Journal of Environmental Engineering

The present paper describes the result of a demonstration project in which optimization models were used to identify efficient and equitable ${\mathrm{SO}}_2$ control strategies that satisfy environmental quality standards at sensitive receptor locations in Maryland. Notable in the modeling is the use of location‐specific critical‐load estimates. These estimates—the critical loads—represent maximum allowable sulfur‐deposition rates, that is, rates below which continued acidification and its attendant possible ecological consequences are believed not to occur. The analyses include scenarios that involve 10,000,000 t/yr ${\mathrm{SO}}_2$ reductions in the United States, uniform percentage‐reduction scenarios, and state‐level sensitivity analyses.

The response of a northeastern U.S. hardwood forest to wet and dry deposition of hydrogen ion and sulfate deposition was performed using the hydrobiogeochemical, lumped‐parameter Terrestrial Aquatic Model for Ecosystems (TAME). Results of model calibration and output stream chemistry show that ion‐exchange and mineral dissolution processes in the B and C horizons buffer the acidic, ambient atmospheric deposition [$864‐\mathrm{eq}‐{\mathrm{SO}}_4^{-2}/(\mathrm{ha}/\mathrm{yr})$ and 718 eq‐H⁺/(ha/yr)] in this hydrologically tight and flashy watershed. Watershed response to a 50% decrease in total deposition of acidity over twenty years indicates that the watershed is linear with respect to sulfate (50% decrease in mass outflow) but less responsive with respect to acid neutralizing capacity, ANC (11% increase in stream volume‐weighted average ANC concentrations). Only moderate improvements in ANC can be expected from emission controls and decreased sulfate deposition.

Field tests using air extraction and injection in both horizontal and vertical wells are evaluated to estimate air conductivity and porosity in the vadose zone. Six extraction tests and four injection tests were conducted. Sixty data sets were developed by measuring gas pressures as a function of time at six gas probes during each of the tests. Two analytical procedures are used to evaluate each data set. The first procedure, which is a modified Theis analysis, neglects the effects of leakage through the top boundary of the flow field. The second procedure, which is a modified Hantush analysis, includes the effects of leakage by assuming that it is generated within the flow layer. Image‐well theory can be used to evaluate data from horizontal wells. Variations in parameter estimates are caused by spatial variability, measurement error, data analysis methodology, well configuration, and the direction of air flow. At this particular field site, variations due to measurement errors were of the same order as those due to spatial heterogeneity.

Soil vapor extraction (SVE) to remove volatile contaminants from contaminated soil in the unsaturated zone has been successful in sand and gravel formations. In less permeable glacial till, the usefulness of SVE is unclear. Field experiments in the loam till of central Iowa were performed to determine air permeabilities. A radial and vertical, anisotropic, heterogeneous compressible‐flow model coupled with an optimization routine solved the inverse problem by using vacuum pressure and flow‐rate data to estimate air permeabilities. Air‐permeability anisotropy was determined to be less important than depth variations. Using a four‐layer description of the deposit to account for varying moisture content with depth, the average predicted air permeability varied from $4\times {10}^{-8}{\mathrm{cm}}^2$ in the deepest layer to $1\times {10}^{-5}{\mathrm{cm}}^2$ in the layer nearest the ground surface.

Laboratory measurements were carried out to determine the vapor adsorption of the solvent trichloroethylene (TCE) on a dry quartz sand of two different mesh sizes. Using a static adsorption laboratory procedure and inverse gas chromatography (IGC), the sorption of TCE vapor in nitrogen was measured at concentration ranges of approximately 0.1 to 440,000 ppm by volume. Adsorption was measured on 30/40 and 100/200 mesh dry quartz sand, with the finer material created by mechanically crushing and sieving coarser material. The observed sorption isotherms fit a Freundlich isotherm and are also well represented by a simple linear sorption isotherm.

This paper provides those interested in hazardous‐waste‐site cleanups with both an assessment of robotic opportunities for cleaning up hazardous waste and strong arguments for pursuing the development of this technique. Currently available robotic technology appears to be underutilized in the cleanup of hazardous waste, although it is considered a viable alternative because it offers restoration solutions that are potentially safer and more cost effective than present‐day methods. Environmental‐cleanup contractors need to become familiar with these issues and strongly consider using robotic techniques for cleaning up hazardous waste that may help them maintain a competitive edge in the fast‐growing environmental‐cleanup market.

A biofilm model for the cometabolic degradation of trichloroethylene (TCE) by methane oxidizing (methanotrophic) bacteria is derived. Methane utilization and TCE transformation were modeled using diffusive mass transport, Monod kinetics, competitive inhibition, TCE transformation product toxicity, and growth, decay and inactivation of the methanotrophic bacteria. Reported low rates of TCE degradation by biofilms were found to be compatible with the high rates found in dispersed growth studies. The slower rates result from phenomena inherent in biofilms, and not necessarily from a difference in performance characteristics of the organisms. The possibility that biofilms may not be copper‐limited is also considered. Other model predictions include an optimum methane concentration that maximizes TCE flux. Also, survival of a biofilm should only occur when the methane concentration is above a certain minimum value $\left(S_{\min }\right)$, which is linearly related to TCE concentration. The model is general and can be applied to other primary substrates and chlorinated aliphatic hydrocarbons (CAHs).

Commercial coal ash makes up a large amount of the material in United States landfills. Studies to promote recycling of these materials are conducted on a case‐by‐case basis. The objective of the present work is to provide ash generators with a strategy for developing ash‐recycling options in order to reduce landfill usage and create profits from the sale of their by‐products. A protocol is used to identify beneficial use options for many types of nonhazardous, industrial‐process by‐products. In the present paper, the protocol is demonstrated with stoker‐boiler coal ash recycled in construction products, mainly concrete and concrete block. The protocol contains five steps: a preliminary characterization, a market survey, screening tests and pilot production, an environmental‐impact assessment, and a cost analysis. These steps are required before any potential use can be recommended to a generator.

The use of granular activated carbon (GAC) columns to treat lead wastewaters was investigated. Synthetic wastewaters containing Pb (10 or 50 mg/ L), acetic acid (0.001 N) or EDTA (1:0.1 or 1:1 Pb:EDTA molar ratios) were studied. For lead‐only and lead‐acetic acid experiments significant quantities [70 to 325 bed volumes (BV)] of wastewater were treated prior to breakthrough $(C_e=0.03C_0)$; $X/M‐\mathrm{values}$ were as high as about 30 mg Pb/g carbon. For EDTA experiments, $C_e$ was always $>0.03C_0$. The amount of lead not removed corresponded to the amount that was complexed by EDTA. Column pH is the critical parameter influencing column performance. The increase in effluent Pb concentration corresponded with the decrease in column pH. GAC columns were successfully regenerated using a $1L(\approx 8\mathrm{BV})0.1N{\mathrm{HNO}}_3$ rinse followed by a $1L0.1N\mathrm{NaOH}$ rinse. Column performance was not adversely affected by regeneration. When the regeneration step was used on virgin carbon, a dramatic improvement in column performance was observed and was attributed to the increase in carbon surface $\mathrm{pH}(\mathrm{pH}\approx 11)$ and the deposition of OH⁻ in the pore liquid. Possible removal mechanisms are precipitation of lead on the carbon surface, precipitation in the pore liquid, and adsorption (surface complexation).

A continuous process of combined ozonation and chemical coagulation was employed for treatment of textile wastewaters from several dyeing and finishing plants. Ozonation was found to be highly effective in color removal with complete discolorization of textile wastewater being achieved in less than 10 min in the continuous reactor. Chemical coagulation was observed to be mainly responsible for removing dissolved and suspended solids with a COD removal efficiency of up to 66%. The treatment efficiency of the combined process can be further enhanced when used in conjunction with the activated sludge process. Preliminary economic analysis of the process shows that ozonation for decolorization is highly competitive in terms of its total cost compared with use of decoloring agent. The cost saving is further complemented by a considerable improvement in the overall quality of the treated wastewater.

Traditional network analysis (Hardy Cross, Newton‐Raphson, or linear theory methods) presumes that the nodal demands are always satisfied in a water‐distribution system (WDS) and determines the available heads. However, when a pump fails or a pipe breaks, the WDS may be unable to supply all nodal demands at required heads. Thus, the traditional network analysis does not correctly describe the partially failed WDS. In reliability analysis of WDSs, however, the nodal flows that would be available under deficient conditions should be evaluated and used. Therefore, an approach termed node flow analysis that determines the available nodal flows under deficient conditions by considering the nodal demands and heads, simultaneously, is presented for determining WDS reliability. The reliability is based on a node‐reliability factor, volume‐reliability factor, and network‐reliability factor. Even though WDS reliability depends on several parameters, only the pipe break and pump failure conditions are considered. However, several loading patterns, including fire flow requirements, can be considered as illustrated by a hypothetical example.

Heavy metal leaching by sulfur‐oxidizing bacteria, one of the most promising sludge detoxification methods, uses elemental sulfur as a microbial energy substrate. The addition of elemental sulfur in a powdered form makes it impossible to recover unused sulfur and can promote microbial reacidification of disposed sludge. Hence, recoverable forms of sulfur are preferred. The purpose of the present study was to verify the effect of sulfur forms, sulfur concentration, and the effect of sulfur recycling on the efficiency of microbial process. Powder, pastille, and sphere forms of sulfur were tested. Despite their relatively smaller surface areas, the sphere and pastille sulfur forms did not affect the consumption of sulfur substrate by the microbial process and were also comparable to the powder form in sludge acidification. Upon recycling in fresh sludge, the recovered elemental sulfur was as effective in pH reduction as new sulfur. Elemental sulfur can therefore be added in a microbial leaching process in recyclable forms such as stationary blocks, small sulfur prills or suspended sulfur rods depending on the needs of a waste treatment plant.

Field tests were performed on a small marine outfall discharging domestic wastes. Dye was injected into the effluent flow entering the pump house and samples were taken in the sump and offshore in the sewage boil. Dilutions were evaluated from the sample concentrations and compared with theoretical predictions. Data were first collected with the outfall discharging freely in the horizontal direction. Following these tests a mixing tube was attached to the outfall. This consisted of a horizontal cylinder designed to provide some predilution before the effluent jet entered the receiving water. Data were again collected after the mixing tube was installed and the dilutions measured were compared with theoretical predictions. These showed that the theory used for the mixing tube under‐predicted measured values by more than 25%.