Radha Krishnan

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.

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 a UV/Ozone Treatment Process for Removal of MTBE in Groundwater Supplies in New Mexico

EPA’s Office of Research and Development is funding pilot-scale studies on MTBE contaminated groundwater using UV/ozone treatment technology (254 nm UV, 5.8 mg/L ozone). The pilot-scale treatment system consists of a GW well pump, a feed tank, a pretreatment system (water softener with iron reduction), a low-pressure UV/ozone treatment system, and GAC post treatment. Treatability studies have been conducted by graduate students at New Mexico State University to determine the effectiveness of UV/ozone treatment on well water contaminated by underground plumes of MTBE and other volatile organic compounds. NMSU found UV/ozone treatment to be highly effective for removing MTBE and MTBE byproducts in groundwater. The MTBE concentrations after treatment were significantly lower (0.4-7.7 μg/L) as compared to the initial influent concentrations (127-251 μg/L). However, acetone was formed during oxidation of MTBE. Future field studies are planned to investigate the impact of enhanced ozone/medium-pressure UV on MTBE and MTBE byproduct removal and alternative technologies for acetone removal.

CONDITION ASSESSMENT MODELING FOR DRINKING WATER DISTRIBUTION SYSTEMS: AN EXAMPLE OF SHARED FRAILTY ANALYSIS

It has been estimated that replacement of drinking water infrastructure will need to increase from the current estimated replacement rate of 0.3 percent per year to 2.0 percent per year by 2040 in order to meet the needs of US drinking water utilities. This is approximately four times the current replacement rate. In addition to maintenance, structural and regulatory issues, there is concern over the ability of US drinking water distribution systems to maintain water quality to the consumer. Consequently, drinking water utilities are increasingly interested in the potential for the application of techniques such as Condition Assessment (CA) methodology for managing drinking water infrastructure. The USEPA has therefore initiated a project (carried out by the Eastern Research Group) with the goal of developing new CA techniques that can assist utilities in dealing with some of these issues. Several tools have been developed (which will be discussed) including a modeling approach that can be applied to a drinking water utilities break and leak database and that will help managers understand the factors affecting the “survival” of drinking water pipe sections. The model is based on the application of the Cox Proportional Hazard Model (CPHM) modified by a frailty function. Shared frailty represents unobserved external factors, known to be important, which vary randomly and which are more consistent among sections in the same pipe run than among sections in different pipe runs. Examples of factors which may be represented in this way are soil corrosivity, variations in external mechanical loading, pressure transients, vibration, nearby construction, etc. The CPHM has been applied to a pipe break data base collected by the Laramie Water Utility (located in Laramie, Wyoming (USA)). Preliminary results, for example, indicate that, on the average, metallic pipe has fewer beaks than Poly Vinyl Chloride (PVC) pipe but is more subject to undefined random factors. That is, metallic pipe has more “random frailty” then PVC pipe. This has implications for infrastructure management policies such as the application of advanced monitoring techniques and replacement strategies. In addition to the CPHM for individual pipe sections a general pipe break model has been developed.

Impact of Nanoparticles on the Removal of Organic Pollutants by Activated Carbon Adsorption

The presence of nanoparticles in drinking water sources could impact organic pollutant removal by activated carbon due to agglomerated nanoparticles, which could act as adsorption sites for pollutants. Trichloroethylene (TCE) adsorption onto activated carbon in the presence of nanoparticles was evaluated in this study. Iron oxide (Fe 2 O 3 ), titanium dioxide (TiO 2 ), and silicon dioxide (SiO 2 ) nanoparticles at two concentration levels (0.5 and 1.0 mg/L for Fe 2 O 3 and TiO 2 , and 5.0 and 10 mg/L for SiO 2 ) were evaluated. Particle size distribution (PSD) of the above nanoparticle solutions was analyzed in order to determine the extent of aggregation. Adsorption isotherm experiments were conducted at three initial TCE concentrations, two nanoparticle concentrations, and with varying amounts of powdered activated carbon (PAC). Isotherm experiments were also conducted in the presence of natural organic matter (NOM) in order to more closely model natural water conditions. The primary objective of this study is to evaluate the efficacy of activated carbon adsorption of TCE in the presence of the aforementioned commercially available nanomaterials and NOM.