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•Carbon nanotubes activate persulfates via nonradical mechanisms.•The CNT/persulfate system effectively oxidizes phenolic compounds.•Reactive complexes of CNT–persulfate are ...responsible for the compound degradation.
Carbon nanotubes (CNTs) have been found to activate persulfates (i.e., peroxymonosulfate and peroxydisulfate) into reactive species that are capable of oxidizing organic compounds in water. In the presence of single- or multi-walled CNTs, persulfates effectively degraded phenolic compounds and certain pharmaceuticals. Phenyl derivatives substituted with electron-withdrawing groups, such as benzoic acid and nitrobenzene, were resistant to degradation by the CNT/persulfate system. Based on observations regarding persulfate decomposition and linear sweep voltammetry using a CNT electrode, it has been suggested that persulfates bind onto the surface of CNTs, forming reactive complexes that are immediately decomposed upon reaction with organic compounds. Electron paramagnetic resonance spectroscopy with spin-trapping indicates that these reactive species are distinct from sulfate radical anions or hydroxyl radicals. The CNT-activated persulfate system shows promise as a novel treatment technology for the selective oxidation of organic contaminants in water.
Electrochemical disinfection has gained increasing attention as an alternative for conventional drinking water treatment due to its high effectiveness and environmental compatibility. The most common ...method of electrochemical disinfection is the use of electro-generated oxidants, such as active chlorine and reactive oxygen species, as disinfectants. This study examined the role of electrode material on the generation of oxidants, and elucidated the different reaction pathways for generating individual oxidants by employing boron-doped diamond (BDD), Ti/RuO
2, Ti/IrO
2, Ti/Pt–IrO
2, and Pt as anode materials. The efficiency of
OH production, as determined by
para-chlorobenzoic acid (
pCBA) degradation, was in the order of BDD
≫
Ti/RuO
2
≈
Pt. No significant production of
OH was observed at Ti/IrO
2 and Ti/Pt–IrO
2. The
OH was found to play a key role in O
3 generation at BDD, but not at the other electrodes. The production of active chlorine was in the order of Ti/IrO
2
>
Ti/RuO
2
>
Ti/Pt–IrO
2
>
BDD
>
Pt. The large difference in this order from that of ROS was attributed to the difference in the electrocatalytic activity of each electrode material toward the production of active chlorine, as evidenced by linear sweep voltammetry (LSV) measurements. In addition, the characteristics of microbial inactivation as a function of electrode material were examined under the presence of an inert electrolyte, using
Escherichia coli as an indicator microorganism.
This study involves elucidating the destruction mechanisms of four tetracyclines via reactions with
OH and solvated electrons (
e
aq
-
). The first step is to evaluate the bimolecular rate constants ...for the reaction of
OH and
e
aq
-
. Transient absorption spectra for the intermediates formed by the reaction of
OH were also measured over the time period of 1–250
μs to assist in selecting the appropriate wavelength for the absolute bimolecular reaction rate constants. For these four compounds, tetracycline, chlortetracycline, oxytetracycline, and doxycycline, the absolute rate constants with
OH were (6.3
±
0.1)
×
10
9, (5.2
±
0.2)
×
10
9, (5.6
±
0.1)
×
10
9, and (7.6
±
0.1)
×
10
9 M
−1 s
−1, and for
e
aq
-
were (2.2
±
0.1)
×
10
10, (1.3
±
0.2)
×
10
10, (2.3
±
0.1)
×
10
10, and (2.5
±
0.1)
×
10
10 M
−1 s
−1, respectively. The efficiencies for
OH reaction with the four tetracyclines ranged from 32% to 60%. The efficiencies for
e
aq
-
reaction were 15–29% except for chlortetracycline which was significantly higher (97%) than the other tetracyclines in spite of the similar reaction rate constants for
e
aq
-
in all cases. To evaluate the use of advanced oxidation/reduction processes for the destruction of tetracyclines it is necessary to have reaction rates, reaction efficiencies and destruction mechanisms. This paper is the first step in eventually realizing the formulation of a detailed kinetic destruction model for these four tetracycline antibiotics.
Electrochemical disinfection has emerged as one of the most promising alternatives to the conventional disinfection of water in many applications. Although the mechanism of electrochemical ...disinfection has been largely attributed to the action of electro-generated active chlorine, the role of other oxidants, such as the reactive oxygen species (ROS) *OH, O3, H2O2, and *O2- remains unclear. In this study, we examined the role of ROS in the electrochemical disinfection using a boron-doped diamond (BDD) electrode in a chloride-free phosphate buffer medium, in order to avoid any confusion caused by the generation of chlorine. To determine which species of ROS plays the major role in the inactivation, the effects of several operating factors, such as the presence of *OH scavenger, pH, temperature, and the initial population of microorganisms, were systematically investigated. This study clearly showed that the *OH is the major lethal species responsible for the E. coli inactivation in the chloride-free electrochemical disinfection process, and that the E. coli inactivation was highly promoted at a lower temperature, which was ascribed to the enhanced generation of O3.
Particulate matter (PM) and volatile organic compounds (VOCs) are recognised as hazardous air pollutants threatening human health. Disposable filters are generally used for air purification despite ...frequent replacement and waste generation problems. However, the development of a novel regenerable and robust filter for long-term use is a huge challenge. Here, we report on a new class of facile water-washing regenerable ceramic catalyst filters (CCFs), developed to simultaneously remove PM (>95%) and VOCs (>82%) in single-pass and maximized space efficiency by coating the inner and outer filter channels with an inorganic membrane and a Cu
O/TiO
photocatalyst, respectively. The CCFs reveal four-fold increase in the maximum dust loading capacity (approximately 20 g/L) in relation to conventional filters (5 g/L), and can be reused after ten regeneration capability with simple water washing retaining initial PM and VOC removal performances. Thus, the CCFs can be well-suited for indoor and outdoor air purification for 20 years, which shows a huge increase in lifetime compared to the 6-month lifespan of conventional filters. Finally, we believe that the development and implementation of CCFs for air purification can open new avenues for sustainable technology through renewability and zero-waste generation.
Recently, the electrochemical disinfection has gained a great interest as one of the alternatives to conventional chlorination due to its high effectiveness and environmental compatibility. Despite ...the extensive reports on electro-chlorination disinfection, few researches were reported on the systems without generating chlorine. This study mainly focused on the potential disinfecting ability of electro-generated oxidants other than chlorine with using an inert medium (chloride-free phosphate buffer solution), which was intended to exclude the formation of chlorine during the electrolysis, as the
Escherichia coli as an indicator bacterium was disinfected by applying the current to a platinum anode. The electrochemical inactivation of
E. coli without chlorine production was demonstrated to occur in two distinct stages. The first stage inactivation takes place rapidly at the beginning of electrolysis, which appears to be achieved by the electrosorption of negatively charged
E. coli cells to the anode surface, followed by a direct electron transfer reaction. As the electrolysis continues further, the inactivation becomes slower but steady, in contrast to the first stage of inactivation. This was attributed to the action of reactive oxidants generated from water discharge, such as hydroxyl radical. Overall, this study suggests that the electrochemical disinfection could be successfully performed even without producing chlorine, recommending the potential application for disinfecting water that does not allow including any chloride ions (such as the production of ultra-pure sterilized water for semiconductor washing).
In this study, the relative importance of the dual reaction pathways of CO2− in the photo/ferrioxalate system, where it acts both as a reductant for reducing the ferric ion and as an agent for the ...formation of H2O2, was investigated as a function of the concentrations of ferrioxalate and oxygen. We studied the two competitive reactions of CO2− in the photo/ferrioxalate system, which depend on the relative concentrations of ferrioxalate to oxygen, with the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), which was used as a target pollutant. At high concentrations of ferrioxalate, almost all of the CO2− reacted with ferrioxalate to reduce Fe(III) to Fe(II), whereas at low concentrations of ferrioxalate, a majority of the CO2− contributed to the formation of H2O2, as a result of its reaction with oxygen, which allows the Fenton reaction to occur without any external supply of H2O2.
Dissolved organic nitrogen (DON) accounts for a large fraction of the total nitrogen discharged to surface waters by municipal wastewater treatment plants designed for biological nutrient removal ...(BNR). Previous research indicates that some but not all of the DON in wastewater effluent is available to bacteria and algae over time scales that are relevant to rivers and estuaries. To separate bioavailable DON from nitrate and less reactive DON species, an XAD-8 resin coupled with an anion exchange treatment was employed prior to chemical analysis and algal bioassays. Analysis of effluent samples from a range of municipal BNR plants (total DON concentrations ranging from 0.7 to 1.8 mg N/L) employing a range of technologies indicated that hydrophilic DON, which typically accounted for approximately 80% of the total DON, stimulated algal growth, whereas hydrophobic DON, which accounted for the remaining DON, remained at nearly constant concentrations and had little or no effect on algal growth during a 14-day incubation period. The hydrophobic DON exhibits characteristics of humic substances, and is likely to persist for long periods in the aquatic environment. The distinct differences between these two classes of DON may provide a basis for considering them separately in water quality models and effluent discharge regulations.
In wastewater treatment using the Fenton and photofenton processes, pH is one of the critical operating parameters, due to the fact that the Fenton reaction can work only under acidic pH conditions. ...It is hoped that Ferric iron complexed with oxalate (Fe(III)-oxalate; ferrioxalate) will provide an alternative to the traditional Fenton process with its limited range of pH conditions, since its high solubility in aqueous media can broaden the available pH range of the Fenton reaction up to the near neutral pH regime. In this study, we investigated the pH dependency of
OH production in the photo/ferrioxalate system, in the presence and absence of externally supplied H
2O
2, where 2,4-D was used as the probe compound for
OH production at a wide range of pH values (1.2–7.4). In the absence of externally supplied H
2O
2, the 2,4-D degradation was considerably enhanced with increasing pH, whereas it was reduced with increasing pH in the presence of an excess amount of H
2O
2. These variations in the degradation of 2,4-D were thus found to be precisely related to the formation of H
2O
2, a factor to which little attention was paid in previous studies. In the absence of H
2O
2 addition, the in situ formation of H
2O
2 is facilitated with increasing pH by the reaction of Fe(II) with
O
2
-
, which increases with pH, augmenting the production of
OH and thereby leading to the faster degradation of 2,4-D. This same reaction can also provide an explanation for the opposite pH dependence of 2,4-D degradation in the presence of H
2O
2.
The presence of iodinated X-ray contrast media compounds (ICM) in surface and ground waters has been reported. This is likely due to their biological inertness and incomplete removal in wastewater ...treatment processes. The present study reports partial degradation mechanisms based on elucidating the structures of major reaction by-products using γ-irradiation and LC-MS. Studies conducted at concentrations higher than observed in natural waters is necessary to elucidate the reaction by-product structures and to develop destruction mechanisms. To support these mechanistic studies, the bimolecular rate constants for the reaction of
OH and e
−
aq with one ionic ICM (diatrizoate), four non-ionic ICM (iohexol, iopromide, iopamidol, and iomeprol), and the several analogues of diatrizoate were determined. The absolute bimolecular reaction rate constants for diatrizoate, iohexol, iopromide, iopamidol, and iomeprol with
OH were (9.58 ± 0.23)×10
8, (3.20 ± 0.13)×10
9, (3.34 ± 0.14)×10
9, (3.42 ± 0.28)×10
9, and (2.03 ± 0.13) × 10
9 M
−1 s
−1, and with e
−
aq were (2.13 ± 0.03)×10
10, (3.35 ± 0.03)×10
10, (3.25 ± 0.05)×10
10, (3.37 ± 0.05)×10
10, and (3.47 ± 0.02) × 10
10 M
−1 s
−1, respectively. Transient spectra for the intermediates formed by the reaction of
OH were also measured over the time period of 1–100 μs to better understand the stability of the radicals and for evaluation of reaction rate constants. Degradation efficiencies for the
OH and e
−
aq reactions with the five ICM were determined using steady-state γ-radiolysis. Collectively, these data will form the basis of kinetic models for application of advanced oxidation/reduction processes for treating water containing these compounds.
