Journal of Environmental Engineering

The relationships among adsorption-desorption kinetics, equilibrium partitioning, and fixed-column breakthrough curves are elucidated for airborne benzene and vinyl chloride on activated carbon grains and fibers. An electrobalance is used to measure adsorption/desorption kinetics and to obtain equilibrium partitioning data; column experiments are conducted to determine additional equilibrium partitioning data and to measure breakthrough curves. A porous sphere/cylinder intragrain diffusion model, coupled with a Freundlich isotherm to describe equilibrium partitioning, conforms closely to the experimental kinetic data for both adsorption and desorption. In addition, it is shown that the adsorption isotherm may be accurately predicted based on the asymmetry between adsorption and desorption rates measured in a single kinetic experiment. The parameters extracted from the kinetic experiment, when combined with the appropriate transport equations, can be used to accurately forecast column breakthrough curves.

Control of organic vapors by adsorption on activated carbon can be impacted by the presence of water vapor in the gas stream. As a foundation to better understand this issue, the transport and sorption of water vapor within activated carbon grains was studied. Adsorption/desorption kinetics and equilibrium partitioning of water between gas and sorbed phases were determined at relative humidities (RH) in the range of 0–86% and at 20°C using an electrobalance. A model that accounts for transport within grains by pore and surface diffusion was used to interpret the sorption kinetic data. The model assumes instantaneously attained local equilibrium between sorbed and gas phases within the pores, based on a piecewise-linear isotherm measured for a small ensemble of activated carbon grains. Despite the complicated observed shape of the isotherms, including hysteresis, the model conforms well to all of the experimental data, and the asymmetry between adsorption and desorption is well resolved. The model results indicate that gas-phase diffusion dominates transport through the pores at RH ≤ 60%. Surface diffusion is found to be important at higher RH values.

A novel receptor-oriented methodology has been developed to apportion source contributions of the nitrogen species measured in the south coast air quality basin (SoCAB) in the 1987 southern California air quality study (SCAQS). This method begins by calculating a conditional probability field [potential source contribution function (PSCF)] relating the probability of a 5 km by 5 km area to observed high concentrations at a receptor site. Comparison of the locations of known sources with areas of high PSCF values indicates the power of the PSCF results. The source contribution of a grid cell (i.e., a source area) was then computed by multiplying the available emissions inventory emissions rate by the PSCF value and including the contributions from the species into which the emitted compounds could be transformed. The probability weighted emission rate can then be interpreted in terms of source contribution “as observed” at the receptor site. The estimated source contribution includes the atmospheric transport, removal, and transformation processes. The PSCF-constructed source apportionment map could be effective in the design of emission control strategies than emission inventory values, because the PSCF results indicate the actual impact of each grid source on the total amount of material received at the receptor site.

The three basic types of biological treatment systems for the control of volatile organic compounds in air streams are the following: biofilters, in which microorganisms grow on a medium, such as soil, compost, peat, or mixtures of these materials with wood chips or polystyrene particles; suspended-growth bioscrubbers, in which microorganisms are suspended in a liquid; and fixed-film bioscrubbers, in which microorganisms are attached to a packing material. Design and application of biological treatment methods for air pollution control are difficult because only limited experimental data and few theoretical models are available. This paper utilizes an engineering simulation model of a fixed-film bioscrubber to investigate the applicability, removal efficiency, operational parameters, and design requirements for gaseous waste streams. Model results indicate that the removal efficiencies can be increased by increasing the column height, decreasing the superficial gas velocity or the superficial liquid velocity, or by treating the liquid prior to recirculation to the absorber. High removal efficiencies can be obtained for compounds with relatively low values of the Henry's Law coefficient with either cocurrent or countercurrent operation. However, as the Henry's Law coefficient increases, the removal efficiency decreases and high removal efficiencies can be obtained only with cocurrent flow. Cocurrent operation is usually more efficient because stripping does not occur at the top of the column.

An experimental anaerobic biofilm fluidized bed reactor (ABFBR) unit was run with artificial substrate during 314 days. The experimental data were classified according to the value of the influent flow rate, and a set of data corresponding to flow rates between 35.44 and 41.83 mL/min was selected for model testing. This test resulted in a reasonable agreement between the zero-order kinetic model (with complete substrate penetration) and the experimental data. The regression equation had a value of R²= 0.88. The zero-order kinetic constant was calculated to be ρk₀= 4.7 × 10 ⁻³ mg COD/(s)⋅(cm ³ biofilm).

Traditional set point control and operation of a pumping station using fixed speed pumps usually amplify both the frequency and magnitude of variations in the influent flow rate. The purpose of the present study is to develop a control strategy to minimize these unwanted hydraulic surges. To realize this, an optimum control model was developed using computer simulation. The model is suitable for both separate and combined pumping installations. It is superior to conventional set point control techniques and reduces the frequency of starting and stopping pumps as well as energy consumption. The model uses energy saving and outflow smoothing factors to provide the improved control. Appropriate values of the two factors will depend on specific site conditions, such as pump lift height, wet-well depth, number of pumps and their sizes.

Frozen soil barriers are used for the subsurface containment of liquid contaminants so as to prevent their migration before and during soil remediation. Questions concerning the imperviousness of a frozen soil barrier to liquid contaminants provided the impetus for this study. Hydraulic-conductivity measurements, using a conventional falling-head permeameter with close control on temperature, have been performed on a frozen gravelly sand for ice-saturation levels of 0–100%. The dry frozen soil (−10°C), with decane (a nonaqueous liquid) as the permeant, has a hydraulic conductivity ( K ) about the same as the unfrozen soil would have for water. An increase in ice saturation with a decrease in the open pore space reduced the frozen soil conductivity. At full ice saturation, measured K -values were less than 10 ⁻⁴ mm/s (10 ⁻⁵ cm/s). Data show that a clay additive (bentonite) will help retain water so as to give a high degree of ice saturation in a granular soil. The effects of ice erosion in the frozen soil by water-soluble liquid contaminants and brines are introduced.

TiO ₂ catalysts supported on stainless-steel plates were tested for the photocatalytic degradation of formic acid in an aqueous solution. The metal-supported TiO ₂ catalysts showed reaction activities comparable to the commonly used glass-supported catalysts. Preirradiation was needed to activate fully both of the supported catalysts and to obtain reproducible activity data. During the photodegradation reaction, the oxidized surface of the metallic support was reduced and bleached. The activity of the catalyst decreased with an increase in firing temperature, which implies a positive correlation of the activity with the decrease in BET surface area of the TiO ₂ catalyst. The apparent reaction rate, R _a, increased as the thickness of the TiO ₂ film on the support increased. However, the specific reaction rate, R _s, calculated per unit of catalyst weight, decreased with an increase in the film thickness for the catalysts fired at temperatures of 300°C or less, and it was nearly constant irrespective of the film thickness for the catalysts fired at temperatures of 400°C or more. The X-ray diffraction patterns of the supported TiO ₂ catalysts that were fired at temperatures up to 600°C showed that all of the TiO ₂ films had only an anatase structure, and the particle size increased as the firing temperature increased.

The liability provisions of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) have added a new twist to the concept of “buyer beware” in commercial real estate transactions. The Phase I Environmental Assessment was developed partly to provide a defense against that liability. Recent attempts to improve that defense by standardizing the approach to Phase I assessments may, in some cases, be counter-productive. This standardization has occurred at a time when the assessment market has created a surfeit of assessors, often with little practical training or experience. Some of these assessors have used the standards to develop a formulaic approach to assessments, despite the fact that many sites warrant different approaches due to differences in site characteristics and data quality. Every research step of the Phase I process—environmental and historical records review, site reconnaissance, and interviews—has potential problems that defy standardization. These problems must be properly understood to ensure the adequacy of a site assessment.

Electrophoretic mobilities were measured and zeta potentials calculated for oocysts of Cryptosporidium and for cysts of both Giardia lamblia and G. muris . Measurements were made in both distilled water and in an unfiltered low-turbidity river water, and included measurements for both fresh and preserved organisms. Electrophoretic mobilities of oocysts and cysts were between −2.72 and −3.12 μm/s/V/cm corresponding to zeta potentials of −35 and −40 mV at neutral pH and decreased to less than −0.78 μm/s/V/cm (−10 mV) as pH was decreased to about 3.5. The electrophoretic mobilities and corresponding zeta potentials of oocysts and cysts were substantially modified in the presence of fulvic acid and of natural organics in unfiltered water. Common methods of oocyst and cyst preservation also altered electrophoretic mobilities and corresponding zeta potentials indicating that caution should be taken when conducting laboratory and pilot studies using preserved organisms.

Field venting tests were conducted in alluvial sands residing between the water table and a clay layer. Flow rate, barometric pressure, and well-pressure data were recorded using pressure transmitters and a personal computer. Data was logged as frequently as every second during periods of rapid change in pressure. Tests were conducted at various extraction rates. The data from several tests were analyzed concurrently by normalizing the well pressures with respect to extraction rate. The normalized pressures vary logarithmically with time and fall on one line allowing a single match of the Jacob approximation to all tests. Though the Jacob approximation was originally developed for hydraulic pump test analysis, it is now commonly used for venting test analysis. Only recently, however, has it been used to analyze several transient tests simultaneously. For the field venting tests conducted in the alluvial sands, the air permeability and effective porosity determined from the concurrent analysis are 8.2 × 10 ⁻⁷ cm ² and 20%, respectively.

This note investigates using the waste soot generated in fullerene manufacture as an adsorbent. Both oven-dried and air-activated samples of waste soot are compared with three commercially available powdered activated carbons (PACs): Nuchar-SA, HDH, and Calgon-RC. Three model compounds were chosen for adsorbtion tests—TCE, Benzene, and Phenol—representing a small branched molecule, a small nonpolar ring molecule, and relatively polar ring molecule. Additionally, the effectiveness of total organic carbon (TOC) removal from wastewater was evaluated. Oven-dried soot performed poorly as compared to the commercial carbons, but activation of the waste soot for 60 min at 450°C in air resulted in an activated carbon (aFWS) with properties similar to those of commercially available PACs. The aFWS performed better than one would predict from the typical characterization measures of iodine number, molasses number, and methylene blue number. The data for phenol suggests some functional groups are created during the activation of the waste soot. These results show that large-scale fullerene manufacturing can be a zero-waste industry, because its primary waste product can be converted into a useful material.