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CONTENTS
Volume 3, Number 2, June 2014
 

Abstract
This study aimed to synthesize dispersed and reactive nanoscale zero-valent iron (nZVI) with poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA), nontoxic and biodegradable stabilizer. The nZVI used for the experiments was prepared by reduction of ferric solution in the presence of PVP/VA with specific weight ratios to iron contents. Colloidal stability was investigated based on the rate of sedimentation, hydrodynamic radius and zeta potential measurement. The characteristic time, which demonstrated dispersivity of particles resisting aggregation, increased from 21.2 min (bare nZVI) to 97.8 min with increasing amount of PVP/VA (the ratios of 2). For the most stable nZVI coated by PVP/VA, its reactivity was examined by nitrate reduction in a closed batch system. The pseudo-first-order kinetic rate constants for the nitrate reduction by the nanoparticles with PVP/VA ratios of 0 and 2 were 0.1633 and 0.1395 min-1 respectively. A nitrogen mass balance, established by quantitative analysis of aqueous nitrogen species, showed that the addition of PVP/VA to nZVI can change the reduction capacity of the nanoparticles.

Key Words
Poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA); nanoscale zero-valent iron (nZVI); colloidal stability; nitrate reduction

Address
(1) Nara Lee, Kyunghoon Choi, Woojin Lee:
Department of Civil and Environmental Engineering, Korea Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea;
(2) Basil Uthuppu, Mogens H. Jakobsen:
Department of Micro- and Nanotechnology, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark;
(3) Yuhoon Hwang, Mette M. Broholm:
Department of Environmental Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.

Abstract
Groundwater contamination is seeking a lot of attention due to constant degradation of water by landfills and waste lagoons. In many cases heterogeneous soil system is encountered and hence, a finite element model is developed to solve the advection-dispersion equation for layered soil system as FEM is a robust tool for modelling problems of heterogeneity and complex geometries. Recently developed Meshfree methods have advantage of eliminating the mesh and construct approximate solutions and are observed that they perform effectively as compared to conventional FEM. In the present study, both FEM and Meshfree method are used to simulate phenomenon of contaminant transport in one dimension. The results obtained are agreeing with the values in literature and hence the model is further used for predicting the transport of contaminants. Parametric study is done by changing the dispersion coefficient, average velocity, geochemical reactions, height of leachate and height of liner for obtaining suitability.

Key Words
contaminants; drinking water; FEM and meshfree methods; landfill tech; pollutants (metals, organics, organometallics)

Address
Department of Civil Engineering, Indian Institute of Technology Roorkee - 247667, India.

Abstract
Two different model selection indices, the Akaike information criterion (AIC) and the coefficient of determination (R2), are used to discriminate competing isotherm equations for aqueous pollutant removal systems. The former takes into account model accuracy and complexity while the latter considers model accuracy only. The five types of isotherm shape in the Brunauer-Deming-Deming-Teller (BDDT) classification are considered. Sorption equilibrium data taken from the literature were correlated using isotherm equations with fitting parameters ranging from two to five. For the isotherm shapes of types I (favorable) and III (unfavorable), the AIC favors two-parameter equations which can easily track these simple isotherm shapes with high accuracy. The R2 indicator by contrast recommends isotherm equations with more than two parameters which can provide marginally better fits than two-parameter equations. To correlate the more intricate shapes of types II (multilayer), IV (two-plateau) and V (S-shaped) isotherms, both indices favor isotherm equations with more than two parameters.

Key Words
adsorption isotherm; Akaike information criterion; equilibrium data; modeling

Address
Honeychem, Nanjing Chemical Industry Park, Nanjing 210047, China.

Abstract
Among the combination of 4 different second metals and 3 different noble metals, Ni 10%-Pd 1%/hematite (Ni(10)-Pd(1)/H) showed best tetrachloroethylene (PCE) removal (75.8%) and production of non-toxic products (39.8%) in closed batch reactors under an anaerobic condition. The effect of environmental factors (pH, contents of Ni and Pd in catalyst, and hydrogen gas concentration) on the reductive dechlorination of PCE by Pd-Ni/hematite catalysts was investigated. PCE was degraded less at the condition of Ni(5)/H (13.7%) than at the same condition with Ni(10)/H (20.6%). Removals of PCE were rarely influenced by the experimental condition of different Pd amounts (Pd(1)/H and Pd(3)/H). Acidic to neutral pH conditions were favorable to the degradation of PCE, compared to the alkaline condition (pH 10). Increasing Ni contents from 1 to 10% increased the PCE removal to 89.8% in 6 hr. However, the removal decreased to 74.2% at Ni content of 20%. Meanwhile, increasing Pd contents to 6% showed no difference in PCE removal at Pd content of more than 1%. Increasing H2 concentration increased the removal of PCE until 4% H2 which was maximumly applied in this study. Chlorinated products such as trichloroethylene, 1,1-dichloroethylene, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, and vinyl chloride were not observed while PCE was transformed to acetylene (24%), ethylene (5%), and ethane (11%) by Ni(10)-Pd(1)/H catalyst in 6 hr.

Key Words
tetrachloroethylene; Pd; Ni; hematite; bimetallic catalyst

Address
(1) Kyunghoon Choi:
Department of Environmental Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 305-764, Republic of Korea;
(2) Nara Lee, Woojin Lee:
Department of Civil and Environmental Engineering, Korea Advanced Institute for Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.

Abstract
Magnetite was chosen as a typical adsorbent to study its phosphate adsorption capacity in water body with low concentration of phosphorus (below 2 mg P L-1). Magnetite was collected from Luoyang City, Henan Province, China. In this research, three factors have been studied to describe the adsorption of phosphate on magnetite, which was solution concentration (concentration ranging from 0.1 to 2.5 mg P L-1), suspension pH (1 to 13) and temperature (ranging from 10°C to 40°C). In addition, the modified samples had been characterized with XRD and FE-SEM image. The results show that iron ions contains in magnetite were the main factors of phosphorus removal. The behavior of phosphorus adsorption to substrates could be fitted to both Langmuir and Freundlich isothermal adsorption equations in the low concentration phosphorus water. The theoretical saturated adsorption quantity of magnetite is 0.158 mg/g. pH has great influence on the phosphorus removal of magnetite ore by adsorption. And pH of 3 can receive the best results. While temperature has little effect on it. Magnetite was greatly effective for phosphorus removal in the column experiments, which is a more practical reflection of phosphorous removal combing the adsorption isotherm model and the breakthrough curves. According to the analysis of heavy metals release, the release of heavy metals was very low, they didn

Key Words
magnetite; low concentration; phosphorus adsorption

Address
(1) Heng Xiang, Chaoxiang Liu:
Institute of Urban Environment, CAS, Xiamen, 361021, China;
(2) Heng Xiang, Ruiling Pan, Yun Han:
Key Lab of Northwest Water Resources, Environment and Ecology, MoE; Xi'an University of Architecture and Technology, Xi#39;an 710055, China;
(3) Jing Cao:
North China Institute of Science & Technology, Beijing, 101601, China.

Abstract
A comprehensive mathematical model was developed for this study to estimate on-site and off-site GHG emissions from wastewater treatment plants (WWTPs). The model was applied to three different hybrid WWTPs (S-WWTP, J-WWTP, and T-WWTP) including anaerobic, anoxic, and aerobic process, located in Seoul City, South Korea. Overall on-site and off-site GHG emissions from S-WWTP, J-WWTP, and T-WWTP were 305,253 kgCO2e/d, 282,682 kgCO2e/d, and 117,942 kgCO2e/d, respectively. WWTP treating higher amounts of wastewater produced more on-site and off-site GHG emissions. On average, the percentage contribution of on-site and off-site emissions was 3.03% and 96.97%. The highest amount of on-site GHG emissions was generated from anoxic process and the primary on-site GHG was nitrous oxide (N2O). Off-site GHG emissions related to electricity consumption for unit operation was much higher than that related to production of chemicals for on-site usage. Recovery and reuse of biogas significantly reduced the total GHG emissions from WWTPs. The results obtained from this study can provide basic knowledge to understand the source and amount of GHG emissions from WWTPs and strategies to establish lower GHG emitting WWTPs.

Key Words
greenhouse gas (GHG); wastewater treatment plant; on-site GHG emission; off-site GHG emission

Address
Department of Civil and Environment Engineering, Korea Advanced Institute of Science & Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Korea.


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