R. Ravikrishna

Reusable adsorbents for dilute solution separation. 6. Batch and continuous reactors for the adsorption and degradation of 1,2-dichlorobenzene from dilute wastewater streams using titania as a photocatalyst

Two types of external lamp reactors were investigated for the titania catalyzed photodegradation of 1,2-dichlorobenzene (DCB) from a dilute water stream. The first one was a batch mixed slurry reactor and the second one was a semi-batch reactor with continuous feed recycle with titania immobilized on inert supports (quartz and low density polyethylene, LDPE). The batch reactor was used to study the intermediates and reaction kinetics of DCB degradation. Four intermediate products were observed in the degradation of DCB; these being 2-chlorophenol (CP), 2,3-dichlorophenol (DCP), 1,2-dihydroxybenzene (catechol) and, o-benzoquinone. A mechanism based on these observations is proposed. Increasing the pH of the solution increased the intial rate of photodegradation of DCB. Added oxidant (hydrogen peroxide) did not have any appreciable effect on the degradation of DCB. The Langmuir–Hinshelwood kinetic parameters for DCB, DCP and CP were obtained. The steady state removals and apparent rate constants were obtained for the plug-flow reactor with different supports and compared under similar conditions. The titania supported on LDPE showed a better rate of photocatalysis than titania supported on quartz, although the titania film thickness on LDPE was five times lower than on quartz. The modification of titania surface by adsorption of a non-photodegradable polyfluorinated surfactant vastly improved the rate of DCB degradation on both LDPE and quartz. The rate of photodegradation in the immobilized tubular reactor was mass transfer controlled for the flow regimes investigated, viz., Reynolds numbers, Re<550. The steady state removal was directly proportional to the radiant flux within the range 4–16 mW cm−2.

Reusable adsorbents for dilute solution separation. 5. Photodegradation of organic compounds on surfactant-modified titania

A semiconductor titania (TiO2) surface was modified by surfactant adsorption to make it more hydrophobic and to increase the adsorption of hydrophobic organic compounds (HOCs) and their photodegradation rates under UV irradiation. Photocatalytic experiments using TiO2 suspensions were conducted in the batch mode in a 10 ml reactor made of quartz. Two anionic surfactants, a hydrocarbon-based surfactant, sodium dodecylsulfate (SDS), and a fluorocarbon-based surfactant, potassium perfluorooctylsulfonate (PFOS), were used for titania surface modification. A hydrophobic organic compound namely, 1,2-dichlorobenzene (DCB), a chlorinated aromatic compound, was used as the test HOC. PFOS, which is resistant to UV irradiation, increased both the adsorption and photodegradation of DCB on titania. SDS, however, competed for photodegradation and inhibited the degradation of PCB.

Air emissions from exposed, contaminated sediments and dredged materials. 1. Experimental data in laboratory microcosms and mathematical modelling

The air emissions of two polycyclic aromatic hydrocarbons (pyrene and phenanthrene) and one heterocyclic compound (dibenzofuran) from an ‘aged’ contaminated sediment (Rouge River, Michigan) were studied in an experimental microcosm. The sediment-to-air flux of the above semivolatile organic compounds (SOCs) was obtained from an initially water-saturated sediment. The magnitude of flux varied as dibenzofuran > phenanthrene > pyrene. At a low air flow rate (10 ml min−1 the flux was low and stable and air-phase resistance controlled. At a larger flow rate (100 ml min−1) the flux was high initially and then declined, indicating the effects of sediment-side diffusion on mass transfer to air. The flux was also sensitive to the relative humidity (RH) of the air flowing above the sediment. It was observed that the flux, though high initially, declined rapidly as dry air (0% RH) was passed over the wet sediment. Loss of sediment moisture which increased the sorptive capacity of the sediment for the contaminants was also noted. Subsequent exposure of the dry sediment to humid air increased the flux. The steady state flux was consistently high when humid air was passed over dry sediment. The experimental data were analyzed using a mathematical model which estimated the air emission from an exposed sediment layer under both sediment-side and air-side resistance controlled conditions. The model incorporated an advancing ‘drying front’ in the direction of airflow for water evaporation in accordance with our observations. The sharp decrease in contaminant flux was attributed to the drying-out of the sediment and a consequent increase in its sorptive capacity for the contaminant. The framework of the theory underlying the air emission modelling from exposed sediment, dredged and placed in a confined disposal facility (CDF) is summarized.

Air emissions from exposed, contaminated sediment and dredged materials: 2. Diffusion from laboratory-spiked and aged field sediments

The mass transfer of three polycyclic aromatic hydrocarbons (naphthalene, phenanthrene and pyrene) and a heterocyclic aromatic hydrocarbon (dibenzofuran) from sediment to air was studied in a large-area flux chamber. A laboratory-spiked local (University Lake, UL) sediment and an aged contaminated field (Indiana Harbor Canal, IHC) sediment was used. The effects of initial sediment moisture content, and changing air relative humidity were investigated. For high moisture conditions in the UL sediment, the flux remained large whereas for low moisture conditions, there was a sharp decrease in flux as a result of surface drying of the sediment. Under similar air velocities and moisture conditions, the flux from the aged IHC sediment was considerably smaller than from the laboratory-spiked UL sediment. Whereas, the flux from laboratory-spiked UL sediment was predicted satisfactorily by a conceptual mathematical model, that from the aged IHC sediment did not agree with the model predictions. It was concluded that only a portion of the contaminant was available for desorption from the aged sediment due to the differences in the sorption characteristics of relatively fresh and aged contaminated sediments.

Air emission flux from contaminated dredged materials stored in a pilot-scale confined disposal facility.

ABSTRACT A pilot-scale field simulation was conducted to estimate the air emissions from contaminated dredged material stored in a confined disposal facility (CDF). Contaminated dredged material with a variety of organic chemicals, obtained from Indiana Harbor Canal, was used in the study. It was placed in an outdoor CDF simulator (i.e., a lysi-meter of dimensions 4 ft x 4 ft x 2 ft). A portable, dynamic flux chamber was used to periodically measure emissions of various polynuclear aromatic hydrocarbons (PAHs). A weather station was set up to monitor and record the meteorological conditions during the experiment. The fluxes of several PAHs were monitored over time for 61/2 months. Initial 6-hr average fluxes varied from 2 to 20 ng/cm2/hr for six different PAHs. The flux values declined rapidly for all compounds soon after placement of the dredged material in the CDF. Chemical concentrations derived from flux values were generally of low magnitude compared with ambient standards. Data obtained from the experiment were compared against those predicted using models for air emissions. Model simulations showed that initially the flux was largely from exposed pore water from saturated (wet) sediment, whereas the long-term flux was controlled by diffusion through the pore air of the unsaturated sediment. Model predictions generally overestimated the measured emissions. A rainfall event was simulated, and the dredged material was reworked to simulate that typical of a CDF operation. Increased flux was observed upon reworking the dredged material.

Volatilization of Contaminants from Suspended Sediment in a Water Column during Dredging

Abstract Remedial dredging of contaminated bed sediments in rivers and lakes results in the suspension of sediment solids in the water column, which can potentially be a source for evaporation of hydrophobic organic compounds (HOCs) associated with the sediment solids. Laboratory experiments were conducted in an oscillating grid chamber to simulate the suspension of contaminated sediments and flux to air from the surface of the water column. A contaminated field sediment from Indiana Harbor Canal (IHC) and a laboratory-inoculated University Lake (UL) sediment, Baton Rouge, LA, were used in the experiments, where water and solids concentration and particle size distribution were measured in addition to contaminant fluxes to air. A transient model that takes into account contaminant desorption from sediment to water and evaporation from the water column was used to simulate water and sediment concentrations and air fluxes from the solids suspension. In experiments with both sediments, the total suspended solids (TSS) concentration and the average particle diameter of the suspended solids decreased with time. As expected, the evaporative losses were higher for compounds with higher vapor pressure and lower hydrophobicity. For the laboratory-inoculated sediment (UL), the water concentrations and air fluxes were high initially and decreased steadily implying that contaminant release to the water column from the suspended solids was rapid, followed by evaporative decay. For the field sediments (IHC), the fluxes and water concentrations increased initially and subsequently decreased steadily. This implied that the initial desorption to water was slow and that perhaps the presence of oil and grease and aging influenced the contaminant release. Comparison of the model and experimental data suggested that a realistic determination of the TSS concentration that can be input into the model was the most critical parameter for predicting air emission rates.

Terrestrial Macrofungal Diversity from the Tropical Dry Evergreen Biome of Southern India and Its Potential Role in Aerobiology

Macrofungi have long been investigated for various scientific purposes including their food and medicinal characteristics. Their role in aerobiology as a fraction of the primary biological aerosol particles (PBAPs), however, has been poorly studied. In this study, we present a source of macrofungi with two different but interdependent objectives: (i) to characterize the macrofungi from a tropical dry evergreen biome in southern India using advanced molecular techniques to enrich the database from this region, and (ii) to assess whether identified species of macrofungi are a potential source of atmospheric PBAPs. From the DNA analysis, we report the diversity of the terrestrial macrofungi from a tropical dry evergreen biome robustly supported by the statistical analyses for diversity conclusions. A total of 113 macrofungal species belonging to 54 genera and 23 families were recorded, with Basidiomycota and Ascomycota constituting 96% and 4% of the species, respectively. The highest species richness was found in the family Agaricaceae (25.3%) followed by Polyporaceae (15.3%) and Marasmiaceae (10.8%). The difference in the distribution of commonly observed macrofungal families over this location was compared with other locations in India (Karnataka, Kerala, Maharashtra, and West Bengal) using two statistical tests. The distributions of the terrestrial macrofungi were distinctly different in each ecosystem. We further attempted to demonstrate the potential role of terrestrial macrofungi as a source of PBAPs in ambient air. In our opinion, the findings from this ecosystem of India will enhance our understanding of the distribution, diversity, ecology, and biological prospects of terrestrial macrofungi as well as their potential to contribute to airborne fungal aerosols.

Vapor-Phase Transport of Explosives from Buried Sources in Soils

Abstract The fate and transport of explosives in the soil pore vapor spaces affects both the potential detection of buried ordnance by chemical sensors and vadose zone transport of explosives residues. The efficacy of chemical sensors and their potential usefulness for detecting buried unex-ploded ordnance (UXO) is difficult to determine without understanding how its chemical signatures are transported through soil. The objectives of this study were to quantify chemical signature transport through soils under various environmental conditions in unsaturated soils and to develop a model for the same. Flux chambers, large soil containers, and batch tests were used to determine explosives signature movement and process descriptors for model development. Low signatures were observed for explosives (2,4-dinitrotoluene, 2,6-dinitrotoluene, and 1,3-dinitrobenzene) under all environmental conditions. A diffusion model was used to describe the chemical transport mechanism in the soil pore air. The soil-air partition constant was treated as a fit parameter in the model owing to the uncertainty in its a priori estimation. The model predictions of the trends in experimental fluxes and the soil concentration were only marginal at best. It was concluded that better estimates of the partition constant are required for more accurate estimation of the chemical concentration at the soil-air interface. Chemical sensors will need to be very sensitive because of low signatures. However, this may result in many false alarms because of explosives residues not associated with UXO on firing ranges. Low explosives signatures also should result in insignificant air environmental exposures.

Seasonal variation of the dominant allergenic fungal aerosols – One year study from southern Indian region

Quantitative estimations of fungal aerosols are important to understand their role in causing respiratory diseases to humans especially in the developing and highly populated countries. In this study we sampled and quantified the three most dominantly found allergenic airborne fungi, Aspergillus fumigatus, Cladosporium cladosporioides, and Alternaria alternata from ambient PM10 samples using the quantitative PCR (qPCR) technique in a southern tropical Indian region, for one full year. Highest concentrations of A. fumigatus and C. cladosporioides were observed during monsoon whereas A. alternata displayed an elevated concentration in winter. The meteorological parameters such as temperature, relative humidity, wind speed, and precipitation exhibited a substantial influence on the atmospheric concentrations of allergenic fungal aerosols. The morphological features of various allergenic fungal spores present in the PM10 were investigated and the spores were found to possess distinct structural features. In a maiden attempt over this region we correlate the ambient fungal concentrations with the epidemiological allergy occurrence to obtain firsthand and preliminary information about the causative fungal allergen to the inhabitants exposed to bioaerosols. Our findings may serve as an important reference to atmospheric scientists, aero-biologists, doctors, and general public.

Effects of Oil and Grease on the Vaporization of Organic Compounds from Contaminated Sediments

Contaminated sediments, which contain hazardous compounds such as polynuclear aromatic hydrocarbons (PAHs), are dredged and stored in confined disposal facilities (CDFs). Exposure of the sediment to air results in volatilization of contaminants. Many of the field sediments also contain substantial amounts of oil and grease. An uncontaminated sediment from a local lake (University Lake, Baton Rouge) was spiked with motor oil and PAHs. The air emission flux of three compounds (dibenzofuran, phenanthrene, and pyrene) from the oily sediment was compared to that from the same sediment without oil. The oil content of the sediment was 2.3%, and it had a moisture content of 6.5% to provide 100% pore air relative humidity. Experiments were also conducted with another moisture content of 55% in the sediment. Experiments were performed in dynamic flux chambers in the laboratory. The experimental flux measurements for all three compounds were lowered substantially in the presence of the oil in the sediment. At the en...