Vasiliki Syngouna

The increased mass production and application of engineered nanomaterials (ENMs) have resulted in the release of nanoparticles (NPs) in the environment, raising uncertainties regarding their environmental impacts. This study examines the effect of graphene oxide (GO) and titanium dioxide (TiO2) NPs on the inactivation of the three model bacteria originated by mammalians including humans: Escherichia (E.) coli, Enterococcus (E.) faecalis, and Staphylococcus (S.) aureus. A series of dynamic batch experiments were conducted at constant room temperature (22 °C) in order to examine the inactivation of co-existing bacteria by NPs, in the presence and absence of quartz sand. The inactivation experimental data were satisfactorily fitted with a pseudo-first order expression with a time dependent rate coefficient. The inactivation of E. coli and S. aureus was shown to increase in the co-presence of GO or TiO2 NPs and quartz sand comparing with the presence of GO or TiO2 NPs alone. For E. faecalis, no clear trend was observed. Moreover, quartz sand was shown to affect inactivation of bacteria by GO and TiO2 NPs. Among the bacteria examined, the highest inactivation rates were observed for S. aureus.

Accidental or intentional groundwater contamination with infective human fecal viruses, is close related with a range of waterborne gastrointestinal and other serious diseases. Towards the development of effective purification techniques and sustainable water management strategies, knowledge of physicochemical factors, conditions and processes controlling the fate and transport of pathogens in soil is required. The aim of present doctoral thesis is to provide an overview of the transport and co-transport behavior of two biocolloids, virus substitutes, the bacteriophages MS2 and ΦΧ174, in water saturated porous media of variant granulometry, under different solution chemistry and flow conditions, and to assess/predict their interactions with suspended clay colloids (kaolinite and montmorillonite), naturally occurring in subsurface systems, at environmentally compatible conditions. Firstly, batch experiments were conducted at two different temperatures (4 and 25 °C), under static and ...

Groundwater may be contaminated with infective human enteric viruses from various wastewater discharges, sanitary landfills, septic tanks, agricultural practices, and artificial groundwater recharge. Coliphages have been widely used as surrogates of enteric viruses, because they share many fundamental properties and features. Although a large number of studies focusing on various factors (i.e. pore water solution chemistry, fluid velocity, moisture content, temperature, and grain size) that affect biocolloid (bacteria, viruses) transport have been published over the past two decades, little attention has been given toward human adenoviruses (hAdVs). The main objective of this study was to evaluate the effect of pore water velocity on hAdV transport in water saturated laboratory-scale columns packed with glass beads. The effects of pore water velocity on virus transport and retention in porous media was examined at three pore water velocities (0.39, 0.75, and 1.22 cm/min). The results indicated that all estimated average mass recovery values for hAdV were lower than those of coliphages, which were previously reported in the literature by others for experiments conducted under similar experimental conditions. However, no obvious relationship between hAdV mass recovery and water velocity could be established from the experimental results. The collision efficiencies were quantified using the classical colloid filtration theory. Average collision efficiency, α, values decreased with decreasing flow rate, Q, and pore water velocity, U, but no significant effect of U on α was observed. Furthermore, the surface properties of viruses and glass beads were used to construct classical DLVO potential energy profiles. The results revealed that the experimental conditions of this study were unfavorable to deposition and that no aggregation between virus particles is expected to occur. A thorough understanding of the key processes governing virus transport is pivotal for public health protection.

ABSTRACT h i g h l i g h t s Investigation of MS2 and X174 cotransport with clay colloids in porous media. The mass recovery of viruses and clay colloids decreased with decreasing U. The mass recovery of viruses decreased in the presence of clay colloids. Clay particles can facilitate or hinder virus transport in porous media. XDLVO is important only in the case of clay colloid attachment onto glass beads. g r a p h i c a l a b s t r a c t a b s t r a c t This study examines the cotransport of clay colloids and viruses in laboratory packed columns. Bacterio-phages MS2 and X174 were used as model viruses, kaolinite (kGa-1b) and montmorillonite (STx-1b) as model clay colloids, and glass beads as model packing material. The combined and synergistic effects of clay colloids and pore water velocity on virus transport and retention in porous media were examined at three pore water velocities (0.38, 0.74, and 1.21 cm/min). The results indicated that the mass recovery of viruses and clay colloids decreased as the pore water velocity decreased; whereas, for the cotransport experiments no clear trend was observed. Temporal moments of the breakthrough concentrations sug-gested that the presence of clays significantly influenced virus transport and irreversible deposition onto glass beads. Mass recovery values for both viruses, calculated based on total virus concentration in the effluent, were reduced compared to those in the absence of clays. The transport of both suspended and attached onto suspended clay-particles viruses was retarded, compared to the tracer, only at the highest pore water velocity. Moreover both clay colloids were shown to hinder virus transport at the highest pore water velocity. At the lower velocities MS2 transport was hindered and X174 transport was facilitated with the exception of U = 0.74 cm/min in the presence of KGa-1b. Both MS2 and X174 were attached in greater amounts onto KGa-1b than STx-1b. Also, MS2 exhibited greater affinity than X174 for both clays.

Human adenoviruses (hAdVs) are pathogenic viruses responsible for public health problems worldwide. They have also been used as viral indicators in environmental systems. Coliphages (e.g., MS2, ΦX174) have also been studied as indicators of viral pollution in fecally contaminated water. Our objective was to evaluate the distribution of three viral fecal indicators (hAdVs, MS2, and ΦΧ174), between two different phyllosilicate clays (kaolinite and bentonite) and the aqueous phase. A series of static and dynamic experiments were conducted under two different temperatures (4, 25°C) for a time period of seven days. HAdV adsorption was examined in DNase I reaction buffer (pH=7.6, and ionic strength (IS)=1.4mM), whereas coliphage adsorption in phosphate buffered saline solution (pH=7, IS=2mM). Moreover, the effect of IS on hAdV adsorption under static conditions was evaluated. The adsorption of hAdV was assessed by real-time PCR and its infectivity was tested by cultivation methods. The co...

ABSTRACT Graphene oxide (GO) nanomaterials are used extensively in a wide range of commercial applications. With GO production growing rapidly, it is expected that GO eventually could reach sensitive environmental systems, including subsurface formations, where montmorillonite, one of the most common minerals, is in abundance. This study examines the interaction of GO with quartz sand and montmorillonite (MMT) colloids at pH = 7, ionic strength IS = 2 mM, and 25°C, under dynamic conditions. Moreover, the effect of pH on MMT kinetic attachment onto quartz sand was investigated. The experimental data suggested that pH affected slightly the attachment of MMT colloids onto quartz sand. GO was attached in greater amounts onto MMT than quartz sand. Also, the attachment of GO onto quartz sand was shown to increase slightly in the presence of MMT colloids. However, when GO and MMT coexisted, the total GO mass attached onto quartz sand, suspended MMT, and attached MMT was increased. Furthermore, the equilibrium attachment experimental data were fitted nicely with a Freundlich isotherm, and the attachment kinetics were satisfactorily described with a pseudo-second-order model. Finally, the extended DLVO (XDLVO) theory was used to quantify the various interaction energy profiles based on electrokinetic and hydrodynamic measurements. GRAPHICAL ABSTRACT

One of the oldest and most promising applications of natural zeolites (NZs) is in water and wastewater treatment processes. Modified zeolites (MZs), with improved ion exchange and adsorption capacities, have been extensively applied to the removal of pollutants from aqueous solutions. However, the application of MZs in pathogens or indicator organisms has not been extensively explored. This study examines the effect of both natural Greek zeolite (NZ), with a clinoptilolite content of up to 85% (OLYMPUS SA-INDUSTRIAL MINERALS), and modified Greek zeolite through incorporation with silver ions (Ag-MNZ), on the survival of two selected faecal indicator bacteria (Escherichia coli and Enterococcus faecalis). A series of dynamic batch experiments with a slow agitation of 12 rpm were conducted at a constant ambient temperature (22°C) in order to examine the inactivation of the above bacteria by NZ and Ag-MNZ. It was found that the Ag-MNZ resulted in a much higher reduction in the bacterial...

Virus inactivation by nanoparticles (NPs) is hypothesized to affect virus fate and transport in the subsurface. This study examines the interactions of viruses with titanium dioxide (TiO2) anatase NPs, which is a good disinfectant with unique physiochemical properties. The bacteriophage MS2 was used as a model virus. A series of batch experiments of MS2 inactivation by TiO2 NPs were conducted at room temperature (25°C), in the presence and absence of quartz sand, with and without ambient light. Three sets of experiments were performed in phosphate buffered saline solution (PBS) and one in distilled deionized water (ddH2O). The virus inactivation experimental data were satisfactorily fitted with a pseudo-first order expression with a time dependent rate coefficient. Quartz sand was shown to affect MS2 inactivation by TiO2 NPs both in the presence and absence of ambient light, because, under the experimental conditions of this study, the quartz sand offers a protection to the attached...

This study focuses on the effects of two clay colloids (kaolinite, KGa-1b and montmorillonite, STx-1b) and titanium dioxide (TiO2) nanoparticles (NPs) on human adenovirus transport and retention in water saturated porous media at three different pore water velocities (0.38, 0.74, and 1.21cm/min). Transport and cotransport experiments were performed in 30-cm long laboratory columns packed with clean glass beads with 2mm diameter. The experimental results suggested that the presence of KGa-1b, STx-1b and TiO2 NPs increased human adenovirus inactivation and attachment onto the solid matrix, due to the additional attachment sites available. Retention by the packed column was found to be highest (up to 99%) in the presence of TiO2 NPs at the highest pore water velocity, and lowest in the presence of KGa-1b. The experimental results suggested that adenoviruses would undergo substantial aggregation or heteroaggregation during cotransport. However, no distinct relationships between mass rec...

The transport and fate of viruses in subsurface formations are mainly governed by virus attachment onto the solid matrix and inactivation. Furthermore, virus attachment onto clay colloids is primarily controlled by electrostatic interactions between surfaces. Bacteriophage MS2 and ΦX174 were used as surrogates for human viruses in order to investigate the interaction between viruses and clay particles. The selected phyllosilicate clays were kaolinite and bentonite. Numerous reactor vessels were filled with 0.5 g of clay and 50 mL of sterile phosphate buffered at pH 7.0. A series of static and dynamic experiments for various bacteriophage concentrations were conducted at two different temperatures. Half of the reactor vessels were placed in a refrigerator at 4°C and the rest in a constant temperature room at 25°C. The dynamic batch experiments were performed with the reactor vessels attached to a small bench-top tube rotator. Appropriate adsorption isotherms were determined. Subsequently, the Derjaguin-Landau-Verwey-Overbeek theory was applied in order to determine the interaction energies between the bacteriophage and clay surfaces. The electric properties of the viral surfaces were also obtained at different pH values and ionic strength levels. The experimental results show that virus adsorption increases linearly with suspended virus concentration. The observed distribution coefficient (Kd) was higher for MS2 than ΦX174. Also, the observed Kd values were higher for the dynamic than static experiments, and increased with temperature. Moreover, the results indicate that the electrostatic interactions between viruses and the clays are significantly influenced by the solution’s ionic strength and pH. At pH 7, bacteriophage-clay energy barriers were higher for MS2 than ΦX174.

Bacteriophage MS2 and φX174 were used as surrogates for human viruses in order to investigate the interaction between viruses and clay particles. The selected phyllosilicate clays were kaolinite and bentonite. Numerous reactor vessels were filled with 0.5 g of clay and 50 mL of sterile phosphate buffered at pH 7.0. A series of static and dynamic experiments for various bacteriophage concentrations were conducted at two different temperatures. Half of the reactor vessels were placed in a refrigerator at 4 ° C and the rest in a constant temperature room at 25 ° C. The dynamic batch experiments were performed with the reactor vessels attached to a small bench-top tube rotator. Appropriate adsorption isotherms were determined. Subsequently, the Derjaguin-Landau-Verwey-Overbeek theory was applied in order to determine the interaction energies between the bacteriophage and clay surfaces. The electric properties of the viral surfaces were also obtained at different pH values and ionic strength levels. The experimental results show that virus adsorption increases linearly with suspended virus concentration. The observed distribution coefficient (Kd) was higher for MS2 than φX174. Also, the observed Kd values were higher for the dynamic than static experiments, and increased with temperature. Moreover, the results indicate that the electrostatic interactions between viruses and the clays are significantly influenced by the solution's ionic strength and pH. At pH 7, bacteriophage-clay energy barriers were higher for MS2 than φX174.

ABSTRACT In this study, the attachment behavior of model viruses (bacteriophages MS2 and ΦX174) onto quartz sand of three different grain sizes for various pore water velocities with and without the presence of suspended model clay colloids (kaolinite: KGa-1b and montmorillonite: STx-1b) were evaluated. No obvious relationships between virus mass recoveries and water velocity or grain size could be established from the experimental results. The observed mean dispersivity values for each sand grain size were higher for MS2 than ΦX174. The interaction of viruses with KGa-1b and STx-1b was investigated with batch as well as virus-clay cotransport experiments. The batch experimental data suggested that virus attachment onto KGa-1b and STx-1b is adequately described by the Freundlich isotherm equation. The presence of suspended colloids was shown to significantly influence virus deposition. In both batch and co-transport experiments, MS2 and ΦX174 were attached in greater amounts onto KGa-1b than STx-1b with MS2 having greater affinity than ΦX174 for both clays. Furthermore, extended-DLVO interaction energy calculations explained that the attachment of viruses onto model clay colloids was primarily caused by hydrophobic interaction. The theoretical and experimental results of this study were found to be in good agreement with previous findings.

Protection of groundwater supplies from microbial contamination necessitates a solid understanding of the factors controlling the migration and retention of pathogenic organisms (biocolloids) in the subsurface. The transport behavior of three waterborne pathogens (Escherichia coli, MS2, and PhiChi174) was investigated using laboratory-scale columns packed with clean quartz sand. Various grain sizes and pore water velocities were examined. Though coliform bacteria and coliphages are used worldwide to indicate fecal pollution of groundwater, the various parameters controlling the transport of Escherichia coli MS2 and PhiChi174 in the subsurface are not fully understood. In this study, the attachment behavior of Escherichia coli, MS2, and PhiChi174 onto ultra-pure quartz sand were evaluated. The mass recoveries of the three biocolloids examined were found to be proportional to the sand size. The observed mass recoveries were in the order: Escherichia coli > PhiChi174 > MS2. To assess the importance of biocolloid attachment, the single collector removal efficiency, and the collision efficiency were quantified using the classical colloid filtration theory. Our results indicate that the secondary energy minimum plays an important role in biocolloid deposition even for smaller biocolloid particles (e.g. viruses).

The cotransport of clay colloids and viruses in vertically oriented laboratory columns packed with glass beads was investigated. Bacteriophages MS2 and ΦX174 were used as model viruses, and kaolinite (ΚGa-1b) and montmorillonite (STx-1b) as model clay colloids. A steady flow rate of Q=1.5mL/min was applied in both vertical up (VU) and vertical down (VD) flow directions. In the presence of KGa-1b, estimated mass recovery values for both viruses were higher for VD than VU flow direction, while in the presence of STx-1b the opposite was observed. However, for all cases examined, the produced mass of viruses attached onto suspended clay particles were higher for VD than VU flow direction, suggesting that the flow direction significantly influences virus attachment onto clays, as well as packed column retention of viruses attached onto suspended clays. KGa-1b hindered the transport of ΦX174 under VD flow, while STx-1b facilitated the transport of ΦX174 under both VU and VD flow direction...

The transport and fate of viruses in subsurface formations are mainly governed by virus attachment onto the solid matrix and inactivation. Furthermore, virus attachment onto clay colloids is primarily controlled by electrostatic interactions between surfaces. Bacteriophage MS2 and ΦX174 were used as surrogates for human viruses in order to investigate the interaction between viruses and clay particles. The selected phyllosilicate clays were kaolinite and bentonite. Numerous reactor vessels were filled with 0.5 g of clay and 50 mL of sterile phosphate buffered at pH 7.0. A series of static and dynamic experiments for various bacteriophage concentrations were conducted at two different temperatures. Half of the reactor vessels were placed in a refrigerator at 4°C and the rest in a constant temperature room at 25°C. The dynamic batch experiments were performed with the reactor vessels attached to a small bench-top tube rotator. Appropriate adsorption isotherms were determined. Subseque...

Biocolloid inactivation in water with the use of ultrasound can be quite effective, because the implosion of cavitation bubbles can generate high temperatures and pressures at the heart of collapsed bubbles. Biocolloid inactivation by cavitation takes place due to a combination of simultaneously acting processes involving mechanical effects (caused by turbulence generation, microstreaming, liquid circulation currents, and shear stresses), chemical effects of cavitation (generation of active free radicals), and heat effects (generation of local hot spots). Generally, the mechanical effects are more responsible for biocolloid disinfection, whereas the chemical and heat effects play only a supporting role. The present study focuses on inactivation of MS2 and ΦΧ174 at three different relatively high frequencies (i.e. 582, 862, and 1142 kHz). The experimental results indicate that, for all three frequencies and power input of 133 W, both phages were at least 90% inactivated after 60 min ...

ABSTRACT Groundwater protection from microbial contamination necessitates a solid understanding of the factors controlling the migration and retention of pathogenic organisms (biocolloids) in the subsurface. Although coliform bacteria and coliphages are used worldwide to indicate fecal pollution of groundwater, their transport behavior is not fully understood. This study focuses on the transport behavior of three waterborne pathogens (Escherichia coli, MS2, and ΦX174) in laboratory-scale columns packed with clean quartz sand. Three different grain sizes and three pore water velocities were examined. The attachment behavior of Escherichia coli, MS2, and ΦX174 onto quartz sand was evaluated. The mass recoveries of the biocolloids examined were shown to be proportional to the sand size, and they were shown to be highest for Escherichia coli and lowest for MS2. The single collector removal and collision efficiencies were quantified using the classical colloid filtration theory.

ABSTRACT Protection of groundwater supplies from microbial contamination necessitates a solid understanding of the factors controlling the migration and retention of pathogenic organisms (biocolloids) in the subsurface. The transport behavior of three waterborne pathogens (Escherichia coli, MS2, and ΦΧ174) was investigated using laboratory-scale columns packed with clean quartz sand. Various grain sizes and pore water velocities were examined. Though coliform bacteria and coliphages are used worldwide to indicate fecal pollution of groundwater, the various parameters controlling the transport of Escherichia coli MS2 and ΦΧ174 in the subsurface are not fully understood. In this study, the attachment behavior of Escherichia coli, MS2, and ΦΧ174 onto ultra-pure quartz sand were evaluated. The mass recoveries of the three biocolloids examined were found to be proportional to the sand size. The observed mass recoveries were in the order: Escherichia coli > ΦΧ174 > MS2. To assess the importance of biocolloid attachment, the single collector removal efficiency, and the collision efficiency were quantified using the classical colloid filtration theory. Our results indicate that the secondary energy minimum plays an important role in biocolloid deposition even for smaller biocolloid particles (e.g. viruses).

ABSTRACT In this study, the attachment behavior of model viruses (bacteriophages MS2 and ΦX174) onto quartz sand of three different grain sizes for various pore water velocities with and without the presence of suspended model clay colloids (kaolinite: KGa-1b and montmorillonite: STx-1b) were evaluated. No obvious relationships between virus mass recoveries and water velocity or grain size could be established from the experimental results. The observed mean dispersivity values for each sand grain size were higher for MS2 than ΦX174. The interaction of viruses with KGa-1b and STx-1b was investigated with batch as well as virus-clay cotransport experiments. The batch experimental data suggested that virus attachment onto KGa-1b and STx-1b is adequately described by the Freundlich isotherm equation. The presence of suspended colloids was shown to significantly influence virus deposition. In both batch and co-transport experiments, MS2 and ΦX174 were attached in greater amounts onto KGa-1b than STx-1b with MS2 having greater affinity than ΦX174 for both clays. Furthermore, extended-DLVO interaction energy calculations explained that the attachment of viruses onto model clay colloids was primarily caused by hydrophobic interaction. The theoretical and experimental results of this study were found to be in good agreement with previous findings.

This study is focused on the transport of Pseudomonas (P.) putida bacterial cells in a three-dimensional model aquifer. The pilot-scale aquifer consisted of a rectangular glass tank with internal dimensions: 120 cm length, 48 cm width, and 50 cm height, carefully packed with well-characterized quartz sand. The P. putida attachment onto the aquifer sand was determined with batch experiments, and was adequately described by a linear isotherm. Transport experiments with a conservative tracer and P. putida were conducted to characterize the aquifer and to investigate the bacterial behavior during transport in water saturated porous media. A three-dimensional, finite-difference numerical model for bacterial transport in saturated, homogeneous porous media was developed and was used to successfully fit the experimental data. Furthermore, theoretical interaction energy calculations suggested that the extended DLVO theory seems to predict bacteria attachment onto the aquifer sand better tha...