Given the ubiquity of silver nanoparticles (AgNPs), the largest and fastest growing category of n... more Given the ubiquity of silver nanoparticles (AgNPs), the largest and fastest growing category of nanomaterials, and their potential for toxic effects to both humans and the environment, it is important to understand their environmental fate and transport.
The chemometric techniques were applied for evaluation of the seasonal variation of water qualiti... more The chemometric techniques were applied for evaluation of the seasonal variation of water qualities at 17 stations along a stretch of the Bagmati river of Nepal for 23 water quality parameters measured during 1999–2003. The application of discriminant analysis confirmed the classification of the water quality measurements into three seasons: pre-monsoon, monsoon,
and post-monsoon affording 93.8% correct classification.
Factor analysis and box–whisker plots facilitated to investigate the seasonal variation of water quality and the pattern of pollution sources. Application of FA revealed that the influence of water quality parameters changes from season to season. A parameter that is most important in contributing to water quality variation for one season may not be important for another season. Comparison of the discriminant analysis and factor analysis helped to identify the most important water quality parameters, as water temperature, DO, EC, COD, CL, Ca, alkalinity, PO4P, and TP,
that are most important for seasonal variation and play a significant role in establishment of water quality control strategy
The review discusses six major public domain water quality models currently available for rivers ... more The review discusses six major public domain water quality models currently available for rivers and streams. These major models, which differ greatly in terms of processes they represent, data inputs requirements, assumptions, modeling capability, their strengths and weaknesses, could yield useful results if appropriately selected for the desired purposes. The public domain models, which are most suitable for simulating dissolved oxygen along rivers and streams, chosen in this review are simulation catchment (SIMCAT), temporal overall model for catchments (TOM-CAT), QUAL2Kw, QUAL2EU, water quality analysis simulation program (WASP7), and quality simulation along rivers (QUASAR). Each of these models is described based on a consistent set of criteria-conceptualization, processes, input data, model capability, limitations, model strengths, and its application. The results revealed that SIMCAT and TOMCAT are over-simplistic but useful to quickly assess impact of point sources. The QUAL2Kw has provision for conversion of algal death to carbonaceous biochemical oxygen demand (CBOD) and thus more appropriate than QUAL2EU, where macrophytes play an important interaction. The extensive requirement of data in WASP7 and QUASAR is difficult to justify the time and costs required to set up these complex models. Thus, a single model could not serve all wide range of functionalities required. The choice of a model depends upon availability of time, financial cost and a specific application. This review may help to choose appropriate model for a particular water quality problem. Public Domain Water Quality Models 185 186 P.R. Kannel et al.
Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two commo... more Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles may be applicable to other adsorbate-adsorbent systems as well.
Three polycyclic aromatic hydrocarbons (PAHs), phenanthrene, anthracene, and pyrene in sand slurr... more Three polycyclic aromatic hydrocarbons (PAHs), phenanthrene, anthracene, and pyrene in sand slurries, were subjected to a heterogeneous catalytic oxidation process using goethite catalyzed by hydrogen peroxide. Specifically, we studied the effects of different concentrations of goethite, H 2 O 2 , bicarbonate, and pH. The kinetics of the degradation of PAHs followed pseudo first-order kinetics. Determined rate constants varied between 2.0 ϫ 10 Ϫ4 to 1.1 ϫ 10 Ϫ3 , 1.5 ϫ 10 Ϫ4 to 9 ϫ 10 Ϫ4 , and 1.1 ϫ 10 Ϫ4 to 7 ϫ 10 Ϫ4 min Ϫ1 , for phenanthrene, anthracene, and pyrene, respectively. The highest rate of PAHs degradation was observed in 5 M H 2 O 2 with 33.5 g/kg of goethite. The intermediate product formed during the degradation of phenanthrene was salicyclic acid, and was shown to degrade to CO 2 and H 2 O. Intermediate products of anthracene and pyrene oxidation were not detected, but their final products were CO 2 and H 2 O. More than 80% of the 5 M H 2 O 2 was consumed within 30 min, and the reaction was almost complete after 3 h. The degradation of phenanthrene, anthracene, and pyrene was 73, 60, and 55%, respectively, after 3 h. It is of significant advantage that this method produces optimal PAHs removal at neutral pH. PAHs degradation was also dependent on the bicarbonate concentration, suggesting that it may act as an OH radical scavenger. Our experimental results may suggest the potential use of goethite catalyzed by H 2 O 2 for the remediation of soils contaminated with PAHs.
The study presents the assessment of variation of water qualities, classification of monitoring n... more The study presents the assessment of variation of water qualities, classification of monitoring networks and detection of pollution sources along the Bagmati River and its tributaries in the Kathmandu valley of Nepal. Seventeen stations, monitored for 23 physical and chemical parameters in pre-monsoon, monsoon, post-monsoon and winter seasons, during the period 1999-2003, were selected for the purpose of revealed distinct groups of sources and pollutions (organics, nutrients, solutes and physicochemical).
A stream water quality model, QUAL2Kw, was calibrated and validated for the river Bagmati of Nepa... more A stream water quality model, QUAL2Kw, was calibrated and validated for the river Bagmati of Nepal. The model represented the field data quite well with some exceptions. The influences of various water quality management strategies have on DO concentrations were examined considering: (i) pollution loads modification; (ii) flow augmentation; (iii) local oxygenation. The study showed the local oxygenation is effective in raising DO levels. The combination of wastewater modification, flow augmentation and local oxygenation is necessary to ensure minimum DO concentrations. This reasonable modeling guarantees the use of QUAL2Kw for future river water quality policy options.
This article reports a novel approach for the controllable synthesis of nanoscale zerovalent iron... more This article reports a novel approach for the controllable synthesis of nanoscale zerovalent iron (NZVI) particles with specific high Brunauer-Emmett-Teller (BET) surface areas. Borohydride reduction is a primary and effective liquid phase reduction method for the synthesis of zerovalent iron nanoparticles. However, previous methods for synthesizing NZVI did not suggest a standard technique for controlling the size of particles during the synthesis process; in addition, previous literature generally reported that NZVI had a BET surface area of \37 m 2 /g. In this communication, a novel approach for the controllable synthesis of NZVI particles with specific high BET surface areas is presented. As a result, the BET surface areas of the NZVI particles synthesized increased to 47.49 and 62.48 m 2 /g, and the particle sizes decreased to 5-40 and 3-30 nm. Additionally, the physical and chemical properties of the synthesized NZVI particles were investigated by a series of characterizations, and magnetic analysis indicated that the synthesized NZVI particles had super-paramagnetic properties.
Various approaches for analyzing adsorption data were examined to determine the best method for r... more Various approaches for analyzing adsorption data were examined to determine the best method for reporting and interpreting the results of adsorption experiments and ultimately extrapolating laboratory measurements to the field. The interactions of arsenate and goethite were used as representative adsorbate and adsorbent, respectively, although the general principles are applicable to other adsorbate–adsorbent systems as well. A modeling exercise was conducted first to determine the theoretical principles governing the comparison and scaling of adsorption data. These principles were then tested on a suite of experimental data, both new and previously published. LogKDLogKD is significantly more sensitive to variations in adsorbate (AsT) or adsorbent (FeT) concentrations than either adsorbed concentration (q) or percentage adsorbed. The sensitivity of KDKD relative to q occurs due to the non-linearity of the adsorption isotherm at a given pH, since as the equilibrium aqueous concentration approaches zero, q also approaches zero while KDKD approaches infinity. Varying AsT and FeT while keeping AsT/FeT fixed yields more consistent values of percentage adsorbed, logKDlogKD, and q, although the adsorbate-to-adsorbent ratios used in laboratory studies often have a rather narrow range compared to those possible in the field. Specific surface area is also a better scaling parameter than the mass of adsorbent, especially between systems with differing adsorbents with markedly different specific surface areas (e.g., natural versus synthetic goethite). Our results have significant implications to contaminant transport modeling, as the constant KDKD approach is the most common method of modeling contaminant transport, while contaminant concentrations in the field are typically low, precisely the conditions where KDKD is most sensitive.In this work we examine the factors governing the normalization, comparison, and scaling of adsorption data using arsenate and goethite as a model system. Using a theoretical model and experimental data the article highlights the advantages and limitations of the various approaches commonly adopted for analyzing adsorption data.
Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was pr... more Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the
adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with
Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured
the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles
may be applicable to other adsorbate–adsorbent systems as well
Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two commo... more Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles may be applicable to other adsorbate-adsorbent systems as well.
Zero valent iron nanoparticles (INP) are often used to treat various types of environmental conta... more Zero valent iron nanoparticles (INP) are often used to treat various types of environmental contaminants. In this study, we synthesized a new class of iron nanoparticles and stabilized it using poly-acrylic acid (PAA). A two dimensional groundwater aquifer model was used to study the fate and transport of pristine INP and SINP (stabilized iron nano particles) under steady-state flow conditions. Transport data for a non-reactive tracer, INP, and SINP were collected under similar experimental conditions. The results clearly demonstrate the ability of PAA to stabilize INP. Furthermore, the transport data indicated that the S-INP plume will sink in a groundwater aquifer, indicating that small density gradients have significant influence on two-dimensional transport. This observation has enormous implication for designing field scale remediation systems that use iron nano particles. We used the variable-density groundwater model SEAWAT to model INP as a density driven tracer. The model results along with the experimental data show that the density influence transport controlled the migration patterns of SINP. Since the influence of density effects cannot be fully discerned using column experiments, two dimensional experiments are essential for fully understanding the transport characteristics of INP.
Widespread use of nanoscale zinc oxide
(nZnO) in various fields causes subsurface environment
c... more Widespread use of nanoscale zinc oxide
(nZnO) in various fields causes subsurface environment
contamination. Even though the transport of
dissolved zinc ions in subsurface environments such
as soils and sediments has been widely studied, the
transport mechanism of nZnO in such environments
is poorly understood. In addition, nZnO is often
combined with stabilizers or dispersing agents to
prevent its aggregation in products. The purpose of
this study is to determine the influence of pH on the
transport properties of pristine nZnO and carboxymethyl
cellulose (CMC) stabilized nZnO (CMC–
nZnO) suspensions in silica sand packed column
under saturated flow conditions. Transport data were
collected at different pHs (pHs: 3, 7, 9, and 11) under
1 mL/min flow rate conditions in a 1.1 cm diameter
column. It is found that the transport trends of pristine
nZnO and CMC–nZnO were different. For pristine
nZnO, mobility of total Zn reached a minimum
around its point of zero charge (pH 8.9). Whereas in
the case of CMC–nZnO, the mobility of total Zn
decreased as the pH of the solution pH increased
from 3 to 11. ZnO and Zn ion mixture were separated
using diafiltration membrane. It showed that most of
the nZnO and CMC–nZnO exists as Zn ion at pH 3
before and after eluting from the sand packed column
whereas at pH 11, they exist as particles. This study
shows the strong influence of pH and stabilizing
agents on nZnO transport. These factors should be
considered during subsurface transport of nZnO.
Highly efficient, versatile, adsorbent, nanoscale zero-valent iron (NZVI) was synthesised and enc... more Highly efficient, versatile, adsorbent, nanoscale zero-valent iron (NZVI) was synthesised and encapsulated by an anionic polymer to make it a mobile delivery vehicle (DV-NZVI) for in-situ groundwater and soil remediation. NZVI was found to be highly dispersed with surfactant within a size of 1-100 nm. Laboratory column experiments were conducted by employing glass beads as a porous medium to delineate the characteristics of DV-NZVI transport as a reactive material in saturated zones under a number of conditions. It was observed that there was an optimum concentration of polymer, i.e. 6 g/L, for maximum transport of DV-NZVI, at which point, as the flow rate increases, the transport of DV-NZVI increases. Similarly, at the optimum concentration we observed that as the depth of porous media increased, the breakthrough of DV-NZVI was retarded. These results confirmed that DV-NZVI has significant potential for use as a colloidal reactive barrier material in deep groundwater systems in lieu of pump and treat approaches and conventional permeable reactive barriers (PRB).
Zero-valent iron nanoparticles (INP) were synthesized and stabilized using poly acrylic acid (PAA... more Zero-valent iron nanoparticles (INP) were synthesized and stabilized using poly acrylic acid (PAA) to yield stabilized INP (S-INP). A two-dimensional physical model was used to study the fate and transport of the INP and S-INP in porous media under saturated, steady-state flow conditions. Transport data for a nonreactive tracer, INP, and S-INP were collected under similar flow conditions. The results show that unstabilized INP cannot be transported into groundwater systems. On the other hand, the S-INP can be transported like a tracer without significant retardation. However, the S-INP plume migrated downward as it moved horizontally in the physical model, indicating that small density gradients have significant influence on twodimensional transport. The variable-density groundwater flow model SEAWAT was used to model the observed densitydriven transport patterns. This is the first time a twodimensional transport data set is reported for demonstrating the multidimensional transport characteristics of nanoparticles. The data shows the importance of density effects, which cannot be fully discerned using one-dimensional, column experiments. Finally, we also demonstrate that the numerical model SEAWAT can be used to predict the density-driven transport characteristics of S-INP in groundwater aquifers.
Blast furnace slag (BFS), a steel industrial by-product, was tested for the removal of As(III), w... more Blast furnace slag (BFS), a steel industrial by-product, was tested for the removal of As(III), which is a highly toxic, mobile and predominant species in anoxic groundwater. Batch adsorption experiments were performed to determine the feasibility of BFS as an adsorbent for removing As(III) from groundwater as As(III) concentration and the pH of water were varied. The maximum As(III) adsorption capacity by BFS was 1.40 mg As(III)/g of BFS at 1 mg/L As(III) initial concentration, at 25 o C, which was calculated using the Langmuir isotherm. The homogeneous surface diffusion model (HSDM) was successfully applied to predict the sorptive removal of As(III) onto the BFS. Kinetic studies indicated that the film diffusion as well as surface diffusion of As in the BFS was involved. It was found that the film diffusion coefficient (kf) was 5.27 × 10 -5 to 4.06 × 10 -6 m/s and surface diffusion coefficient (Ds) was 2.31 × 10 -14 to 7.13 × 10 -14 m 2 /s for the initial As(III) concentrations of 0.1 to 100 mg/L. Oxidation of As(III) to As(V) and its adsorption/precipitation onto BFS is involved during the As(III) removal mechanism. It was also found that H4SiO4 0 , PO4 3-, NO3 -, SO4 2and HCO3are potential interferences in the As(III) adsorption reaction. Results suggest that 99.9% As(III) at 1 mg/L can be removed by 10 g/L BFS, which can be used as a permeable reactive barrier (PRB) material to remove As(III) from groundwater. Details of As(III) adsorption and coprecipitation systems and interferences of As(III) molecular interactions were also studied.
The usefulness of water quality indices, as the indicators of water pollution, for assessment of ... more The usefulness of water quality indices, as the indicators of water pollution, for assessment of spatial-temporal changes and classification of river water qualities was verified. Four water quality indices were investigated: WQI (considering 18 water quality parameters), WQI min and WQI m (considering five water quality parameters: temperature, pH, DO, EC and TSS) and WQI DO (considering a single parameter, DO). The water quality indices WQI min , WQI m and WQI DO could be of particular interest for the developing countries because of the minimum analytical cost involved. As a case study, water quality indices were used to evaluate spatial and temporal changes of the water quality in the Bagmati river basin (Nepal) for the study period 1999-2003. The results allowed us to determine the serious negative effects of the city urban activity on the river water quality. In the studied section of the river, the water quality index (WQI) was 71 units (classified as good) at the entry station and 47.6 units (classified as bad) at the outlet station. For the studied period, a significant decrease in water quality (mean WQI decrease=11.6%, p=0.042) was observed in the rural areas. A comparative analysis revealed that the urban water quality was significantly bad as compared with rural. The analysis enabled to classify the water quality stations into three groups: good water quality, medium water quality and bad water quality. WQI min resulted in overestimation of the water quality but with similar trend as with WQI and is useful for the periodic routine monitoring program. The correlation of WQI with WQI min and DO resulted two new indices WQI m and WQI DO , respectively. The classification of waters based on WQI m and WQI DO coincided in 90% and 93% of the samples, respectively.
Given the ubiquity of silver nanoparticles (AgNPs), the largest and fastest growing category of n... more Given the ubiquity of silver nanoparticles (AgNPs), the largest and fastest growing category of nanomaterials, and their potential for toxic effects to both humans and the environment, it is important to understand their environmental fate and transport.
The chemometric techniques were applied for evaluation of the seasonal variation of water qualiti... more The chemometric techniques were applied for evaluation of the seasonal variation of water qualities at 17 stations along a stretch of the Bagmati river of Nepal for 23 water quality parameters measured during 1999–2003. The application of discriminant analysis confirmed the classification of the water quality measurements into three seasons: pre-monsoon, monsoon,
and post-monsoon affording 93.8% correct classification.
Factor analysis and box–whisker plots facilitated to investigate the seasonal variation of water quality and the pattern of pollution sources. Application of FA revealed that the influence of water quality parameters changes from season to season. A parameter that is most important in contributing to water quality variation for one season may not be important for another season. Comparison of the discriminant analysis and factor analysis helped to identify the most important water quality parameters, as water temperature, DO, EC, COD, CL, Ca, alkalinity, PO4P, and TP,
that are most important for seasonal variation and play a significant role in establishment of water quality control strategy
The review discusses six major public domain water quality models currently available for rivers ... more The review discusses six major public domain water quality models currently available for rivers and streams. These major models, which differ greatly in terms of processes they represent, data inputs requirements, assumptions, modeling capability, their strengths and weaknesses, could yield useful results if appropriately selected for the desired purposes. The public domain models, which are most suitable for simulating dissolved oxygen along rivers and streams, chosen in this review are simulation catchment (SIMCAT), temporal overall model for catchments (TOM-CAT), QUAL2Kw, QUAL2EU, water quality analysis simulation program (WASP7), and quality simulation along rivers (QUASAR). Each of these models is described based on a consistent set of criteria-conceptualization, processes, input data, model capability, limitations, model strengths, and its application. The results revealed that SIMCAT and TOMCAT are over-simplistic but useful to quickly assess impact of point sources. The QUAL2Kw has provision for conversion of algal death to carbonaceous biochemical oxygen demand (CBOD) and thus more appropriate than QUAL2EU, where macrophytes play an important interaction. The extensive requirement of data in WASP7 and QUASAR is difficult to justify the time and costs required to set up these complex models. Thus, a single model could not serve all wide range of functionalities required. The choice of a model depends upon availability of time, financial cost and a specific application. This review may help to choose appropriate model for a particular water quality problem. Public Domain Water Quality Models 185 186 P.R. Kannel et al.
Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two commo... more Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles may be applicable to other adsorbate-adsorbent systems as well.
Three polycyclic aromatic hydrocarbons (PAHs), phenanthrene, anthracene, and pyrene in sand slurr... more Three polycyclic aromatic hydrocarbons (PAHs), phenanthrene, anthracene, and pyrene in sand slurries, were subjected to a heterogeneous catalytic oxidation process using goethite catalyzed by hydrogen peroxide. Specifically, we studied the effects of different concentrations of goethite, H 2 O 2 , bicarbonate, and pH. The kinetics of the degradation of PAHs followed pseudo first-order kinetics. Determined rate constants varied between 2.0 ϫ 10 Ϫ4 to 1.1 ϫ 10 Ϫ3 , 1.5 ϫ 10 Ϫ4 to 9 ϫ 10 Ϫ4 , and 1.1 ϫ 10 Ϫ4 to 7 ϫ 10 Ϫ4 min Ϫ1 , for phenanthrene, anthracene, and pyrene, respectively. The highest rate of PAHs degradation was observed in 5 M H 2 O 2 with 33.5 g/kg of goethite. The intermediate product formed during the degradation of phenanthrene was salicyclic acid, and was shown to degrade to CO 2 and H 2 O. Intermediate products of anthracene and pyrene oxidation were not detected, but their final products were CO 2 and H 2 O. More than 80% of the 5 M H 2 O 2 was consumed within 30 min, and the reaction was almost complete after 3 h. The degradation of phenanthrene, anthracene, and pyrene was 73, 60, and 55%, respectively, after 3 h. It is of significant advantage that this method produces optimal PAHs removal at neutral pH. PAHs degradation was also dependent on the bicarbonate concentration, suggesting that it may act as an OH radical scavenger. Our experimental results may suggest the potential use of goethite catalyzed by H 2 O 2 for the remediation of soils contaminated with PAHs.
The study presents the assessment of variation of water qualities, classification of monitoring n... more The study presents the assessment of variation of water qualities, classification of monitoring networks and detection of pollution sources along the Bagmati River and its tributaries in the Kathmandu valley of Nepal. Seventeen stations, monitored for 23 physical and chemical parameters in pre-monsoon, monsoon, post-monsoon and winter seasons, during the period 1999-2003, were selected for the purpose of revealed distinct groups of sources and pollutions (organics, nutrients, solutes and physicochemical).
A stream water quality model, QUAL2Kw, was calibrated and validated for the river Bagmati of Nepa... more A stream water quality model, QUAL2Kw, was calibrated and validated for the river Bagmati of Nepal. The model represented the field data quite well with some exceptions. The influences of various water quality management strategies have on DO concentrations were examined considering: (i) pollution loads modification; (ii) flow augmentation; (iii) local oxygenation. The study showed the local oxygenation is effective in raising DO levels. The combination of wastewater modification, flow augmentation and local oxygenation is necessary to ensure minimum DO concentrations. This reasonable modeling guarantees the use of QUAL2Kw for future river water quality policy options.
This article reports a novel approach for the controllable synthesis of nanoscale zerovalent iron... more This article reports a novel approach for the controllable synthesis of nanoscale zerovalent iron (NZVI) particles with specific high Brunauer-Emmett-Teller (BET) surface areas. Borohydride reduction is a primary and effective liquid phase reduction method for the synthesis of zerovalent iron nanoparticles. However, previous methods for synthesizing NZVI did not suggest a standard technique for controlling the size of particles during the synthesis process; in addition, previous literature generally reported that NZVI had a BET surface area of \37 m 2 /g. In this communication, a novel approach for the controllable synthesis of NZVI particles with specific high BET surface areas is presented. As a result, the BET surface areas of the NZVI particles synthesized increased to 47.49 and 62.48 m 2 /g, and the particle sizes decreased to 5-40 and 3-30 nm. Additionally, the physical and chemical properties of the synthesized NZVI particles were investigated by a series of characterizations, and magnetic analysis indicated that the synthesized NZVI particles had super-paramagnetic properties.
Various approaches for analyzing adsorption data were examined to determine the best method for r... more Various approaches for analyzing adsorption data were examined to determine the best method for reporting and interpreting the results of adsorption experiments and ultimately extrapolating laboratory measurements to the field. The interactions of arsenate and goethite were used as representative adsorbate and adsorbent, respectively, although the general principles are applicable to other adsorbate–adsorbent systems as well. A modeling exercise was conducted first to determine the theoretical principles governing the comparison and scaling of adsorption data. These principles were then tested on a suite of experimental data, both new and previously published. LogKDLogKD is significantly more sensitive to variations in adsorbate (AsT) or adsorbent (FeT) concentrations than either adsorbed concentration (q) or percentage adsorbed. The sensitivity of KDKD relative to q occurs due to the non-linearity of the adsorption isotherm at a given pH, since as the equilibrium aqueous concentration approaches zero, q also approaches zero while KDKD approaches infinity. Varying AsT and FeT while keeping AsT/FeT fixed yields more consistent values of percentage adsorbed, logKDlogKD, and q, although the adsorbate-to-adsorbent ratios used in laboratory studies often have a rather narrow range compared to those possible in the field. Specific surface area is also a better scaling parameter than the mass of adsorbent, especially between systems with differing adsorbents with markedly different specific surface areas (e.g., natural versus synthetic goethite). Our results have significant implications to contaminant transport modeling, as the constant KDKD approach is the most common method of modeling contaminant transport, while contaminant concentrations in the field are typically low, precisely the conditions where KDKD is most sensitive.In this work we examine the factors governing the normalization, comparison, and scaling of adsorption data using arsenate and goethite as a model system. Using a theoretical model and experimental data the article highlights the advantages and limitations of the various approaches commonly adopted for analyzing adsorption data.
Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was pr... more Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the
adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with
Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured
the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles
may be applicable to other adsorbate–adsorbent systems as well
Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two commo... more Editorial handling by R.N.J. Comans a b s t r a c t Iron-coated sands were prepared via two common protocols, a precipitation method, where Fe was precipitated directly onto the sand in a single step, and an adsorption method, where pure goethite was prepared in the first step and then adsorbed onto the sand in a second step. The coated sands from both the systems were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and selective Fe extraction. Although neither of the methods produced a completely crystalline Fe coating, the precipitation method produced sands with larger portions of amorphous Fe than the adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles may be applicable to other adsorbate-adsorbent systems as well.
Zero valent iron nanoparticles (INP) are often used to treat various types of environmental conta... more Zero valent iron nanoparticles (INP) are often used to treat various types of environmental contaminants. In this study, we synthesized a new class of iron nanoparticles and stabilized it using poly-acrylic acid (PAA). A two dimensional groundwater aquifer model was used to study the fate and transport of pristine INP and SINP (stabilized iron nano particles) under steady-state flow conditions. Transport data for a non-reactive tracer, INP, and SINP were collected under similar experimental conditions. The results clearly demonstrate the ability of PAA to stabilize INP. Furthermore, the transport data indicated that the S-INP plume will sink in a groundwater aquifer, indicating that small density gradients have significant influence on two-dimensional transport. This observation has enormous implication for designing field scale remediation systems that use iron nano particles. We used the variable-density groundwater model SEAWAT to model INP as a density driven tracer. The model results along with the experimental data show that the density influence transport controlled the migration patterns of SINP. Since the influence of density effects cannot be fully discerned using column experiments, two dimensional experiments are essential for fully understanding the transport characteristics of INP.
Widespread use of nanoscale zinc oxide
(nZnO) in various fields causes subsurface environment
c... more Widespread use of nanoscale zinc oxide
(nZnO) in various fields causes subsurface environment
contamination. Even though the transport of
dissolved zinc ions in subsurface environments such
as soils and sediments has been widely studied, the
transport mechanism of nZnO in such environments
is poorly understood. In addition, nZnO is often
combined with stabilizers or dispersing agents to
prevent its aggregation in products. The purpose of
this study is to determine the influence of pH on the
transport properties of pristine nZnO and carboxymethyl
cellulose (CMC) stabilized nZnO (CMC–
nZnO) suspensions in silica sand packed column
under saturated flow conditions. Transport data were
collected at different pHs (pHs: 3, 7, 9, and 11) under
1 mL/min flow rate conditions in a 1.1 cm diameter
column. It is found that the transport trends of pristine
nZnO and CMC–nZnO were different. For pristine
nZnO, mobility of total Zn reached a minimum
around its point of zero charge (pH 8.9). Whereas in
the case of CMC–nZnO, the mobility of total Zn
decreased as the pH of the solution pH increased
from 3 to 11. ZnO and Zn ion mixture were separated
using diafiltration membrane. It showed that most of
the nZnO and CMC–nZnO exists as Zn ion at pH 3
before and after eluting from the sand packed column
whereas at pH 11, they exist as particles. This study
shows the strong influence of pH and stabilizing
agents on nZnO transport. These factors should be
considered during subsurface transport of nZnO.
Highly efficient, versatile, adsorbent, nanoscale zero-valent iron (NZVI) was synthesised and enc... more Highly efficient, versatile, adsorbent, nanoscale zero-valent iron (NZVI) was synthesised and encapsulated by an anionic polymer to make it a mobile delivery vehicle (DV-NZVI) for in-situ groundwater and soil remediation. NZVI was found to be highly dispersed with surfactant within a size of 1-100 nm. Laboratory column experiments were conducted by employing glass beads as a porous medium to delineate the characteristics of DV-NZVI transport as a reactive material in saturated zones under a number of conditions. It was observed that there was an optimum concentration of polymer, i.e. 6 g/L, for maximum transport of DV-NZVI, at which point, as the flow rate increases, the transport of DV-NZVI increases. Similarly, at the optimum concentration we observed that as the depth of porous media increased, the breakthrough of DV-NZVI was retarded. These results confirmed that DV-NZVI has significant potential for use as a colloidal reactive barrier material in deep groundwater systems in lieu of pump and treat approaches and conventional permeable reactive barriers (PRB).
Zero-valent iron nanoparticles (INP) were synthesized and stabilized using poly acrylic acid (PAA... more Zero-valent iron nanoparticles (INP) were synthesized and stabilized using poly acrylic acid (PAA) to yield stabilized INP (S-INP). A two-dimensional physical model was used to study the fate and transport of the INP and S-INP in porous media under saturated, steady-state flow conditions. Transport data for a nonreactive tracer, INP, and S-INP were collected under similar flow conditions. The results show that unstabilized INP cannot be transported into groundwater systems. On the other hand, the S-INP can be transported like a tracer without significant retardation. However, the S-INP plume migrated downward as it moved horizontally in the physical model, indicating that small density gradients have significant influence on twodimensional transport. The variable-density groundwater flow model SEAWAT was used to model the observed densitydriven transport patterns. This is the first time a twodimensional transport data set is reported for demonstrating the multidimensional transport characteristics of nanoparticles. The data shows the importance of density effects, which cannot be fully discerned using one-dimensional, column experiments. Finally, we also demonstrate that the numerical model SEAWAT can be used to predict the density-driven transport characteristics of S-INP in groundwater aquifers.
Blast furnace slag (BFS), a steel industrial by-product, was tested for the removal of As(III), w... more Blast furnace slag (BFS), a steel industrial by-product, was tested for the removal of As(III), which is a highly toxic, mobile and predominant species in anoxic groundwater. Batch adsorption experiments were performed to determine the feasibility of BFS as an adsorbent for removing As(III) from groundwater as As(III) concentration and the pH of water were varied. The maximum As(III) adsorption capacity by BFS was 1.40 mg As(III)/g of BFS at 1 mg/L As(III) initial concentration, at 25 o C, which was calculated using the Langmuir isotherm. The homogeneous surface diffusion model (HSDM) was successfully applied to predict the sorptive removal of As(III) onto the BFS. Kinetic studies indicated that the film diffusion as well as surface diffusion of As in the BFS was involved. It was found that the film diffusion coefficient (kf) was 5.27 × 10 -5 to 4.06 × 10 -6 m/s and surface diffusion coefficient (Ds) was 2.31 × 10 -14 to 7.13 × 10 -14 m 2 /s for the initial As(III) concentrations of 0.1 to 100 mg/L. Oxidation of As(III) to As(V) and its adsorption/precipitation onto BFS is involved during the As(III) removal mechanism. It was also found that H4SiO4 0 , PO4 3-, NO3 -, SO4 2and HCO3are potential interferences in the As(III) adsorption reaction. Results suggest that 99.9% As(III) at 1 mg/L can be removed by 10 g/L BFS, which can be used as a permeable reactive barrier (PRB) material to remove As(III) from groundwater. Details of As(III) adsorption and coprecipitation systems and interferences of As(III) molecular interactions were also studied.
The usefulness of water quality indices, as the indicators of water pollution, for assessment of ... more The usefulness of water quality indices, as the indicators of water pollution, for assessment of spatial-temporal changes and classification of river water qualities was verified. Four water quality indices were investigated: WQI (considering 18 water quality parameters), WQI min and WQI m (considering five water quality parameters: temperature, pH, DO, EC and TSS) and WQI DO (considering a single parameter, DO). The water quality indices WQI min , WQI m and WQI DO could be of particular interest for the developing countries because of the minimum analytical cost involved. As a case study, water quality indices were used to evaluate spatial and temporal changes of the water quality in the Bagmati river basin (Nepal) for the study period 1999-2003. The results allowed us to determine the serious negative effects of the city urban activity on the river water quality. In the studied section of the river, the water quality index (WQI) was 71 units (classified as good) at the entry station and 47.6 units (classified as bad) at the outlet station. For the studied period, a significant decrease in water quality (mean WQI decrease=11.6%, p=0.042) was observed in the rural areas. A comparative analysis revealed that the urban water quality was significantly bad as compared with rural. The analysis enabled to classify the water quality stations into three groups: good water quality, medium water quality and bad water quality. WQI min resulted in overestimation of the water quality but with similar trend as with WQI and is useful for the periodic routine monitoring program. The correlation of WQI with WQI min and DO resulted two new indices WQI m and WQI DO , respectively. The classification of waters based on WQI m and WQI DO coincided in 90% and 93% of the samples, respectively.
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and post-monsoon affording 93.8% correct classification.
Factor analysis and box–whisker plots facilitated to investigate the seasonal variation of water quality and the pattern of pollution sources. Application of FA revealed that the influence of water quality parameters changes from season to season. A parameter that is most important in contributing to water quality variation for one season may not be important for another season. Comparison of the discriminant analysis and factor analysis helped to identify the most important water quality parameters, as water temperature, DO, EC, COD, CL, Ca, alkalinity, PO4P, and TP,
that are most important for seasonal variation and play a significant role in establishment of water quality control strategy
adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with
Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured
the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles
may be applicable to other adsorbate–adsorbent systems as well
(nZnO) in various fields causes subsurface environment
contamination. Even though the transport of
dissolved zinc ions in subsurface environments such
as soils and sediments has been widely studied, the
transport mechanism of nZnO in such environments
is poorly understood. In addition, nZnO is often
combined with stabilizers or dispersing agents to
prevent its aggregation in products. The purpose of
this study is to determine the influence of pH on the
transport properties of pristine nZnO and carboxymethyl
cellulose (CMC) stabilized nZnO (CMC–
nZnO) suspensions in silica sand packed column
under saturated flow conditions. Transport data were
collected at different pHs (pHs: 3, 7, 9, and 11) under
1 mL/min flow rate conditions in a 1.1 cm diameter
column. It is found that the transport trends of pristine
nZnO and CMC–nZnO were different. For pristine
nZnO, mobility of total Zn reached a minimum
around its point of zero charge (pH 8.9). Whereas in
the case of CMC–nZnO, the mobility of total Zn
decreased as the pH of the solution pH increased
from 3 to 11. ZnO and Zn ion mixture were separated
using diafiltration membrane. It showed that most of
the nZnO and CMC–nZnO exists as Zn ion at pH 3
before and after eluting from the sand packed column
whereas at pH 11, they exist as particles. This study
shows the strong influence of pH and stabilizing
agents on nZnO transport. These factors should be
considered during subsurface transport of nZnO.
and post-monsoon affording 93.8% correct classification.
Factor analysis and box–whisker plots facilitated to investigate the seasonal variation of water quality and the pattern of pollution sources. Application of FA revealed that the influence of water quality parameters changes from season to season. A parameter that is most important in contributing to water quality variation for one season may not be important for another season. Comparison of the discriminant analysis and factor analysis helped to identify the most important water quality parameters, as water temperature, DO, EC, COD, CL, Ca, alkalinity, PO4P, and TP,
that are most important for seasonal variation and play a significant role in establishment of water quality control strategy
adsorption method, with the fraction of amorphous Fe decreasing with increasing Fe content. Uranium(VI) adsorption isotherms and pH adsorption edges were measured on three coated sands with
Fe contents ranging from 0.04% to 0.3%. Experimentally, the adsorption of U(VI) onto the three sands was more comparable when normalized to surface area than when normalized to Fe content. A surface complexation model, although originally developed for U(VI) adsorption onto amorphous Fe oxide, captured
the differences in adsorption when adjusted for the surface area of the coated sand. The findings indicate that surface area is a better scaling parameter than Fe content in predicting U(VI) adsorption to Fe-dominated media. These findings are significant because many common surface complexation models are parameterized on the basis of Fe content rather than specific surface area. Although the interactions of U(VI) and Fe-coated sands were used as representative adsorbate and adsorbent, the general principles
may be applicable to other adsorbate–adsorbent systems as well
(nZnO) in various fields causes subsurface environment
contamination. Even though the transport of
dissolved zinc ions in subsurface environments such
as soils and sediments has been widely studied, the
transport mechanism of nZnO in such environments
is poorly understood. In addition, nZnO is often
combined with stabilizers or dispersing agents to
prevent its aggregation in products. The purpose of
this study is to determine the influence of pH on the
transport properties of pristine nZnO and carboxymethyl
cellulose (CMC) stabilized nZnO (CMC–
nZnO) suspensions in silica sand packed column
under saturated flow conditions. Transport data were
collected at different pHs (pHs: 3, 7, 9, and 11) under
1 mL/min flow rate conditions in a 1.1 cm diameter
column. It is found that the transport trends of pristine
nZnO and CMC–nZnO were different. For pristine
nZnO, mobility of total Zn reached a minimum
around its point of zero charge (pH 8.9). Whereas in
the case of CMC–nZnO, the mobility of total Zn
decreased as the pH of the solution pH increased
from 3 to 11. ZnO and Zn ion mixture were separated
using diafiltration membrane. It showed that most of
the nZnO and CMC–nZnO exists as Zn ion at pH 3
before and after eluting from the sand packed column
whereas at pH 11, they exist as particles. This study
shows the strong influence of pH and stabilizing
agents on nZnO transport. These factors should be
considered during subsurface transport of nZnO.