The production of biodiesel through a transesterification method produces a large amount of wastewater that contains high levels of chemical oxygen demand （COD） and oil and grease （O＆G）. Currently, flotation is t...The production of biodiesel through a transesterification method produces a large amount of wastewater that contains high levels of chemical oxygen demand （COD） and oil and grease （O＆G）. Currently, flotation is the conventional primary treatment for O＆G removal prior to biological treatments. In this study, electrocoagulation （EC） was adopted to treat the biodiesel wastewater. The effects of initial pH, applied voltage, and reaction time on the EC process for the removal of COD, O＆G, and suspended solids （SS） were investigated using one factor at a time experiment. Furthermore, the Box-Behnken design, an experimental design for response surface methodology （RSM）, was used to create a set of 15 experimental runs needed for optimizing of the operating conditions. Quadratic regression models with estimated coefficients were developed to describe the pollutant removals. The experimental results show that EC could effectively reduce COD, O＆G, and SS by 55.43%, 98.42%, and 96.59%, respectively, at the optimum conditions of pH 6.06, applied voltage 18.2 V, and reaction time 23.5 min. The experimental observations were in reasonable agreement with the modeled values.展开更多
Measurements and monitoring of volatile organic compounds （VOCs） have been conducted in the metropolitan Bangkok. However, in-vehicle levels of VOCs are still lacking. This study investigated VOCs concentrations in ...Measurements and monitoring of volatile organic compounds （VOCs） have been conducted in the metropolitan Bangkok. However, in-vehicle levels of VOCs are still lacking. This study investigated VOCs concentrations in four public transportation modes in Bangkok, Thailand during two rush hour periods （7：00–9：00 a.m. and 4：00–7：00 p.m.）. The four modes included an air-conditioned bus （A/C bus）, non-air-conditioned bus （non-A/C bus）, electric sky train, and a passenger boat traveling along the canal. Comparison among three important bus routes was also studied. In-vehicle air samples were collected using charcoal sorbent tubes and then analyzed by a gas chromatography-mass spectrometer. Results showed that the transportation modes significantly influenced the abundance of in-vehicle benzene, toluene, ethylbenzene, and m,p-xylene （BTEX）. Median concentrations of BTEX were 11.7, 103, 11.7, and 42.8 μg/m3 in A/C bus; 37.1, 174, 14.7, and 55.4 μg/m3 in non-A/C bus; 2.0, 36.9, 0.5, and 0.5 μg/m3 in sky train; and 3.1, 58.5, 0.5, and 6.2 μg/m3 in boat, respectively. Wilcoxon rank sum test indicated that toluene and m,p-xylene in the sky trains were statistically lower than that in the other three modes at a p-value of 0.05. There were statistical differences in TEX concentrations among the bus routes in the non-A/C buses. In addition, the benzene to toluene ratios implied that tail-pipe emissions were important contributor to the abundance of in-vehicle VOCs.展开更多
基金supported by the Energy Policy and Planning Office, Ministry of Energy Royal Thai Government under the grant for supporting conservation of energy
文摘The production of biodiesel through a transesterification method produces a large amount of wastewater that contains high levels of chemical oxygen demand （COD） and oil and grease （O＆G）. Currently, flotation is the conventional primary treatment for O＆G removal prior to biological treatments. In this study, electrocoagulation （EC） was adopted to treat the biodiesel wastewater. The effects of initial pH, applied voltage, and reaction time on the EC process for the removal of COD, O＆G, and suspended solids （SS） were investigated using one factor at a time experiment. Furthermore, the Box-Behnken design, an experimental design for response surface methodology （RSM）, was used to create a set of 15 experimental runs needed for optimizing of the operating conditions. Quadratic regression models with estimated coefficients were developed to describe the pollutant removals. The experimental results show that EC could effectively reduce COD, O＆G, and SS by 55.43%, 98.42%, and 96.59%, respectively, at the optimum conditions of pH 6.06, applied voltage 18.2 V, and reaction time 23.5 min. The experimental observations were in reasonable agreement with the modeled values.
基金supported by the Faculty of Engineering, Mahasarakham University, Thailand
文摘Measurements and monitoring of volatile organic compounds （VOCs） have been conducted in the metropolitan Bangkok. However, in-vehicle levels of VOCs are still lacking. This study investigated VOCs concentrations in four public transportation modes in Bangkok, Thailand during two rush hour periods （7：00–9：00 a.m. and 4：00–7：00 p.m.）. The four modes included an air-conditioned bus （A/C bus）, non-air-conditioned bus （non-A/C bus）, electric sky train, and a passenger boat traveling along the canal. Comparison among three important bus routes was also studied. In-vehicle air samples were collected using charcoal sorbent tubes and then analyzed by a gas chromatography-mass spectrometer. Results showed that the transportation modes significantly influenced the abundance of in-vehicle benzene, toluene, ethylbenzene, and m,p-xylene （BTEX）. Median concentrations of BTEX were 11.7, 103, 11.7, and 42.8 μg/m3 in A/C bus; 37.1, 174, 14.7, and 55.4 μg/m3 in non-A/C bus; 2.0, 36.9, 0.5, and 0.5 μg/m3 in sky train; and 3.1, 58.5, 0.5, and 6.2 μg/m3 in boat, respectively. Wilcoxon rank sum test indicated that toluene and m,p-xylene in the sky trains were statistically lower than that in the other three modes at a p-value of 0.05. There were statistical differences in TEX concentrations among the bus routes in the non-A/C buses. In addition, the benzene to toluene ratios implied that tail-pipe emissions were important contributor to the abundance of in-vehicle VOCs.
