Hyung-Eun Kim

Disintegration of Waste Activated Sludge by Thermally-Activated Persulfates for Enhanced Dewaterability.

Oxidation by persulfates at elevated temperatures (thermally activated persulfates) disintegrates bacterial cells and extracellular polymeric substances (EPS) composing waste-activated sludge (WAS), facilitating the subsequent sludge dewatering. The WAS disintegration process by thermally activated persulfates exhibited different behaviors depending on the types of persulfates employed, that is, peroxymonosulfate (PMS) versus peroxydisulfate (PDS). The decomposition of PMS in WAS proceeded via a two-phase reaction, an instantaneous decomposition by the direct reaction with the WAS components followed by a gradual thermal decay. During the PMS treatment, the WAS filterability (measured by capillary suction time) increased in the initial stage but rapidly stagnated and even decreased as the reaction proceeded. In contrast, the decomposition of PDS exhibited pseudo first-order decay during the entire reaction, resulting in the greater and steadier increase in the WAS filterability compared to the case of PMS. The treatment by PMS produced a high portion of true colloidal solids (<1 μm) and eluted soluble and bound EPS, which is detrimental to the WAS filterability. However, the observations regarding the dissolved organic carbon, ammonium ions, and volatile suspended solids collectively indicated that the treatment by PMS more effectively disintegrated WAS compared to PDS, leading to higher weight (or volume) reduction by postcentrifugation.

Oxidant production from corrosion of nano- and microparticulate zero-valent iron in the presence of oxygen: a comparative study.

In aqueous solution, zero-valent iron (ZVI, Fe(0)) is known to activate oxygen (O2) into reactive oxidants such as hydroxyl radical and ferryl ion capable of oxidizing contaminants. However, little is known about the effect of the particle size of ZVI on the yield of reactive oxidants. In this study, the production of reactive oxidants from nanoparticulate and microparticulate ZVIs (denoted as nZVI and mZVI, respectively) was comparatively investigated in the presence of O2 and EDTA. To quantify the oxidant yield, excess amount of methanol was employed, and the formation of its oxidation product, formaldehyde (HCHO), was monitored. The concentration of HCHO in the nZVI/O2 system rapidly reached the saturation value, whereas that in the mZVI/O2 system gradually increased throughout the entire reaction time. The mZVI/O2 system exhibited higher yields of HCHO than the nZVI/O2 system under both acidic and neutral pH conditions. The higher oxidant yields in the mZVI/O2 system are mainly attributed to the less reactivity of the mZVI surface with hydrogen peroxide (H2O2) relative to the surface of nZVI, which minimize the loss of H2O2 by ZVI (i.e., the two-electron reduction of H2O2 into water). In addition, the slow dissolution of Fe(II) from mZVI was found to be partially responsible for the higher oxidant yields at neutral pH.

Microbial inactivation by cupric ion in combination with H2O2: role of reactive oxidants.

The cupric ion mediated inactivation of Escherichia coli was enhanced by the presence of hydrogen peroxide (H2O2), with increasing inactivation efficacy observed in response to increasing concentrations of H2O2. The biocidal activity of the Cu(II)/H2O2 system is believed to result from the oxidative stress caused by reactive oxidants such as the hydroxyl radical ((•)OH), cupryl species (Cu(III)), and the superoxide radical (O2(•-)), which are produced via the catalytic decomposition of H2O2. In E. coli cells treated with Cu(II) and H2O2, the intracellular level of (•)OH and Cu(III) increased significantly, leading to complete disruption of cell membranes. On the basis of experimental observations made using an (•)OH scavenger, copper-chelating agents, and superoxide dismutase, it is concluded that Cu(III) is the predominant species responsible for the death of E. coli cells. It was also found that the production of Cu(III) was promoted by the reactions of copper with intracellular O2(•-). MS2 coliphage was found to be even more susceptible than E. coli to the oxidative stress induced by the Cu(II)/H2O2 system.

Polyphosphate-enhanced production of reactive oxidants by nanoparticulate zero-valent iron and ferrous ion in the presence of oxygen: Yield and nature of oxidants

The production of reactive oxidants from nanoparticulate zero-valent iron (nZVI) and ferrous ion (Fe(II)) in the presence of oxygen was greatly enhanced by the addition of tetrapolyphosphate (TPP) as an iron-chelating agent. Compared to other ligands, TPP exhibited superior activity in improving the oxidant yields. The nZVI/TPP/O2 and the Fe(II)/TPP/O2 systems showed similar oxidant yields with respect to the iron consumed, indicating that nZVI only serves as a source of Fe(II). The degradation efficacies of selected organic compounds were also similar in the two systems. It appeared that both hydroxyl radical (OH) and ferryl ion (Fe(IV)) are produced, and OH dominates at acidic pH. However, at pH > 6, little occurrence of hydroxylated oxidation products suggests that Fe(IV) is a dominant oxidant. The degradation rates of selected organic compounds by the Fe(II)/TPP/O2 system had two optimum points at pH 6 and 9, and these pH-dependent trends are likely attributed to the speciation of Fe(IV) with different reactivities.

Activation of Oxygen and Hydrogen Peroxide by Copper(II) Coupled with Hydroxylamine for Oxidation of Organic Contaminants

This study reports that the combination of Cu(II) with hydroxylamine (HA) (referred to herein as Cu(II)/HA system) in situ generates H2O2 by reducing dissolved oxygen, subsequently producing reactive oxidants through the reaction of Cu(I) with H2O2. The external supply of H2O2 to the Cu(II)/HA system (i.e., the Cu(II)/H2O2/HA system) was found to further enhance the production of reactive oxidants. Both the Cu(II)/HA and Cu(II)/H2O2/HA systems effectively oxidized benzoate (BA) at pH between 4 and 8, yielding a hydroxylated product, p-hydroxybenzoate (pHBA). The addition of a radical scavenger, tert-butyl alcohol, inhibited the BA oxidation in both systems. However, electron paramagnetic resonance (EPR) spectroscopy analysis indicated that (•)OH was not produced under either acidic or neutral pH conditions, suggesting that the alternative oxidant, cupryl ion (Cu(III)), is likely a dominant oxidant.

Enhanced Inactivation of Escherichia coli and MS2 Coliphage by Cupric Ion in the Presence of Hydroxylamine: Dual Microbicidal Effects

The inactivation of Escherichia coli and MS2 coliphage by Cu(II) is found to be significantly enhanced in the presence of hydroxylamine (HA). The addition of a small amount of HA (i.e., 5-20 μM) increased the inactivation efficacies of E. coli and MS2 coliphage by 5- to 100-fold, depending on the conditions. Dual effects were anticipated to enhance the biocidal activity of Cu(II) by the addition of HA, viz. (i) the accelerated reduction of Cu(II) into Cu(I) (a stronger biocide) and (ii) the production of reactive oxidants from the reaction of Cu(I) with dissolved oxygen (evidenced by the oxidative transformation of methanol into formaldehyde). Deaeration enhanced the inactivation of E. coli but slightly decreased the inactivation efficacy of MS2 coliphage. The addition of 10 μM hydrogen peroxide (H2O2) greatly enhanced the MS2 inactivation, whereas the same concentration of H2O2 did not significantly affect the inactivation efficacy of E. coli Observations collectively indicate that different biocidal actions lead to the inactivation of E. coli and MS2 coliphage. The toxicity of Cu(I) is dominantly responsible for the E. coli inactivation. However, for the MS2 coliphage inactivation, the oxidative damage induced by reactive oxidants is as important as the effect of Cu(I).

Nanoparticulate zero-valent iron coupled with polyphosphate: the sequential redox treatment of organic compounds and its stability and bacterial toxicity

Nanoparticulate zero-valent iron (nZVI) coupled with tetrapolyphosphate (TPP) (nZVI/TPP) was examined for the degradation of organic compounds, such as trichloroethylene (TCE), pentachlorophenol (PCP), and phenol, and the effects of TPP on the stability and toxicity of nZVI were studied. A sequential redox treatment (i.e., anoxic followed by oxic treatment) was attempted as a means to improve the utilization of nZVI for compound degradation. In the first anoxic treatment, chlorinated organic compounds, such as TCE and PCP, were degraded reductively by electron transfer from nZVI to the compounds at relatively slow rates. In the following oxic treatment, all organic compounds were rapidly degraded by the reactive oxidant (Fe(IV) species) produced via the reaction of the Fe(II)–TPP complexes with oxygen. In both anoxic and oxic treatment stages, the nZVI/TPP system exhibited greater activity in the degradation of organic compounds than that of nZVI alone. The anoxic/oxic reactivity of nZVI/TPP was affected by the pH and nZVI dose. The coupling of nZVI with TPP also enhanced the stability of nZVI; TPP was observed to inhibit the agglomeration and sedimentation of nZVI. In addition, the bacterial toxicity of nZVI and its oxidation products (i.e., Fe(II) and Fe(III)) was significantly reduced by the addition of TPP; TPP lowered the degree of E. coli inactivation by nZVI and its products, mitigating cell membrane damage.

Binder-free immobilization of TiO2 photocatalyst on steel mesh via electrospraying and hot-pressing and its application for organic micropollutant removal and disinfection

An immobilized photocatalyst was prepared by thermally treating TiO2-coated steel mesh (TiO2-IS) in a laboratory hot-press with no binder. TiO2 coating was performed by electrospraying a 1 mg/mL methanol dispersion of Evonik P25 powder. The thermal treatment conditions at 350 °C, 100 Mpa, and 1 h were found to be the optimum conditions. Scanning electron microscopic images displayed a robust and adherent TiO2 layer on steel mesh. X-ray photoelectron spectroscopy and elemental mapping studies confirmed that the Fe3O4 interface formed during thermal treatment strongly bound the TiO2 on steel mesh. The XRD patterns of TiO2-IS indicated the preservation of crystalline structure of Evonik P25 (anatase and rutile mixture) and the existence of iron oxide interface. Under UVA irradiation, 10 μM of methylene blue was completely decolorized within 40 min using an immobilized photocatalyst with 2.120 mg of TiO2 per 2.5 × 5.0 cm2 and showed stable efficacy in 25 consecutive photocatalytic runs. Furthermore, this sample degraded the organic micropollutants (e.g., pharmaceuticals) such as carbamazepine, ranitidine, acetaminophen, and trimethoprim at the rates of 0.041, 0.165, 0.089, and 0.079 min-1, respectively. Under UVA irradiation, it exhibited high photocatalytic disinfection activity for Escherichia coli and MS2 coliphage.

Oxidative Degradation of Phenol Using Zero-Valent Iron-Based Fenton-Like Systems

ABSTRACT For the last couple of decades, the Fenton (-like) systems have been extensively studied for oxidation of organiccontaminants in water. Recently, zero-valent iron (ZVI) has received attention as a Fenton catalyst as well as a reducingagent capable of producing reactive oxidants from oxygen. In this study, the ZVI-based Fenton reaction was assessed forthe oxidative degradation of phenol using ZVI/O 2 , ZVI/H 2 O 2 , ZVI/Oxalate/O 2 and hv/ZVI/Oxalate/O 2 systems. Reactionparameters such as pH and reagent dose (e.g., ZVI, H 2 O 2 , and oxalate) were examined. In the presence of oxalate (ZVI/Oxalate/O 2 and hv/ZVI/Oxalate/O 2 systems), the degradation of phenol was greatly enhanced at neutral pH values. It wasfound that ZVI accelerates the Fenton reaction by reducing Fe(III) into Fe(II). The conversion of Fe(III) into Fe(II) by ZVIwas more stimulated at acidic pH than at near-neutral pH values.Key words :Advanced oxidation process, Fenton reaction, Zero-valent iron, Hydroxyl radical, Phenol oxidation