Deactivation of titanium dioxide photocatalyst by oxidation of polydimethylsiloxane and silicon sealant off-gas in a recirculating batch reactor

We have studied deactivation of titanium dioxide (TiO2) photocatalyst by oxidation of polydimethylsiloxane and silicone sealant off-gas in a recirculating batch reactor. Polydimethylsiloxane vapor is a model indoor air pollutant. It does not adsorb strongly on TiO2 in the dark, but undergoes oxidation when the ultraviolet (UV) photons are also present. Commercial silicone (room-temperature vulcanizing) sealant off-gas is an actual indoor air pollutant subject to short-term spikes in concentration. It does adsorb on the TiO2 surface in the dark, but UV photons also catalyze its oxidation. The oxidation of the Si-containing vapors was monitored using a Fourier transform infrared spectroscope equipped with a gas cell. Subsequent to each incremental exposure, a hexane oxidation reaction was performed to track the titania catalyst's activity. The exposures were repeated until substantial deactivation was achieved. We have also documented the regenerative effect of washing the catalyst surface with water. Surface science techniques were used to view the topography of the catalyst and to identify the elements causing the deactivation. Procedural observations of interest in the context of our recirculating batch reactor include the following: the rate of oxidation of hexane was used to assess the activity of a photocatalyst sample; hexane is an appropriate choice of a probe molecule because it does not adsorb in the dark and it undergoes photocatalytic oxidation (PCO) completely, forming CO2; and hexane does not deactivate the photocatalyst surface.     

Geochemical and geostatistical investigations of chromium pollution in groundwater.

Geochemical and geostatistical study of the chromium concentration in groundwater occurring at variable depths of 12 to 33.5 m (40 to 110 ft) in the Karachi urban area of Pakistan have been made. Samples were collected at variable distances, with a maximum of 1 km interval, on the bases of population, industries, types, and density. The chromium concentration has also been worked out to deduce the threshold value of the area under study and the estimation of probability impact modeling, in terms of concentration variation, by using the disjunctive kriging technique. The outcome of the present work appears to be a good tool to decipher pollution variation in the groundwater of highly urbanized areas, with respect to the population and industries. The patterns of distribution of chromium concentration in groundwater and pollution hotspots in particular localities appear to be more related to the types of industries than to the effect of population types.     

Implications of urine-to-feces ratio in the thermophilic anaerobic digestion of swine waste.

Thermophilic anaerobic digestion of swine manure represents a potential waste treatment technology to address environmental concerns, such as odor emissions and removal of pathogenic microorganisms. However, there are concerns relative to the stability of this process when swine manure is the sole substrate. In this study, the potential of biogas production from swine manure as the sole substrate under thermophilic (50 degrees C) conditions was investigated in the laboratory, to determine whether separation of urine and feces as part of the waste collection process would benefit anaerobic digestion. Effluent from a continuously stirred tank reactor was used as the inoculum for batch tests, in which the substrate contained three different concentrations of urine (urine-free, as-excreted urine-to-feces ratio and double the as-excreted urine-to-feces ratio). Inocula were acclimated to these same urine-to-feces ratios to determine methane production. Results show that both urine-free and as-excreted substrates were not inhibitory to anaerobic inocula. Anaerobic microorganisms can be readily acclimated to substrate with double the as-excreted urine concentration, which contained nitrogen concentrations up to 7.20 g/L. Cumulative methane production reached similar levels in the batch tests, regardless of the substrate urine concentration.     

Phosphorus removal from municipal wastewater by hydrous ferric oxide reactive filtration and coupled chemically enhanced secondary treatment: part I--performance.

This work examines the performance of a hydrous ferric oxide (HFO) reactive filtration (RF) process with coupled chemically enhanced secondary treatment (RECYCLE) for phosphorus removal from municipal wastewater (HFO-RF-RECYCLE). A 3-month, 0.95-ML/d (0.25-mgd) demonstration of HFO-RF-RECYCLE was performed at a municipal wastewater treatment plant equipped with oxidation ditches and secondary clarifiers. Influent to the plant averaged 6.0 mg/L phosphorus, with a tertiary effluent average of 0.011 mg/L phosphorus. Iron doses to the plant were low, at 5 mg/L. Inline recycling of HFO solution rejects to the plant influent resulted in a maximum 90.3%, dose-dependent reduction of phosphorus in the secondary effluent at 4.5 ML/d (1.2 mgd). Other results included reduction of total suspended solids and turbidity. A mass balance analysis was performed. We conclude that HFO-RF-RECYCLE may allow very low levels of phosphorus discharge from municipal wastewater treatment plants with a ferric-iron-based tertiary filtration process and residual recycling.     

The impact of the 2004 tsunami on coastal Thai communities: assessing adaptive capacity

The suddenness and scale of the 26 December 2004 tsunami and the challenges posed to affected communities highlighted the benefits of their members having a capacity to confront and adapt to the consequences of such a disaster. Research into adaptive capacity or resilience has been conducted almost exclusively with Western populations. This paper describes an exploratory study of the potential of a measure of collective efficacy developed for Western populations to predict the capacity of members of a collective society, Thai citizens affected by the 2004 tsunami, to confront effectively the recovery demands associated with this disaster. Following a demonstration that this measure could predict adaptive capacity, the role of religious affiliation, ethnicity and place of residence in sustaining collective efficacy is discussed. The implications of the findings for future research on, and intervention to develop, adaptive capacity among Thai citizens in particular and collectivist societies in general are discussed.     

Reevaluation of ENCORE: support for the eutrophication threshold model for coral reefs

The results from the multimillion dollar Enrichment of Nutrients on Coral Reefs Experiment (ENCORE) on One Tree Island Reef (OTIR) suggest that increased nutrient loads to coral reefs will have little or no effect on the algal growth rates and, hence, on the associated effects that increased algal growth might have on the functioning and stability of coral reefs. However, a comparison of the concentrations of nutrients within the OTIR lagoon with the proposed nutrient threshold concentrations (NTC) for coral reefs suggests that all sites, including the control sites, were saturated with nutrients during ENCORE, and, hence, one would not expect to get any differences between treatments in the algal-growth related measurements. Thus, ENCORE results provide strong support for the proposed NTCs and support the ecological principle that algal productivity and, consequently, the functioning of coral reefs are sensitive to small changes in the background concentrations of nutrients. The principal conclusion of ENCORE, namely that the addition of nutrients did not cause the "pristine" OTIR to convert from coral communities to algal dominated reefs, is contrary to the fact that there was prolific macroalgal growth on the walls and crests of the experimental microatolls by the end of ENCORE.     

Persistent organic pollutants in atmospheric deposition and biomonitoring with Tillandsia usneoides (L.) in an industrialized area in Rio de Janeiro state, southeast Brazil--Part II: PCB and PAH

Monitoring of immission of persistent organic pollutants in the industrialized area of Volta Redonda (V.R.) and in the National Park of Itatiaia (PNI) in southeast Brazil was performed using an endemic bromeliad species as biomonitor and measuring bulk deposition rates of polychlorinated biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH). For the sum of PCB, overall deposition rates were between 17 and 314 ng/(m2 day) in winter and between 43 and 81 ng/(m2 day) in summer, respectively. Deposition rates of dioxin-like PCBs ranged from 0.14 to 2.8 pg WHO-TEQ/(m2 day) in winter and from 0.90 to 4.3 pg WHO-TEQ/(m2 day) in summer. PCB deposition rates (total PCB and WHO-TEQ) were in the same range in winter in V.R. and PNI. In summer, contamination levels in V.R. were 6-10-folds higher than in PNI. PCB concentrations in biomonitor samples from V.R. and PNI were in the same range in summer and in winter. Concentrations of total PCB ranged from 14 to 95 microg/kg dry matter (d.m.) in winter and from 18 to 27 microg/kg d.m. in summer, respectively. The TEQ values were between 1.7 and 4.1 ng WHO-TEQ/kg d.m. in winter and between 1.9 and 2.9 ng WHO-TEQ/kg d.m. in summer. PCB concentrations of di-ortho PCB but not of non-ortho PCB were a factor of 2-4 lower in summer in both areas. PCB congener profiles resembled those from technical formulations. The profiles shifted to the higher chlorinated congeners in summer, probable due to revolatilisation of the lighter components at higher temperatures. PCB profiles in biomonitor resembled those from deposition samples and the shift to the heavier congeners in summer was even more pronounced. PAH deposition rates were in a similar range in both areas (131-2415 ng/(m2 day)). PAH levels in biomonitor samples from V.R. were about one order of magnitude higher than in samples from PNI indicating the impact of local sources. PAH profiles revealed stationary thermal processes as main source of contamination in V.R. whereas in PNI, biomass burning seems to be the main contamination source.     

Preliminary evidence of a decline in perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) concentrations in American Red Cross blood donors

The purpose of this pilot study was to determine whether perfluorooctanesulfonate (PFOS,C(8)F(17)SO(3)(-)) and perfluorooctanoate (PFOA,C(7)F(15)CO(2)(-)) concentrations in American Red Cross blood donors from Minneapolis-St. Paul, Minnesota have declined after the 2000-2002 phase-out of perfluorooctanesulfonyl-fluoride (POSF, C(8)F(17)SO(2)F)-based materials by the primary global manufacturer, 3M Company. Forty donor plasma samples, categorized by age and sex, were collected in 2005, and PFOS and PFOA concentrations were compared to 100 (non-paired) donor serum samples collected in 2000 from the same general population that were analyzed at the time using ion-pair extraction methods with tetrahydroperfluorooctanesulfonate as an internal standard. Eleven of the 100 samples originally collected were reanalyzed with present study methods that involved (13)C- labeled PFOA spiked into the donor samples, original samples, control human plasma, and the calibration curve prior to extraction, and was used as a surrogate to monitor extraction efficiency. Quantification was performed by high performance liquid chromatography tandem mass spectrometry methods. Among the 100 serum samples analyzed for PFOS, the geometric mean was 33.1 ng ml(-1) (95% CI 29.8-36.7) in 2000 compared to 15.1 ng ml(-1) (95% CI 13.3-17.1) in 2005 (p<0.0001) for the 40 donor plasma samples. The geometric mean concentration for PFOA was 4.5 ng ml(-1) (95% CI 4.1-5.0) in 2000 compared to 2.2 ng ml(-1) (95% CI 1.9-2.6) in 2005 (p<0.0001). The decrease was consistent across donors' age and sex. To confirm these preliminary findings, additional sub-sets of year 2000 samples will be analyzed, and a much larger biomonitoring study of other locations is planned.     

Atrazine sorption and fate in a Ultisol from humid tropical Brazil

This study combined laboratory based microcosm systems as well as field experiments to evaluate the mobility of atrazine on a Ultisol under humid tropical conditions in Brazil. Results from sorption experiments fit to the Freundlich isotherm model [K(f) 0.99 mg kg(-1)/(mg l(-1))(1/n)], and indicate a low sorption capacity for atrazine in this soil and consequently large potential for movement by leaching and runoff. Microcosm systems using (14)C-atrazine to trace the fate of the applied herbicide, showed that 0.33% of the atrazine was volatilized, 0.25% mineralized and 6.89% was recorded in the leachate. After 60 d in the microcosms, 75% of the (14)C remained in the upper 5 cm soil layer indicating atrazine or its metabolites remained close to the soil surface. In field experiments, after 60 d, only 5% of the atrazine applied was recovered in the upper soil layers. In the field experiments atrazine was detected at a depth of 50 cm indicating leaching. Simulating tropical rain in field experiments resulted in 2.1% loss of atrazine in runoff of which 0.5% was adsorbed onto transported soil particles and 1.6% was in solution. Atrazine runoff was greatest two days after herbicide application and decreased 10 fold after 15 d. The use of atrazine on Ultisols, in the humid tropics, constitutes a threat to water quality, causing surface water and ground water pollution.     

Biological denitrification of high strength nitrate waste using preadapted denitrifying sludge

Denitrification of synthetic high nitrate waste containing 9032 ppm NO(3)-N (40,000 ppm NO(3)) in a time period of only 6h has been achieved in our previous study using activated sludge. The activated sludge culture was acclimatized by a stepwise increase in the nitrate concentration of synthetic waste. In the present work, studies were carried out on the changing microbial population of the sludge and the physiology of nitrate metabolism during the various stages of adaptation process to high strength synthetic nitrate waste. During the course of adaptation, with an increase in the nitrate concentration, a sharp increase in the number of denitrifiers was found with an equally rapid decrease in the nitrifying community. Two key enzymes involved in the first two steps of the denitrification process were also studied during this period. The results of the study suggest that specific enzyme levels increase as the activated sludge adapts itself to higher nitrate concentrations. Biological denitrification of high nitrate waste is a slow process and to increase the rate of denitrification, parameters such as pH, temperature, C:N and biomass concentration of the process were optimized using orthogonal array method. Optimized conditions increased the specific nitrate reduction rate by 54% and specific nitrite reduction rate by 45%.