Journal of Environmental Engineering

A catalytic reactor model (CatReac) that describes the transport and series reactions of compounds in a three-phase fixed-bed catalytic reactor is developed for the purpose of describing the volatile assembly reactor system within the potable water processor on-board the International Space Station. CatReac includes these mechanisms: advective flow, axial dispersion, gas-to-liquid and liquid-to-solid mass transport, intraparticle mass transport with pore and surface diffusion, and series reactions of multiple compounds. A dimensional analysis of CatReac revealed the following seven dimensionless groups may be used to determine the controlling transport and/or reaction mechanisms: (1) the Peclet number is the ratio of the advective to the dispersive transport; (2) the Stanton number is the ratio of the external mass transfer rate to the advective rate; (3) the Damköhler number compares the reaction rate to the advective transport rate; (4) the surface diffusion ratio equals the rate of transport by surface diffusion divided by the rate of transport by advection; (5) the pore diffusion modulus is the ratio of the rate of transport by pore diffusion to the rate of transport by advection; (6) the ratio of the gas to liquid advective rates; and, (7) the Biot numbers for surface and pore diffusion compare the external mass transfer rate to the intraparticle mass transfer rate. These dimensionless numbers are used to evaluate the impacts of the different mechanisms on the overall performance of the reactor. The numerical solution using orthogonal collocation was validated for a wide range of controlling mechanisms by comparing model simulations with several analytical solutions: (1) Gas-to-Liquid mass transfer controlling the overall mass transfer-reaction mechanisms, for a wide range of Pe number values; (2) Liquid-phase dispersion controlling the overall process; (3) Liquid-to-solid mass transfer resistance controlling the overall mass transfer-reaction process; (4) Reactions in series with two possibilities (4a): No intraparticle mass transfer resistance, and (4b): Significant intraparticle mass transfer resistance; (5) Langmuir isotherm (5a): single compound, no mass transfer resistance, and (5b): multicomponent competitive adsorption without mass transfer resistance; (6) Unsteady state operation: Plug flow with mass transfer and no reaction. These validations systematically examine all the mechanisms that are included in the general model and examine the model limitations based on the controlling mechanisms.

In this study, anaerobic treatment of synthetic textile wastewater containing a reactive azo dye, namely, Remazol Brilliant Violet 5R, was investigated. A fluidized bed reactor (FBR) was used in the study. Before the operation period, start-up of the FBR was completed in 128 days with an immobilized microorganism level of 0.069 g volatile suspended solids per g support material (pumice). Anaerobic treatment of synthetic textile wastewater revealed that 300 mg/L dye was removed in the FBR system. Chemical oxygen demand (COD) and color reduction in the system were approximately 60 and 94%, respectively. Under anaerobic conditions, formation of two sulfonated aromatic amines (SAAs) was detected due to anaerobic reduction of the dye. The SAAs were not degraded under anaerobic conditions. In addition to the anaerobic treatment, the effectiveness of aerobic treatment was investigated in order to further reduce the COD after the anaerobic treatment.

A method is presented to assess oxygen uptake rates which operates at constant dissolved oxygen concentration (DO). This method involves DO-stat titrations by controlled addition of a diluted $H_2{O}_2$ solution to a batch volume of activated sludge. The titrant flow rate is proportional to the biomass respiration rate, while the mass of $H_2{O}_2$ added is proportional to the oxidized organics. Classical batch respirometries (with and without gas flow, i.e., “open” and “closed”) were compared to the DO-stat technique using first ${\mathrm{NaSO}}_2$ as reducing chemical and then respiring aerobic biomass. An excellent correlation was found among estimates of oxygen consumption rate and short term yield coefficient by the three techniques. Inhibition by $H_2{O}_2$ was found to be negligible for biomass concentration as volatile suspended solids of $⩾1.5-2$ g /L.

This study investigated the transient and steady-state performance of a bench-scale biotrickling filter for the removal of an organic mixture (acetone, toluene, and trichloroethylene) typically emitted by the microelectronics industry. The microbial consortium consisting of seven bacterial strains that were fully acclimated prior to inoculation onto activated carbon media. Among the seven strains, the Pseudomonas and Sphingomonas strains appeared to be the major groups degrading toluene $(>25 \mathrm{ppmv}/h\cdot {10}^8$ cell) and trichloroethylene $(>2.3 \mathrm{ppmv}/h\cdot {10}^8$ cell), while Mycobacteria and Acetobacteriaceae strains were the primary decomposers of acetone $(>90 \mathrm{ppmv}/h\cdot {10}^8$ cell). The column performance was evaluated by examining its responses to the fluctuating influent total hydrocarbon concentrations, which varied from 850 to 2,400 ppmv. Excellent steady-state removal efficiencies greater than 95% were consistently observed, and system recovery was typically within two days after a significant increase in the inlet loading was experienced. The overall mass-transfer rate and the biokinetic constants were determined for each organic component. Mathematical simulations based on these parameters demonstrated that the removal of acetone was kinetically limiting, whereas the removals of toluene and trichloroethylene were at least partially mass-transfer limiting.

Evolving environmental legislation has received increased attention worldwide in the last two decades, reported by Bradfield, Schultz, and Stone in 1996 in Environmental management in the Australian minerals and energy industries. The focus of concern by the industry, environmental regulatory agencies, and members of the public is the potential impacts associated with unstable landscapes which sometimes lead to slope failures, especially in hillside development. Engineered landscape profiles, though stable at the end of construction, may deteriorate over time due to erosion. There is thus a need to increase the base of knowledge on the existing practices of engineered profile design, hillside development, reshaping practices, and erosion control. With escalating production costs and the keen competitiveness in the industry world wide, the necessity to increase the efficiency of engineered profile development is further gaining prominence. This paper reviews the advancement of erosion management research in the industry, economics of landscape profiling, the practical application of the Point Estimate probabilistic technique, and the optimum design selection for the systematic planning and reshaping of engineered landscape profiles. The probabilistic engineering design erosion nomographs developed is useful in determining and illustrating quantitatively the reliability of final engineered landscape designs and the reshaping costs involved for different soil texture types. Landscape designs, which meet environmentally acceptable levels of reliability against erosion failure at optimum earthmoving reshaping costs, can be obtained using this probabilistic engineering design approach whilst satisfying environmental standards and community expectations for erosion minimisation.

Rainfall-runoff quantity and quality relationships are impacted by both the built environment in particular “impervious” paved surfaces and anthropogenic activities such as traffic. Through the capture, analysis, and modeling of eleven discrete rainfall-runoff events, the impacts of the paved urban surface and traffic were examined with respect to the temporal delivery of storm water runoff quantity. A kinematic wave model accurately captured the significant aspects of typical urban runoff events such as time to peak, total volume of flow and peak discharge from a 300-m² paved surface subject to traffic. Abstractions associated with traffic, represented as the volume-based runoff coefficient, were estimated based on the relationship between runoff and vehicular traffic. It was found that for high intensity storms, with less than 10 vehicles/L of runoff volume (VRV), the runoff coefficient asymptotically approached a maximum value between 0.6 and 0.9. For low intensity storms, with more than 10 vehicles/L (as VRV), the runoff coefficient asymptotically approached a lower maximum value between 0.2 and 0.4. The kinematic wave theory also gave predictions of the time of concentration that were more accurate than other, more common methods currently in use including those by the FAA and the Soil Conservation Service. Prediction of the rainfall-runoff process impacted by the built environment and traffic permits determination of urban pavement hydrographs to determine the unsteady loadings of in situ treatment strategies under a variety of storm conditions. Such unsteady loadings are necessary inputs for selection, design and analyses of in situ storm water unit operations and processes that are developing for the control of both urban runoff quantity and quality.

A range or arsenic containing compounds, including arsenic trioxide, pentoxide and a lead arsenate insecticide have been stabilized using formulations of cement alone, $\mathrm{cement}+\mathrm{lime}$ and $\mathrm{cement}+\mathrm{ferrous}$ sulfate and subsequently exposed to a range of leaching regimes in order to compare their effectiveness for metal stabilization. Leaching tests used were two regulatory tests, the Toxicity Characteristic Leaching Procedure (TCLP) and the Australian Bottle Leaching Procedure (ABLP), as well as column leaching. Arsenic leachate concentrations from cement-stabilized lead arsenate insecticide were similar when subjected to either the TCLP or ABLP using the same leachant. Lead, known to be immobilized by means different to that of arsenic, yielded varying leachate concentrations when using either of the regulatory tests, even though the leachant was of the same type. The leaching of calcium influences the filtered arsenic leachate, whereas the leaching of lead is greatly affected by leachate pH. As expected, both regulatory tests generally proved to be very severe in terms of the masses of the hazardous constituents leached when compared to conceptually more realistic column leaching scenarios. Sodium arsenate-containing formulations behaved anomalously, with column leaching tests resulting in larger arsenic masses being leached than the regulatory tests. Sodium arsenate, known to inhibit cementation reactions, serves as a reminder of the perils that can be faced when generalizing the results obtained from leaching tests.

Intrinsic biodegradation of methyl tert-butyl ether (MTBE) in aquifer sediments under oxic conditions was investigated using laboratory microcosms. Aquifer samples were collected from three different areas (source area, upgradient, and downgradient) of a shallow gasoline-contaminated aquifer within the Atlantic Coastal Plain Province located in Virginia. Biodegradation of MTBE was observed in the source-area microcosms in which MTBE declined from a starting concentration of 2.7 to 0.28 mg/L over a 58-day period, following an initial lag period of 20 days. The same set of microcosms was respiked with MTBE to an initial concentration of 4.8 mg/L and MTBE concentrations declined to 0.20 mg/L over a 52-day period with no lag in biodegradation. First-order MTBE biodegradation rates for the first and second periods were 0.037±0.003 and 0.063±0.003 day⁻¹, respectively. When another set of source-area microcosms was spiked with MTBE (5 mg/L), toluene and ethylbenzene (1 mg/L each), the initial lag period increased to 33 days but there was no significant change in the MTBE biodegradation rate (0.065±0.026 day⁻¹) and MTBE was not detected after 134 days. Biodegradation of MTBE was also observed in the microcosms constructed using aquifer sediment with only limited exposure to MTBE but the degradation rate was lower and statistically different (0.022±0.005 day⁻¹) than the source area microcosms. Biodegradation of MTBE ceased when oxygen was depleted. Methyl tert-butyl ether did not biodegrade in the uncontaminated, upgradient microcosms; however, rapid biodegradation of toluene was observed. Methyl tert-butyl ether biodegradation appears to be limited in the absence of dissolved oxygen and in aquifer sediments where petroleum hydrocarbons including MTBE were not previously observed.

Computational fluid dynamics-based (CFD) software tools enable engineers to simulate flow patterns and sediment transport in ancillary structures of sewer systems. Lagrangian particle tracking represents a computationally efficient technique for modeling sediment transport. In order to represent the process of sedimentation in storage tanks, careful consideration must be given to the boundary condition at the bottom of the tanks. None of the boundary conditions currently available in the FLUENT CFD software appears to represent the observed behavior of sediment particles, which may become resuspended after first contact with the bed if the local flow velocity is sufficiently high. In this study, a boundary condition based on bed shear stress has been implemented in FLUENT and evaluated against laboratory data. A particle is trapped if the local bed shear stress is below the critical bed shear stress; otherwise, the particle is resuspended. The approach gives satisfactory agreement with measured sedimentation efficiency data, and the simulated spatial distribution is very similar to the sediment distribution observed in a laboratory tank.

Two sediment cores were collected from a marina in the San Francisco Bay to characterize historical sediment contamination resulting from the direct discharge of industrial wastewater from Naval Air Station Alameda. Depth profiles of trace metals, petroleum hydrocarbons, and radionuclides were determined with a 12-cm spacing down to a depth of 120 cm. The chronology of sediment accumulation is established by depth profiles of sedimentary time markers in conjunction with information on site history. The traditional approach of determining sediment accumulation rates by measuring atmospheric ${}^{210}\mathrm{Pb}$ deposition was obscured by a larger source of ${}^{210}\mathrm{Pb}$ in the sediments from the decay of anthropogenic ${}^{226}\mathrm{Ra}\text{,}$ likely from luminescent paints used at this facility and released to the marina. The sedimentation rates inferred from the data indicate that the greatest amount of contamination by trace metals and petroleum hydrocarbons took place between 1940 and 1960. In addition, anthropogenic ${}^{226}\mathrm{Ra}$ activities are positively correlated with some of the contaminants in the sediments, allowing the wastewater discharged from the facility to be distinguished from baywide contamination. In locations such as this, where there is a complex history of contaminant deposition, a source-specific tracer may be the only feasible method of attributing historical contamination to a point source.

An empirical model is developed to predict daily maximum stream temperatures for the summer period. The model is created using a stepwise linear regression procedure to select significant predictors. The predictive model includes a prediction confidence interval to quantify the uncertainty. The methodology is applied to the Truckee River in California and Nevada. The stepwise procedure selects daily maximum air temperature and average daily flow as the variables to predict maximum daily stream temperature at Reno, Nev. The model is shown to work in a predictive mode by validation using three years of historical data. Using the uncertainty quantification, the amount of required additional flow to meet a target stream temperature with a desired level of confidence is determined.