Journal of Environmental Engineering

A deterministic linear programming model is presented that can be used to aid decision makers in the long-term scheduling of disposal and diversion options in a regional integrated solid waste management system. The model can be used to determine what types of integrated solid waste management programs to implement, and when to implement them, in order to minimize costs over a long planning period. The model is capable of handling multiple communities, landfills, and incinerators, and can incorporate the possible implementation of numerous collection and diversion options, such as recycling and composting programs. The model can incorporate mutually exclusive collection and facility options. The model also uses innovative approaches in determining the volume of waste land filled and energy content of wastes incinerated, given the effect of implemented diversion options on the waste stream. Alternative methods to handle costs in the objective function are discussed, including (1) units costs; (2) mutually exclusive facility options, each with an associated unit cost; (3) fixed and operating costs; and (4) variable costs using the piecewise linear approximation method. In a companion paper, a hypothetical case study is used to explore the capabilities of the model.

In this paper, solutions of a regional-scheduling model are presented to demonstrate the ability of the model to optimally schedule processing, conversion, and landfilling options to realize the lowest possible long-term costs for a regional integrated solid waste management system. The model is driven by the capacity and tipping fees for each existing or proposed landfill along with the capacity, costs, and revenues of implementing each processing or conversion option. Model results indicate that the implementation of processing and conversion options can reduce long-term costs by increasing the life of less expensive landfills, thus pushing the opening of more expensive landfills further into the future. Model solutions are used to show the effect of landfill capacities and tipping fees on scheduling. Figures are presented to illustrate interactions between model parameters, optimal costs, and scheduling.

A quasi-two-dimensional partition-diffusion transport model was developed to determine the diffusion coefficient and partition coefficient for various types of geomembranes from measurements of aqueous organic compound concentrations in a confined, double-compartment apparatus with a geomembrane separating the two compartments. The geomembranes tested were high-density polyethylene (HDPE), very low-density polyethylene (VLDPE), and polyvinyl chloride (PVC) and the permeants were mixtures of methylene chloride, toluene, trichloroethylene (TCE), and m -xylene at 10–100 mg/L. The diffusion coefficient increased exponentially with aqueous concentration and decreased exponentially with geomembrane thickness. The partition coefficient was unaffected by compound concentration and membrane thickness. As HDPE geomembranes were stretched by 5% of their original length, the partition coefficient increased by 0.15–0.6 times. VLDPE had 1.8–3.3 times greater partition coefficients and 1.6–2.8 times greater diffusion coefficients than HDPE, while PVC had 6.2–8.3 times greater partition coefficients and 1–1.8 times greater diffusion coefficients than HDPE.

The transient and steady-state mass fluxes were estimated based on partition and diffusion coefficients and compared with fluxes through holes in liner systems under representative field conditions. Stretched high-density polyethylene (HDPE), unstretched very low-density polyethylene (VLDPE), and unstretched polyvinyl chloride (PVC) had 2.0–2.5, 4.4–5.2, and 8.4–10.8 times greater permeabilities than unstretched HDPE, respectively. The maximum instantaneous mass flux decreased by more than 15 times as the initial aqueous concentration decreased from 100 to 10 mg/L and as the HDPE thickness increased from 0.76 to 2.54 mm. The maximum instantaneous mass flux increased by 1.7 times when a HDPE geomembrane was stretched by 5% of its original length. The flux caused by steady-state permeation through the intact geomembrane, which has so far been neglected, was comparable to the flux through the geomembrane with large holes alone but more than three to 34 times greater than the flux through the geomembrane with small holes alone, implying that the permeation through the intact geomembrane may pose serious environmental contamination.

Nearly all distribution systems in the United States include storage tanks and reservoirs. They are the most visible components of a water distribution system but are generally the least understood in terms of their impact on water quality. Long residence times in storage tanks can have negative impacts on water quality in drinking water distribution systems, including the loss of chlorine residuals and the regrowth of microorganisms. It is generally accepted that complete mixing maximizes water quality but little is understood about mixing regimes in general. This paper demonstrates the use of compartment models to characterize mixing in three tanks. It was found that the mixing regimes in these tanks were well characterized by compartment-type models and that these tanks were not completely mixed, contrary to conventional wisdom. It is clear that much more research is needed in order to truly understand mixing regimes in tanks and reservoirs and that this understanding, if properly applied, can have a positive impact on water quality.

An expert system based on a combination of forward chaining, backward chaining, and metarules has been developed for water treatment plant operations. The expert system was developed by interviewing a number of plant operators and chemists. Decision trees and fault trees were used to speed the development of the expert system. The combined strategy of using both backward and forward chaining within the expert system allows the number of questions asked of an operator to be minimized to prevent the asking of redundant questions. The methodology developed is applied to a case study water treatment plant. Two of the modules of the expert system are described in this paper. In the first, turbidity treatment module assists an operator in deciding a change in alum dosing in response to a change in treated water quality. In the second, a fault diagnosis module to detect the cause of equipment failure in the plant is presented.

Field studies of solute fate and transport in streams and rivers often involve an experimental release of solutes at an upstream boundary for a finite period of time. A review of several standard references on surface-water-quality modeling indicates that the analytical solution to the constant-parameter advection-dispersion equation for this type of boundary condition has been generally overlooked. Here an exact analytical solution that considers a continuous load of finite duration is compared to an approximate analytical solution presented elsewhere. Results indicate that the exact analytical solution should be used for verification of numerical solutions and other solute-transport problems wherein a high level of accuracy is required.

A reactive, radial-transport model to simulate biological processes near a nutrient injection well is presented. An improved numerical procedure that incorporates the attractive features of Eulerian-Lagrangian and reaction-operator split methods is used to solve the model. The numerical procedure is efficient, stable, and mass conserving. An in-situ biostimulation model incorporating aerobic kinetics is solved to demonstrate the usefulness of the modeling procedure and to study the sensitivity of biomass distribution to variations in biokinetic parameters. The resulting mathematical model adequately describes near-well biological processes under varying conditions. The sensitivity analysis shows that the microbial detachment and attachment processes are important transport parameters that control biomass distribution in an aquifer. The results strongly suggest that other expressions that describe these processes and their relationship to growth rate should be examined.

Spent abrasive media from bridge repainting operations contain metals which may result in the media being classified as hazardous under the Environmental Protection Agency (EPA) Toxicity Characteristic (TC) criteria. The management of spent abrasive media by recycling it as a component of nonstructural concrete was investigated. Success was measured with respect to the TC criteria for leaching and a compressive strength requirement of 6.9 MPa (1,000 psi). Portland cement, with and without the additives used, successfully immobilized the metals present in the media. However, not all of the mixes prepared set, indicating that there is a limit to the amount of media that can be recycled in a concrete product. Mixes incorporating 100% unseparated spent abrasive sand and dust or slag in place of clean sand successfully met the project criteria. Mixes containing up to 25% addition of separated spent abrasive dust met the project criteria with the inclusion of appropriate mix additives. Based on results from this and earlier studies, the Texas Department of Transportation has begun to recycle spent abrasive media using portland cement.

The solidification/stabilization (S/S) process is applicable to soil contaminated by metals and other inorganics. However, this process is not currently viewed by the U.S. Environmental Protection Agency (EPA) as applicable for remediation of soils contaminated solely with volatile organic compounds, because these organic compounds have been shown to have a detrimental effect on the macrostructural properties of ordinary portland cement (OPC) and could be released during the mixing and curing process. The aim of the present study is mainly to investigate the feasibility of using quaternary ammonium-modified clays (organophilic clays) to stabilize organics (phenol, 2-chlorophenol, and 2,4-dichlorophenol) in contaminated soils prior to conventional cement-based solidification. The effectiveness of the S/S process, using organophilic clays, was evaluated, based on experimental findings from batch sorption, leachability of hazardous constituents, unconfined compressive strength, and permeability tests. Results from these experimental tests indicate that the use of organophilic clay as a presolidification adsorbent gives a successful S/S process in the treatment of phenol-contaminated soils.

In the modern urban atmosphere SO₂ and NO₂ attack calcite (CaCO₃) in marble exposed at rain-sheltered surfaces creating largely gypsum (CaSO₄⋅2H₂O) crusts that eventually exfoliate. In combination with CO₂ these gases erode the marble at unsheltered surfaces. We report the development of mathematical models to predict the rate of growth of crust and the rate of surface recession. To determine the rate of growth of crust the kinetic rate constant, diffusion rate, and the order of reaction were determined by the application of the shrinking-core model applied to data generated in laboratory experiments. Based on these parameters and average ambient levels of 10 parts per billion (ppb) SO₂ and 25 ppb NO₂ in Louisville, Ky., the rate of crust formation for this metro area was calculated to be 1.8 μm in the first year. However, the rate of recession was modeled from data obtained by exposing marble slabs to rainfalls. A surface recession of 15 μm/yr was calculated. The models predicted well the rate of growth of crust observed at several sites in Louisville and the predicted surface recession compared well with values reported in the literature.

An experimental study was carried out to investigate the resuspension (fluidization) of a loosely held monodispersed particle bed by a momentum jet, discharging from below. The work was motivated by its applications to limnological situations where the bottom sediments are suspended by a series of jets fed by a ground-water karstic system. Two different flow regimes were identified, and the conditions under which they occur were mapped on a regime diagram between the two important nondimensional variables, h _o /d _p and h _o /$({\mathit{M}}_{\mathit{o}}^{1/2}$/w _s), where h _o is the height of the particle layer; w _s is the particle-settling velocity; and M _o is the momentum flux of the jet. The maximum height of rise of particles within the jet was also determined as a function of these nondimensional variables. Comparisons of laboratory and field observational results were also made.

As regulatory limits for contaminants in air and water become increasingly stringent, interest in steam stripping to remove synthetic organic compounds (SOCs) from industrial waters has increased. To identify situations in which steam stripping could be a cost-competitive option for treating waters contaminated with low concentrations ( <10 mg/L) of synthetic organic chemicals, the performance and cost of steam-stripping towers were modeled, and a range of hypothetical contaminated waters was examined. The cost of steam stripping was compared to that of air stripping, liquid-phase carbon adsorption, and air stripping with off-gas adsorption. Steam stripping was found to be a highly specialized treatment technology that will not frequently be cost-effective, but it does have a small niche in the environmental remediation market. Steam stripping is cost-effective when site-specific factors significantly reduce capital or operating costs, or when the target chemical is only marginally volatile, adsorbable, and biodegradable, effectively making all other conventional treatment methods more expensive.

Bench scale and pilot plant studies were conducted using anoxic anaerobic and aerobic reactor sequence for enhanced biological phosphorus removal. The influent quality and operational characteristics such as return sludge, food-to-microorganism (F/M) ratio, and mean cell residence time varied greatly in these studies. The data collected over a 10-year period for phosphorus removal was analyzed with respect to many parameters. A strong relationship between the concentration of soluble 5-day biochemical oxygen demand (BOD ₅ ) in the mixture of the influent and return sludge, phosphorus release in the anoxic and anaerobic reactors, and phosphorus uptake in the aeration basin was observed. The total phosphorus (TP) removal was greatly influenced by the availability of biodegradable carbon in high enough concentration in the mixture. Two statistical curves between average BOD ₅ of the mixture and total phosphorus removal have been fitted with excellent results. More than 90% total phosphorus removal is achieved when the soluble BOD ₅ of the mixture is over 120 to 125 mg/L.