Glutathione as a matrix for the synthesis of CdS nanocrystallites

GSH-capped CdS nanocrystallites were synthesized by reacting Cd(II)-GSH with aqueous sodium sulfide using specific initial sulfide/Cd(II) ratios. Spectroscopic analyses of fractions obtained from a size exclusion column showed varying absorption spectra indicating a significant dispersion in size-distribution of nanocrystallites at lower sulfide/Cd(II) ratios. However, size distribution of the nanocrystallites was narrower at initial sulfide/Cd(II) ratios that exceeded 1.0. An ethanol precipitation procedure was used to remove free Cd(II)-GSH complexes and selectively isolate GSH-capped nanocrystallites in a very narrow size range. Size exclusion chromatography indicated similar chemical compositions and overlapping spectral profiles of ethanol-precipitated samples suggesting apparent uniformity in both the size and the cap content. All of the GSH-capped CdS nanocrystallites with varying cap contents degraded p-nitrophenol upon irradiation at 366 nm. However, photocatalytic degradation of p-nitrophenol was significantly higher in samples with higher sulfide/Cd ratio and less capping material. The addition of H2O2 enhanced levels of photo-oxidation of p-nitrophenol.     

Chemo-denitrification of nitrate-polluted water

Nitrate-nitrogen reduction was studied in the presence of ferrous iron and a copper catalyst. In a batch system, it was found that the reduction was very fast at pH 8.1 and slow at pH 7.5. A temporary accumulation of nitrate and hydroxylamine was noted. It was found that the reduction of nitrite-nitrogen in the presence of ferrous iron partly continued to ammonium. Decreasing the amount of reagents led to a slower reduction rate but a lower accumulation of nitrite and hydroxylamine. A continuous system was described whereby more than 50% of the initial nitrate could be removed.     

Relation between the molecular structure and the adsorption of arylcarbamate, phenylurea and anilide pesticides in soil and model organic adsorbents

The adsorption data of the pesticides have been correlated with several molecular parameters. The most significant relation was obtained with a multilinear combination of the hydrophobicity constant π and the Hildebrand's constant δ which is influenced by the molecular interactions properties of the aromatic ring of the solutes.     

Performance assessment of a zeolite treatment wall for removing Sr-90 from groundwater

Laboratory and modeling studies were conducted to assess the potential performance of a permeable reactive barrier constructed of a natural zeolite material at the West Valley Demonstration Project in western New York State. The results of laboratory column tests indicated that the barrier material would be effective at removing strontium from groundwater under natural gradient conditions. Two one-dimensional contaminant transport models were developed to interpret the data. A single-solute retardation factor model provided good agreement with the column test data, but time-consuming extraction and analysis of the zeolite material was required to parameterize the model. A preliminary six-solute model was also developed based on the assumption of competitive cation exchange as the primary removal mechanism. Both models yielded similar predictions of the long-term performance of the barrier, but the cation exchange model predicted higher effluent concentrations during the first 1000 pore volumes of operation. The cation exchange framework has several advantages, including the ability to calibrate the model using only data from column effluent samples, and the ability to account for site-specific differences in the groundwater cation composition. However, additional laboratory work is needed to develop a suitably robust model.     

Laboratory evaluation of thermophilic-anaerobic digestion to produce Class A biosolids. 2. Inactivation of pathogens and indicator organisms in a continuous-flow reactor followed by batch treatment.

Thermophilic-anaerobic digestion in a single-stage, mixed, continuous-flow reactor is not approved in the United States as a process capable of producing Class A biosolids for land application. This study was designed to evaluate the inactivation of pathogens and indicator organisms in such a reactor followed by batch treatment in a smaller reactor. The combined process was evaluated at 53 degrees C with sludges from three different sources and at 51 and 55 degrees C with sludge from one of the sources. Feed sludge to the continuous-flow reactor was spiked with the pathogen surrogates Ascaris suum and vaccine-strain poliovirus. Feed and effluent were analyzed for these organisms and for indigenous Salmonella spp., fecal coliforms, Clostridium perfringens spores, and somatic and male-specific coliphages. No viable Ascaris eggs were observed in the effluent from the continuous reactor at 53 or 55 degrees C, with greater than 2-log removals across the digester in all cases. Approximately 2-log removal was observed at 51 degrees C, but all samples of effluent biosolids contained at least one viable Ascaris egg at 51 degrees C. No viable poliovirus was found in the digester effluent at any of the operating conditions, and viable Salmonella spp. were measured in the digester effluent in only one sample throughout the study. The ability of the continuous reactor to remove fecal coliforms to below the Class A monitoring limit depended on the concentration in the feed sludge. There was no significant removal of Clostridium perfringens across the continuous reactor under any condition, and there also was limited removal of somatic coliphages. The removal of male-specific coliphages across the continuous reactor appeared to be related to temperature. Overall, at least one of the Class A pathogen criteria or the fecal coliform limit was exceeded in at least one sample in the continuous-reactor effluent at each temperature. Over the range of temperatures evaluated, the maximum time required to meet the Class A criteria by batch treatment of the continuous-reactor effluent was 1 hour for Ascaris suum and Salmonella spp. and 2 hours for fecal coliforms.     

Gas-phase mercury reduction to measure total mercury in the flue gas of a coal-fired boiler

Gaseous elemental and total (elemental + oxidized) mercury (Hg) in the flue gas from a coal-fired boiler was measured by a modified ultraviolet (UV) spectrometer. Challenges to Hg measurement were the spectral interferences from other flue gas components and that UV measures only elemental Hg. To eliminate interference from flue gas components, a cartridge filled with gold-coated sand removed elemental Hg from a flue gas sample. The Hg-free flue gas was the reference gas, eliminating the spectral interferences. To measure total Hg by UV, oxidized Hg underwent a gas-phase, thermal-reduction in a quartz cell heated to 750 degrees C. Simultaneously, hydrogen was added to flash react with the oxygen present forming water vapor and preventing Hg re-oxidation as it exits the cell. Hg concentration results are in parts per billion by volume Hg at the flue gas oxygen concentration. The modified Hg analyzer and the Ontario Hydro method concurrently measured Hg at a field test site. Measurements were made at a 700-MW steam turbine plant with scrubber units and selective catalytic reduction. The flue gas sampled downstream of the selective catalytic reduction contained 2100 ppm SO2 and 75 ppm NOx. Total Hg measured by the Hg analyzer was within 20% of the Ontario Hydro results.     

Risk assessment of heavy metal pollution for detritivores in floodplain soils in the Biesbosch, The Netherlands, taking bioavailability into account

Floodplains of the European rivers Rhine and Meuse are heavily polluted. We investigated the risk of heavy metal pollution (Cd, Cu, Pb, Zn) for detritivores living in a floodplain area, the Biesbosch, the Netherlands, affected by these rivers. Total soil, pore water and 0.01 M CaCl(2) extractable concentrations and concentrations in plant leaves, earthworms, isopods and millipedes were measured in two sites and compared with literature data to assess possible risks. Based on total metal concentrations in soil, serious effects on detritivores were expected. However, 0.01 M CaCl(2) extractable, pore water and plant leaf concentrations were similar to metal concentrations found in unpolluted areas. Concentrations of Cu and Cd in earthworms and Cu in millipedes were higher in the Biesbosch than in animals from reference areas. All other measured concentrations of heavy metals in earthworms, isopods and millipedes were similar to the ones found in reference areas. Despite high total soil concentrations, effects of Zn, Cu, Pb and Cd pollution on isopods are therefore not expected, while millipedes may only be affected by Cu. Since Cu and Cd levels in earthworms were increased compared to animals in unpolluted soils, this faunal group seems to be most at risk. Given the engineering role of earthworms in ecosystems, effects on the ecological functioning of floodplain soils therefore cannot be excluded.     

Monitoring of polychlorinated biphenyls in Belgian human adipose tissue samples

Polychlorinated biphenyls (PCBs) were monitored in Belgian human adipose tissue samples from deceased individuals (n=100). Their mean age was 52, ranging from 2 to 91 years. There were 57 men and 43 women. Other known variables were date of autopsy and place of residence. No information about diet or occupation was available. The seven marker congeners PCB 28, 52, 101, 118, 138, 153 and 180 were analysed in the samples with a GC-MS/MS method validated according to Commission Decision 2002/657/EC. Extracted fat was cleaned-up over a glass column filled with n-hexane, acid silica, deactivated alumina and anhydrous sodium sulfate. The whole procedure was subjected to a rigorous quality control programme with retention times, ion chromatograms and intensity ratios of the monitored product ions as identification criteria. The total PCB concentration ranged between 10 and 1640 ng g-1 fat, with a mean value of 658 ng g-1 fat. In the age groups of 0-9 (n=1), 10-19 (n=4), 20-29 (n=11), 30-39 (n=13), 40-49 (n=15), 50-59 (n=14), 60-69 (n=14), 70-79 (n=20), 80-89 (n=6) and 90-99 (n=2), the mean total PCB concentrations were 10, 134, 253, 445, 557, 687, 807, 962, 959, and 1191 ng g-1 fat, respectively. So, there was an increase of PCB body burden with age. For the male subjects (n=57; mean age of 53) the mean total PCB concentration was 633 ng g-1 fat. For the female subjects (n=43; mean age of 52) it was 690 ng g-1 fat. There was no significant sex-related difference in the concentrations of marker PCBs.     

Removal of PCBs from wastewater using fly ash

Liquids and sludges containing polychlorinated biphenyls (PCBs) can be treated to concentrate the PCBs in a solid residue. The latter can then be handled to destroy the PCBs. A study on sorption kinetics of PCBs on fly ash was conducted in controlled batch systems. TCB and HeCB are removed at 25 degrees C by adsorption on fly ash up to 97% at pH 7, with an adsorbent dose of 5 g/l. An examination of the thermodynamic parameters shows that the adsorption of TCB and HeCB by fly ash is a process occurring spontaneously at ambient conditions. Activation energies for the sorption process ranged between 5.6 and 49.1 kJ/mol. It was observed that the rate at which TCB and HeCB are adsorbed onto fly ash showed a diffusion limitation. The uptake rate of TCB and HeCB increases with increasing initial concentration and gradually tends to a constant value. A decrease in the adsorption of TCB and HeCB was observed when interfering ions and other PCB congeners were present. Changing the pH in the aqueous solution from 2 to 10 had no effect on the adsorption process. Overall, fly ash can be used for an efficient removal of PCBs from several aqueous solutions.     

Regeneration of a compost biofilter degrading high loads of ammonia by addition of gaseous methanol

The long-term stability of a biofilter loaded with waste gases containing NH3 concentrations larger than 100 ppmv was studied in a laboratory-scale compost reactor. At an empty bed residence time (tau) of 21 sec, elimination capacities of more than 300 g NH3/m3/day were obtained at elimination efficiencies up to 87%. Because of absorption and nitrification, almost 80% of the NH3-N eliminated from the waste gas could be recovered in the compost as NH4(+)-N or NO2-/NO3(-)-N. The high elimination capacities could be maintained as long as the NH4+/ NOX- concentration in the carrier material was less than 4 g NH4+/NOx(-)-N/kg wet compost. Above this critical value, osmotic effects inhibited the nitrifying activity, and the elimination capacity for NH3 decreased. To restore the biofilter performance, a carbon source (methanol) was added to reduce NH4+/NOx- accumulated in the compost. Results indicate that methylotrophic microorganisms did convert NH4+/NOx- into biomass, as long as the NO3- content in the compost was larger than 0.1 g NO3(-)-N/kg compost. Removal efficiencies of CH3OH of more than 90% were obtained at volumetric loads up to 11,000 g CH3OH/ m3/day. It is shown that addition of CH3OH is a suitable technique for regenerating the compost material from osmotic inhibition as a result of high NH3 loading. The biofilter was operated for 4 months with alternating load ing of NH3 and CH3OH.