Showing papers in "Journal of Environmental Engineering in 1998"
TL;DR: Water quality of highway runoff in the Austin, Texas, area was determined by monitoring runoff at three locations on the MoPac Expressway as mentioned in this paper, where a grassy swale at one site was effective in reducing the concentrations of most constituents in runoff.
Abstract: Water quality of highway runoff in the Austin, Texas, area was determined by monitoring runoff at three locations on the MoPac Expressway. Daily traffic volumes, surrounding land uses, and highway drainage system types were different at each site. The concentrations of constituents in runoff at all sites were similar to median values compiled in a nationwide study of highway runoff quality. A grassy swale at one site was effective in reducing the concentrations of most constituents in runoff. The lower runoff coefficient at this site is attributable to infiltration of runoff into the grassy swale. The pollutant loads discharged from the pipe draining the swale were lower than those observed at the sites where runoff drained directly from the pavement. A first flush effect (i.e., higher pollutant concentrations at the beginning of an event) was evident during selected events, but was generally limited to a small volume. The overall effect was negligible when all monitored events were considered.
359 citations
TL;DR: In this paper, the physical characteristics of solids transported in lateral pavement sheet flow (LPSF) from a heavily traveled roadway in Cincinnati, Ohio were measured using a light obscuration particle counter.
Abstract: Urban stormwater runoff from paved surfaces transports a wide gradation of solids ranging in size from smaller than 1 micrometer to greater than 10,000 micrometers. This study measured physical characteristics of solids transported in lateral pavement sheet flow (LPSF) from a heavily traveled roadway in Cincinnati, Ohio. Particles smaller than 25 micrometers were counted and sized using a light obscuration particle counter. Particles larger than 25 micrometers were separated mechanically to generate particle size distributions. Solids in the 2-8 micrometer range generated the largest counts and were rapidly washed from the pavement. LPSF rate and duration controlled yield and size of transported solids. Particle transport was mass limited during long duration high intensity events, but flow limited during intermittent low intensity events with high traffic. Particle counts exhibited a first flush from the pavement. Specific surface area generally increased with decreasing particle size, but measured values deviated from the monotonic pattern expected for spherical particles. Particles 425-850 micrometers in size contributed the greatest total surface area. Results provide guidance for assessment of the impact of urban runoff water quality and for design of in situ treatment strategies.
321 citations
TL;DR: In this article, three highway segments typical of urban, semi-urban, and rural settings in the Piedmont region of North Carolina were monitored to characterize the respective runoff constituent concentrations and pollutant discharge or export loadings.
Abstract: Three highway segments typical of urban, semiurban, and rural settings in the Piedmont region of North Carolina were monitored to characterize the respective runoff constituent concentrations and pollutant discharge or export loadings. Runoff from the impervious bridge deck (Site I) carried total suspended solids (TSSs) concentrations and loadings that are relatively higher than typical urban highways, whereas nitrogen and phosphorus loadings are similar to agricultural runoff. Site II included a pervious roadside shoulder with traffic volume equal to that of Site I. Site III was a nonurban highway having lower traffic counts and imperviousness due to the presence of a roadside median. The existing roadside shoulder and median appeared to attain at least 10–20% hydrologic attenuation of peak runoff discharges, more than 60% reduction of event mean concentration of TSSs, and attenuation of the first-flush concentrations for most pollutant constituents. Bulk precipitation data collected at the bridge deck s...
283 citations
Abstract: Membrane filtration coupled with ozonation of the retentate was used for the treatment of colored textile wastewater The textile wastewater examined was simulated from a commercial batch formula and contained organic dyes, sodium chloride, and copper among its components A selected membrane filtration process generated a permeate with over 99 of the color and copper removed, while 85 of salt by mass and 85 of the original water were reusable The effect of pressure, cross-flow velocity, feed concentration, and membrane fouling on permeate flux also was investigated Subsequent ozonation of several different concentrated retentates each followed first-order reaction kinetics and removed color effectively However, the decolorization rate constant decreased with increasing initial dye color An empirical correlation was established for the apparent first-order rate constant of ozonation and the initial dye concentration The relationship between the apparent rate constant and the dosage of ozone input als
250 citations
TL;DR: In this article, surface catalyzed loss of quinoline, a model pollutant, in the presence of three iron oxides: ferrihydrite, goethite, and a semicrystalline iron oxide was examined and compared.
Abstract: The objective of this research was to examine and compare the surface catalyzed loss of quinoline, a model pollutant, in the presence of three iron oxides: ferrihydrite, goethite, and a semicrystalline iron oxide. These are ubiquitous in the subsurface environment and have been implicated in the possible abiotic loss of contaminants when hydrogen peroxide is injected for augmenting bioremediation. This suggests the possible use of hydrogen peroxide specifically as an oxidant of some compounds in the subsurface. A comparison also reveals the best candidate for use in a supported oxide fixed bed treatment system utilizing hydrogen peroxide as an oxidant. The catalytic activity toward quinoline oxidation was highest for goethite, much less for the semicrystalline material, and negligible in the presence of ferrihydrite. Several water constituents affected reaction rates and stoichiometry by adsorption or through effects on solution chemistry. The stoichiometric efficiency relating quinoline loss to hydrogen peroxide decomposition was not a function of oxide concentration, nor was it affected by the presence of carbonate or phosphate that reduced the rate of hydrogen peroxide decomposition. The effect of humic acid on quinoline loss and hydrogen peroxide decomposition rate depended on its concentration, suggesting that it may act as a radicalmore » scavenger, radical chain promoter, and catalytic site inhibitor.« less
208 citations
TL;DR: In this article, the authors investigated the capability of vegetated highway medians for treating storm water runoff in the Austin, Tex. area, and two medians on major highways were monitored to document pollutant removal efficiencies.
Abstract: Vegetative storm water controls include grassed swales and vegetated filter strips. The effectiveness of these controls for removing pollutants found in runoff from highways and other urban areas has not been demonstrated to the satisfaction of regulatory agencies; therefore, these technologies have been limited to applications as pretreatment devices for other structural runoff controls. Many highways in Texas and other areas discharge storm water to grassy medians and shoulder areas, which act as both filter strips and grassed swales. The runoff flows overland down the sides of the median as in a filter strip and then parallel to the highway as in a grassed swale. This study investigated the capability of vegetated highway medians for treating storm water runoff in the Austin, Tex. area. Two medians on major highways were monitored to document pollutant removal efficiencies. The medians were designed solely for storm water conveyance and differed in slope and vegetation type. In addition, the highways a...
199 citations
TL;DR: In this article, a detailed description of the field-measuring facilities used in the Belgrade catchment and the results of the measurements from both sites are presented, along with detailed examination of possible errors in measurement, only the reliable data were used for statistical analysis.
Abstract: Continuous water quality measurements of storm runoff into a single road inlet have been carried out at two experimental catchments in Belgrade, Yugoslavia, and Lund, Sweden. Both sites were equipped with similar instrumentation for measurements of overland flow, turbidity, pH, conductivity, and temperature. The data were recorded at 10-s time intervals during rainfall events. To measure suspended solids concentration, turbidity meters were calibrated in conditions very similar to the real world. A detailed description of the field-measuring facilities used in the Belgrade catchment and the results of the measurements from both sites are presented. After detailed examination of possible errors in measurement, only the reliable data were used for statistical analysis. Event mean, extreme, and aggregated values were analyzed. The results indicate that the antecedent dry weather period length has only a minor effect upon road sediments wash-off, but it has an influence upon conductivity. The "first-flush effect" of suspended solids appears only in a limited number of events. Cross-correlation coefficients of rainfall, overland flow, and water quality were calculated for each event, taking into account the time lag between observed characteristics. These coefficients showed that suspended solids loading rate is influenced by rainfall intensity and overland flow rate. The results presented in this paper have been used in development of the physically based wash-off model published by Deletic and colleagues.
196 citations
TL;DR: In this paper, second-order kinetics was applied to describe the relationship between the formation of total trihalomethanes (TTHM) and the demand for chlorine in drinking water distribution systems.
Abstract: Much effort has been expended in attempting to develop mathematical models for chlorine demand in water and wastewater. Most of these efforts have centered around the use of first-order functions or modifications of first-order functions. Recently there has also been interest in characterizing the formation of total trihalomethanes. These efforts have taken on new meaning because of the importance of maintaining chlorine residuals for microbial protection and concerns over the formation of trihalomethanes in drinking water distribution systems. This paper applies second-order kinetics to describe both of these relationships, using data collected from a recent collaborative study between the EPA and the American Water Works Association Research Foundation. It demonstrates that TTHM formation can be characterized as a function of chlorine demand.
188 citations
TL;DR: It was found that the Chick–Watson model did not adequately represent the ozone disinfection kinetics, and a Hom-type model incorporating a first-order disappearance term for ozone residual was found to best describe the observed inactivation of heterotrophic plate count bacteria.
Abstract: Various empirical and probabilistic kinetic inactivation models that can be used to assist in the design and analysis of potable water disinfection systems were reviewed. Models were derived for both disinfectant demand-free and demand conditions. Ozone was used to inactivate heterotrophic plate count bacteria that were grown in natural water under low nutrient conditions and enumerated using R2A agar at 20°C for 7 days. Experiments were conducted at 22°C in 0.05 M (pH 6.9) phosphate buffer in bench-scale, batch 250 mL reactors. This disinfection data set, characterized by tailing-off behavior, was used to assess Chick–Watson, Hom-type, Rational, Hom–Power law, and Selleck model fit to the observed logarithmic survival ratios. It was found that the Chick–Watson model did not adequately represent the ozone disinfection kinetics. A Hom-type model incorporating a first-order disappearance term for ozone residual was found to best describe the observed inactivation of heterotrophic plate count bacteria. Named...
181 citations
TL;DR: The first field test of IWPT was conducted in a hydraulically isolated test cell to quantify the total amount of a complex NAPL (a mixture of JP-4 jet fuel and chlorinated solvents) trapped within a 1.5m smear zone in a shallow, unconfined sand and gravel aquifer at Hill Air Force Base (AFB), Utah as mentioned in this paper.
Abstract: The difficult task of locating and quantifying nonaqueous phase liquids (NAPLs) present in the vadose and saturated zones has prompted the development of innovative, nondestructive characterization techniques. The use of the interwell partitioning tracer`s (IWPT) test, in which tracers that partition into the NAPL phase are displaced through the aquifer, is an attractive alternative to traditional coring and analysis. The first field test of IWPT was conducted in a hydraulically isolated test cell to quantify the total amount of a complex NAPL (a mixture of JP-4 jet fuel and chlorinated solvents) trapped within a 1.5-m smear zone in a shallow, unconfined sand and gravel aquifer at Hill Air Force Base (AFB), Utah. Tracer breakthrough curves (BTCs) were measured in three extraction wells (EWs) following a tracer pulse introduction through four injection wells (IWs). The measured retardation of the partitioning tracer (2,2-dimethyl-3-pentanol) relative to the nonreactive tracer (bromide) was used to quantify the NAPL present. The EW data were used to estimate an average NAPL saturation of 4.6--5.4% within the test cell. NAPL saturations estimated by using measured concentrations in soil cores of two significant compounds present in the NAPL were 3.0 and 4.6%.
148 citations
TL;DR: In this article, 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.
Abstract: To simulate stream temperatures on a watershed scale, shading dynamics of topography and ri parian 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.
TL;DR: In this article, a model that predicts both TTHMs and chlorine residuals based on the consumption of chlorine and can be used to assist in evaluating the complex balance between microbial and DBP risks associated with disinfecting drinking water with chlorine.
Abstract: Chlorination is the most widely practiced form of disinfection in the United States. It is highly effective against most microbiological contaminants. However, there is concern that the disinfection by-products (DBPs) formed by the use of chlorine might be carcinogenic. One class of DBPs that are formed and the only class of DBPs that currently are regulated are total trihalomethanes (TTHMs). Therefore, much effort is being expended in developing models that can be used to predict both TTHMs and chlorine residual levels in treated drinking water. This paper presents a model that predicts both TTHMs and chlorine residuals based on the consumption of chlorine and can be used to assist in evaluating the complex balance between microbial and DBP risks associated with disinfecting drinking water with chlorine. The parameters of the model have been found to be functions of total organic carbon, pH, temperature, and initial chlorine residual level. Bromide and the subsequent formation of brominated by-products were not considered in this paper.
TL;DR: In this article, the authors compared the performance of Bacillus coagulans and Pseudomonas aeruginosa with Bacillus circulans, a pure culture obtained from the Institute of Microbial Technology.
Abstract: Investigation on Cr(VI) reduction was conducted using bacteria isolated from soil samples receiving electroplating wastewater. Chromium reduction capacity of these isolates was compared with that of Pseudomonas aeruginosa, a pure culture procured from the Institute of Microbial Technology, as well as Bacillus circulans, a laboratory isolate from garden soil. Bacillus coagulans, isolated and identified from chromium polluted soil, gave maximum reduction potential among all organisms studied. Malate was found to yield maximum biotransformation out of four electron donors employed. B. coagulans was able to reduce Cr(VI) even at 10 mM initial Cr(VI) concentration. With an increase in initial cell density, Cr(VI) reduction capacity was also increased; however, maximum specific biotransformation occurred at low cell densities. The optimum pH for Cr(VI) reduction was 7. Sulphates and nitrates did not compete with Cr(VI) for accepting the electrons. The presence of respiratory inhibitors like DNP and NaN3 margina...
TL;DR: The results showed that the amount of the sediments at a street surface was evidently affected by the presence of a sidewalk, and the sidewalk also affected the particle size distribution as discussed by the authors.
Abstract: Sediments that had accumulated during the winter season, and which were left at the surface when the snow had melted, were studied with regard to physical and chemical characteristics. The investigation was carried out in the city of Lulea, which is located in northern Sweden. Sediment samples were collected in the city center and in a housing area at streets with different traffic loads. The results showed that the amount of the sediments at a street surface was evidently affected by the presence of a sidewalk. The street with a sidewalk accumulated much more sediment than the street without a sidewalk did. Both of these streets had approximately the same traffic load. The sidewalk also affected the particle size distribution. The content of heavy metals in the sediments varied with the traffic load and the area type. The highest concentration of cadmium, lead, and zinc was found in the street with the highest traffic load.
TL;DR: The simulative results indicate that the leachate recycle for the LFBR resulted in a more rapid methane production from the consumption of the carbohydrate but in less rapid production from that of the protein and lipid.
Abstract: A mathematical model for the development of methane production from a landfill bioreactor (LFBR) treating the organic fraction of municipal solid wastes was developed from the Gompertz equation. The model incorporates three biokinetic parameters: methane production lag phase time, rate, and potential. The methane converting capacity test experiment was conducted to monitor the specific methane production rate consuming anaerobic fermentative intermediates, including carbohydrates, proteins, and lipids. The model developed in this study can be used to predict methane production based on the chemical nature and the decomposition characteristics of the organic fraction of municipal solid wastes. The simulative results indicate that the leachate recycle for the LFBR resulted in a more rapid methane production from the consumption of the carbohydrate but in less rapid production from that of the protein and lipid. Moreover, the same specific methane production rate of 2.6 mL/g volatile solid (VS) per day occurred at the LFBR with/without leachate recycle; however, a sharp drop in methane production lag phase time, from 125 to 25 days, was obtained at the LFBR incubated with leachate recycle.
TL;DR: In this article, the Superfund Amendments and Reauthorization Act requires the use of remedial technologies that permanently and significantly reduce the volume, toxicity, or mobility of contaminated materials at affected sites.
Abstract: The Superfund Amendments and Reauthorization Act requires the use of remedial technologies that permanently and significantly reduce the volume, toxicity, or mobility of contaminated materials at affected sites. Extractive processes can accomplish the requirements of the Superfund Amendments and Reauthorization Act. Ethylenediaminetetraacetic acid (EDTA), N-2(acetamido)iminodiacetic acid (ADA), pyridine-2,6-dicarboxylic acid (PDA), and hydrochloric acid (HCl) were evaluated over a range of concentrations and reaction times in batch studies for their ability to remove lead (Pb) and cadmium (Cd) from a Superfund soil (Pbtotal= 65,200 mg/kg, Cdtotal= 52 mg/kg). Lead extraction was limited by a slow overall reaction. The order of Pb removal by extractant was EDTA > ADA > PDA > HCL. The soil was subjected to three repeated 1 h extractions in which a maximum of 86, 84, 70, and 54% of the total soil Pb was removed with EDTA, ADA, PDA, and HCl, respectively. The soil was not treated to below the Pb regulatory lim...
TL;DR: In this article, stormwater data collected from an expressway in the Austin, Tex. area were used to develop regression models for predicting loads for a number of constituents commonly found in highway runoff.
Abstract: Storm-water data collected from an expressway in the Austin, Tex. area were used to develop regression models for predicting loads for a number of constituents commonly found in highway runoff. The goal of the model development was to identify the processes that affect the quality of highway runoff. Linear regression was selected as the most appropriate technique for analyzing the data because of its ability to identify constituent specific causal variables. The regression equations indicate that the majority of variations observed in highway storm-water loading can be explained by causal variables measured during the rainstorm event, the antecedent dry period, and the previous rainstorm event. Loads for each of the constituents were dependent upon a unique subset of the identified variables, indicating that processes responsible for the generation, accumulation, and washoff of storm-water pollutants are constituent specific. Loads of some constituents, such as total suspended solids, were dependent on th...
TL;DR: The genetic algorithm (GA) is found to be a useful calibration tool, capable of providing least-squares parameter estimates while incorporating field observations as constraints and accumulating useful information about the response surface.
Abstract: The genetic algorithm (GA) is used as an optimization tool to estimate water quality model parameters in a calibration scenario. The GA is found to be a useful calibration tool, capable of providing least-squares parameter estimates while incorporating field observations as constraints and accumulating useful information about the response surface. Because the GA provides a directed, randomized search using a population of points, a database of information about the response surface, parameter correlation, and objective function sensitivity to model parameters is obtained. Synthetic data with and without error are used initially to investigate the potential of the GA for model calibration applications. A case study is then carried out to confirm GA performance with field data. Constraints are included successfully in the GA search using either a penalty function or a special decoding operation. However, results show that the GA with the penalty function outperforms the GA with the decoder. Furthermore, parameter estimation is found to be improved by the inclusion of multiple-response data. For ill-posed problems, the GA provides several parameter estimates, all performing equally well mathematically.
TL;DR: In this paper, the authors compared trichloroethylene (PCE) and TCE to cast iron, graphite, and iron-containing minerals and found that non-reactive soprtion is due to exposed graphite inclusions in the cast iron.
Abstract: Tetrachloroethylene (PCE) and trichloroethylene (TCE) exhibited significant nonlinear sorption to nonreactive sites when exposed to four cast irons. Cast iron is a reactive material that promotes reductive dechlorination and has recently been used for \Iin-situ\N remediation of chlorinated solvent contminated ground water. Comparisons between PCE sorption to cast iron, graphite, and iron-containing minerals indicate that nonreactive soprtion is due to exposed graphite inclusions in the cast iron. Sorption of the homologous series of chloroethenes to a cast iron adheres to Traube’s rule; thus, the extent of sorption is related primarily to compound hydrophobicity. An analytical model incorporating rate-limited sorption/desorption to nonreactive sites was used to assess sorption nonequilibrium. Effective sorption and desorption rate coefficients determined how significant mass transfer limitations to nonreactive sorption sites exist for PCE and not for TCE. The nonreactive sorption observed indicates that flow-through cast iron treatment systems will exhibit significant delayed attainment of steady-state conditions for chlorinated ethenes, particularly PCE and TCE.
TL;DR: In this paper, a low lime fly ash with lime and gypsum was studied through large scale tests on the stabilized material designed to simulate field recycling conditions as closely as possible, and found to be a very effective means to control hydraulic conductivity and leachate characteristics.
Abstract: Disposal of fly ash on land amounts to sacrificing precious land space. Recycling of fly ash is one of the methods of solving the disposal problem. Stabilization of a low lime fly ash with lime and gypsum was studied through large scale tests on the stabilized material designed to simulate field recycling conditions as closely as possible, and found to be a very effective means to control hydraulic conductivity and leachate characteristics. The effects of moulding water content, lime content, gypsum content, curing period, and flow period on hydraulic conductivity, and on leachate of metals flowing out of the stabilized fly ash are reported herein. With proper proportioning of the mix, and adequate curing, the values of hydraulic conductivity on the order of 10\u–\u7 cm/s were achieved. The concentrations of As, Cd, Cr, Cu, Fe, Hg, Mg, Ni, Pb, and Zn in the effluent emanating from the hydraulic conductivity specimens of mixes with higher proportions of lime or lime and gypsum were below threshold limits acceptable for contaminants flowing into ground water.
TL;DR: In this paper, the aeration properties of a triangular plan labyrinth weir were investigated and it was shown that the aerated efficiency of these weirs generally is better than their equivalent-length linear weir and this advantage becomes more pronounced as the weir included angle becomes smaller and also at lower overfall drop heights and higher discharges.
Abstract: A high level of dissolved oxygen is vital for the maintenance of healthy streams and rivers. Structures in rivers can increase dissolved oxygen levels by creating turbulent conditions where small air bubbles are carried into the bulk of the flow. Plunging overfall jets from weirs are a particular instance of this, and the aeration properties of such structures have been studied widely in the laboratory and field over a number of years. On the other hand, labyrinth weirs, where the weir sill is cranked in planform thus increasing their length, have received little or no attention in this context. They have a proven hydraulic advantage over straight weirs of increased discharge at the same head for design conditions. However, they also serve to modify the combined overfall jet as individual jets from adjacent sections of the weir collide. This paper describes an experimental investigation into the nature of these jets and how they affect the aeration performance of a triangular plan labyrinth weir. It is demonstrated that the aeration efficiency of these labyrinth weirs generally is better than their equivalent-length linear weir and that this advantage becomes more pronounced as the weir included angle becomes smaller and also at lower overfall drop heights and higher discharges. These results point to the possible advantage of these type of weir in situations where both hydraulic and aeration performance needs to be optimized.
TL;DR: In this paper, the effects of solution chemistry, surface shear, and composition of natural organic matter (NOM) were investigated for their impact on accumulation of foulant material at the surface of charged polymeric nanofiltration membranes.
Abstract: The effects of solution chemistry, surface shear, and composition of natural organic matter (NOM) were investigated for their impact on accumulation of foulant material at the surface of charged polymeric nanofiltration membranes. The source of NOM was the Suwannee River. A bench-scale, batch recycle system was used with 20 hollow fiber, nanofiltration membranes. Membrane flux decline and foulant accumulation increased at low pH and high ionic strength as a result of neutralization of charge, electric double layer compression, and the apparent shift in conformation of charged NOM macromolecules. The rate of NOM accumulation decreased with operating time, suggestive of an eventual steady state between adsorption and desorption. The effect of NOM composition on membrane fouling could not be discerned by a standard technique to isolate hydrophobic and hydrophilic NOM fractions, quite possibly because of the fractionation methodology's failure to recover a small but important fouling fraction or because of NO...
TL;DR: In this article, a theory relating SOD to flow velocity using boundary layer concepts was presented and an experimental validation and extension of those results was performed in laboratory experiments in which sediments are exposed to water flowing at different velocities.
Abstract: Sedimentary oxygen demand (SOD) is the uptake of dissolved oxygen by sediments. The oxygen is removed from the water column by chemical oxidation and by the respiration of microbes in the sediments. In 1994, Nakamura and Stefan published a theory relating SOD to flow velocity using boundary layer concepts. This paper is an experimental validation and extension of those results. In this study, SOD is investigated in laboratory experiments in which sediments are exposed to water flowing at different velocities. The experiments were performed in a recirculating channel with well defined flow characteristics. The results verify that SOD increases linearly with the velocity of the water above the sediments when the velocities are low. As the velocity is increased, the SOD reaches an upper bound. Both the rate of increase with velocity as well as the upper bound of SOD were found to depend strongly on the sediment material, the benthic biology, and the temperature. Characterization of the highly variable benthi...
TL;DR: 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 as discussed by the authors, and the 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.
Abstract: 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. Re...
TL;DR: In this article, the mean multiplicative error (MME) metric was proposed for estimating the stream reaeration coefficient, which is equal to the geometric mean of the factors, greater than unity, by which estimates would have to be multiplied or divided to equal the corresponding measurements.
Abstract: Numerous equations employing depth, velocity, and slope have been developed to estimate the stream reaeration coefficient. These have been evaluated previously using statistics based on differential errors, which are shown to be biased toward underprediction. A new metric, the mean multiplicative error (MME), overcomes this defect and offers other advantages, including identical results for both reaeration and gas transfer coefficients and less sensitivity to extreme errors. It is equal to the geometric mean of the factors, greater than unity, by which the estimates would have to be multiplied or divided to equal the corresponding measurements. With the use of the MME to test 10 selected equations, against a compilation of field measurements based on gas tracers, current equations are shown to be of little value at low slopes, whereas some frequently used equations are shown to have little general value. Slope is found to be an essential component of reaeration equations. Recommendations are made for estimating the reaeration coefficient.
TL;DR: In this article, mixed cultures were enriched from three diverse soil sources: surface soil, subsurface soil, and river sediment, and three mixed cultures obtained from diverse soil samples were transferred to batch reactors and exhibited similar chromium reduction enzyme kinetics at stationary phase.
Abstract: Most previous studies of bacterial reduction of chromium have been done with pure cultures that are not likely to be found in ground water, and at hexavalent chromium concentrations much greater than typically present in contaminated ground water. Further, most previous work has been performed with complex laboratory substrates that would not be suitable for in situ application. In this study, mixed cultures were enriched from three diverse soil sources: surface soil, subsurface soil, and river sediment. The enrichment medium contained 10 mg Cr{sup 6+}/L and sucrose as the carbon source. The three mixed cultures obtained from the diverse soil samples were transferred to batch reactors and exhibited similar chromium reduction enzyme kinetics at stationary phase. The maximum specific reduction rates were between 0.98 and 3.3 mg Cr{sup 6+}/(g dry cells {center_dot} h) and the half velocity constants were between 0.39 and 1.48 mg Cr{sup 6+}/L. The relatively narrow range of values for kinetic parameters suggests that a conservative engineering design for in situ remediation could be applied over a wide range of contaminated sites at the Cr(VI) concentrations examined.
TL;DR: In this paper, the authors examined the solute exchange between sediments and the water column induced by the interaction of a current and a half-buried spherical obstruction, where the interaction results in pressure perturbations on the sediment surface, which in turn drive flows through the sediment.
Abstract: Laboratory experiments are used to examine solute exchange between sediments and the water column induced by the interaction of a current and a half-buried spherical obstruction The sphere is a model of a stone half buried in the bed of a stream or coastal sea The interaction results in pressure perturbations on the sediment surface, which in turn drive flows through the sediment This interaction can significantly enhance solute exchange Using an experimentally derived surface pressure field and a numerical transport model, the measured mass of effused solutes is accurately predicted, providing quantitative validity of the exchange mechanism To assess the biochemical significance of this exchange process, the behavior of a relative solute was simulated An example of a reactive solute of major significance to water quality in rivers is oxygen, which is consumed within sediments by oxidizing organic matter Depending on the water flow velocity, specific solute consumption rate, and properties of the s
TL;DR: In this article, the effect of temperature and caustic soda concentration in the bauxite digestion process on the settling behavior and the physical, chemical, and mineralogical characteristics of the derived red mud was investigated.
Abstract: The objective of the paper is to investigate the effect of temperature and caustic soda concentration in the bauxite digestion process on the settling behavior and the physical, chemical, and mineralogical characteristics of the derived red mud. The study was carried out on Jamaican bauxite. The results demonstrate the influence of the goethite-hematite conversion on the settling rate of red mud. This iron mineral transformation affects the specific gravity, which is one of the factors that affects the settling rate of the red muds. The iron conversion in turn is mainly affected by the temperature in the digestion step despite the variation of caustic soda concentration. The results also demonstrate that the specific surface area and the settling rate of red muds are inversely proportional and that a positive correlation exists between the amorphous and cryptocrystalline iron (Fed) and the settling rate of the Jamaican red muds.
TL;DR: In this paper, the reduction reaction is coupled to the oxidation of Fe(II) sorbed on iron corrosion products such as hematite, which is indicated by the equilibrium E{sub h} values measured during uranium immobilization and PCE degradation reactions of zerovalent iron.
Abstract: Uranium (UO{sub 2}{sup 2+}) and chlorinated aliphatics [tetrachloroethane (PCE) and trichloroethane (TCE)] can be reduced and thus immobilized or degraded, respectively, by the same abiotic mechanism. In this mechanism the reduction reaction is coupled to the oxidation of Fe(II) sorbed on iron corrosion products such as hematite. This is indicated by the equilibrium E{sub h} values measured during uranium immobilization and PCE degradation reactions of zerovalent iron. These values fit closely with those measured in the Fe(II)-{alpha}Fe{sub 2}O{sub 3}-H{sub 2}O system (in the absence of U or PCE), not those of the Fe(o)/Fe(II) or H{sub 2}(g)/H{sub 2}O couples. Because iron (II) is very unstable in environments that are not strictly anaerobic, Fe(o) serves as a source of Fe(II). The reduction kinetic rate, analyzed in detail for the reduction of U(VI), is found to be a function of the concentration of OH{sup {minus}}, Fe{sup 2+} and reactive surface sites, and is given in terms of sorbed species concentrations by {l_brace}d[U(VI)]{sub ads}{r_brace}/dt = {l_brace}{minus}k{prime}[{triple_bond}FeOFeOH{sup 0}][U(VI)]{sub ads}{r_brace}. This rate law applies to organic pollutants as well, as long as they can be reduced by surface Fe(II): {l_brace}d[Pollutant]{r_brace}/dt = {l_brace}{minus}k{prime}[{triple_bond}FeOFeOH{sup 0}][Pollutant]{r_brace}. This mechanism suggests new possibilities for the improvement of low-cost decontamination techniques formore » U- and chlorinated aliphatic-rich waters.« less