a sorbent and in this form, applied in water and wastewater treatment process. However, the most promising technology is in situ electrochemical generation of ferrate(VI) from sacrificing anode containing iron [33,34]. Preliminary, pilot-scale studies shown that the estimated specific energy consumption is 0.2 kWh/g ferrate produced [35]. Hence, based on obtained results of FLU and FLX removal and toxicity reduction, it may be assumed that treatment of wastewater contaminated with these pharmaceuticals by ferrate oxidation is a viable option. However, efficiency of ferrate(VI) formation depends on current density, anode material, space between the electrodes and pH of electrolyte. Changing of the reactor design may improve efficiency of ferrate(VI) production by electrochemical process [34]. Therefore, improving of ferrate(VI) production in electrochemical process and its injection into wastewater stream is a subject of ongoing studies conducting by many researchers [33,34].