Journal of Environmental Engineering

Experiments on air‐water gas transfer were performed in a flume with a mechanical wave maker for the determination of the gas‐transfer coefficient with waves. Oxygen was used as the transferred gas. The experiments indicate that nonbreaking deep‐water gravity waves significantly influence air‐water gas transfer. The gas‐transfer coefficient was correlated with the wave characteristics. A renewal model was used for the analysis of the data, and the renewal rate was dependent on a wave Reynolds number. The gas‐transfer coefficient was linearly dependent upon the product of wave height and wave frequency. This is also equivalent to the gas‐transfer coefficient being directly proportional to the wave velocity at the water surface. Comparison with data reported in the literature indicates that a significant portion of the observed gas transfer in wind‐wave flume experiments can be attributed to nonbreaking waves. The presence of bubbles or bubble‐entraining breaking waves enhances the gas‐transfer coefficient considerably. Visual correlation between breaking intensity and the transfer coefficient was good, although the relation has not been quantified.

Chlorinated aliphatic solvents arc common contaminants of unsaturated soils. This research focuses on the feasibility of treatment by in situ bioremediation with indigenous methanotrophs. Batch biodegradation experiments are conducted with three unsaturated soils in which indigenous methanotrophs are stimulated by exposure to a methane/air atmosphere. Of the three chlorinated solvents tested, 1,2‐dichloroethane is degraded the fastest, followed by trichloroethylene, and finally chloroform. Zero‐order rate constants for conversion to ${\mathrm{CO}}_2$ range from 0.05 to 1.4 μg solvent/g dry soil‐day. Assuming contaminant concentrations on the order of 100 μg/g soil, these rates imply that in situ bioremediation would require several months to several years for completion. Depending upon the particular chlorinated solvent and soil, microbial activity produces, in addition to ${\mathrm{CO}}_2\text{,}$ significant quantities of nonvolatile products. The products represent disappearance of the parent chlorinated solvent, but may or may not represent acceptable bioremediation depending upon the nature of the products and the treatment goals. Availability of nutrients also significantly affects degradation rates.

The purpose of this paper is to summarize aspects of the permeable treatment bed concept for the containment of metals from a plating sludge when landfilled. Background information presented in the literature and an experimental proof‐of‐concept investigation are included. Laboratory experiments were performed under controlled conditions, using model reactors to simulate the leachability of a metal hydroxide sludge placed in a humid landfill environment. The effects of simulated natural and acid rains on the leachability of selected metals are considered. The results indicate the effectiveness of the concept to control the release of heavy metals from the sludge into ground water.

A generic parameter estimation algorithm was developed for the simultaneous extraction of multiple parameters from experimental or field observations. The basis of the method lies in the minimization of the variation between model predictions and observations via the iterative numerical determination of the functional minima of the model with respect to the parameters being determined. A multivariable Newton technique, and derivatives thereof, are used for this purpose. By relying on numerical differentiation in the iterative process, the technique is not limited by the model complexity, solution methodology, or scale of its domain. Model parameters have been estimated successfully for analytical and numerical solutions to dispersive and advective‐dispersive particle transport model equations. The effect of sampling or measurement error and initial parameter estimates on algorithm performance has been evaluated. This approach has been successfully applied to determine data requirements and constraints (quantity, quality, and location) for measurement of hydrodynamic and transport characteristics of dye clouds and aquatic particles in laboratory‐mixed settling columns.

A quasi‐two‐dimensional model for the simulation of temperature, salinity, and density in a reservoir is described. The model is based upon the one‐dimensional reservoir simulation model DYRESM, and is extended into two dimensions using a Lagrangian formulation of self‐contained parcels within the layer structure of the one‐dimensional model. These parcels resolve the horizontal motions and gradients by moving vertically or horizontally and splitting and combining to simulate the various physical processes in the reservoir occurring in response to the prevailing climatological conditions. The model is not a full two‐dimensional model, because not all horizontal processes are included. Algorithms to simulate inflow, selective withdrawal, and adjustment of horizontal density gradients are included, however, and the model is therefore quite useful for examining some simple scenarios in which these processes are dominant. The results of simulations of Canning Reservoir in Western Australia showing several inflow and intrusion events at different times of the year, and the return of the reservoir temperature field to a one‐dimensional structure after the cessation of inflow, are presented. These results are compared with measurements taken in the field, with good agreement. The usefulness of the model in its present form for following the path and estimating the detention time of various parcels of water is discussed.

A decision support system based on a modified fuzzy‐composite programming method is developed to assist decision makers in solving multiple‐objective decision problems under uncertainty. The method is applied to a dredged material management problem involving disposal of polluted dredged material at multiple disposal sites, where there are conflicting objectives such as environmental risk and cost, and the information regarding the impacts of dredged material disposal on each site is uncertain. Using the modified fuzzy‐composite programming method, values of the risk and cost are transformed into fuzzy numbers (i.e., fuzzy risk and fuzzy cost) to incorporate uncertainties associated with the risk and cost into the risk‐versus‐cost trade‐off analysis.

One of the main problems facing water‐quality modelers is obtaining laboratory data and determining the biokinetic parameters required to run a model simulating the biotransformation process, termed reductive dehalogenation, that transforms chlorinated hydrocarbons into intermediate compounds, then into a final compound that is not always easily biodegradable. The numerical values of these parameters are estimated by fitting the batch data to the Michaelis‐Menten equation. However, when dealing with more than one intermediate compound in a sequential bioconversion process, the standard graphical techniques are not sufficient. Therefore, it is the purpose of this study to present a general technique to obtain Michaelis‐Menten biokinetic parameters of sequential multi‐intermediate systems. A simplification of the general technique is introduced for low‐concentration compounds, and biotransformation data are simulated for carbon tetrachloride using the estimated rate coefficients.

A simple approach, the delta method, is derived to estimate stream reaeration, primary production, and respiration rates on the basis of diurnal dissolved oxygen measurements. The method uses three features of the diurnal curve to determine these quantities. The time of minimum deficit (relative to solar noon) is used to estimate the reaeration rate. Given the reaeration rate, the deficit range Δ is employed to predict photosynthetic production. Finally, the average deficit can be used in conjunction with the reaeration and production rates to compute respiration. A graphical procedure is presented to implement the method. The approach is demonstrated by applying it to the Grand River in Michigan. Although the method has general applicability, a sensitivity analysis indicates that it is particularly effective for streams with lower reaeration rates (i.e., $<1.0d^{-1}$). An efficient piecewise solution of the diurnal oxygen deficit balance is derived as an alternative to a Fourier series and numerical solutions. Finally, we develop some simplified analytical solutions that make the delta method easier to implement.

The analysis focuses on a steady‐state budget model. To simplify the analysis, the mechanisms of decay and diffusive sediment feedback are ignored. These omissions result in a lower‐bound representation of the net loss rate that is dependent on three processes: sorption, volatilization, and sediment resuspension. In order to investigate the interaction of these processes, the net loss rate is mapped on a space defined by sorption and volatilization dimensions. On this space, three zones are identified. The air zone contains substances that sorb weakly, are highly insoluble, and would exhibit high removal rates due to volatilization. At the other extreme, the water zone, substances that sorb weakly and are soluble have low removal rates because they are not subject to sedimentation or volatilization. The third area, the sediment zone, is populated by strong sorbers that are primarily governed by sediment resuspension. Among the organic priority pollutants, the halogenated aliphatics and most of the monocyclic aromatics reside in the air zone and should experience rapid purging. A significant number of pesticides, phenols, phthalate esters and nitrosamines fall in the water and sediment zones. These could represent problem compounds from the perspective of a weak assimilative capacity.

Many local agencies responsible for the sewage treatment process manage a large number of small treatment facilities that serve low-density residential areas. This process is often noisy and, as a result, frequently generates complaints from nearby residents. Most of these agencies do not have staff with the requisite expertise to determine when noise complaints represent significant noise impacts. Further, if problems do exist, then the specialized knowledge required to mitigate noise impacts is not present. This paper presents the results of a study conducted for the Louisville Metropolitan Sewer District (MSD) in which a measurement procedure was developed, along with guidelines for determining the noise level at which impacts can be expected. Finally, an abatement solution was developed and tested, demonstrating the feasibility of a low-cost method of significantly lowering high noise levels generated by the operation of a typical low-volume sewage treatment facility.

Development of remedial plans for sites contaminated with petroleum hydrocarbons requires relatively accurate estimate of recoverable free liquid retained in pore spaces. Several techniques available to make such estimates are evaluated. Methods based on the CONCAWE factor and the formation factor tend to overestimate the free product volume, perhaps because these models do not consider the variation of saturation with depth. The recently developed OILEQUIL model and the SOILPROP program are tested using pilot-scale experimental data obtained for large sand tanks. The parameter estimation by the van Genuchten method, followed by free product volume estimation using OILEQUIL, gives a fairly accurate estimate of free liquid under equilibrium conditions.

Methanogenic, fluidized-bed biofilm reactors having a granular activated carbon (GAC) medium are fed continuously with milk colloids. Steady state results for increasing loads of chemical oxygen demand (COD) show that the removal efficiency for influent colloids increased as the amount of attached biofilm increased due to the higher COD loading. Short-term filtration experiments using small-scale, once-through columns are used to assess the cohesion efficiency (α) for GAC samples taken from the biofilm reactor. GAC with the highest amount of biomass, 1.74 mg cellular carbohydrate per gram of dry carbon, has a much higher cohesion coefficient (α = 0.90 on average) than does GAC with no biomass (α = 0.00) and GAC with 0.134 mg cellular carbohydrate per gram of dry carbon (α = 0.21). Thus, the increased accumulation of biofilm dramatically improves the cohesion of the milk colloids.