Journal of Environmental Engineering

To simulate stream temperatures on a watershed scale, shading dynamics of topography and riparian vegetation must be computed for estimating the amount of solar radiation that is actually absorbed by water for each stream reach. A series of computational procedures identifying the geometric relationships among the sun position, stream location and orientation, and riparian shading characteristics were used to develop a computer program called SHADE. The SHADE-generated solar radiation data are used by the Hydrologic Simulation Program-FORTRAN (HSPF) to simulate hourly stream temperatures. A methodology for computing the heat flux between water and streambed was selected, evaluated, and implemented in the HSPF code. This work advances the state of the art in watershed analysis by providing a quantitative tool for relating riparian forest management to stream temperature, which is a vital component of aquatic habitat. This paper describes the modeling strategies, the SHADE program in terms of algorithms and procedures, the integration of SHADE with HSPF, and the algorithms and evaluation of the bed conduction of heat. A companion paper presents an application of the SHADE-HSPF modeling system for the Upper Grande Ronde watershed in northeast Oregon.

The SHADE-HSPF modeling system described in a companion paper has been tested and applied to the Upper Grande Ronde (UGR) watershed in northeast Oregon. Sensitivities of stream temperature to the heat balance parameters in Hydrologic Simulation Program-FORTRAN (HSPF) and the riparian shading parameters in SHADE were analyzed for stream temperature calibration. Solar radiation factors (SRF), as well as diurnal, seasonal, and longitudinal variations, were evaluated to verify the accuracy and reliability of SHADE computations. Simulated maximum values of stream temperature, on which the riparian restoration forecasts are based, are accurate to 2.6–3.0°C compared with 8–10°C exceedances over stream temperature goals for salmon habitat restoration under the present riparian vegetation conditions. Hourly simulations have approximately the same accuracy and precision. Stream temperature regimes were simulated for different hydroclimatic conditions and hypothetical restoration scenarios of riparian vegetation. Regardless of natural weather cycles, the restoration of riparian vegetation is needed along many headwater streams to significantly alleviate the lethal and sublethal stream temperatures currently associated with salmon habitat in the UGR basin.

The installation of soil/bentonite (SB) slurry walls is a popular strategy for containing subsurface contamination. An important aspect of performance assessment for SB systems is an evaluation of the rate of contaminant transport across the barrier. The one-dimensional (1D) advective-dispersive-reactive equation is often applied to this analysis, under the common assumption of linear local equilibrium sorption. For cases in which sorption to barrier materials is not rapid, application of the local equilibrium assumption in the design and analysis of barrier systems will be nonconservative. Computational strategies are presented for incorporating first-order kinetic sorption into predictions of 1D contaminant transport in vertical walls. In particular, an extension to the popular finite-layer approach is developed that allows treatment of nonequilibrium sorption while retaining the computational advantage associated with the semianalytical framework. Application of the method is illustrated through sensitivity analysis and simulation of published experimental results. While it is unlikely that nonequilibrium sorption will influence the performance of installed slurry walls, it is suggested that kinetic effects may complicate the interpretation of laboratory experiments for some systems.

This paper describes and demonstrates a numerical model for subsurface solute transport with aerobic and sequential anaerobic biodegradation. The model can depict multiple constituents in a three-dimensional (3D), anisotropic, heterogeneous domain. Hydrocarbon contaminants are simulated as electron donors for microbial growth, and available electron acceptors (EAs) may be utilized simultaneously or in the following sequence: O₂, ${\mathrm{NO}}_3^{-}\text{,}$ Mn(IV), Fe(III), ${\mathrm{SO}}_4^{2-}\text{,}$ and CO₂. The model can account for Mn(II), Fe(II), H₂S, CH₄, and a user-defined nitrogenous compound as products of biodegradation. Biodegradation of each hydrocarbon substrate follows Monod kinetics, modified to include the effects of EA and nutrient availability. Inhibition functions allow any EA to inhibit the utilization of all other EAs that provide less energy to the microbes. Microbial biomass is conceptualized as scattered microcolonies attached to the porous medium. The model assumes that interphase diffusional limitations to microbial growth are negligible and no geometrical parameters are assigned to the colonies. The behavior of the model was demonstrated using simple, hypothetical test cases. Transport of a biodegradable hydrocarbon was compared to a nonbiodegradable tracer in a 3D, hypothetical domain. Anaerobic biodecay significantly reduced predicted contaminant concentrations and travel distance. Biodegradation of the total contaminant mass depended on EA availability and did not follow first-order kinetics.

The microbial acclimation potential of acetate-enriched Methanosarcina cultures to acrylic acid was investigated. Acrylate-acclimated and unacclimated, acetate-enriched Methanosarcina cultures maintained at a nearly constant acetate concentration of 7,500 mg/L were used in batch and fed-batch serum bottles. The results revealed that the 6-d lag period observed before the onset of acrylic acid biotransformation for an unacclimated culture disappeared for a 150-d acrylate acclimated culture. Even though acrylic acid was notably inhibitory to an unacclimated Methanosarcina culture above slug-doses of 20 mg/L [0.019 mg acrylic acid/mg volatile suspended solids (VSS)], the toxic effects of acrylic acid could be significantly reduced through acclimation. The inhibition and recovery periods of the cultures were dependent on administration patterns. The activity level (or gas production) of a culture can be kept around a desired level by applying a predetermined acrylic acid administration strategy. Acclimation to acrylic acid could not be achieved below a threshold 40-d loading rate of 10 mg/L. Higher solids retention time (SRT) systems provided better tolerance to acrylic acid toxicity for the same acrylic acid loading. The acrylic acid inhibition was reversible but exposure to acrylic acid had a negative residual effect on the biomass that was manifested for over 30 d after the toxic supernatant was removed by centrifugation.

The objective of this research was to evaluate the effects of a number of landfill inputs on hydrogen sulfide production and on competition between methane production and sulfate reduction during refuse decomposition. Tests were conducted in four-liter reactors that contained residential municipal waste; decomposed refuse as a seed; and various mixtures of anaerobically digested polymer-treated sludge, anaerobically digested lime-stabilized sludge, and wallboard (calcium sulfate) simulating construction and demolition waste. Tests demonstrated that wallboard was the major cause of hydrogen sulfide production and that methanogenesis and sulfate reduction occur concurrently during refuse decomposition. Additionally, both polymer- and lime-treated sludge enhanced refuse decomposition. Despite the presence of excess sulfate, 2.9 to 7.0 times more organic carbon was biodegraded through methanogenesis than through sulfate reduction.

We demonstrate that the facultative chemoautotroph Thiobacillus novellus CH 3 removes hydrogen sulfide (H₂S) gas in continuous reactors under nutrient-limiting conditions. Extensive tests including removal characteristics, metabolic products, and removal efficiencies of H₂S by T. novellus CH 3 were conducted in autotrophic and mixotrophic environments. The optimal pH value and temperature required to remove hydrogen sulfide are found to be pH 7 and 26°C. The biofilter had an H₂S removal efficiency greater than 99.5% under the mixotrophic condition after 10-day operation. The results show that the maximum removal rate and saturation constant were 1.9 g S/d per kg bead and 69.2 ppm, respectively. The main metabolic product of H₂S oxidation was determined to be sulfate, but the conversion ratio was dependent on the growth environment. These results suggest that the mixotrophic potential of T. novellus CH 3 biofilter provides a significant advantage in H₂S removal over autotrophic biofilters.

New European government policies aim at the closure of material flows as part of integrated chain management (ICM). One of the main implementation instruments is extended producer responsibility, which makes original equipment manufacturers (OEMs) formally responsible for take-back, recovery, and reuse of discarded products. One of the key problems for OEMs is to determine a recovery strategy, i.e., determine to what extent return products must be disassembled and which recovery and disposal (RD) options should be applied. On a tactical management level, this involves anticipation of problems such as meeting legislation, limited volumes of secondary end markets, bad quality of return products, and facility investments in recycling infrastructure. In this paper, a model is presented that can be used to determine a recovery strategy for multiple-type consumer products. The objective function incorporates technical, ecological, and commercial decision criteria and optimization occurs using a two-level optimization procedure. First, a set of potential product recovery and disposal (PRD) strategies is generated for each separate product type. Secondly, optimal PRD strategies are assigned to the products within a coherent multiproduct or product group policy. The aim is to find an optimal balance between maximizing net profit and meeting constraints like recovery targets, limited market volumes, and processing capacities. A TV case is worked out to illustrate the working of the model. Also, the managerial use of the model is discussed in view of establishing an economically and ecologically sound base for achieving ICM.

Stochastic risk assessment models offer the potential for being more objective by explicitly considering variability. Such a model has been developed for a site contaminated with polychlorinated biphenyls (PCBs) by representing the parameters used in the risk assessment as probability distribution functions (pdf) rather than single values. The pdf for total risk calculated by the model is approximately lognormal, although the pdf of parameters in the model take on a variety of forms. A first-order approximation to the model provides good estimates for the high end of the distribution, which is of concern when conservative risk assessments are desirable. The first-order approximation provides good estimates even when the level of variation of the parameters is increased well above levels that are normally expected. A procedure was developed to apply the stochastic risk assessment model in a series of calculations to determine preliminary remediation goals for the site. In addition, a simplified technique was developed to calculate preliminary remediation goals using only results from simulating risk with initial site conditions.

A laboratory comparison is made between the ability to steam strip organic contaminants from soil in the confined state and the ability to do so in the “fluidized” state. The soil used was a 50/50 mixture of beach sand and river silt. It was found that the removal of benzene, toluene, and xylene and dodecane occurred much faster and to a much greater extent in the “fluidized” soil than in the confined soil.