Journal of Environmental Engineering

As an increasingly adopted storm-water best management practice (BMP) to remedy hydrology and water quality impairment from urban development, bioretention facilities need rigorous investigation to quantify performance benefits and to allow design improvements. This study examines water quality improvements [total arsenic, total cadmium, chloride, total chromium, total and dissolved copper, E. coli, fecal coliform, lead, mercury, nitrogen species, oil and grease, phosphorus, total organic carbon (TOC), total suspended solids, and total zinc] via monitoring for a 15-month period at two bioretention cells in Maryland. Both bioretention cells effectively removed suspended solids, lead, and zinc from runoff through concentration reduction. Runoff volume reduction promotes pollutant mass removal and links BMP water quality benefits with hydrologic performance. From a load perspective $\left(\text{kg}/\text{ha}\text{year}\right)$ , all but TOC at one cell showed pollutant reduction. Bioretention effluents exhibited good water quality for all significant pollutants except for nitrate, copper, and phosphorus in one cell, the latter two of which may be attributed to media organic matter dissolution. Copper dissolved/particulate analyses showed that significant changes in copper speciation behavior result from transport through the bioretention media.

A study was conducted in western North Carolina, along the southeastern extent of the U.S. trout populations, to examine the effect of bioretention areas on runoff temperature. Four bioretention areas were monitored during the summers of 2006 and 2007. It was found that smaller bioretention areas, with respect to the size of their contributing watershed, were able to significantly reduce both maximum and median water temperatures between the inlet and outlet. The proportionately larger bioretention areas were only able to significantly reduce maximum water temperatures between the inlet and outlet; however, these systems showed evidence of substantial reductions in outflow quantity, effectively reducing the thermal impact. Despite temperature reductions, effluent temperatures still posed a potential threat to coldwater streams during the peak summer months. During the summer months, effluent temperatures were generally coolest at the greatest soil depths, supporting evidence of an optimum drain depth between 90 and 120 cm. The ability of bioretention areas to reduce storm-water temperature and flows supports their application to reduce the thermal impacts of urban storm-water runoff.

Excessive quantities of nutrients in urban storm-water runoff can lead to problems such as eutrophication in receiving water bodies. Accurate process based models are difficult to construct due to the vast array of complex phenomena affecting nutrient concentrations. Furthermore, it is often impossible to successfully apply process based models to catchments with limited or no sampling. This has created the need for simple models capable of predicting nutrient concentrations at unmonitored catchments. In this study, simple statistical models were constructed to predict six different types of nutrients present in urban storm-water runoff: ammonia $\left({\text{NH}}_3\right)$ , nitrogen oxides $\left({\text{NO}}_x\right)$ , total Kjeldahl nitrogen, total nitrogen, dissolved phosphorus, and total phosphorus. Models were constructed using data from the United States, collected as a part of the Nationwide Urban Stormwater Program more than two decades ago. Comparison between the models revealed that regression models were generally more applicable than the simple estimates of mean concentration from homogeneous subsets, separated based upon land use or the metropolitan area. Regression models were generally more accurate and provided valuable insight into the most important processes influencing nutrient concentrations in urban storm-water runoff.

An existing accumulation and wash-off model was applied and calibrated on a standard asphalt parking lot located in the northeastern United States. The field measured data consisted of rainfall, flow, and runoff samples taken from over 26 storm events monitored from 2004 to 2006. The contaminants under consideration include: total suspended solids, total petroleum hydrocarbons-diesel range hydrocarbons (TPH-D), dissolved inorganic nitrogen (DIN) (comprised of nitrate, nitrite, and ammonia), and zinc (Zn). The objective of the study was to provide probability distributions of model parameters for contaminants that have not been documented much (TPH-D, DIN, and Zn). The best fitting parameter values were found on a storm by storm basis. Subsequently, the range and variability of these parameters are provided for modeling purposes and other urban storm-water quality applications. A normal distribution was fitted to the optimized model parameter values to describe their distributions. A simulated annealing algorithm was used as the parameter optimization technique. Several examples are given to illustrate the methodology and the performance of the model. Finally, a Monte Carlo simulation was performed to assess the capability of the model to predict contaminant concentrations at the watershed’s outlet.

Volumetric clarification is a common storm-water unit operation for hydrologic attenuation that couples particulate matter (PM) separation. Recent volumetric clarification can also include integrated filtration. This study examines the unsteady hydraulic and head loss response of a volumetric clarifying filter (VCF) system to urban source area hydrologic loadings in Baton Rouge, La for 19 fully captured events. The rainfall-runoff response of the $\mathrm{1,088}{\text{m}}^2$ paved watershed is examined as a direct VCF loading. Watershed responses yielded two classes of behavior; high volume events with an equilibrium volumetric runoff coefficient from 0.6–0.8 while low volume events were 0.4–0.6. Runoff PM as suspended sediment concentration (SSC) yielded coarse heterodisperse influent particle-size distributions (PSDs); transformed to finer and more monodisperse PSDs after treatment. While event-mean head loss is less than 25 mm, instantaneous values up to 200 mm were dependent on instantaneous flow to the filters. Without backwashing, filter ripening head loss is small due to the coarse uniform filter media and radial filter configuration, with a loss of 2% porosity across the series of 19 events. Despite filter ripening an Ergun model was capable of predicting head loss across the entire flow rate range. Head loss and flow frequency distributions were exponential. Results indicate that a volumetric clarifier, filter geometry, and engineered media combination are capable of reducing effluent SSC to $<30\text{mg}/\text{L}$ through serial mechanisms of sedimentation followed by filtration.

Many pollutants in storm-water runoff associate with the particulate fraction, as well as cause receiving water degradation themselves. Therefore, removing a substantial amount of the solids (such as all particles above a critical particle size) can reduce the concentrations of many pollutants. Enhanced sedimentation methods have been encouraged to reduce the footprint of treatment devices and meet the 80% suspended solids reduction goal established in many locations. Inclined plates/tube settlers, where overlapping plates result in large settling areas and small device footprints, treated multiple contaminants when operated in laminar flow conditions (Pitt et al. 1999). This project extends that work by investigating the potential of inclined plate settlers to treat runoff when Reynolds numbers ranged from 7.5 to 50,000. These settlers achieved high removals for particles with a density of sand over the range of Reynolds’ numbers. The influent-to-effluent median particle-size reduction in field testing was $80–11\mu \text{m}$ .

The feasibility of enhancing suspended solids settling by using the newly proposed vortex plates in clarifiers, instead of conventional smooth lamellae, was studied using computational fluid dynamics (CFD) modeling and laboratory experiments in which suspended particles were mimicked by crushed walnut shells and glass beads. The vortex plate was formed by attaching perpendicular ribs to the plate, forming slots of $25\times 25\text{mm}$ $\left(\text{depth}\times \text{width}\right)$ and placing the plate parallel to the longitudinal clarifier axis at an angle of 60° from the horizontal. Rib walls were placed either in vertical planes, perpendicular to the clarifier longitudinal axis, or were slightly sloping in the main flow direction (20° about the vertical). Three hydraulic concepts were explored with respect to enhancing suspended particle settling: (1) the use of flow energy to generate steady vortices inside the slots and thereby entrain particles into the slots, where they would be sheltered from the fast horizontal flow and could settle without much hindrance; (2) enhancing the particle settling by increasing the contact surface area and thereby reducing the length of travel of settling particles; the same principle is used in conventional lamellar settlers but the surface area of a vortex plate is three times that of a smooth lamella; and (3) increasing the particle collision frequency within the swirling flow inside slots to prompt particle flocculation. The CFD modeling and experimental observations confirmed the formation of strong vortices in the parallel slots of the vortex plate. Such vortices entrained the passing by particles and retained some of them in slots, which provided a quiescent settling zone. Both the simulation and measured results indicated that the vortex plate contributed to a slightly improved removal of suspended particles. A CFD particle tracking model was applied to clarifiers with two vortex plates or two smooth plates and indicated that the vortex plate removed about 8% more particles than the smooth plate. In laboratory tests with plate arrays, the vortex plate array also contributed to better particle removals, especially for slower settling particles and larger inflow rates (by up to 26%).

This study examined the effects of uncertain model boundary conditions on dissolved oxygen (DO) predictions for the lower Truckee River, Nevada using an augmented version of the EPA’s Water Quality Analysis Simulation Program Version 5 (WASP5) that included periphyton, or attached algae, in eutrophication kinetics. Uncertainty analyses were performed on selected organic nitrogen (ON) and carbonaceous biochemical oxygen demand boundary conditions using Monte Carlo techniques. The stochastic model was run using boundary concentrations assigned from observed probability distributions. Ranges of simulated values were used to construct confidence intervals, the magnitudes of which indicated the uncertainty associated with model predictions. Uncertainty in agricultural ditch return concentrations had minimal effects on in-stream model predictions, as predicted values of daily minimum and maximum DOs, daily average ON, and periphyton biomass all failed to show significant variability as a result of ditch concentration uncertainty. This result indicates that while ditch return nutrient loads are not trivial, their exact concentrations are not needed to make relatively accurate predictions of in-stream DO. However, uncertainty in the upstream ON boundary did result in significant uncertainty during summer months with regard to in-stream model predictions of ON, periphyton biomass, and DO. The model is clearly more sensitive to changes in this boundary than to changes in agricultural ditch concentrations.

Nutrient enrichment of the South Umpqua River, Oregon was linked to periphyton growth and large diel fluctuations in dissolved oxygen and hydrogen ion (pH) concentrations using the water quality model QUAL2Kw. The available data provide a good case study for the relatively new water quality model. QUAL2Kw simulates a dynamic diel heat budget and water quality kinetics for a one-dimensional, steady-flow system and is part of a family of models meant to serve as an update to the widely used QUAL2E. The model was used to quantify nonpoint source loading, determine the pollutant of concern, estimate natural conditions, and calculate a phosphorus total maximum daily load during summer, low-flow conditions. Control of both nonpoint and point sources is required to achieve the low instream phosphorus concentrations necessary to meet water quality criteria. To our knowledge, this is the first paper that reports on the application of a model for computing the maximum allowable load necessary to manage the diel variation in pH.

A theoretical model is developed to predict the wind-streamflow-driven gas-liquid transfer rate. When wind blows over the stream surface, turbulence is generated at both the air-water interface and the water-bed interface, which is the driving force of the surface renewal movement of water parcels. The total surface renewal rate is considered as the sum of the effective surface renewal rates driven by the turbulence generated at these two interfaces. The gas-liquid transfer rate is formulated as a function of the total surface renewal rate based on the surface renewal theory. The concept of serial resistance, shear velocity, and effective viscous layer play significant roles in the model development. This model correlates the gas-liquid transfer rate with the dynamic fluid parameters such as wind speed and stream velocity. The predictions of this model show good agreement with existing experimental data. This model can be applied to predict the gas-liquid transfer rate in wind-streamflow-driven systems.

A risk based approach to engineering provides a rational way to balance cost against the need to avoid failure. Such an approach has not been systematically incorporated into the design and operation of wastewater treatment plants. This is perhaps because engineers do not have the means to make risk based predictions of performance. We have adapted a classical technique for incorporating risk in engineering predictions to the oxidation of ammonia, the first step in nitrification. The approach incorporated random changes in load, aeration, and kinetic parameters. Two and three species models were used to evaluate the effect of increasing aeration on the risk of failure. Surprisingly, increased aeration did not lead to a monotonically decreasing risk of failure. Intermediate aeration rates typically increased the standard deviation of the effluent ammonia and thus the risk of failure. Reliable performance was predicted when there was a high abundance of one species or a similar abundance of both. These preliminary but encouraging results suggest risk based approaches offer new and important insights into the operation of biological treatment systems.

A technology was developed to stimulate autotrophic biological denitrification by supplying hydrogen $\left({\text{H}}_2\right)$ to groundwater via gas-permeable membranes. The purpose of this project was to investigate this technology at field scale, determining whether it could be successfully scaled up from the laboratory. The field site was located in Becker, Minnesota and contained high levels of ${\text{NO}}_3^{-}$ $\left(22.8\pm 2.0\text{mg}/\text{L-N}\right)$ and dissolved oxygen (DO) $\left(7\pm 1\text{mg}/\text{L}\right)$ . Membranes installed in groundwater wells were successful in delivering ${\text{H}}_2$ to the groundwater over the two-year operating period. Hydrogen stimulated microbial reduction of DO and ${\text{NO}}_3^{-}$ , degrading up to 6 mg/L DO and converting up to 10.0 mg/L ${\text{NO}}_3^{-}\text{-N}$ to ${\text{NO}}_2^{-}\text{-N}$ when operated passively. When recirculation pumps were installed performance in the field did not improve significantly because of mixing with more oxygenated water. However, complementary modeling studies showed that complete DO reduction and denitrification to ${\text{N}}_2$ was possible but the zone of influence and total ${\text{H}}_2$ demand were limiting factors. Water was recirculated in the field from downgradient to upgradient membrane-containing wells to increase the ${\text{H}}_2$ delivery through the membrane by an increase in water velocity. The depth to groundwater $\left(\sim 13.7\text{m}\right)$ caused some water reoxygenation during recirculation, which may preclude the use of this technology at deep sites, as this makes it more difficult to install sufficient wells and control recirculation.

This paper presents a laboratory investigation of hydraulic conductivity of municipal solid waste (MSW) in landfills and provides a comparative assessment of measured hydraulic conductivity values with those reported in the literature based on laboratory and field studies. A series of laboratory tests was conducted using shredded fresh and landfilled MSW from the Orchard Hills landfill (Illinois, United States) using two different small-scale and large-scale rigid-wall permeameters and a small-scale triaxial permeameter. Fresh waste was collected from the working phase, while the landfilled waste was exhumed from a borehole in a landfill cell subjected to leachate recirculation for approximately 1.5 years. The hydraulic conductivity tests conducted on fresh MSW using small-scale rigid-wall permeameter resulted in a range of hydraulic conductivity $2.8\times {10}^{-3}–11.8\times {10}^{-3}\text{cm}/\text{s}$ with dry unit weight varied in a narrow range between $3.9–5.1\text{kN}/{\text{m}}^3$ . The landfilled MSW tested using the same permeameter produced results between $0.6\times {10}^{-3}$ – $3.0\times {10}^{-3}\text{cm}/\text{s}$ for $4.5–5.5\text{kN}/{\text{m}}^3$ dry unit weights. The hydraulic conductivity obtained from large-scale rigid-wall permeameter tests decreased with the increase in normal stress for both fresh and landfilled waste. The hydraulic conductivity for fresh MSW ranged from 0.2 cm/s for $4.1\text{kN}/{\text{m}}^3$ dry unit weight (under zero vertical stress) and then decreased to $4.9\times {10}^{-5}\text{cm}/\text{s}$ for $13.3\text{kN}/{\text{m}}^3$ dry unit weight (under the maximum applied normal stress of 276 kPa). The hydraulic conductivity of the landfilled MSW decreased from 0.2 cm/s to $7.8\times {10}^{-5}\text{cm}/\text{s}$ when the dry unit weight increased from 3.2 to $9.6\text{kN}/{\text{m}}^3$ . The results clearly demonstrated that the hydraulic conductivity of MSW can be significantly influenced by vertical stress and it is mainly attributed to the increase in density leading to low void ratio. In small-scale triaxial permeameter, when the confining pressure was increased from 69 to 276 kPa the hydraulic conductivity decreased from approximately ${10}^{-4}\text{to}{10}^{-6}\text{cm}/\text{s}$ , which is much lower than those determined from rigid-wall permeameter tests. The published field MSW hydraulic conductivities are found to be higher than the laboratory results. Landfilled MSW possesses lower hydraulic conductivity than fresh MSW due to increased finer particles resulting from degradation. The decreasing hydraulic conductivity with increasing dry unit weight is expressed by an exponential decay function.

Oxygen transfer is one of the key processes in the bioreactor. Herein a computational fluid dynamics model for the oxygen transfer in high-speed surface aeration tank has been developed and validated through a full-scale aeration test. The test results indicate that the oxygen transfer mainly comes from the spray water in air and that the gas entrainment by the plunging of spray water and the surface reaeration in the aeration tank contribute little to the total oxygen transfer in high-speed surface aerator. A simple method was proposed to measure the oxygen transfer rate for high-speed surface aerator.

The objective of this paper is to evaluate the change in Bacillus subtilis spore survival and dimensions following ultraviolet and chlorine disinfection in water. Disinfection was monitored by using tools such as atomic force microscopy (AFM), particle sizing by the electrozone sensing technique and fluorescence of spores after staining with an optical brightener. Results indicated that there was a change in the adsorbed fluorescence following chlorine; however, the magnitude of this change was only approximately twofold at 90% of spore kill. In addition, changes in spore particle-size distribution following chlorine occur at above 99.9% of spore kill. Even the roughness (RMS), width, and length of spores as measured by AFM change only after about 99% of spore killing with chlorine. Use of optical brighteners, AFM, and sizing are not sensitive enough for detecting the disinfection of chlorine-resistant spores and as expected no changes occurred with ultraviolet treated spores. Even though, these techniques may have the potential for determining oxidative disinfection and for the development of monitors and sensors of chemical disinfection for chlorine-sensitive microorganisms.

Fluidization of biogranules in an anaerobic expanded granular sludge bed (EGSB) reactor is stochastic in nature and it is a function of the size distribution and the frequency of generation of flow-through gas bubbles in the reactor. Other factors that contribute to the distribution of granules along the height of the reactor are the settling characteristics of granules and the fluid velocity. A simulation was conducted in a test column to obtain a relationship between the flow-through gas and granules at different heights along the column. This relationship was combined with the pattern of gas flow through an identical EGSB reactor to create a model to predict the concentration of granules at different heights along the reactor. The model can predict well the stochastic nature of the axial distribution of granules but underestimates the number of granules at different heights. The reasons for such deviations are explained. The pattern of granule shedding from the primary wake associated with spherical cap bubbles and terminal velocities of bubbles have also been studied and modeled to estimate the maximum height of ascent of granules under isolated spherical cap bubbles. The results of this model agreed well with the experimental observations.

Arsenite [As(III)] oxidation by Thiomonas arsenivorans Strain b6 was investigated in batch reactors at pH 6 and $30°\text{C}$ over As(III) concentrations ranging from 10 to 1,000 mg/L in the absence of added organic carbon. Strain b6 completely oxidized As(III) to arsenate [As(V)] during exponential growth phase for lower levels of As(III) concentrations $\left(\le 100\text{mg}/\text{L}\right)$ . At higher levels of 500 and 1,000 mg/L, As(III) oxidation was observed mostly in the exponential phase but continued into the stationary phase of growth. The Haldane substrate inhibition model was used to estimate biokinetic parameters for As(III) oxidation. The best fit parameters of half saturation constant $K_s=33.2\pm 1.87\text{mg}/\text{L}$ , maximum specific substrate utilization rate $k=\left(0.85\pm 0.18\right)\text{-mg}$ As(III)/mg dry cell weight/h, substrate inhibition coefficient $K_i=602.4\pm 33.6\text{mg}/\text{L}$ , yield coefficient $Y=\left(0.088\pm 0.0048\right)\text{-mg}$ cell dry weight/mg As(III), and endogenous decay coefficient $k_d=0.006\pm 0.002{\text{h}}^{-1}$ were obtained using the Adams-Bashforth-Moulton algorithm and nonlinear regression technique. Sensitivity analysis revealed that $Y$ and $K_i$ are the most sensitive to model predictions, while $k_d$ is the least sensitive to model simulation at both low and high concentrations of As(III).

The present study involves the treatment of high strength Bulk Drug Industry Wastewater by electrochemical method. The treatability studies were carried out with four different electrodes made of mild steel, aluminum, carbon, and stainless steel. The treatment efficiencies for chemical oxygen demand (COD)/biochemical oxygen demand (BOD), color, and heavy metal removals were assessed at different electrolysis time. A comparative study for heavy metal removal between chemical precipitation using aluminum and electrocoagulation with aluminum electrode has shown electrocoagulation to be more effective. Carbon electrode has shown COD removal of 34.0% and high ${\text{BOD}}_{5f}/{\text{COD}}_f$ ratio of 0.581 at 120-min exposure time. Among all electrodes, aluminum was found as the most efficient in removal of color, suspended solids, and heavy metals with the least energy consumption of $95.83\text{Wh}{\text{kg}}^{-1}{\text{COD}}_r$ and anode efficiency of $5.76\text{kg}\text{COD}{\text{A}}^{-1}{\text{m}}^{-2}{\text{h}}^{-1}$ . After electrochemical treatment, certain increase in BOD/COD ratio attributed to increase in biodegradability of wastewater. The study reveals that the wastewater could be effectively pretreated by electrochemical method.

For a wastewater collection system, the maximum volume that can be attained with an inline storage pipe is shown to occur when the pipe diameter is chosen to be 2/3 of the thickness of soil profile available for burial of the storage pipe, irrespective of pipeline slope.