Journal of Environmental Engineering

A microbial dissolved oxygen (DO) uptake model was developed for a stream bed, including the effect of turbulence in the flow over the bed and pore water flow in the porous bed. The fine-grained sediment bed has hydraulic conductivities $0.01\le k\le 1\mathrm{cm}/\mathrm{s}$, i.e., sediment particle diameter $0.006\le d_s\le 0.06\mathrm{cm}$. The pore water flow is driven by pressure fluctuations at the sediment-water interface, mostly attributable to near-bed coherent motions in the turbulent boundary layer above the sediment bed. An effective mass transfer coefficient ($D_e$) coupled to a pore water flow model was used in the DO transport and DO uptake model. DO flux across the sediment-water interface and into the sediment, i.e., sedimentary oxygen demand (SOD), was related to hydraulic conductivity and microbial oxygen uptake rate in the sediment and shear velocity at the sediment-water interface. Simulated SOD values were validated against experimental data. For hydraulic conductivities of the sediment bed up to $k\approx 0.01\mathrm{cm}/\mathrm{s}$, the pore water flow effect on SOD was found negligible. Above this threshold, the effective mass (DO) transfer coefficient in the sediment bed ($D_e$) becomes larger as the hydraulic conductivity ($k$) becomes larger as the interstitial flow velocities increase; consequently, DO penetration depth increases with larger hydraulic conductivity of the sediment bed ($k$), and SOD increases as well. The enhancement of vertical DO transport into the sediment bed is strongest near the sediment-water interface, and rapidly diminishes with depth into the sediment layer. An increase in shear velocity at the sediment-water interface also enhances DO transfer. Shear velocity increases at the sediment-water interface will raise SOD regardless of the maximum oxidation rate if the hydraulic conductivity is above the threshold of $k\approx 1\mathrm{cm}/\mathrm{s}$. The relationship is nearly linear when $U_{*}<0.8\mathrm{cm}/\mathrm{s}$. At shear velocity $U_{*}=1.6\mathrm{cm}/\mathrm{s}$, SOD for oxidation rates $\mu =1000$ and $2000\mathrm{mg}{\mathrm{l}}^{-1}{\mathrm{d}}^{-1}$ are almost five times larger than those with no pore water flow. When pore water transport of DO is not limiting, SOD is a linear function of oxygen demand rate $\mu$ in the sediment when $0\le \mu \le 200\mathrm{mg}{\mathrm{l}}^{-1}{\mathrm{d}}^{-1}$.

A Bayesian statistical approach for determining the parameter uncertainty of a storm-water treatment model is reported. The storm-water treatment technologies included a sand filter and a subsurface gravel wetland. The two field systems were loaded and monitored in a side-by-side fashion over a two-year period. The loading to each system was storm-water runoff generated by ambient rainfall on a commuter parking lot. Contaminant transport is simulated by using a one-dimensional advection-dispersion model. The unknown parameters of the model are the contaminant deposition rate and the hydrodynamic dispersion. The following contaminants are considered in the study: total suspended solids, total petroleum hydrocarbons–diesel range hydrocarbons, and zinc. Parameter uncertainties are addressed by estimating the posterior probability distributions through a conventional Metropolis-Hastings algorithm. Results indicate that the posterior distributions are unimodal and, in some instances, exhibit some level of skewness. The Bayesian approach allowed the estimation of the 10th, 25th, 50th, 75th, and 95th percentiles of the posterior probability distributions. The prediction capabilities of the model were explored by performing a Monte Carlo simulation using the calculated posterior distributions and two rainfall-runoff events not considered during the calibration phase. The objective is to estimate effluent concentrations from the treatment systems under different scenarios of flow and contaminant loads. In general, estimated effluent concentrations and the total estimated mass fell within the defined uncertainty limits.

Over the last three decades, storm-water quality modeling has been used increasingly commonly to describe the general system behavior and assess the pollution loads transferred in and spilled out of combined sewer systems. The calibration of quality models is, in most cases, based on conventionally obtained calibration data, e.g., by automated sampling. Long-term high-resolution online measurement data are available for the Graz West catchment (Graz, Austria), allowing an assessment of the full dynamics of discharge and pollution concentrations. This paper focuses on the application and comparison of single-event and two different multievent optimization schemes for sewer-water quality model calibration. While both single- and multievent optimization lead to satisfying results for the calibration events in discharge calibration, it is shown that validation events are better reproduced by using multievent calibration. Single- and multievent autocalibration of pollution concentration is based on the best dataset obtained from the discharge calibration. As for discharge, the pollutographs are reproduced satisfactorily, and multievent calibration is more stable. In all cases, the two multievent approaches performed equally well.

The aim of this work was to determine if the aging of polyethylene (HDPE, PEX-A and PEX-B) water pipes by exposure to chlorinated water altered polar and nonpolar contaminant diffusivity and solubility by analyzing new, laboratory-aged, and exhumed water-distribution system polyethylene (PE) pipes. After 141 days of aging in pH 6.5 water with $45\mathrm{mg}/\mathrm{L}$ free chlorine, the surface chemistry and bulk properties of PEX-A pipe were unaffected. Carbonyl bonds ($\sigma =1,713{\mathrm{cm}}^{-1}$) were detected on the surfaces of HDPE and PEX-B pipe, and these oxygenated surfaces became more hydrophilic, resulting in statistically significant increases in diffusion rates. All 10 contaminant and four pipe material combinations had diffusivity increases on average of 50% for polar contaminants and 5% for nonpolar contaminants. Contaminant solubility was slightly increased for aged PEX-A and slightly decreased for PEX-B pipes. Toluene and trichloromethane diffusivity and solubility values for 7- to 25-year-old buried water utility pipes were similar to values for new and laboratory-aged HDPE-based materials. Because chlorinated water exposure alters how polar contaminants interact with aged PE pipes, results of this work should be considered in future health risk assessments, water quality modeling, pipe performance, and service-life considerations.

This paper presents results describing the effectiveness of chlorine dioxide penetration into a drinking-water distribution system biofilm/corrosion matrix and decontamination of adhered Bacillus globigii spores, a surrogate for Bacillus anthracis. Biofilm and corrosion products were developed using biofilm annular reactors containing oxidized scaled, iron coupons. Reactors were inoculated with B. globigii spores after biofilm development, and decontamination was undertaken with bulk-phase chlorine dioxide concentrations of 5, 10, 15, and $25\mathrm{mg}/\mathrm{L}$. Initial biofilm viable B. globigii spore densities of ${10}^6\mathrm{CFU}/{\mathrm{cm}}^2$ were reduced to 50 to $300\mathrm{CFU}/{\mathrm{cm}}^2$ at chlorine dioxide concentrations of 25 and $15\mathrm{mg}/\mathrm{L}$, respectively, within 6 days. B. globigii spore distribution throughout the biofilm/corrosion matrix depth and the change in viable spore count during chlorine dioxide disinfection were examined using a microslicing technique. Four layers of 360 μm thickness were sliced, and these showed that B. globigii spores were equally distributed throughout the biofilm/corrosion matrix depth. Furthermore, chlorine dioxide acted on all layers simultaneously, but spores still persisted in the deepest layer of the biofilm/corrosion matrix after 6 days of disinfection at 15 and $25\mathrm{mg}/\mathrm{L}$ chlorine dioxide.

Study of flow pattern and chlorine distribution is of major interest in the characterization, design, and evaluation of service conditions of a service reservoir. With the advancement of computational science and resources, the computational fluid dynamics (CFD) method could be a reliable alternative to flow and tracer tests. A salient feature of flow in the service reservoir is the changing inflow and outflow caused by variations in water demand and supply. To overcome the challenge of tracking water-level variations, two different numerical methods (i.e., multiphase analysis and dynamic meshes) were implemented in this study. The multiphase analysis demonstrates that sloshing of water is not significant because of the relatively low velocity in contrast to the large dimensions of the service reservoir. Therefore, it is valid to assume that the water-air interface remains as a horizontal plane. Dynamic meshes are then used to track the water-level variations to reduce the computational cost. The predicted chlorine concentration at the outlet matches well with that of on-site measurement. The study on a common service condition reveals short-circuiting of the flow. The subsequent formation of recirculation zones implies poor lateral and moderate vertical mixings, which result in nonuniform chlorine distribution in the reservoir. To provide the spatial distributions of the local mean residence time of the chlorine, the “mean age” concept was introduced in the present study. It can be used as a quantitative indicator to guide the design of service reservoirs for achieving a homogenous chlorine distribution.

Enhancements to the two-dimensional lake and reservoir water quality model W2Tn to simulate the effects of currents and waves on sediment resuspension and turbidity are described. Bed stress attributable to currents was computed by the hydrothermal component of W2Tn, whereas a surface wave component was added to W2Tn to determine bed stress owing to waves. Resuspension flux is computed from bed stress and is included as a source of turbidity to the water column. The model is tested through application to Schoharie Reservoir, a drinking water supply that experiences episodes of elevated turbidity caused by runoff events and exacerbated by drawdown. Model predictions of bed stress attributed to currents are validated by using measurements obtained from acoustic Doppler instrumentation. The surface wave component of the model is established on a framework that has been previously validated for Schoharie Reservoir. Testing of the enhanced turbidity component of W2Tn was completed for a 3.5-year period of historical observations, which included a number of runoff events covering a range of severity and variations in reservoir drawdown. The enhanced model performed well in simulating observed conditions in the water column. The resuspension mechanism made a significant contribution to the predicted turbidity during periods of reservoir drawdown and during a severe runoff event. The model also performed well in simulating the observed turbidity of the drinking water withdrawal. Resuspension of particles contributing to turbidity was largely attributable to reservoir currents with surface wave-induced resuspension playing a smaller role. The potential application of this model to other water bodies and water quality issues is discussed.

Optimization of organic matter (OM) removal is of key importance for effective water treatment, as its presence affects treatment processes. In particular, OM increases the operational cost of treatment caused by increased coagulant and disinfectant demands. In the work reported here, fluorescence spectroscopy is used to assess the effect of changing coagulation pH on OM removal, character, and composition. The results of a 3-month trial of low pH coagulation operation at a major surface water treatment works in the Midlands region of the UK are discussed, together with the effect upon total organic carbon (TOC) removal. OM removal was assessed on the basis of both measured removal and fluorescence-inferred removal (through intensity-reduction measurements). Fluorescence spectroscopy demonstrated that optimized coagulation affects the quantitative and qualitative OM properties. Fluorescence analyses were shown to complement other OM measurements, with reductions of peak intensities correlating well with removal of TOC in a range of different treatment conditions.

In this study, a four-phase remedial scheme was developed for in situ cleanup of petroleum-hydrocarbon contaminated soils. The developed remedial scheme contained the following four phases: surfactant flushing, groundwater flushing, chemical oxidation using ${\mathrm{KMnO}}_4$ as the oxidant, and enhanced bioremediation. Laboratory bench-scale experiments were performed to evaluate the effectiveness of this developed remedial scheme on the treatment of diesel oil contaminated soils. In the surfactant and groundwater flushing batch experiment (the first and second phases), biodegradable surfactant, Simple Green (SG) (5% by weight) was applied to flush diesel oil contaminated soils with initial total petroleum-hydrocarbon (TPH) concentration of approximately $31,500\mathrm{mg}{\mathrm{kg}}^{-1}$. Results show that more than 90% of TPH could be removed after flushing with 40 pore volumes (PVs) of SG, followed by 25 PVs of groundwater. In the ${\mathrm{KMnO}}_4$ oxidation experiment (third phase) with initial soil TPH concentration at approximately $4,900\mathrm{mg}{\mathrm{kg}}^{-1}$, up to 65% of TPH removal efficiency can be obtained when 1% by weight of ${\mathrm{KMnO}}_4$ was applied for oxidation. Results also reveal that the slight increase in TPH removal was observed in experiments with SG addition (0.1% by volume) owing to increased dissolution and desorption of TPH from soils. In the enhanced bioremediation (fourth phase) batch experiments, a petroleum-hydrocarbon degrading bacterium was isolated from the soil materials after the ${\mathrm{KMnO}}_4$ oxidation experiments and identified as Pseudomonas sp. via biochemical tests and further confirmation of DNA sequencing. Results from biodegradation experiments indicate that the isolated bacterium, which survived after ${\mathrm{KMnO}}_4$ oxidation process, was capable of degrading TPH caused by diesel oils, and caused the TPH to drop from $2,105$ to $487\mathrm{mg}{\mathrm{kg}}^{-1}$ within 15 days of incubation. The effectiveness of the four-phase remedial scheme was further confirmed by a semicontinuous batch experiment. Results from this study indicate that the four-phase scheme is a promising technology for the treatment of petroleum-hydrocarbon contaminated soils.

A ${\mathrm{TiO}}_2/\mathrm{\text{hydroxyapatite}}$ composite (Ti-HAP) was prepared by a hydrothermal method with hydroxyapatite and titanium sulfate and tested for photocatalytic degradation of methyl orange with an 8 W ultraviolet (UV) lamp irradiation. The properties of Ti-HAP were characterized by X-ray diffraction, scanning electron microscope, and Fourier transform infrared spectroscopy (FT-IR) analysis. The effect of the $\mathrm{Ti}/(\mathrm{Ca}+\mathrm{Ti})$ mole ratio on the photocatalytic degradation efficiency of methyl orange by Ti-HAP and the photocatalytic degradation dynamics were investigated. The results show that the addition of Ti slightly changes the structure of HAP. A higher $\mathrm{Ti}/(\mathrm{Ca}+\mathrm{Ti})$ mole ratio results in the generation of anatase in Ti-HAP and higher removal efficiency of methyl orange by Ti-HAP under UV irradiation. The removal efficiency decreases with the initial content of methyl orange increasing from $10–200\mathrm{mg}/\mathrm{L}$. The photocatalytic degradation process of methyl orange by Ti-HAP and HAP follow the Langmuir-Hinshelwood kinetics model.

Watershed recovery from acidic deposition, such as the Noland Divide Watershed in the Great Smoky Mountains National Park, is difficult to predict because of complex biogeochemical processes exhibited in soils. Laboratory soil columns and in situ pan lysimeters were used to investigate soil solution response to simulated reductions in acid deposition. Controlling for influent ${\mathrm{SO}}_4^{2-}$, ${\mathrm{NO}}_3^{-}$, and ${\mathrm{NH}}_4^{+}$ concentrations in the column experiments, effluent pH declined similarly to 4.4 among five experimental scenarios from an initial pH of approximately 4.7 and 6.1. Influent-effluent chemical comparisons suggest nitrification and/or ${\mathrm{SO}}_4^{2-}$ desorption controls effluent pH. Sulfate adsorption occurred when ${\mathrm{SO}}_4^{2-}$ influent was greater than $25\mu \mathrm{mol}{\mathrm{L}}^{-1}$ and desorption occurred below $15\mu \mathrm{mol}{\mathrm{L}}^{-1}$, which would equate to approximately a 61% reduction in current ${\mathrm{SO}}_4^{2-}$ deposition levels. Base cation depletion occurred in column experiments, in which $64–60\mu \mathrm{mol}{\mathrm{L}}^{-1}$ ${\mathrm{Ca}}^{2+}$ and $24–27\mu \mathrm{mol}{\mathrm{L}}^{-1}$ ${\mathrm{Mg}}^{2+}$ reductions were measured. Cation depletion rates were pH dependent, primarily caused by soil cation exchange and not weathering. In these soils with base saturation below 7%, complete ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$ depletion was estimated as 90 to 140 years. Protons released by ${\mathrm{SO}}_4^{2-}$ desorption via ligand exchange are expected to cause further base cation depletion, thereby delaying watershed recovery. Field experiments found ${\mathrm{SO}}_4^{2-}$ sorption dynamics to be limited by kinetics and hydrologic interflow rates, illustrating how precipitation intensity can influence ion transport from soil to stream. Results from this study provide important information for predicting watershed recovery in the future and suggest needs for further research.

Rock chutes or block ramps are fishway passages with low environmental impact. They also contribute to reaeration of rivers with low dissolved oxygen content, owing to the turbulence enhanced by their three-dimensional macroroughness conditions. This paper analyzes the air entrainment inception in flows over beds in macroroughness condition and the self-aerated flow features of the developing flow downstream of the inception point. Air concentration, inception point locations, and water depth elevations have been measured on two different scaled chutes for slopes ranging between 1V:5.88H and 1V:2.17H. Moreover, two different ogee crest lengths have been tested to assess the role of the inlet conditions on the location of the inception point. New equations have been developed to estimate the location of the point of inception and the respective water depth. Longitudinal variations of the mean air concentration downstream from the inception point have been studied and compared with data from the literature. An expression is presented to estimate the optimum length of the block ramp in natural rivers for maximizing air-water mixing.

The aim of the study was to evaluate the toxicity and biodegradability of para-chlorophenol ($p$-CP) model wastewater when treated by UV and $\mathrm{UV}/{\mathrm{H}}_2{\mathrm{O}}_2$ processes. We investigated the correlations between the toxicity and the concentration of $p$-CP and its oxidation by-products, as well as other parameters—summarizing characteristics which potentially indicate hazardous water components, e.g., AOX (adsorbable organic halides), TOC (total organic carbon), and COD and ${\mathrm{BOD}}_5$ (chemical and biochemical oxygen demand). Biodegradability is estimated by the ${\mathrm{BOD}}_5/\mathrm{COD}$ ratio. The toxic effects were investigated on luminescent bacteria Vibrio fischeri, determining the ${\mathrm{EC}}_{50}$ value. The correlation between each data pair was estimated using a statistical approach calculating the Spearman rank coefficients. The biodegradability of the $p$-CP model wastewater was improved by the $\mathrm{UV}/{\mathrm{H}}_2{\mathrm{O}}_2$ process; the ${\mathrm{BOD}}_5/\mathrm{COD}$ ratio increased from 0.37 to 0.73 after a 1-h treatment ($F=1243\mathrm{mJ}{\mathrm{cm}}^{-2}$). According to the calculated Spearman rank coefficient, the highest correlation with toxicity data among all monitored parameters was obtained for hydroquinone and benzoquinone, as by-products of $p$-CP degradation, as well as for the ${\mathrm{BOD}}_5/\mathrm{COD}$ ratio.