Youmi Jung

Removal of iopromide and degradation characteristics in electron beam irradiation process

The aim of this study is to evaluate the removal efficiency of iopromide using electron beam (E-beam) irradiation technology, and its degradation characteristics with hydroxyl radical (OH) and hydrated electron (e(aq)(-)). Studies are conducted with different initial concentrations of iopromide in pure water and in the presence of hydrogen peroxide, bicarbonate ion, or sulfite ion. E-beam absorbed dose of 19.6 kGy was required to achieve 90% degradation of 100 μM iopromide and the E-beam/H(2)O(2) system increased the removal efficiency by an amount of OH· generation. In the presence of OH scavengers (10 mM sulfite ion), the required dose for 90% removal of 100 μM iopromide was only 0.9 kGy. This greatly enhanced removal was achieved in the presence of OH· scavengers, which was rather unexpected and unlike the results obtained from most advanced oxidation process (AOP) experiments. The reasons for this enhancement can be explained by a kinetic study using the bimolecular rate constants of each reaction species. To explore the reaction scheme of iopromide with OH· or e(aq)(-) and the percent of mineralization for the two reaction paths, the total organic carbon (TOC), released iodide, and intermediates were analyzed.

Inactivation characteristics of ozone and electrolysis process for ballast water treatment using B. subtilis spores as a probe

Since ballast water affects the ocean ecosystem, the International Maritime Organization (IMO) sets a standard for ballast water management and might impose much tighter regulations in the future. The aim of this study is to evaluate the inactivation efficiency of ozonation, electrolysis, and an ozonation-electrolysis combined process, using B. subtilis spores. In seawater ozonation, HOBr is the key active substance for inactivation, because of rapid reactivity of ozone with Br(-) in seawater. In seawater electrolysis, it is also HOBr, but not HOCl, because of the rapid reaction of HOCl with Br(-), which has not been recognized carefully, even though many electrolysis technologies have been approved by the IMO. Inactivation pattern was different in ozonation and electrolysis, which has some limitations with the tailing or lag-phase, respectively. However, each deficiency can be overcome with a combined process, which is most effective as a sequential application of ozonation followed by electrolysis.

Performance of electron beam irradiation for treatment of groundwater contaminated with acetone

The purposes of this study were to evaluate the efficiency of acetone removal by electron beam irradiation in groundwater and the effect of various conditions. According to the results, the removal kinetics of acetone were pseudo first-order, and the removal efficiencies were expressed to the (%) removal and G-values. By adding sulfite, it was confirmed that acetone was mainly degraded by the reaction with the hydrated electrons. The presence of nitrate caused the removal of acetone to decrease. But there was no significant effect of alkalinity on the removal of acetone. The effect of the initial pH values (pH 5 to 9) on the acetone removal efficiency was negligible, but the pH value decreases due to the formation of acidic compounds after irradiation. Consequently, the radiation-induced removal reactions of acetone followed the pseudo-first-order kinetic model; in addition to the initial concentration of acetone, nitrate and the absorbed dose were important factors in removing acetone from an aqueous solution using electron beam irradiation. The effects of general pH and alkalinity on the degrading acetone were negligible.

Evaluation of the formation of oxidants and by-products using Pt/Ti, RuO2/Ti, and IrO2/Ti electrodes in the electrochemical process.

The aim of this study was to evaluate the formation of oxidants and by-products by using different electrode materials, such as Pt/Ti, RuO2/Ti, and IrO2/Ti, in the electrochemical process. The harmful by-products and were formed during the electrolysis of a Cl− electrolyte solution, as well as active chlorine, which is the most common water disinfectant. With regard to drinking water treatment, the most efficient electrode was defined as that leading to a higher formation of active chlorine and a lower formation of hazardous by-products. Overall, it was found that the Pt/Ti electrode should not be used for drinking water treatment applications, while the IrO2/Ti and RuO2/Ti electrodes are ideal for use.

Formation of Bromate and Chlorate during Ozonation and Electrolysis in Seawater for Ballast Water Treatment

Many effective technologies have been developed and approved for ballast water treatment, and the effectiveness of a process should be evaluated considering its environmental friendliness. The aim of this study was to evaluate the formation and formation mechanisms of bromate (BrO3−) and chlorate (ClO3−) in seawater during ozonation, electrolysis, and a combined (ozonation/electrolysis) process. In seawater ozonation, BrO3− was generated exceeding a 5 mg/L ozone dose despite the high Br− (65 mg/L). The formation of BrO3− and ClO3− by electrolysis depended on the electrode materials where two types of electrodes (IrO2/Ti and Pt/Ti) were used. The combined (ozonation/electrolysis) process generated much higher levels of BrO3− and ClO3− than either individual process. In ozonation or electrolysis, mixed oxidant including HOCl/OCl− and HOBr/OBr− is the main parameter for inactivation, which is called total residual oxidant, TRO. In this study, a predictive model for BrO3− and ClO3− was suggested in terms of TRO formation. This predictive model can recommend allowable TRO (generated by ozonation or electrolysis) for practical applications in seawater treatment.

Evaluation of the Catalytic Effect of the Ozone/Carbon Nanotube (O3/CNT) Process Using para-Chlorobenzoic Acid (pCBA)

The catalytic effects and mechanisms of the ozone/carbon nanotube (O3/CNT) process using para-chlorobenzoic acid (pCBA) were evaluated. To use pCBA as an O3-resistant OH• probe compound in a pure water system at pH 7, an adequate amount of scavenger was needed. During the O3/CNT process, a synergetic catalytic effect by OH• generation on the CNT surface could be evaluated in the condition of excess tert-butyl alcohol (TBA) concentration. The OH• radicals were generated and existed on both the bulk phase and CNT surface. The OH-ct values of the CNT surface and bulk phase in the O3/CNT process for 10 min were 2.1 × 10−5 and 2.5 × 10−5μ M·s, respectively. In modifying CNT evaluation, the catalytic effects were the most apparent in the following order: CNT treated with acid then heat (CNT-T), original untreated CNT (CNT-O), and CNT treated with an acid (CNT-A).

Characteristics of intracellular algogenic organic matter and its reactivity with hydroxyl radicals

The aim of this study was to investigate the reactivity of intracellular algogenic organic matter (IOM) with hydroxyl radicals (·OH), a key reaction species in advanced oxidation processes. IOM was extracted from two green algae, Chlamydomonas reinhardtii and Scenedesmus sp., and two blue-green algae, Anabaena sp. and Microcystis aeruginosa using a freeze-thaw method. The second-order rate constants of the extracted IOM with ·OH were determined as 7.95 × 108 MC-1 s-1 (Chlamydomonas reinhardtii), 6.71 × 108 MC-1 s-1 (Scenedesmus sp.), 4.02 × 108 MC-1 s-1 (Anabaena sp.), and 4.45 × 108 MC-1 s-1 (Microcystis aeruginosa). These rate constants were significantly higher than values reported for dissolved organic matter in various water sources. This implies that IOM formation during algal bloom season could change the ·OH water matrix demand and adversely affect the performance of advanced oxidation processes. To investigate the physical and chemical composition characteristics of IOM and their relationship to the rate constants determined for the reaction between IOM and ·OH, liquid chromatography-organic carbon detection (LC-OCD) and fluorescence excitation-emission matrix & parallel factor analysis (FEEM-PARAFAC) were used. The IOM mainly consisted of low molecular weight (LMW) matter and protein-related compounds, as evidenced LMW neutrals (38-65%), biopolymers (7-19%), and tryptophan-like compounds (74-94%). Based on the composition characteristics of IOM, it was concluded that the molecular weight and the presence of nitrogen-containing compounds are influential parameters for determining the reactivity of IOM with ·OH.

Removal of sulfamethoxazole, ibuprofen and nitrobenzene by UV and UV/chlorine processes: A comparative evaluation of 275 nm LED-UV and 254 nm LP-UV

The aim of this study is to evaluate the micropollutant removal capacity of a 275 nm light-emitting diode (LED)-UV/chlorine system. The sulfamethoxazole, ibuprofen, and nitrobenzene removal efficiencies of this system were compared with those of a conventional 254 nm low-pressure (LP)-UV system as a function of the UV dose. In a direct photolysis system, the photon reactivity of sulfamethoxazole is higher than that of nitrobenzene and ibuprofen at both wavelengths. The molar absorption coefficients and quantum yields of each micropollutant were as follows: sulfamethoxazole (εSMX, 275 nmprotonated = 17,527 M-1 cm-1, ΦSMX, 275 nmprotonated = 0.239, εSMX, 275 nmdeprotonated = 8430 M-1 cm-1, and ΦSMX, 275 nmdeprotonated = 0.026), nitrobenzene (εNB, 275 nm = 7176 M-1 cm-1 and ΦNB, 275 nm = 0.057), and ibuprofen (εNB, 275 nm = 200 M-1 cm-1 and ΦIBF, 275 nm = 0.067). The photon reactivity of chlorine species, i.e., HOCl and OCl-, were determined at 275 nm (εHOCl, 275 nm = 28 M-1 cm-1, ΦHOCl, 275 nm = 1.97, εOCl-, 275 nm = 245 M-1 cm-1, and ΦOCl-, 275 nm = 0.8), which indicate that the decomposition rate of OCl- is higher and that of HOCl is lower by 275 nm photolysis than that by 254 nm photolysis (εHOCl, 254 nm = 60 M-1 cm-1, ΦHOCl, 254 nm = 1.46, εOCl-, 254 nm = 58 M-1 cm-1, and ΦOCl-, 254 nm = 1.11). In the UV/chlorine system, the removal rates of ibuprofen and nitrobenzene were increased by the formation of OH and reactive chlorine species. The 275-nm LED-UV/chlorine system has higher radical yields at pH 7 and 8 than the 254 nm LP-UV/chlorine system.

Evaluation of Moringa oleifera seed extract by extraction time: effect on coagulation efficiency and extract characteristic

The seed of Moringa oleifera (MO) is a well-known coagulant used in water and wastewater treatment, especially in developing countries. The main mechanism of MO seed extract in coagulation is the positive protein component for charge neutralization. The method for efficient extraction of MO seed is very important for high coagulation activity. In this study, the effects of extraction mixing speed and extraction time of MO on coagulation activity were evaluated using a distilled water extraction method. Although the rotation per minute for extraction did not affect the coagulation efficiency, the extraction time strongly affected the coagulation efficiency of the extract. To evaluate the characteristic change of MO extract by extraction time, the charge of MO extract and protein characteristic in MO extract were analysed. As the extraction time was short, more positive charge and higher protein content were observed. For detailed protein analysis, the fluorescence spectroscopic study (EEM analysis) was performed. The tryptophan-like peak increased at longer extraction times. For efficient extraction of MO seed, a short extraction time is strongly recommended.

Determination of Efficient Operating Condition of UV/H 2 O 2 Process Using the OH Radical Scavenging Factor

This study investigated a method to determine an efficient operating condition for the process. The OH radical scavenging factor is the most important factor to predict the removal efficiency of the target compound and determine the operating condition of the process. To rapidly and simply measure the scavenging factor, Rhodamine B (RhB) was selected as a probe compound. Its reliability was verified by comparing it with a typical probe compound (para-chlorobenzoic acid, pCBA); the difference between RhB and pCBA was only 1.1%. In a prediction test for the removal of Ibuprofen, the RhB method also shows a high reliability with an error rate of about 5% between the experimental result and the model prediction using the measured scavenging factor. In the monitoring result, the scavenging factor in the influent water of the pilot plant was changed up to 200% for about 8 months, suggesting that the required UV dose could be increased about 1.7 times to achieve 90% caffeine removal. These results show the importance of the scavenging factor measurement in the process, and the operating condition could simply be determined from the scavenging factor, absorbance, and information pertaining to the target compound.