Although the Fe(VI)–sulfite process has shown great potential for the rapid removal of organic contaminants, the major active oxidants (Fe(IV)/Fe(V) versus SO4 •–/•OH) involved in this process are ...still under debate. By employing sparingly soluble CaSO3 as a slow-releasing source of SO3 2–, this study evaluated the oxidation performance of the Fe(VI)–CaSO3 process and identified the active oxidants involved in this process. The process exhibited efficient oxidation of a variety of compounds, including antibiotics, pharmaceuticals, and pesticides, at rates that were 6.1–173.7-fold faster than those measured for Fe(VI) alone, depending on pH, CaSO3 dosage, and the properties of organic contaminants. Many lines of evidence verified that neither SO4 •– nor •OH was the active species in the Fe(VI)–CaSO3 process. The accelerating effect of CaSO3 was ascribed to the direct generation of Fe(IV)/Fe(V) species from the reaction of Fe(VI) with soluble SO3 2– via one-electron steps as well as the indirect generation of Fe(IV)/Fe(V) species from the self-decay of Fe(VI) and Fe(VI) reaction with H2O2, which could be catalyzed by uncomplexed Fe(III). Besides, the Fe(VI)–CaSO3 process exhibited satisfactory removal of organic contaminants in real water, and inorganic anions showed negligible effects on organic contaminant decomposition in this process. Thus, the Fe(VI)–CaSO3 process with Fe(IV)/Fe(V) as reactive oxidants may be a promising method for abating various micropollutants in water treatment.
This paper focuses on the decentralized optimal control algorithm for distribution management system by considering distribution network as coupled microgrids. Based on the autonomous control model ...of each single microgrid, coordinated information and strategies among different microgrids are used to decrease the operating cost of distributed generation, improve the efficiency of the distributed storages utilization, and reduce the complexity of distribution network operation. The optimal control problem of microgrids is modeled as a decentralized partially-observable Markov decision process (DEC-POMDP), and a coordinated dynamic programming algorithm is used to solve the problem by introducing a look-head dual multiplier mechanism as decentralized control signals from centralized information. The performances of this algorithm and the impacts of different coordinated information are discussed by some study cases in the end of this paper.
The detection of soluble Mn(III) is typically accomplished using strong complexing agents to trap Mn(III), but the generation of soluble Mn(III) induced by strong complexing agents has seldom been ...considered. In this study, pyrophosphate (PP), a nonredox active ligand, was chosen as a typical Mn(III) chelating reagent to study the influence of ligands on soluble Mn(III) formation in reactions involving Mn oxides and Mn(VII). The presence of excess PP induced the generation of soluble Mn(III)-PP from α- and δ-MnO2 and led to the conproportionation reaction of α-, β-, δ-, or colloidal MnO2 with Mn(II) at pH 7.0. Compared to MnO2 minerals, colloidal MnO2 showed much higher reactivity toward Mn(II) in the presence of PP and the conproportionation rate of colloidal MnO2 with Mn(II) elevated with increasing PP dosage and decreasing pH. The generation of Mn(III) was not observed in MnO4 –/S2O3 2– or MnO4 –/NH3OH+ system without PP while the introduction of excess PP induced the generation of Mn(III)-PP. Thermodynamic calculation results were consistent with the experimental observations. These findings not only provide evidence for the unsuitability of using strong ligands in quantification of soluble Mn(III) in manganese-involved redox reactions, but also advance the understanding of soluble Mn(III) generation in aquatic environment.
Recently, reactive iron species (RFeS) have shown great potential for the selective degradation of emerging organic contaminants (EOCs). However, the rapid generation of RFeS for the selective and ...efficient degradation of EOCs over a wide pH range is still challenging. Herein, we constructed FeN4 structures on a carbon nanotube (CNT) to obtain single-atom catalysts (FeSA-N-CNT) to generate RFeS in the presence of peroxymonosulfate (PMS). The obtained FeSA-N-CNT/PMS system exhibited outstanding and selective reactivity for oxidizing EOCs over a wide pH range (3.0–9.0). Several lines of evidences suggested that RFeS existing as an FeN4O intermediate was the predominant oxidant, while SO4 ·– and HO· were the secondary oxidants. Density functional theory calculation results revealed that a CNT played a key role in optimizing the distribution of bonding and antibonding states in the Fe 3d orbital, resulting in the outstanding ability of FeSA-N-CNT for PMS chemical adsorption and activation. Moreover, CNT could significantly enhance the reactivity of the FeN4O intermediate by increasing the overlap of electrons of the Fe 3d orbital, O 2p orbital, and bisphenol A near the Fermi level. The results of this study can advance the understanding of RFeS generation in a heterogeneous system over a wide pH range and the application of RFeS in real practice.
The increasing use of smartphones as personal computing platforms to access personal information has stressed the demand for secure and usable authentication techniques, and for constantly protecting ...privacy. Smartphone sensors can measure users' unique behavioral characteristics when they interact with smartphones, based on different habits, gestures, and angle preferences of touch actions. This paper investigates the reliability and applicability of using motion-sensor behavior for active and continuous smartphone authentication across various operational scenarios, and presents a systematic evaluation of the distinctiveness and permanence properties of the behavior. For each sample of sensor behavior, kinematic information sequences are extracted and analyzed, which are characterized by statistic-, frequency-, and wavelet-domain features, to provide accurate and fine-grained characterization of users' touch actions. A Markov-based decision procedure, using one-class learning techniques, is developed and applied to the feature space for performing authentication. Analyses are conducted using the sensor data of 520 200 touch actions from 102 subjects across various operational scenarios. Extensive experiments show that motion-sensor behavior exhibits sufficient discriminability and stability for active and continuous authentication, and can achieve a false-rejection rate of 5.03% and a false-acceptance rate of 3.98%. Additional experiments on usability to operation length, sensitivity to application scenario, scalability to user size, contribution to different sensors, and response to behavior change are provided to further explore the effectiveness and applicability. We also implement an authentication system into the Android system that can react to the presence of the legitimate user.
Over the past 20 years, zero-valent iron (ZVI) has been extensively applied for the remediation/treatment of groundwater and wastewater contaminated with various organic and inorganic pollutants. ...Based on the intrinsic properties of ZVI and the reactions that occur in the process of contaminants sequestration by ZVI, this review summarizes the limitations of ZVI technology and the countermeasures developed in the past two decades (1994–2014). The major limitations of ZVI include low reactivity due to its intrinsic passive layer, narrow working pH, reactivity loss with time due to the precipitation of metal hydroxides and metal carbonates, low selectivity for the target contaminant especially under oxic conditions, limited efficacy for treatment of some refractory contaminants and passivity of ZVI arising from certain contaminants. The countermeasures can be divided into seven categories: pretreatment of pristine ZVI to remove passive layer, fabrication of nano-sized ZVI to increase the surface area, synthesis of ZVI-based bimetals taking advantage of the catalytic ability of the noble metal, employing physical methods to enhance the performance of ZVI, coupling ZVI with other adsorptive materials and chemically enhanced ZVI technology, as well as methods to recover the reactivity of aged ZVI. The key to improving the rate of contaminants removal by ZVI and broadening the applicable pH range is to enhance ZVI corrosion and to enhance the mass transfer of the reactants including oxygen and H+ to the ZVI surface. The characteristics of the ideal technology are proposed and the future research needs for ZVI technology are suggested accordingly.
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•The development of ZVI-based technologies in the past two decades was reviewed.•The limitations of ZVI technology and the countermeasures were summarized.•The merits and demerits of each countermeasure were discussed in detail.•The future research needs in the field of ZVI technology were suggested.•The characteristics of an ideal ZVI technology were proposed.
The use of lanthanum (La)-based materials for phosphate removal from water and wastewater has received increasing attention. However, challenges remain to enhance phosphate sorption capacities and ...recover La-based sorbents. In this study, magnetic La(OH)3/Fe3O4 nanocomposites with varied La-to-Fe mass ratios were synthesized through a precipitation and hydrothermal method. Based upon preliminary screening of synthesized La(OH)3/Fe3O4 nanocomposites in terms of phosphate sorption capacity and La content, La(OH)3/Fe3O4 nanocomposite with a La-to-Fe mass ratio of 4:1 was chosen for further characterization and evaluation. Specifically, for these materials, magnetic separation efficiency, phosphate sorption kinetics and isotherm behavior, and solution matrix effects (e.g., coexisting ions, solution pH, and ionic strength) are reported. The developed La(OH)3/Fe3O4 (4:1) nanocomposite has an excellent magnetic separation efficiency of >98%, fast sorption kinetics of 30 min, high sorption capacity of 83.5 mg P/g, and strong selectivity for phosphate in presence of competing ions. Phosphate uptake by La(OH)3/Fe3O4 (4:1) was pH-dependent with the highest sorption capacities observed over a pH range of 4–6. The ionic strength of the solution had little interference with phosphate sorption. Sorption-desorption cyclic experiments demonstrated the good reusability of the La(OH)3/Fe3O4 (4:1) nanocomposite. In a real treated wastewater effluent with phosphate concentration of 1.1 mg P/L, 0.1 g/L of La(OH)3/Fe3O4 (4:1) efficiently reduced the phosphate concentration to below 0.05 mg P/L. Electrostatic attraction and inner-sphere complexation between La(OH)3 and P via ligand exchange were identified as the sorption mechanisms of phosphate by La(OH)3/Fe3O4 (4:1).
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•La(OH)3/Fe3O4 nanocomposites with high sorption capacity of 83.5 mg P/g are obtained.•La(OH)3/Fe3O4 exhibits 98% separation efficiency and fast sorption kinetics (30 min).•Highly efficient removal of phosphate from real wastewater effluent is achieved.•Electrostatic attraction and ligand exchange contribute to high phosphate sorption.
To deal with the difficulties caused by uncertainty of renewable energy sources in solving transmission constrained unit commitment (TCUC), robust optimization (RO) and scenario-based stochastic ...optimization (SO) methods have gained popularity in recent years. However, RO formulations have a multilevel (min-max-min or min-max) structure and the solution methods are usually complicated. On the other hand, when SO-based formulation is adopted, a careful balance is often required between accuracy and scale of the formulation, since they are conflicting with each other when determining the number of scenarios. Moreover, nonanticipative constraints on economic dispatch (ED) decisions are sometimes not considered in two-stage stochastic UC formulation. An example is given in this paper to show that this may have a serious consequence. The motivation of this paper is to establish a TCUC formulation that can address the above concerns. In summary, the proposed formulation has three features including: it is single-level rather than multilevel, it is established based on very limited scenarios while the solution is feasible to all scenarios, and finally, nonanticipativity of both UC and ED decisions is guaranteed by the formulation. Numerical testing is also performed and the results show that the proposed formulation is effective.
The question of whether Fe(IV) or SO4 •– is the dominant intermediate in the Fe(II)-activated peroxydisulfate process Fe(II)/PDS process remains unanswered. In this study, besides Fe(IV), SO4 •– ...and HO• were shown to be produced in the Fe(II)/PDS process by using multiple probes dimethyl sulfoxide, methyl phenyl sulfoxide, p-nitrobenzoic acid (p-NBA), and benzoic acid (BA). The removal of p-NBA and BA and the influence of BA on the yield of methyl phenyl sulfone (PMSO2) indicated that the major oxidizing intermediate changed from Fe(IV) to SO4 •–/HO• with an increase in the PDS/Fe(II) molar ratio at pH 3.0. Fe(IV), SO4 •–, and HO• were all involved in this process at pH 3.0–6.5, but their available amounts that contributed to abating organic contaminants decreased with an increase in pH considering the influence of pH on the generation of PMSO2 and p-hydroxybenzoic acid. Furthermore, Fe(IV), SO4 •–, and HO• contributed differently to abating different organic contaminants because of the different reactivities of these oxidizing oxidants toward different organic contaminants. Overall, this study demonstrates that multiple oxidizing species Fe(IV), SO4 •–, and HO• are generated in the Fe(II)/PDS process, which was significant for the application of this process and understanding the mechanisms of Fe(II)-activated peroxide processes.
Appropriately selecting methods for characterizing the reaction system of zerovalent iron (ZVI) favors its application for water treatment and remediation. Hence, a survey of the available ZVI ...characterization techniques used in laboratory and field studies are presented in this review for clarifying the characteristic properties, (in-situ) corrosion processes, and corrosion products of ZVI system. The methods are generally classified into four broad categories: morphology characterization techniques, (sub-)surface and bulk analysis mainly via the spectral protocols, along with the (physio)electrochemical alternatives. Moreover, this paper provides a critical review on the scopes and applications of ZVI characterization methodologies from several perspectives including their suitable occasions, availability, (semi-)quantitative/qualitative evaluations, in/ex-situ reaction information, advantages, limitations and challenges, as well as economic and technical remarks. In particular, the characteristic spectroscopic peak locations of typical iron (oxyhydr)oxides are also systematically summarized. In view of the complexity and variety of ZVI system, this review further addresses that different characterization methods should be employed together for better assessing the performance and mechanisms of ZVI-involved systems and thereby facilitating the deployment of ZVI-based installations in real practice.
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•The commonly-used methods for characterizing ZVI-based systems are reviewed.•The characterization methods of ZVI used in laboratory and field are categorized.•The information provided by the characterization methods are presented.•The environmental controls of the characterization approaches are discussed.•Characterization tools should be used together to clarify reaction mechanisms.
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