Journal of Environmental Engineering

In recent years the advent of the anaerobic expanded bed reactor (AEBR) has made possible the treatment of wastewaters of comparatively lower strength than have been treated traditionally by anaerobic means. However, regardless of any benefits presented by its use, the process must be shown to be cost effective relative to other options before it will gain acceptance. This paper reports on the results of a series of optimization exercises in which the costs of the AEBR as an expansion alternative for organically overloaded treatment plants are compared with costs for more conventional remedies. The optimization model developed includes the unit processes of primary clarification, AEBR, trickling filtration, secondary clarification, activated sludge, gravity thickening, anaerobic digestion, and vacuum filtration. Several constraint parameters were varied to determine the cases for which the AEBR would be the cost-effective option. These parameters were primary effluent chemical oxygen demand (COD), hydraulic loading, temperature, cost of labor, cost of power, cost of sludge disposal, and amortization interest rate. The results suggest that the AEBR may be a competitive solution for organically overloaded facilities under selected conditions.

This study demonstrates the feasibility of treating storm water contaminated with airport deicing fluid (ethylene glycol) in a batch-loaded aerobic fluidized bed reactor. In addition, the removal rates were measured for batch-loaded and continuously loaded fluidized bed reactors. These values were compared with each other and with more conventional wastewater treatment processes. Treating the contaminated storm water in batches eliminated the operational problems common to a continuously loaded aerobic fluidized bed reactor. Most significantly, excess biofilm growth and the accompanying maintenance and operational problems were controlled through endogenous respiration. Ethylene glycol and chemical oxygen demand removal rates of 710 and 2,200 g/m³/day, respectively, were achieved in the batch-loaded reactor. The resulting batch-loaded full-scale installation is expected to be two to three times larger than a continuously operated fluidized bed reactor; however, it is expected to be equal to or much smaller than more conventional activated sludge and fixed film process installations. An additional benefit of the batch-loaded process is the low quantity of sloughed biofilm, which results in a low level of effluent solids (16 mg/L total suspended solids). As a result, secondary clarification and associated sludge treatment might not be required.

Much effort has been expended in attempting to develop mathematical models for chlorine demand in water and wastewater. Most of these efforts have centered around the use of first-order functions or modifications of first-order functions. Recently there has also been interest in characterizing the formation of total trihalomethanes. These efforts have taken on new meaning because of the importance of maintaining chlorine residuals for microbial protection and concerns over the formation of trihalomethanes in drinking water distribution systems. This paper applies second-order kinetics to describe both of these relationships, using data collected from a recent collaborative study between the EPA and the American Water Works Association Research Foundation. It demonstrates that TTHM formation can be characterized as a function of chlorine demand.

Uranium $\left({\mathrm{UO}}_2^{2+}\right)$ and chlorinated aliphatics [tetrachloroethane (PCE) and trichloroethane (TCE)] can be reduced and thus immobilized or degraded (i.e., dehalogenated), respectively, by the same abiotic mechanism. In this mechanism the reduction reaction is coupled to the oxidation of Fe(II) sorbed on iron corrosion products such as hematite. This is indicated by the equilibrium E_h values measured during uranium immobilization and PCE degradation reactions of zerovalent iron. These values fit closely with those measured in the Fe(II)-αFe₂O₃-H₂O system (in the absence of U or PCE), not those of the Fe(o)/Fe(II) or H₂(g)/H₂O couples. Because iron (II) is very unstable in environments that are not strictly anaerobic, Fe(o) serves as a source of Fe(II). The reduction kinetic rate, analyzed in detail for the reduction of U(VI), is found to be a function of the concentration of OH⁻, Fe²⁺ and reactive surface sites, and is given in terms of sorbed species concentrations by {d[U(VI)]_ads}/dt={−k′[≡FeOFeOH⁰][U(VI)]_ads}. This rate law applies to organic pollutants as well, as long as they can be reduced by surface Fe(II): {d[Pollutant]}/dt={−k′[≡FeOFeOH⁰][Pollutant]}. This mechanism suggests new possibilities for the improvement of low-cost decontamination techniques for U- and chlorinated aliphatic-rich waters.

The objective of this research was to examine and compare the surface catalyzed loss of quinoline, a model pollutant, in the presence of three iron oxides: ferrihydrite, goethite, and a semicrystalline iron oxide. These are ubiquitous in the subsurface environment and have been implicated in the possible abiotic loss of contaminants when hydrogen peroxide is injected for augmenting bioremediation. This suggests the possible use of hydrogen peroxide specifically as an oxidant of some compounds in the subsurface. A comparison also reveals the best candidate for use in a supported oxide fixed bed treatment system utilizing hydrogen peroxide as an oxidant. The catalytic activity toward quinoline oxidation was highest for goethite, much less for the semicrystalline material, and negligible in the presence of ferrihydrite. Several water constituents affected reaction rates and stoichiometry by adsorption or through effects on solution chemistry. The stoichiometric efficiency relating quinoline loss to hydrogen peroxide decomposition was not a function of oxide concentration, nor was it affected by the presence of carbonate or phosphate that reduced the rate of hydrogen peroxide decomposition. The effect of humic acid on quinoline loss and hydrogen peroxide decomposition rate depended on its concentration, suggesting that it may act as a radical scavenger, radical chain promoter, and catalytic site inhibitor.

A theoretical relationship is established between the initial settling rate and the concentration of a suspension in a sedimentation process. It is obtained by an analogy between the sedimentation and the filtration processes. The calculated results satisfactorily coincide with those reported in the literature. Consequently, analytical expressions are proposed to calculate the minimum flux and the corresponding critical concentration of a suspension. Dick's method and the proposed expressions give almost the same results for the mentioned parameters. The proposed method provides an opportunity to apply Dick's basic idea for determining the design parameter of a thickener based on two experiments.

This paper presents a study of the integrated management of solid wastes generated in a high-capacity power plant, i.e., coal combustion fly and bottom ash (BA) and flue gas desulfurization (FGD) sludges. Solidification/Stabilization (S/S) processes were tested by analyzing the influence of the variables: binder type, water needs, and land disposal scenario that affect the final solid leaching characteristics. A factorial design of experiments was used to study the influence of these variables in the final S/S solid. After characterization of the leachates according to European regulations, the chemical stability of the S/S solids was analyzed using a standard dynamic leaching test (DLT). A dynamic leaching model of the contaminants (sulfates) contained in the S/S matrix was formulated from the research on the long-term behavior of the solid matrix, establishing the parameters that have an effect on the mobility of the sulfate. One parameter, the effective diffusion coefficient [D_e (cm²/s)] and its logarithmic expression, the leaching index (LX), were evaluated for each S/S process. Values of 1.51 × 10⁻¹¹ (cm²/s) ≤D_e≤ 2.14 × 10⁻⁹ (cm²/s) for 100 humidity-cured S/S wastes and 1.98 × 10⁻¹¹ (cm²/s) ≤D_e≤ 4.36 × 10⁻¹¹ (cm²/s) for water bath–cured S/S wastes were obtained for D_e, leading to LX values of 8.67 ≤ LX ≤ 10.82 and 10.36 ≤ LX ≤ 10.80, respectively. These values suggest that a high immobility was reached in some of the developed S/S processes. The validity of the leaching parameters obtained after a short-term landfill period (56 days) was confirmed after 1 year.

This paper presents the results of a laboratory study on the mixing of circular nonbuoyant multiple jets discharged into relatively deep river-like crossflows. Experiments were performed for the velocity ratio α varying from 3.5 to 10 where α is the ratio of the velocity of the jet to that of the crossflow. Three and five ports were used and the spacing S between the ports was varied from 8d to 16d where d is the diameter of the nozzle. The concentration measurements were carried out for a maximum relative distance of x/d= 160 where x is the distance downstream of the diffuser. The concentration profiles in the vertical as well as the lateral directions in the planes of maximum concentration were found to be similar. The minimum dilution at any section, defined as the inverse ratio of the maximum concentration at that section to that at the ports, reached a value of 80 in the mixing region. The minimum dilution decreased as α increased. Equations have been developed to describe the growth of the width and thickness of these jets. These results are believed to be useful in the design of outfalls in rivers.

A two-dimensional (2D) numerical model for a convection-diffusion flow of a mixture of gases through a multilayered porous medium has been developed with the aim to obtain criteria for the optimal design of venting trenches for gas collection from a landfill. The proposed numerical scheme is based on the boundary element formulation of the governing equations, in which the dual reciprocity method (DRM) is used to transform the resulting domain integrals to the boundary. The scheme is improved by the use of a domain decomposition algorithm, which allows a better representation of the physical problem. From present numerical analysis it can be concluded that it is sufficient to construct venting trenches that only cross the top covering layer of the landfill, as long as there are provided enough pathways to guarantee a gentle gas flow across the separation layers between waste layers inside the landfill. Venting structures that cross the entire depth of the repository, as it is usually done in landfill design, are not necessary.

A spreadsheet model MSWFLOW was developed as an accounting procedure for determining impacts of management decisions on the physical scale and productive outputs of a municipal solid-waste system. The model tracks the disposition of 50 different waste products and includes source reduction, recovery (recycling and composting), waste-to-energy (WTE) combustion, and landfilling. Outputs from the calculations include mass and volume of waste generated, collected, and diverted by source reduction or recovery; physical scale (daily mass and/or volume) of the recovery and combustion facilities; landfilled mass and associated volume requirement; potential (maximum) annual landfill gas production; and net electrical power production from the combustion facility. The spreadsheet was demonstrated by evaluations of several alternative management strategies for municipal solid waste from a typical U.S. city with a population of 100,000.