No description available.

No description available.

The destruction of Direct-Red #79 textile dye in dilute aqueous solution was demonstrated by heterogeneous solar photocatalysis over suspended titanium dioxide. Dye oxidation and adsorption mechanisms, TiO2 photocatalysis, and external oxidant (H2O2) addition are discussed. Experimental data are presented which support previous studies reporting first order destruction of organic contaminants using recirculating batch reactor systems. The observance of optimum catalyst concentration, and reaction rate conformance to the Langmuir-Hinshelwood kinetic model were similar to results obtained by others. Dye destruction by free radicals was investigated. Evidence suggesting involvement of these processes is proposed by relating the rate of dye destruction to solution pH and alkalinity levels. Enhancement of dye destruction rate upon hydrogen peroxide addition was examined. Results of total organic carbon analyses, spectrophotometric absorbance measurements, and molecular weight estimations suggested the formation of reaction intermediates and indicated the extent of dye oxidation.

To investigate the effect of fluid shear on uptake rates of low diffusivity macromolecular substrates by suspended cultures, I measured the radiolabel and oxygen uptake of two model compounds, bovine serum albumin and dextran, in pure cultures of Zoogloea ramigera and E. coli, respectively. Oxygen utilization rates of stirred samples grown on BSA and dextran were 2.3 and 2.9 times higher, respectively, than undisturbed (still) samples. Uptake rates of (3H) BSA and (3H) dextran by stirred samples were 12.6 and 6.2 times higher, respectively, than still samples. These experimentally obtained increases are larger than increases predicted using a mass transfer model. The mass transfer model predicts uptake rate will increase by a factor of 1.6 and 1.8 for BSA and dextran, respectively, as a result of stirring. Uptake rates of low-molecular-weight substrates with high diffusivities, such as leucine and glucose, were only slightly affected by fluid shear. Since macromolecules can comprise a major portion of bacterial substrate in engineered, laboratory, and natural systems, the demonstrated effect of fluid shear has wide implications for the evaluation of engineered bioreactors used for wastewater treatment as well as for kinetic studies performed in basic metabolic research.

Disposable diapers are a possible source of infectious enteric viruses that are disposed of in landfills. A total of 210 disposable diapers were collected from seven sites and ten depths at three landfills. Of these total, 110 diapers were processed with a 1.5% beef-extract-elution organic-flocculation-concentration method to recover viruses. The concentrated samples were assayed on BGM cell cultures for the detection of enteroviruses and with cDNA probes specific for poliovirus, hepatitis A virus and rotavirus. Enteroviruses were not detected in any sample assayed using cell culture techniques. Three samples were positive using nucleic acid probes for poliovirus. These results suggest that poliovirus RNA was present in some diapers but that the viruses were not viable after two years or longer in a landfill.

acase@tulane.edu

No description available.

Arsenic in drinking water affects millions globally causing skin disease and cancers of the liver, stomach, and bladder. Large-scale treatment removes arsenic effectively; however, community- and home-scale treatments are typically less effective, more costly, or labor intensive. Nanomagnetite would enable effective, economical arsenic removal in low maintenance, household sand filters. Adsorption isotherms were used to display the As(V) capacity of nanomagnetite in a variety of natural waters and pH conditions. Column design and operating conditions were assessed for optimal removal. Breakthrough was most affected by nanomagnetite percentage, residence time, inlet concentration, and nanomagnetite aggregate size. NH4OH regenerated the nanomagnetite, allowing for repeated use. No detectable nanomagnetite escaped the column; however, permanent magnets were shown to capture >98% of nanomagnetite aggregates from a fluid stream. A case study proposes the use of nanomagnetite to treat arsenic contaminated groundwater in Guanajuato, Mexico to below the Mexican EPA drinking water standard for $0.23/m3.

In this work, an electrochemical method was developed to destroy liquid chlorinated solvents, and a thermochemical technique was invented to reduce gas-phase chlorinated solvents to hydrocarbons. The developed electrochemical method belongs to the most potential technique for wastewater treatment--only electrochemical method is possible to simultaneously destroy all water contaminants; the invented thermochemical method is the fastest way to destroy chlorinated solvents. In the first part of this work, the anodic oxidation of trichloroethylene (TCE) on an Ebonex ceramic electrode was investigated. TCE could be oxidized to CO₂, CO, Cl⁻, and ClO₃⁻. The disappearance of TCE was first-order, independent of pH, and initial TCE concentrations. TCE oxidation occurred only on the anodic surface and was limited by mass transport at Ea > 4.3 V vs SSCE ( i > 5 mA cm⁻²). Hydroxyl radicals generated on anode surface were detected using a spin trap. A kinetic model was successfully correlated with experimental results. In the second part of this work, TCE and CF were rapidly dechlorinated to hydrocarbons on the Ebonex ceramic cathode using Pt or Pd as catalyst. Pt was found to possess great resistance to sulfur and chlorine poisoning. Pd was quickly deactivated in sulfate solution. TCE and CF cathodic transformation were strongly dependent of pH. The reaction rate was limited by mass transport at Ec<-1.6 V (i > 5 mA cm⁻²). The mass transfer to cathode surface was found to be three times faster than to anode surface. The main products of TCE reduction were ethane, ethylene, and chloride, and for CF were methane and chloride. The proposed reaction mechanism and kinetic model were consistent with experimental results. In the third part of this work, a new hydrodechlorination method was invented for gas-phase chlorinated solvent destruction. Gas-phase chlorinated solvents, such as PCE, TCE, 1,1-DCE, VC, and CF were rapidly reduced to ethane, ethylene, and methane in a continuous-flow column reactor at ambient temperature and pressure. This is the fastest way to destroy chlorinated solvents. The catalyst could be easily regenerated and had a long-life time (over one and half year). The reaction mechanism and kinetics were studied. In the forth part of this work, the first three parts of work were combined together to invent a new destruction method for chlorinated solvents in real wastewater. Ebonex ceramic materials served as electrodes and Pt was plated on cathode used as catalyst in the electrolytic cell. The headspace of the electrolytic cell was connected to the Pd/Ni catalyst column. Liquid chlorinated solvents were destroyed on electrode surface, and gas-phase chlorinated solvents were reduced to hydrocarbons in the Pd/Ni catalyst surface in the presence of hydrogen. Water scale or other deposited materials on Pt coated Ebonex cathode could be removed, and the catalyst could be regenerated by reversing electrode polarity.

Ten dry cleaning sites were evaluated in the Houston area. At the dry cleaning sites studied, the contamination may be attributed to deficiencies in the separation equipment of the dry cleaning equipment, allowing free phase perchloroethene (PCE) to enter the sanitary sewer lines and escape by permeating through the pipe, or through defects in the pipe. Three sites with different geologic characteristics were chosen for intensive study to examine if there exists a pattern of transformation of PCE to the daughter product trichloroethene (TCE) in the sites. Transformation is compared by calculating the ratio of PCE to TCE for each well for a single sampling event, and by modeling at one of the sites. One site was modeled with the model RT3D, and the results from the model confirm the change in PCE to TCE ratio as being a result of a change in the reaction rate. A pattern was noticed in the site data which sites with sandier hydrologies, as measured by hydraulic conductivity, tended to have lower transformation rates than sites with tighter formations. It is suggested that this difference in apparent reaction rate may be due to enhanced reaction in the tighter formations due to lack of oxygen recharge, leading to an anaerobic region that is conducive to reductive dechlorination.