Susan J. Masten

Single-walled carbon nanotubes dispersed in aqueous media via non-covalent functionalization: Effect of dispersant on the stability, cytotoxicity, and epigenetic toxicity of nanotube suspensions

As the range of applications for carbon nanotubes (CNTs) rapidly expands, understanding the effect of CNTs on prokaryotic and eukaryotic cell systems has become an important research priority, especially in light of recent reports of the facile dispersion of CNTs in a variety of aqueous systems including natural water. In this study, single-walled carbon nanotubes (SWCNTs) were dispersed in water using a range of natural (gum arabic, amylose, Suwannee River natural organic matter) and synthetic (polyvinyl pyrrolidone, Triton X-100) dispersing agents (dispersants) that attach to the CNT surface non-covalently via different physiosorption mechanisms. The charge and the average effective hydrodynamic diameter of suspended SWCNTs as well as the concentration of exfoliated SWCNTs in the dispersion were found to remain relatively stable over a period of 4 weeks. The cytotoxicity of suspended SWCNTs was assessed as a function of dispersant type and exposure time (up to 48 h) using general viability bioassay with Escherichia coli and using neutral red dye uptake (NDU) bioassay with WB-F344 rat liver epithelia cells. In the E. coli viability bioassays, three types of growth media with different organic loadings and salt contents were evaluated. When the dispersant itself was non-toxic, no losses of E. coli and WB-F344 viability were observed. The cell viability was affected only by SWCNTs dispersed using Triton X-100, which was cytotoxic in SWCNT-free (control) solution. The epigenetic toxicity of dispersed CNTs was evaluated using gap junction intercellular communication (GJIC) bioassay applied to WB-F344 rat liver epithelial cells. With all SWCNT suspensions except those where SWCNTs were dispersed using Triton X-100 (wherein GJIC could not be measured because the sample was cytotoxic), no inhibition of GJIC in the presence of SWCNTs was observed. These results suggest a strong dependence of the toxicity of SWCNT suspensions on the toxicity of the dispersant and point to the potential of non-covalent functionalization with non-toxic dispersants as a method for the preparation of stable aqueous suspensions of biocompatible CNTs.

Efficacy of in-situ for the remediation of PAH contaminated soils

Abstract Polycyclic aromatic hydrocarbons (PAHs) are of environmental concern because many PAHs are either carcinogens or potential carcinogens. Petroleum products are a major source of PAHs. The occurrence of PAH contamination is widespread and novel treatment technologies for the remediation of contaminated soils are necessary. Ozone has been found to be extremely useful for the degradation of PAHs in soils. For these compounds, the reaction with molecular ozone appears to be the more important degradation pathway. Greater than 95% removal of phenanthrene was achieved with an ozonation time of 2.3 h at an ozone flux of 250 mg h −1 . After 4.0 h of treatment at an ozone flux of 600 mg h −1 , 91 % of the pyrene was removed. We have also found that the more hydrophobic PAHs (e.g. chrysene) react more slowly than would be expected on the basis of their reactivity with ozone, suggesting that partitioning of the contaminant into soil organic matter may reduce the reactivity of the compound. Even so, after 4 h of exposure to ozone, the chrysene concentration in a contaminated Metea soil was reduced from 100 to 50 mg kg −1 . Ozone has been found to be readily transported through columns packed with a number of geological materials, including Ottawa sand, Metea soil, Borden aquifer material and Wurtsmith aquifer material. All of these geological materials exerted a limited (finite) ozone demand, i.e. the rate of ozone degradation in soil columns is very slow after the ozone demand is met. Moisture content was found to increase the ozone demand, most likely owing to the dissolution of gaseous ozone into the pore water. As once the initial ozone demand is met, little degradation of ozone is observed, it should be possible to achieve ozone penetration to a considerable distance away from the injection well, suggesting that in-situ ozonation is a feasible means of treating uncontaminated unsaturated soils. This is substantiated by two field studies where in-situ ozonation was apparently successful at remediating the sites.

Ozonation of swine manure wastes to control odors and reduce the concentrations of pathogens and toxic fermentation metabolites

Abstract The use of ozone for the remediation of nuisance odorous chemicals in liquid swine manure slurry was investigated. Gaseous ozone was bubbled directly into stored swine manure slurry in a continuously stirred batch reactor. One‐liter samples of swine slurry were ozonated to achieve ozone dosages of 1.0, 2.0 and 3.0 g ozone/liter of waste. Olfactometric determinations demonstrated a significant reduction in odors in ozonated samples as compared to raw and oxygenated samples. Volatile fatty acids, nitrate, phosphate and ammonia concentrations were unchanged by ozonation. The biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) were essentially unaffected by ozonation. The concentrations of odorous phenolic microbial metabolites (e.g., phenol, p‐cresol and p‐ethylphenol) and odorous indolic microbial metabolites (e.g., 3‐methylindole and indole) were reduced to non‐detectable levels by ozonation. Hydrogen sulfide concentrations were reduced slightly by the process, with a concurrent i...

Mn oxide coated catalytic membranes for a hybrid ozonation-membrane filtration: Comparison of Ti, Fe and Mn oxide coated membranes for water quality

In this study the performance of catalytic membranes in a hybrid ozonation-ceramic membrane filtration system was investigated. The catalytic membranes were produced by coating commercial ceramic ultrafiltration membranes with manganese or iron oxide nanoparticles using a layer-by-layer self-assembly technique. A commercial membrane with a titanium oxide filtration layer was also evaluated. The performance of the coated and uncoated membranes was evaluated using water from a borderline eutrophic lake. The permeate flux and removal of the organic matter was found to depend on the type of the metal oxide present on the membrane surface. The performance of the manganese oxide coated membrane was superior to that of the other membranes tested, showing the fastest recovery in permeate flux when ozone was applied and the greatest reduction in the total organic carbon (TOC) in the permeate. The removal of trihalomethanes (THMs) and haloacetic acids (HAAs) precursors using the membrane coated 20 times with manganese oxide nanoparticles was significantly better than that for the membranes coated with 30 or 40 times with manganese oxide nanoparticles or 40 times with iron oxide nanoparticles.

Comparison of Ozone and Hydroxyl Radical-Induced Oxidation of Chlorinated Hydrocarbons in Water

The efficiency of ozonation and advanced oxidation processes such as ozone/UV, ozone/H2O2 and H2O2/UV was assessed for chlorinated hydrocarbons using a closed batch-type system. 1,1-Dichloropropene (DCPE), trichloroethylene (TCE), 1-chloropentane (CPA), and 1,2-dichloroethane (DCA) were used as model compounds. The direct reaction between substrates and ozone predominated at lower pH, which resulted in the efficient oxidation of the olefin, DCPE. At higher pH, ozonation resulted in more efficient oxidation of the chlorinated alkanes, with a corresponding decrease in the efficiency of DCPE oxidation. Consistent results were observed for ozone/H2O2 and ozone/UV treatment. Due to slow UV-induced decomposition of H2O2, the process using H2O2/UV (254 nm) resulted in very slow oxidation of all four compounds. The total ozone requirement to achieve a given degree of elimination (to 37% of the original concentration), δ0.37, was used to assess the combined effects of the direct and indirect reactions for differen...

Evaluation of soil pH and moisture content on in-situ ozonation of pyrene in soils.

In this study, pyrene spiked soil (300 ppm) was ozonated at pH levels of 2, 6, and 8 and three moisture contents. It was found that soil pH and moisture content impacted the effectiveness of PAH oxidation in unsaturated soils. In air-dried soils, as pH increased, removal increased, such that pyrene removal efficiencies at pH 6 and pH 8 reached 95-97% at a dose of 2.22 mg O(3)/mg pyrene. Ozonation at 16.2+/-0.45 mg O(3)/ppm pyrene in soil resulted in 81-98% removal of pyrene at all pH levels tested. Saturated soils were tested at dry, 5% or 10% moisture conditions. The removal of pyrene was slower in moisturized soils, with the efficiency decreasing as the moisture content increased. Increasing the pH of the soil having a moisture content of 5% resulted in improved pyrene removals. On the contrary, in the soil having a moisture content of 10%, as the pH increased, pyrene removal decreased. Contaminated PAH soils were stored for 6 months to compare the efficiency of PAH removal in freshly contaminated soil and aged soils. PAH adsorption to soil was found to increase with longer exposure times; thus requiring much higher doses of ozone to effectively oxidize pyrene.

Determination of the Efficacy of Ozone Treatment Systems Using a Gap Junction Intercellular Communication Bioassay

A non-genotoxic bioassay that monitors gap junction intercellular communication (GJIC) was used to assess the presence of potential tumor promoters after the ozonation of pyrene, a polycyclic aromatic hydrocarbon (PAH). Water and ozone were not rate limiting in a solution containing 10% water/90% acetonitrile (v/v) and 5 mM pyrene during ozonation. Pyrene (5 mM) was oxidized at various ozone dosages, and the resultant mixtures were assayed for their effect on GJIC. Approximately 4.5 mol of ozone/mol of pyrene was required to remove all the intermediate byproducts found to be inhibitory to GJIC. At 3.6 mol of O 3 /mol of pyrene, the mixture, which was slightly inhibitory to GJIC, was fractionated by RP-HPLC into 13 components of which only one component was inhibitory to GJIC. Just 1.6 mol of ozone/mol of pyrene was needed to remove >90% of the pyrene, which showed that monitoring only the removal of the parent compound was insufficient for the assessment of the treatment efficacv.

Ozonation of VOC's in the Presence of Humic Acid and Soils

The oxidation of several VOCs in the presence of humic acid and soil is described in this paper. It was found that while ozone does react appreciably with humic acid, as indicated by significant changes in the spectral characteristics of humic acid, the TOC levels in these solutions changed by only 3‰ or less. The oxidation of four olefinic VOCs occurred in solutions containing up to 120 mg/L humic acid, however, the extent to which each of the compounds reacted is very much compound specific. The effect of pH and ozone dosage on these reactions was considered. The effects of pH were weak for all compounds except trichloroethane. Ozone dosage had a significant effect on the extent to which each of the VOCs was oxidized, although no simple relationship between ozone dosage and the amount of VOC which reacted could be obtained. Complete oxidation of dy–dichloroethylene by ozone (22 mg/L) occurred in solutions containing 1.0 g of Eustis soil suspended in 10.0 mL water. However, only 40‰ oxidation of tetrachl...

Oxidation kinetics of phenolic and indolic compounds by ozone: applications to synthetic and real swine manure slurry

In this study, an oxidation model combining the mass transfer of ozone and ozonation kinetics was developed to predict the degradation of several phenolic and indolic compounds in a semi-batch reactor. The mass transfer and partition coefficients were calculated at various physical and chemical conditions. In addition, the reaction rate constants of ozone with phenolic and indolic compounds were also estimated independently using the method of competition kinetics and relative reaction-rate constants. Incorporating mass transfer and chemical reaction concepts, an oxidation model that considers side reactions between ozone and byproducts has been established using non-linear simultaneous differential equations. Thus, numerical computation is capable of simulating the degradation of phenolic and indolic compounds both in synthetic and real manure.

The effect of storage and ozonation on the physical, chemical, and biological characteristics of swine manure slurries

Abstract The reduction of odor emanating from wasted swine manure is a very challenging environmental engineering problem. In an earlier work (Watkins et al., 1997), we showed the effect of ozone in reducing the odor and concentration of phenolic compounds in swine manure obtained from the pits under the slotted floors where the swine were housed. In this paper, we have expanded significantly upon the work of Watkins et al. by determining the effect of storage on the physical, chemical and biological characteristics of the swine manure slurry and whether the efficacy of ozonation is dependent upon storage time.