Effect of gas velocity and influent concentration on biofiltration of gasoline off-gas from soil vapor extraction

This study was conducted to evaluate the effects of gas inlet concentration and velocity on the biofiltration of gasoline vapor. Gasoline vapor was treated using a compost biofilter operated in an upflow mode for about 3 months. The inlet concentration of gasoline total petroleum hydrocarbon (TPH) ranged from about 300 to 7000 mgm(-3) and gas was injected at velocities of 6 and 15 mh(-1) (empty bed residence time (EBRT)=10 and 4 min, respectively). The maximum elimination capacities of TPH at 6 and 15 mh(-1) found in this research were over 24 and 19 gm(-3) of filling material h(-1), respectively. TPH removal data was fit using a first-order kinetic relationship. In the low concentration range of 300-3000 mg m(-3), the first-order kinetic constants varied between about 0.10 and 0.29 min(-1) regardless of gas velocities. At TPH concentrations greater than 3000 mgm(-3), the first-order kinetic constants were about 0.09 and 0.07 min(-1) at gas velocities of 6 mh(-1) and 15 mh(-1), respectively. To evaluate microbial dynamics, dehydrogenase activity, CO2 generation and microbial species diversity were analyzed. Dehydrogenase activity could be used as an indicator of microbial activity. TPH removal corresponded well with CO2 evolution. The average CO2 recovery efficiency for the entire biofilter ranged between 60% and 70%. When the gas velocity was 6 mh(-1), most of the microbial activity and TPH removal occurred in the first quarter of the biofilter. However, when the gas velocity was 15 mh(-1), the entire column contributed to removal. Spatial and temporal variations in the biofilter microbial population were also observed. Nearly 60% of the colonies isolated from the compost media prior to biofiltration were Bacillus. After 90 days of biofiltration, the predominant species in the lower portion (0-50 cm) of the filter were Rhodococcus, while Pseudomonas and Acinetobacter dominated the upper portion (75-100 cm).     

Regional measurements of PCDD/PCDF concentrations in Korean atmosphere and comparison with gas-particle partitioning models

The current investigation was aimed at determining the levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs) in the Korean atmosphere along with their estimation using gas-particle partitioning. Samples collected from six cites showed that large cities were polluted with a concentration of 0.593 pg TEQ/m3. Samples were also collected from residential (nine sites), commercial (five sites), and industrial (seven sites) districts in each city. Higher levels of PCDDs/PCDFs were observed in industrial area than other areas, since it includes many sources. Higher chlorinated 2,3,7,8-substituted congeners were predominantly found in the particulate phase. HpCDD/Fs and OCDD/Fs shared 97-99% of the particulate phase, whereas TCDD/Fs, which dominated the gaseous phase, shared 34.8% and 42.8% in 2,3,7,8-substituted congeners. The regression dataset was transformed due to the relationship between log K(P) and log P(L)o. A wide variation was observed in the slopes for the residential areas when compared with the slopes for the commercial and industrial areas. The Junge-Pankow model and K(oa) adsorption model were both found to be helpful in describing the gas-particle partitioning in the current study.     

The current status and future issues in human evacuation from ships

The International Maritime Organization (IMO) developed guidelines in May 1999 for the evacuation analysis of Ro-Ro passenger ships to prevent loss of life in maritime accidents. However, IMO considered these guidelines only as an interim measure and allocated 3 years for their improvement and further development as very limited experience and data were available. In this paper, the requirements of the IMO and current research regarding ship evacuation are reviewed. In addition, applicable evacuation models are presented as well as several experimental methods of obtaining the data of human behavior in regard to listing and the dynamic effect of waves on a ship are evaluated. Recommendations on further issues are discussed at the end.     

Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA)

Fluorochemicals (FCs) are oxidatively recalcitrant, environmentally persistent, and resistant to most conventional treatment technologies. FCs have unique physiochemical properties derived from fluorine which is the most electronegative element. Perfluorooctanesulfonate (PFOS), and perfluorooctanoate (PFOA) have been detected globally in the hydrosphere, atmosphere and biosphere. Reducing treatment technologies such as reverses osmosis, nano-filtration and activated carbon can remove FCs from water. However, incineration of the concentrated waste is required for complete FC destruction. Recently, a number of alternative technologies for FC decomposition have been reported. The FC degradation technologies span a wide range of chemical processes including direct photolysis, photocatalytic oxidation, photochemical oxidation, photochemical reduction, thermally-induced reduction, and sonochemical pyrolysis. This paper reviews these FC degradation technologies in terms of kinetics, mechanism, energetic cost, and applicability. The optimal PFOS/PFOA treatment method is strongly dependent upon the FC concentration, background organic and metal concentration, and available degradation time.     

Controlling various contaminants in wastewater effluent through membranes and engineered wetland

For effective wastewater reclamation and water recovery, the treatment of natural and effluent organic matters (NOM and EfOM), toxic anions, and micropollutants was considered in this work. Two different NOM (humic acid of the Suwannee River, and NOM of US and Youngsan River, Korea), and one EfOM from the Damyang wastewater treatment plant, Korea, were selected for investigating the removal efficiencies of tight nanofiltration (NF) and ultrafiltration (UF) membranes with different properties. Nitrate, bromate, and perchlorate were selected as target toxic anions due to their well known high toxicities. Tri-(2-chloroethyl)-phosphate (TCEP), oxybenzone, and caffeine, due to their different K _ow and pK _a values, were selected as target micropollutants. As expected, the NF membranes provided high removal efficiencies in terms of all the tested contaminants, and the UF membrane provided fairly high removal efficiencies for anions (except for nitrate) and the relatively hydrophobic micropollutant, oxybenzon. Through the wetlands, nitrate was successfully removed. Therefore, a fair process of combining membranes with an engineered wetland could be proposed for sustainable wastewater reclamation and optimum control of contaminats.     

Probability mass first flush evaluation for combined sewer discharges

The Korea government has put in a lot of e ort to construct sanitation facilities for controlling non-point source pollution. The first flush phenomenon is a prime example of such pollution. However, to date, several serious problems have arisen in the operation and treatment e ectiveness of these facilities due to unsuitable design flow volumes and pollution loads. It is di cult to assess the optimal flow volume and pollution mass when considering both monetary and temporal limitations. The objective of this article was to characterize the discharge of storm runo pollution from urban catchments in Korea and to estimate the probability of mass first flush (MFFn) using the storm water management model and probability density functions. As a result of the review of gauged storms for the representative using probability density function with rainfall volumes during the last two years, all the gauged storms were found to be valid representative precipitation. Both the observed MFFn and probability MFFn in BE-1 denoted similarly large magnitudes of first flush with roughly 40% of the total pollution mass contained in the first 20% of the runo . In the case of BE-2, however, there were significant di erence between the observed MFFn and probability MFFn.     

Predicting the impacts of climate change on nonpoint source pollutant loads from agricultural small watershed using artificial neural network

This study described the development and validation of an artificial neural network (ANN) for the purpose of analyzing the e ects of climate change on nonpoint source (NPS) pollutant loads from agricultural small watershed. The runo discharge was estimated using ANN algorithm. The performance of ANN model was examined using observed data from study watershed. The simulation results agreed well with observed values during calibration and validation periods. NPS pollutant loads were calculated from load-discharge relationship driven by long-term monitoring data. LARS-WG (Long Ashton Research Station-Weather Generator) model was used to generate rainfall data. The calibrated ANN model and load-discharge relationship with the generated data from LARS-WG were applied to analyze the e ects of climate change on NPS pollutant loads from the agricultural small watershed. The results showed that the ANN model provided valuable approach in estimating future runo discharge, and the NPS pollutant loads.