Journal of Environmental Engineering

Combined plasma photolysis (CPP) has been developed and experimentally demonstrated as a new method to simultaneously remove ${\mathrm{SO}}_2$ and $\mathrm{NO}$ from gas streams. This laboratory‐scale device integrates the use of a dielectric barrier discharge (DBD) plasma and ultraviolet radiation. The composition, temperature, and pressure of the treated gas streams simulate gases typically generated by the combustion of fossil fuels. Simultaneous removal efficiencies for ${\mathrm{SO}}_2$ and $\mathrm{NO}$ are as high as 29% and 79%, respectively. CPP enhances ${\mathrm{SO}}_2$ removal efficiencies by 25% when compared to using DBDs only. $\mathrm{NO}$ removal efficiency achieved by CPP is 9% less than $\mathrm{NO}$ removal efficiency achieved by DBDs only. ${\mathrm{SO}}_2$ and $\mathrm{NO}$ removal efficiencies are limited by the power deposited into the gas stream that could be achieved with the existing power supply. This new device shows promise as a new technique to simultaneously remove ${\mathrm{SO}}_2$ and $\mathrm{NO}$ from gas streams generated by the combustion of fossil fuels.

A model of cadmium fate in the Foundry Cove Superfund site is calibrated to the postloading period from 1972 to 1989. Bioturbation (i.e. benthic mixing) of sediment cadmium is calculated to be primarily responsible for the slow decline in surface cadmium over this period. Such mixing increases the flux of cadmium from the cove by about an order of magnitude over the case of no mixing. Hindcasting previous cadmium exposure from consumption of contaminated blue crabs indicates an increased exposure of about 25 times acceptable levels during the peak loading period of 1965–70. Simulation of remedial controls indicates that if no action is taken, cadmium concentrations will continue to be at elevated levels at least to the year 2012. Capping of the inner cove with clean sand over an impermeable barrier (equivalent to “removal” of sediment cadmium), however, results in an immediate and constant decrease in cadmium to background levels.

A model to account for the distribution of particulate matter in a lake is presented. This model represents the coupling of a stratified lake mixing model with a particle settling, coagulation, and diffusion model. Using parameterizations of the fundamental mixing processes, the lake model simulates the response of the stratified water column to external forcing. At the same time, the particle model simulates the settling, aggregation, and diffusion of a given distribution of particles within this changing water column. Three different situations have been chosen in order to test the model. In the first, an input of mineral particles for different size classes has been attributed to an inflow. In the second, the evolution of a distribution of particles initially set up in the epilimnion of a strongly stratified lake has been described and in the third, the same initial distribution of particles has been set up for a weakly stratified lake. These cases show the importance of the different mechanisms (settling, aggregation and diffusion) affecting the dynamics of the particles in natural waters.

The applicability of univariate uncorrelated, univariate ARMA, and diagonalized vector autoregressive moving average (ARMA) processes was studied and compared to published procedures for reliability‐based design of wastewater‐treatment plants. Three applications are presented. In the first application, influent biological oxygen demand (BOD) mass loading was simulated using a univariate, weekly periodic autoregressive process to calculate sustained peak loading. In the second application, three water‐quality variables were simulated jointly using a diagonalized vector autoregressive process to calculate potential nutrient deficiencies in activated sludge processes. In the third application, effluent BOD concentrations were simulated using a univariate autoregressive process to calculate the reliability of meeting permit limits of various durations. It was found that by more completely modeling the statistical structure of available historical data, the ARMA modeling techniques were effective for reliability‐based design applications for which duration is important, as distinct from instantaneous peak loading.

The results of experiments treating high‐strength vegetable‐pickling waste in an experimental rotating biological contactor (RBC) are described. The relationships between TOC, BOD, and COD for the particular waste are presented. A high correlation was found between TOC and BOD. The use of TOC led to a mathematical model describing the effluent concentration in terms of the output TOC concentration and the hydraulic loading rate. It was found that a relationship involving these two independent variables alone explained more than 98% of the variation in the dependent variable. The model predicts that the effluent TOC concentration will be more sensitive to changes in influent TOC concentration than to changes in hydraulic loading rate and that it can be used to predict the effect of recirculation on the substrate effluent concentration. The substrate concentration and fractional substrate loading rate removal are compared with predictions from other models.

A study is conducted to evaluate the pathogen and indicator bacterial reductions in the sludges of two wastewater‐treatment plants. These plants are extended‐aeration and oxidation‐ditch‐type plants that have no aerobic or anaerobic digestion facilities following the secondary treatment except for sludge‐storage facilities. Sludge samples are taken from various locations throughout the plant. Sludge samples from these two plants are also collected to run laboratory investigations to determine the sludge pathogen and bacterial reductions in aerobic digestion and in storage. Fecal coliform, fecal streptococcus, and Salmonella are measured on all sludge samples. Total suspended solids, volatile suspended solids, pH, and temperature are also measured. These plants are meeting the proposed EPA's class B pathogen reduction criteria, a two‐order reduction. The improved pathogen reduction is related to the design conditions of the plant, large sludge age, and long detention times. Laboratory aeration and storage studies indicate further pathogen‐indicator organisms reduction of at least one order.

The City of Indianapolis' Belmont Advanced Wastewater Treatment Facility produces 32 dry metric tonnes per day of ash from incineration of municipal sewage sludge. Available capacity at the existing ash disposal site is limited. To determine the feasibility of an alternate disposal method, a bench‐scale study was conducted to determine the physical characteristics of bricks produced at four ratios of clay content to ash content and fired to temperatures above and below the vitrification temperature of the ash. The bricks were assessed for drying weight change and shrinkage, firing weight change and shrinkage, total weight change and shrinkage, density before and after firing, compressive strength, water absorption, freeze‐thaw resistance, and tendency to leach metals during acid extraction (“EP‐Tox”). The use of sewage sludge ash as an admixture in brick appeared to be promising, especially when the ash amended bricks were fired to above ash vitrification temperature. The City of Indianapolis and an Indianapolis‐area brickmaker are preparing for a full‐scale demonstration run; the parent company of the brick maker advanced to full‐scale ash brick production, using ash from another major city.

This work involves a laboratory‐scale investigation of the effects of suspended particle size and coagulant type on the performance of contact or inline direct filtration (no flocculation). Dilute monodisperse and polydisperse suspensions of polystyrene particles (0.27‐, 1.24‐, 1.32‐, and 10‐μm diameters) were applied to shallow beds of 0.4‐mm glass‐bead filter media after destabilization with either cationic polymer or calcium chloride. The particle removal and head‐loss results show dramatic effects of particle size on filtration performance. Submicron particles significantly improve the removal of larger particles in mixed size suspensions and also dominate head‐loss development. Head‐loss development is typically linear with time and for mixed suspensions is the same as, or somewhat lower than, head loss for monodisperse suspensions of the smaller‐sized particle. Polymer destabilization generally causes more head loss than calcium chloride destabilization for a similar extent of particle deposition.

When liquid hydrocarbons or nonaqueous phase liquids (NAPLs) become entrapped below the water table, flowing ground waters carry soluble NAPL components away from the spill zone. Transport of dissolved NAPL components is controlled by several processes including advection, dispersion, sorption onto aquifer materials, and liquid‐liquid partitioning. A model is developed to predict solute movement through heterogeneous porous media containing residual NAPL. Governing equations describe both instantaneous and time‐dependent processes including: (1) Exchange between mobile and immobile waters; (2) exchange between residual NAPL and water; and (3) exchange between aquifer solids and water. A one‐dimensional analytical Laplace‐space solution to governing equations is presented. The resulting transport model handles combinations of solute exchange activities that cannot be investigated with other analytical or numerical formulations. The model is tested during an investigation of several hypothetical systems. The investigation shows rate‐limited processes causing early solute arrival, a delay in total breakthrough, and asymmetric breakthrough curves.

When liquid hydrocarbons or nonaqueous‐phase liquids (NAPLs) become entrapped below the water table, flowing ground waters carry soluble NAPL components away from the spill zone. Transport of these dissolved NAPL components is controlled by several processes including advection, dispersion, sorption to aquifer materials, and liquid‐liquid partitioning. To better understand these processes, miscible displacement experiments were conducted to generate breakthrough curves (BTCs) of pentafluorobenzoic acid (PFBA), benzene, and toluene on sand columns with and without a fixed decane residual. A departure from equilibrium transport is observed in BTCs from the sand‐decane system. These BTCs show characteristics of early breakthrough, asymmetry, and tailing. The cause of nonequilibrium is hypothesized to be rate‐limited solute exchange between decane and water. A new transport model, capable of handling time‐dependent exchange processes, is successfully applied to reproduce experimental BTCs. Results indicate that time‐dependent partitioning becomes increasingly important as the solute decane‐water partition coefficient and the aqueous‐phase fluid velocity increase.

The application of correction factors to measured ground‐water elevations is an important step in the process of characterizing sites contaminated by petroleum products such as gasoline. The water‐table configuration exerts a significant control on the migration of free product (e.g., gasoline) and dissolved hydrocarbon constituents. An accurate representation of this configuration cannot be made on the basis of measurements obtained from monitoring wells containing free product, unless correction factors are applied. By applying correction factors, the effect of the overlying product on the apparent water‐table configuration is removed, and the water table can be analyzed at its ambient (undisturbed) level. A case history is presented where corrected water‐table elevations and elevations measured at wells unaffected by free product are combined as control points. The use of the combined data facilitates a more accurate assessment of the shape of the water table, which leads to better conclusions regarding the source(s) of contamination, the extent of free‐product accumulation, and optimal areas for focusing remediation efforts.

Adsorption of heavy metals onto activated carbon has been described using the surface‐complex‐formation (SCF) model, a chemical equilibrium model. The SCF model requires a knowledge of the amphoteric nature of activated carbon prior to metal adsorption modeling. In the past, a single‐diprotic‐acid‐site model had been employed to describe the amphoteric nature of activated‐carbon surfaces. During this study, the amphoteric nature of two powdered activated carbons were investigated, and a three‐monoprotic site surface model was found to be a plausible alternative. The single‐diprotic‐acid‐site and two‐monoprotic‐site models did not describe the acid‐base behavior of the two carbons studied adequately. The two‐diprotic site was acceptable for only one of the study carbons. The acid‐base behavior of activated carbon surfaces seem to be best modeled as a series of weak monoprotic acids.

For the computation of uniform flow velocity and discharge in partially filled circular sewers Manning's equation is used. Determination of the hydraulic and geometric elements of flow requires either iterative solutions of the Manning's equation or use of nomographs prepared for this purpose. Both methods are time consuming. A procedure is described for the direct determination of the slope of a partially filled sewer when the minimum velocity of flow is specified. Alternately, the depth of flow can be calculated when the slope is given. The diameter of the sewer and the minimum flow rate expected must be known. The equations developed are valid for circular sewers for which the depth of flow is less than 40% of the sewer diameter representing a reasonable range of initial design conditions. The maximum error between the actual water depths and those computed by the approximate equations is ±2.4%. This is much less than the probable error in selecting an appropriate value for the roughness coefficient.