Soon-Woong Chang

Decomposition and mineralization of cefaclor by ionizing radiation: kinetics and effects of the radical scavengers.

There has been recent growing interest in the presence of antibiotics in different environmental sectors. One considerable concern is the potential development of antibiotic-resistant bacteria in the environment, even at low concentrations. Cefaclor, one of the beta-lactam antibiotics, is widely used as an antibiotic. Kinetic studies were conducted to evaluate the decomposition and mineralization of cefaclor using gamma radiation. Cefaclor, 30 mg/l, was completely degraded with 1,000 Gy of gamma radiation. At a concentration of 30 mg/l, the removal efficiency, represented by the G-value, decreased with increasing accumulated radiation dose. Batch kinetic experiments with initial aqueous concentrations of 8.9, 13.3, 20.0 and 30.0mg/l showed the decomposition of cefaclor using gamma radiation followed a pseudo first-order reaction, and the dose constant increased with lower initial concentrations. At a given radiation dose, the G-values increased with higher initial cefaclor concentrations. The experimental results using methanol and thiourea as radical scavengers indicated that ()OH radicals were more closely associated with the radiolytic decomposition of cefaclor than other radicals, such as e(aq)(-) or ()H. The radical scavenger effects were tested under O(2) and N(2)O saturations for the enhancement of the TOC percentage removal efficiencies in the radiolytic decomposition of cefaclor. Under O(2) saturation, 90% TOC removal was observed with 100,000 Gy. Oxygen is well known to play a considerable role in the degradation of organic substances with effective chain reaction pathways. According to the effective radical reactions, the enhanced TOC percentage removal efficiencies might be based on the fast conversion reactions of e(aq)(-) and ()H with O(2) into oxidizing radicals, such as O(2)(-) and HO(2)(), respectively. 100% TOC removal was obtained with N(2)O gas at 20,000 Gy, as reducing radicals, such as e(aq)(-) and ()H, are scavenged by N(2)O and converted into ()OH radicals, which have strong oxidative properties. The results of this study showed that gamma irradiation was very effective for the removal of cefaclor in aqueous solution. The use of O(2) or N(2)O, with radiation, shows promise as effective radical scavengers for enhancing the TOC or COD removal efficiencies in pharmaceutical wastewaters containing antibiotics. However, the biological toxicity and interactions between various chemicals during the radiolytic treatment, as well as treatments under conditions more representative of real wastewater will require further studies.

Phytoremediation of Atrazine by Poplar Trees: Toxicity, Uptake, and Transformation

Toxicity, uptake, and transformation of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] by three species of poplar tree were assessed. Poplar cuttings were grown in sealed flasks with hydrophonic solutions and exposed to various concentrations of atrazine for a period of two weeks. Toxicity effects were evaluated by monitoring transpiration and measuring poplar cutting mass. Exposure to higher atrazine concentrations resulted in decrease of biomass and transpiration accompanied by leaf chlorosis and abscission. However, poplar cuttings exposed to lower concentrations of atrazine grew well and transpired at a constant rate during experiment periods. Poplar cuttings could take up, hydrolyze, and dealkylate atrazine to less toxic metabolites. Metabolism of atrazine occurred in roots, stems, and leaves and became more complete with increased residence time in tissue. These results suggest that phytoremediation is a viable approach to removing atrazine from contaminated water and should be considered for other contaminants.

Comparison of Fenton and Photo-Fenton Processes for Livestock Wastewater Treatment

In this study, the photochemical degradation of livestock wastewater was carried out by the Fenton and Photo-Fenton processes. The effects of pH, reaction time, the molar ratio of Fe2 +/H2O2, and the Fe2 + dose were studied. The optimal conditions for the Fenton and Photo-Fenton processes were found to be at a pH of 4 and 5, an Fe2 + dose of 0.066 M and 0.01 M, a concentration of hydrogen peroxide of 0.2 M and 0.1 M, and a molar ratio (Fe2 +/H2O2) of 0.33 and 0.1, respectively. The optimal reaction times in the Fenton and Photo-Fenton processes were 60 min and 80 min, respectively. Under the optimal conditions of the Fenton and Photo-Fenton processes, the chemical oxygen demand (COD), color, and fecal coliform removal efficiencies were approximately 70–79, 70–85 and 96.0–99.4%, respectively.

Dynamics of dissolved organic matter during four storm events in two forest streams: source, export, and implications for harmful disinfection byproduct formation

Dynamics of river dissolved organic matter (DOM) during storm events have profound influences on the downstream aquatic ecosystem and drinking water safety. This study investigated temporal variations in DOM during four storm events in two forest headwater streams (the EH and JH brooks, South Korea) and the impacts on the disinfection byproducts (DBPs) formation potential. The within-event variations of most DOM quantity parameters were similar to the flow rate in the EH but not in the larger JH brook. The dissolved organic carbon (DOC) showed clockwise and counterclockwise hysteresis with the flow rate in the EH and JH brooks, respectively, indicating the importance of both flow path and DOM source pool size in determining the effects of storm events. The stream DOM became less aromatic/humified from the first to the last event in both brooks, probably due to the increasing fresh plant pool and the decreasing leaf litter pool during the course of rainy season. The DOC export during each event increased 1.3–2.7- and 1.1–7.0-fold by stormflows in the EH and JH brooks, respectively. The leaf litter and soil together was the major DOM source, particularly during early events. The enhanced DOM export probably increases the risks of DBPs formation in disinfection, as indicated by a strong correlation observed between DOC and trihalomethanes formation potential (THMFP). High correlations between two humic-like fluorescent components and THMFP further suggested the potential of assessing THMFP with in situ fluorescence sensors during storms.

Photocatalytic degradation of 4-chlorophenol using a Ag/TiO2/Fe3O4 composite under UV-A irradiation

Abstract4-Chlorophenol (4-CP), widely used in the production of dyes, drugs, and fungicides is a water pollutant. It can be found in surface water, soil, ecosystems, and the human body. 4-CP is a non-degradable pollutant when subjected to traditional water treatment techniques. The development of advanced oxidation processes provided alternative methods that could potentially be applied to the decomposition of non-degradable compounds; 4-CP could then be removed from water supplies by processes such as photocatalytic degradation. However, the anatase TiO2 typically used in such procedures has a large band gap of 3.2 eV which is only activated by ultraviolet (UV) radiation. In this study, a Ag/TiO2/Fe3O4 composite was synthesized from Ag, TiO2, and Fe3O4 owing to the enhanced photocatalytic activity and catalyst recoverability conferred by Ag and Fe3O4, respectively. The catalyst was characterized by X-ray diffraction, X-ray fluorescence, UV–visible spectrophotometry, scanning electron microscopy, transmis...

Kinetic Study of Adsorption and Photocatalysis on Sulfamethoxazole Degradation by

In this study, it was found that adsorption and photocatalysis methodology of antibiotics such as Sulfamethoxazole with various catalyst(Titanium dioxide; , Hydroxyapatite; HAP). And compared the result of determined kinetics such as pseudo first order, second order and intra particle diffusion model. /HAP adsorbent were found to follow the pseudo second order reaction. And in the result of applied intrapaticle diffusion model, the constant of reaction rate were

TiO_2

TiO_2

/HAP Media

This paper represents the statistical characteristics of sources and receptors for road traffic noise in apartment complex. Also we suggested that the site-specific characteristics of vertical and horizontal distributions in the complex apartment have been derived using a different analysis for evaluating levels of Leq1h by the apartment floor at a given distance from a road in terms of the flow rate, the mean speed of the traffic, and the percentage of the type vehicles in the day and night periods. As a result, the contribution orders of traffic quantity by the type of vehicles showed as followed: light vehicle>medium vehicle>heavy vehicle>motorcycle. Especially, the mixing ratio of entering the road on the heavy vehicle in the daytime was two times higher than that of in the night. The speed in all types of vehicle is in the range of 41 and 81 km/hr and noise level was not significantly different in day and night-time. The sources of road traffic noise had different variations and uncertainties using a random variable and probability distribution. The sound distribution to receptors by the apartment floor showed S curve between 1st floor and floor With the normality test, the normal distributions using Anderson-Darling Test followed and , floor in the daytime and all floors except floor in the night (p>0.05). And also, the value of the pearson correlation coefficient (r) obtained in this study have significantly different at the range of floor. In conclusion, the results suggested that the distribution characteristics of levels of on the sources and receptors of road traffic noise in apartment complex must be improved and developed on the guideline of regulation of road traffic noise.

The Study on the Statistical Characteristics of Road Traffic Noise in Apartment Complex

In order to evaluate the potential use for ex situ remediation, a solar-driven, photocatalyzed reactor system was constructed and applied for the treatment of groundwater contaminated with benzene using selected advanced oxidation processes (AOP) processes, such as H2O2/solar light, TiO2 slurry/solar light and immobilized TiO2/solar light. However; to date, there have been few attempts to characterize the potential impact of residual levels of benzene on human health after treatment. Some papers have focused on the application of treatment methods of benzene, but most have not considered the effects of realistic hazards and human health. Therefore, potential and realistic hazards of benzene to human health were investigated at a gas station site using a risk-based assessment approach. Among the different remediation actions, the solar light/TiO2 slurry/H2O2 system (Action 5) showed higher removal efficiency than the solar light/TiO2 slurry (Action 3) and the solar light/immobilized TiO2 (Action 2) systems for the treatment of benzene. The Action 5 remediation method achieved 98% degradation, and lead to a substantial increase in the removal of benzene due to the synergetic effect of TiO2 with the oxidant, H2O2. Also, using the realistic and potential hazard assessment instead of the point estimation of concentration after benzene treatment, the total health risk exceeded the target risk value (1 × 10− 6). However, the 95th percentile target cancer risk, found using a probabilistic analysis (Monte Carlo method), was around 1 × 10− 6, indicating a low potential carcinogenic risk. Therefore, it was concluded that no adverse health risk was unlikely to be posed if the Action 5 system, which included the addition of TiO2 and H2O2, or if an increased reaction time was applied. In addition, continuous efforts and proper actions must be taken on the “Soil and Groundwater Remediation Action” based on the risk assessment in Korea.

The potential and realistic hazards after a solar-driven chemical treatment of benzene using a health risk assessment at a gas station site in Korea.

In this study, we investigated the possibility of auto control and the proper operating factors in the BNR(Biological Nutrient Removal) process using an NADH(Reduced Nicotinamide Adenine Dinucleotide) fluorometer, which characterized the emitted fluorescence when activated by flashes of UV light at 460 nm. In terms of finding adequate operating parameters, results indicted that nitrification efficiency decreased in the controlled DO while denitrification efficiency decreased in the controlled pH. The above results indicated that controlled operating condition after combination with NADH, DO and pH was resonable. Result obtained from the correlation between NADH and pH showed that variation trend of influent loading was similar to those of NADH and pH, and also the variation cycle was repeated on a daily basis. Consequently, this result showed the increase of BOD loading caused the nitrification efficiency to decrease because air-flow, required for nitrification, was reduced, and so the NADH value was increased. From these results, it is possible to use NADH flourimetry to assess the variation of organic load and nitrification efficiency in the case of small change in influent pH such as in sewage and also to handle and operate the load variation in the auto control system using the NADH fluorometer.