The kinetic of the catalytic decomposition of methyl isobutyl ketone over a Pt/gamma-Al2O3 catalyst

Environmental catalysis also can refer to catalytic technologies for reducing emission of environmentally unacceptable compounds. Catalytic decomposition also is one of the cost-effective technologies to solve the troublesome volatile organic compounds. This study treated methyl isobutyl ketone (MIBK) by a commercial catalyst, Pt/gamma-Al(2)O(3), in an isothermal fixed bed differential reactor. The effects of O(2) and MIBK content in carrier gas on the catalysis's reaction rate are also observed. Three kinetic models, i.e. the Mars and van Krevelen model, Langmuir-Hinshelwood model and power-rate law were applied to best fit the experimental results. The results indicate that the kinetic behavior of MIBK oxidation with catalysis can be accounted for by using the rate expression of the Mars and van Krevelen model and Langmuir-Hinshelwood model. Kinetic parameters are also determined on the basis of the differential reactor data. The experimental results are compared with those of the model predicted.     

A river water quality management model for optimising regional wastewater treatment using a genetic algorithm

To achieve water quality goals and wastewater treatment cost optimisation in a river basin, a water quality management model has been developed through the integration of a genetic algorithm (GA) and a mathematical water quality model. The developed model has been applied to the Youngsan River, where water quality has decreased due to heavy pollutant loads from Kwangju City and surrounding areas. Pollution source, land use, geographic features and measured water quality data of the river basin were incorporated into the Arc/View geographic information system database. With the database, the management model calculated treatment type and treatment cost for each wastewater treatment plant in the river basin. Until now, wastewater treatment policy for polluted rivers in Korea has been, first of all, to construct secondary treatment plants for untreated areas, and secondarily, to construct advanced treatment plants for the river sections whose water quality is impaired and for which the water quality goal of the Ministry of Environment is not met. Four scenarios that do not use the GA were proposed and they were compared with the results of the management model using the GA. It became clear that the results based on the GA were much better than those for the other four scenarios from the viewpoint of the achievement of water quality goals and cost optimisation.     

Concentrations and accumulation profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans in aquatic tissues, and ambient air from South Korea

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/DFs), including 2378-substituted isomers were present in samples of shellfish and fish, and ambient air collected from Masan Bay, and Masan City, South Korea. Total concentrations of PCDDs/DFs in mussel and clam were 750 pg g(-1), lipid weight (lw), and 3418 pg g(-1), lw, respectively. Total concentrations of PCDDs/DFs in mullet, gizzard and flounder were 52, 82, and 122 pg g(-1), lw, respectively. Shellfish tissues contained a greater number of PCDD/DF isomers, contributing greater total concentrations of PCDDs/DFs compared to fish collected from the same locations. The predominance of 2378-substituted PCDDs/DFs in fish is represented in greater total concentrations of 2378-TeCDD equivalents (TEQs), whereas there was very limited occurrence of 2378-substituted isomers in shellfish. TEQ concentrations in samples of mussel and clam were 0.97 and 12 pg g(-1), lw, respectively. Total TEQs in mullet, gizzard and flounder were 12, 22 and 18 pg g(-1), lw, respectively. In fish 2378-substituted PCDDs accounted for 100% of the total concentrations of PCDDs, and 2378-substituted PCDFs accounted from 59% to 73% of the total PCDFs. The 2378-substituted isomers accounted for only 3% of the total PCDDs/DFs in shellfish. Ambient air collected from two sites contained a wide range of isomers of tetra- through heptachlorinated PCDDs/DFs. Even though the total concentration of PCDDs/DFs in ambient air (12.8 pgm(-3)) collected from an industrial area was 2-fold greater than that in air samples (6.3 pgm(-3)) collected from an urban/rural area, total TEQs (0.07 and 0.08 pgm(-3)) there was no statistical difference between the two samples.     

Enhanced desorption of phenanthrene from soils using hydroxypropyl-beta-cyclodextrin: experimental results and model predictions

Objective of this study was to evaluate the effects of hydroxypropyl-beta-cyclodextrin (HPCD) on the removal of phenanthrene from solid phase. Batch tests for the phenanthrene distribution between aqueous and solid phase were conducted in the presence of HPCD. Column tests and numerical simulations were conducted to evaluate the roles of HPCD cavities and interaction rates between water, HPCD, and solid phase in the enhanced removal of phenanthrene. Experimental results showed that HPCD was effective in removing sorbed phenanthrene from subsurface environment, primarily due to its negligible sorption to the solid phase and the partitioning of phenanthrene into HPCD cavities. From the numerical simulations, it was found that rate-limited partitioning of phenanthrene into HPCD cavities was most influential factor in the enhanced elution of phenanthrene. Sorption and desorption rate of phenanthrene between aqueous and solid phase was very fast or near equilibrium state. Interaction rates of contaminant between water, HPCD, and solid phase could be affected by other factors such as soil types and organic matter contents. Results from this study implied that HPCD flushing could be effectively applied for the removal of hydrophobic organic pollutants existing in the soils as sorbed or NAPL state.     

Longitudinal‐Vertical Hydrodynamic and Turbidity Simulations for Prediction of Dam Reconstruction Effects in Asian Monsoon Area1

Abstract: This research investigates possible impacts of enlarged water body according to dam reconstruction on the hydrodynamics and water quality of the reservoir using a laterally averaged, two‐dimensional hydrodynamic and transport model, CE‐QUAL‐W2. The lake was formed by the artificial dam in 1983 for agricultural water supply and is currently under consideration of reconstruction so as to expand the volume of reservoir for flood control as well as water supply in downstream areas. To calibrate and validate the model, field‐collected data were compared with model predictions for water level fluctuations and water temperature during the years of 2001 (from January to December) and 2003 (from March to November). The model results showed a good agreement with field measurements both in calibration and verification. Utilizing the model, impacts of dam reconstruction on the thermal hydrodynamics and turbid current were predicted. From the model results, dam reconstruction limited the depth of thermal stratification below 10 meter and formed steep temperature gradient between epilimnion and hypolimnion. The restricted thermal stratification persisted up to the end of September. This result indicated that thermal stratification would become stronger during summer and stay longer after dam reconstruction. In addition, the restricted thermal stratification caused vertical circulation of water mixing lower than 10 meter and isolated the upper water layer from the lower water layer which increased the volume of hypolimnetic water with low temperature. The vertical circulation near the surface also mitigated propagation of density plume within the depth of 10 m which would remain the hypolimnetic water clean.     

Effects of ozonation and coagulation on effluent organic matter characteristics and ultrafiltration membrane fouling

Effluent organic matter （EfOM） is the major cause of fouling in the low pressure membranes process for wastewater reuse. Coagulation and oxidation of biological wastewater treatment effluent have been applied for the fouling control of microfiltration membranes. However, the change in EfOM structure by pre-treatments has not been clearly identified. The changes of EfOM characteristics induced by coagulation and ozonation were investigated through size exclusion chromatography, UV/Vis spectrophotometry, fluorescence spectrophotometry and titrimetric analysis to identify the mechanisms in the reduction of ultrafiltration （UF） membrane fouling. The results indicated that reduction of flux decline by coagulation was due to modified characteristics of dissolved organic carbon （DOC） content. Total concentration of DOC was not reduced by ozonation. However, the mass fraction of the molecules with molecular weight larger than 5 kDa, fluorescence intensity, aromaticity, highly condensed chromophores, average molecular weight and soluble microbial byproducts decreased greatly after ozonation. These results indicated that EfOM was partially oxidized by ozonation to low molecular weight, highly charged compounds with abundant electron- withdrawing functional groups, which are favourable for alleviating UF membrane flux decline.     

An evaluation of a river health using the index of biological integrity along with relations to chemical and habitat conditions

We evaluated the health condition of a temperate river during June-November 1999 through applications of the index of biological integrity (IBI) using fish assemblages and qualitative habitat evaluation index (QHEI) as well as chemical analyses. Overall IBI values ranged from 13 to 37 and averaged 23 (n = 25, standard error = 1.16), indicating a "poor" or "very poor" condition according to the criteria of modified Karr [Fisheries 6 (1981) 21]. The values of mean IBI declined at a rate of 0.22 km(-1) (R2 = 0.91, p < 0.05) along the longitudinal distance from the headwaters to the downstream sites. Reduced IBI values at downstream sites reflected low forest cover, high population density and high nutrient enrichments. Ecotoxicity tests using the river water also showed that toxic impacts were evident in the downriver sites. These factors resulted in decreases of riffle benthic species and insectivores and increases of tolerant species, anormalies and exotic species in the river. Spatial pattern in IBI agreed with QHEI values, which showed a linear relation (R2 = 0.998, p < 0.001) with species richness. Field measurements of conductivity and pH, an indicators for variation of conservative ions, showed that the river water was diluted by 40% fold by summer monsoon rain and surface run-off from the watershed, resulting in a physical and chemical instability during the monsoon. For these reasons, average IBI values during the monsoon and postmonsoon decreased >20% compared to the premonsoon, indicating that IBI values were also affected by flow regime. Based on the overall physico-chemical data and IBI values, the river health is rapidly degrading due to the combined effect of chemical contaminations and habitat modifications.