Craig L. Patterson

The fate and transport of the SiO2 nanoparticles in a granular activated carbon bed and their impact on the removal of VOCs

Adsorption isotherm, adsorption kinetics and column breakthrough experiments evaluating trichloroethylene (TCE) adsorption onto granular activated carbon (GAC) were conducted in the presence and absence of silica nanoparticles (SiO(2) NPs). Zeta potentials of the SiO(2) NPs and the GAC were measured. Particle size distribution (PSD) of SiO(2) NPs dispersions was analyzed with time to evaluate the extent of aggregation. TEM analysis was conducted. The specific surface area and the pore size distribution of the virgin and the spent GAC were obtained. The fate and transport of the SiO(2) NPs in the GAC fixed bed and their impact on TCE adsorption were found to be a function of their zeta potential, concentration and PSD. The interaction of the SiO(2) NPs and the GAC is of an electrokinetic nature. A weak electrostatic attraction was observed between the SiO(2) NPs and the GAC. This attraction favors SiO(2) NPs attachment on the surface of GAC. SiO(2) NPs attachment onto GAC is manifested by a reduction in the amount of TCE adsorbed during the column breakthrough experiments suggesting a preloading pore blockage phenomenon. However, no effect of SiO(2) NPs was observed on the isotherm and the kinetic studies, this is mainly due to the fast kinetics of TCE adsorption.

Ceramic Filter for Small System Drinking Water Treatment: Evaluation of Membrane Pore Size and Importance of Integrity Monitoring

Ceramic filtration has recently been identified as a promising technology for drinking water treatment in households and small communities. This paper summarizes the results of a pilot-scale study conducted at the U.S. Environmental Protection Agency’s (EPA) Test & Evaluation (TE however, the permeat...

Removal of Trichloroethylene by Activated Carbon in the Presence and Absence of TiO 2 Nanoparticles

Nanoparticles (NPs) are emerging as a new type of contaminant in water and wastewater. The fate of titanium dioxide nanoparticles (TiO2NPs) in a granular activated carbon (GAC) adsorber and their impact on the removal of trichloroethylene (TCE) was investigated. Key parameters governing the TiO2NP–GAC interaction such as specific surface area (SSA), zeta potential, and the TiO2NP particle size distribution (PSD) were determined. The impact of TiO2NPs on TCE adsorption on GAC was tested by conducting TCE adsorption isotherm, kinetic, and column breakthrough studies in the presence and absence of TiO2NPs. SSA and pore size distribution of the virgin and spent GAC were obtained. The fate and transport of the TiO2NPs in the GAC fixed bed and their impact on TCE adsorption were found to be a function of their zeta potential, concentration, PSD, and the nature of their aggregation. The TiO2NPs under investigation are not stable in water and rapidly form larger aggregates. Due to the fast adsorption kinetics of TCE, the isotherm and kinetic studies found no effect from TiO2NPs. However, TiO2NPs attached to GAC and led to a reduction in the amount of TCE adsorbed during the breakthrough experiments suggesting a preloading pore blockage phenomenon. The analysis of the used GAC confirmed the pore blockage and SSA reduction.

Polymorph-dependent titanium dioxide nanoparticle dissolution in acidic and alkali digestions

Multiple polymorphs (anatase, brookite and rutile) of titanium dioxide nanoparticles (TiO2-NPs) with variable structures were quantified in environmental matrices via microwave-based hydrofluoric (HF) and nitric (HNO3) mixed acid digestion and muffle furnace (MF)-based potassium hydroxide (KOH) fusion. The environmental matrices included stream bed sediments, kaolinite and bentonite. The percentage of titanium (Ti) recovered from the mixed acid digestion was not statistically different from KOH fusion when anatase and brookite TiO2-NPs were blended in all three environmental matrices. However, the percentage of Ti recovery of rutile TiO2-polymorph from the samples digested using the mixed acid digestion method was significantly lower [23 (±5), 12 (±6), 11 (±0.6)] than those digested using KOH fusion method [74 (±4), 53 (±7), 75 (±2)]. The recovery percent values reported are for Ti in sediment, kaolinite, and bentonite matrices, respectively. Exposing the TiO2-NP spiked samples to elevated heat and pressure reduced the recovery of Ti from all three polymorphs via mixed acid digestion. In contrast, Ti recoveries from KOH fusion improved after heat and pressure treatment. A narrowing of the X-ray diffraction (XRD) peaks for anatase and brookite after heat and pressure treatment indicated an increase in the aggregation or particle interaction of the TiO2-NPs. The XRD peaks for rutile TiO2-NP polymorph was similar before and after heat and pressure treatment. In summary, regardless of the selected environmental matrix type, the mixed acid digestibility of TiO2-NPs is polymorph-dependent; whereas, the KOH-fusion digestibility is polymorph independent. Therefore, when analyzing environmental samples containing TiO2-NPs with unknown polymorphs, a KOH-fusion digestion method is recommended for yielding consistent results.

Remediation of MTBE from drinking water: air stripping followed by off-gas adsorption.

Abstract The widespread use of methyl tertiary butyl ether (MTBE) as an oxygenate in gasoline has resulted in the contamination of a large number of ground and surface water sources. Even though air stripping has been proven to be an effective treatment technology for MTBE removal, off-gas treatment often is required in conjunction with it. This study evaluated the combined treatment technologies of air stripping followed by off-gas adsorption on a pilot scale for the treatment of MTBE-contaminated water. The effect of air/water ratios on the treatment efficiency was studied, and the mass transfer coefficient was determined. Air/water ratios of 105:1, 151:1, 177:1, 190:1, 202:1, and 206:1 were used, and a treatment efficiency of >99% was achieved for all the runs conducted. The depth of packing required to achieve maximum treatment efficiency decreased with increasing air/water ratio. Relative humidity (RH) impacts on the MTBE adsorption capacity of a granular activated carbon (GAC) and carbonaceous resin were determined from pilot plant studies. Breakthrough profiles obtained from the pilot plant studies conducted at 20, 30, and 50% RH indicated that GAC has a higher adsorptive capacity than resin. The adsorptive capacity of GAC decreased with increasing RH, whereas RH did not impact the resin adsorptive capacity.

Examining the efficiency of muffle furnace-induced alkaline hydrolysis in determining the titanium content of environmental samples containing engineered titanium dioxide particles

A novel muffle furnace (MF)-based potassium hydroxide (KOH) fusion digestion technique was developed and evaluated for different titanium dioxide materials in various solid matrices. Digestion of different environmental samples containing sediments, clay minerals and humic acid with and without TiO(2) particles was first performed utilizing the MF-based KOH fusion technique and its dissolution efficacy was compared to a Bunsen burner (BB)-based KOH fusion method. The three types of TiO(2) particles (anatase, brookite and rutile) were then digested with the KOH fusion techniques and microwave (MW)-based nitric (HNO3)–hydrofluoric (HF) mixed acid digestion methods. Statistical analysis of the results revealed that Ti recoveries were comparable for the KOH fusion methods (BB and MF). For pure TiO(2) particles, the measured Ti recoveries compared to calculated values were 96%, 85% and 87% for anatase, brookite and rutile TiO(2) materials, respectively, by the MF-based fusion technique. These recoveries were consistent and less variable than the BB-based fusion technique recoveries of 104%, 97% and 72% and MW-based HNO3–HF mixed acids digestion recoveries of 80%, 81% and 14%, respectively, for anatase, brookite and rutile. Ti percent recoveries and measurement precision decreased for both the BB and MF methods when TiO(2) was spiked into sediment, clay minerals, and humic acid. This drop in efficacy was counteracted by more thorough homogenization of the spiked mixtures and by increasing the mass of KOH in the MF fusion process from 1.6 g to 10.0 g. The MF-based fusion technique is consistently superior in digestion efficiency for all three TiO(2) polymorphs. The MF-based fusion technique required 20 minutes for digestion of 25 samples (based on in-house Lindberg MF capacity) compared to 8 hours for the same number of samples using the BB-based fusion technique. Thus, the MF-based fusion technique can be used to dissolve a large number of samples in a shorter time (e.g., 500 samples per 8 hours) while conserving energy and eliminating health and safety risks from methods involving HF.

Using Continuous Monitors for Conducting Tracer Studies in Water Distribution Systems

The use of online monitors for conducting a distribution system tracer study is proving to be a helpful tool to accurately understand the flow dynamics in a distribution system. In a series of field tests sponsored by the U. S. Environmental Protection Agency (EPA) and the Greater Cincinnati Water Works (GCWW) in 2002-2003, a food-grade calcium chloride tracer was introduced into a water system network and the movement of the chemical was traced using strategically placed automated online conductivity meters (in conjunction with a limited grab sampling program). The benefits and results of this field testing effort are discussed in this paper. Disclaimer This paper has been reviewed in accordance with the EPAs peer and administrative review policies and approved for presentation and publication. The mention of trade names or commercial products in this paper does not constitute

Evaluating a composite cartridge for small system drinking water treatment.

A pilot-scale evaluation was conducted at the U.S. Environmental Protection Agency (EPA) Test & Evaluation (T&E) Facility in Cincinnati, Ohio, on a multi-layer, cartridge-based system that combines physical filtration with carbon adsorption and ultraviolet (UV) light disinfection to serve as a home-base water treatment security device against accidental or intentional contaminant events. The system was challenged with different levels of turbidity, a number of biological contaminants including Bacillus subtilis, Escherichia coli, MS2 bacteriophage and Polystyrene Latex (PSL) beads as a surrogate for Cryptosporidium and a number of chemical contaminants including super-chlorination, methyl tertiary butyl ether (MTBE), water chlorination disinfection byproducts (DBPs) and diazinon. The results demonstrated that the performance of the system varies as a function of the specific contaminant or surrogate. The overall performance indicated the potential of the system to improve the quality and safety of household water and to serve as an additional treatment barrier in circumstances where there is little or no treatment or where the quality of treated water may have deteriorated during distribution. The results also demonstrated that B. subtilis spore can serve as a more conservative surrogate for Cryptosporidium than PSL beads.

Evaluation of Ceramic Filtration for Drinking Water Treatment in Small Systems

There are approximately 50,000 small community systems and 140,000 noncommunity systems serving over 25 million transient and non-transient populations of 3,300 people or less. Several of these small systems are having difficulty complying with the ever increasing number of regulations and regulated contaminants and it is estimated that small systems contribute 74 % of the Safe Drinking Water Act (SDWA) and its Amendments (SDWAA) violations annually. Nearly 90% of these are for Maximum Contaminant Level (MCL) violations. EPA conducts in-house technology development and evaluation to support the small communities. As part of this research effort, EPA has been evaluating a ceramic filtration system for the production of drinking water. The system is being challenged with various turbidity levels, Cryptosporidium (using polystyrene latex beads as a surrogate) and Bacillus Subtilis (to evaluate bacteria removal). This paper presents the results of studies conducted to date on this system. Future research efforts will include testing the system for removal of total coliforms, MS2 bacteriophage and Cryptosporidium parvum.

The Implications of Fe2O3 and TiO2 Nanoparticles on the Removal of Trichloroethylene by Activated Carbon in the Presence and Absence of Humic Acid

The impact of Fe2O3 and TiO2 nanoparticles (NPs) on the removal of trichloroethylene (TCE) in a granular activated carbon (GAC)-fixed bed adsorber was investigated in the presence of humic acid (HA). The surface charges of GAC and NPs were obtained in the presence and absence of HA with the NPs behaving similarly. Isotherm and column studies were conducted in the presence and absence of the NPs and HA. NPs had no effect on TCE adsorption during isotherm studies. However, in the column studies conducted with organic-free water, the presence of NPs resulted in a reduction in TCE capacity most likely due to pore blockage by aggregating NPs. This effect was completely mitigated in the presence of HAs that prevented an association between the GAC and the NPs, and between NPs. The presence of HA provided a high negative charge on the GAC and on the nanoparticles resulting in repulsive forces between the GAC and the NPs, and between NPs, thereby preventing pore blockage. Both Fe2O3 and TiO2 NPs demonstrated that charge characteristics are more important than chemical characteristics. Pore-size distribution of the fresh and the spent GAC confirmed the adsorption data but points to some HA and NP interaction with the carbon.