Journal of Environmental Engineering

Diel dissolved oxygen (DO) concentrations and temperature were sensed at high-frequency and modeled in an eastern Iowan stream, Clear Creek, in an agricultural setting. The magnitude of the diel changes in DO and temperature were largest at the upstream (headwater) station. Inclusion of temperature change factors increased the accuracy of modeling results and yielded estimates of the reaeration rate constant, primary production rate, and respiration rate. The DO modeling of the high-frequency measurements (15-min intervals) revealed a temperature-driven nonlinear reaeration process that led to increases in nighttime DO concentrations. The DO modeling results from three sensing stations in the watershed revealed decreasing trends in primary productivity, respiration, and the reaeration rate constant with increasing drainage area. Light extinction from suspended solids was the main factor limiting net primary production. As a result, the $P/R$ ratio also decreased with increasing drainage area. High-frequency sensor data and DO modeling revealed the effects of temperature and watershed scale on the primary factors that dictate diel DO dynamics in a stream setting.

Vegetated storage-infiltration best management practices (BMPs) have become an increasingly popular means of attenuating and treating runoff from developed land. However, the hydrologic and pollutant removal performances of these facilities can be highly variable. A mathematical model of an idealized BMP was developed in order to quantify the impact of variable hydrologic and pollutant concentration input on BMP performance by simulating the treatment performance of the model system during 1,250 non-steady-state storm events generated based on historic Maryland rainfall data. The model BMP was effective in attenuating volume (42% total volume reduction) and peak flow (median peak output to peak input flow ratio was 0.058). The simulated mean effluent pollutant event mean concentration was much less than the influent (0.284 compared with 1.51 mg/L) and the overall mass load reduction was 92%. However, the performance parameters demonstrated significant variability. Consequently, the results suggest a need to incorporate into BMP performance guidelines the impact of the variable influent hydrologic and pollutant concentration characteristics. Emphasis should be placed on discharge water quality and statistical distributions rather than on single-percent removal values.

Under the mandate of the Federal Clean Water Act, porous landscaping detention (PLD) has been widely used to increase on-site infiltration. A PLD system consists of a surface storage basin and subsurface filtering layers. The major design parameters for a PLD system are the infiltration rate on the land surface and the seepage rate through the subsurface medium. A low infiltration rate leads to a sizable storage basin while a high infiltration rate results in standing water if the subsurface seepage does not sustain the surface loading. In this study, the design procedure of a PLD basin is revised to take both detention flow hydrology and seepage flow hydraulics into consideration. The design procedure begins with the basin sizing according to the on-site water quality control volume. The ratio of design infiltration rate to sand-mix hydraulic conductivity is the key factor to select the thickness of sand-mix layer underneath a porous bed. The total filtering thickness for both sand-mix and gravel layers is found to be related to the drain time and infiltration rate. The recommended sand-mix and granite gravel layers underneath a PLD basin are reproduced in the laboratory for infiltration tests. The empirical decay curve for sand-mix infiltration rate was derived from the laboratory data and then used to maximize the hydraulic efficiency through the subsurface filtering layers. In this study, it is recommended that a PLD system be designed with the optimal performance to consume the hydraulic head available and then evaluated using the prolonged drain time for potential standing water problems under various clogging conditions.

Water quality degradation due to pathogen pollution is a major concern in the United States. Storm-water runoff is an important contributor to the transport of indicator bacteria from urbanized watersheds to nearby surface waters. With total maximum daily loads being established to reduce the export of indicator bacteria to surface waters, storm-water best management practices (BMPs) may be an important tool in treating indicator bacteria in runoff. However, the ability of these systems to remove indicator bacteria is not well established. A study in Charlotte, N.C., monitored nine storm-water BMPs (one wet pond, two storm-water wetlands, two dry detention basins, one bioretention area, and three proprietary devices) for fecal coliform and Escherichia coli (E. coli). A wet pond, two wetlands, a bioretention area, and a proprietary device all removed fecal coliform with an efficiency higher than 50%; however, only the wetlands and bioretention area had significantly different influent and effluent concentrations $\left(p<0.05\right)$ . For E. coli, only one of the wetlands and the bioretention area provided a concentration reduction greater than 50%, both of which had a significant difference in influent and effluent concentrations $\left(p<0.05\right)$ . Only one of the nine BMPs had a geometric mean effluent concentration of fecal coliform lower than the U.S. EPA target value, while four of the nine BMPs had geometric mean effluent concentrations lower than the U.S. EPA standard for E. coli. This study showed that some BMPs may be useful for treatment of indicator bacteria; however, other BMPs did not perform well. Because wet, nutrient-rich environments exist in many storm-water BMPs, there is a potential for indicator bacteria to persist in these systems.

The paper presents a numerical study of resuspension of deposits from highway detention ponds based on a previous experimental study. The resuspension process is evaluated in dry weather periods with baseflow/infiltration flow through the ponds only. The resuspension is caused by the bed-shear stress induced by the return flow near the bed and waves both generated by the wind. Wind statistics for 30 years have been applied for prediction of the annual discharged bulk of suspended solids and associated pollutants; fluoranthene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene and indeno(1,2,3-cd)pyrene (PAHs) and the heavy metals of cadmium, chromium, copper, lead, nickel, and zinc. The current and wave-generated bed-shear stresses entail a discharged bulk of pollutants corresponding to approximately 10% of the annual accumulation of pollutants in the present pond due to the baseflow in the pond. The mean outlet concentration of suspended solids is well correlated with the wind speed. To reduce the resuspension of deposited materials, two mechanisms are prevailing; either by increase of the water depth of the pond to minimize the effect of the wind in the near-bed region or by reduction of the wind to some degree. The most efficient action for reducing the wind impact on the shallow waters is the establishment of shelterbelts as known from the agriculture. Just a 20% reduction of the yearly wind speeds will reduce the outlet mass with 70% and a 50% reduction with almost 100%. A 50% reduction of the wind speed is far from impossible to achieve with relatively small investments.

Temporal variability in water quality sampling can lead to under or overestimation of pollution. More frequent sampling during times of expected high variability can reduce temporal bias. However, bacterial indicator measurements require manual sampling and time-intensive and expensive laboratory analysis. Thus, methods to assess the effect of temporal variability would be useful. In this work, fecal coliform and E. coli samples were taken weekly during the recreational season at 25 sites in an urban watershed. The data were categorized into wet versus dry days, and upper versus lower watershed, and the geometric means and geometric standard deviations of various five-sample data sets were analyzed to determine if sample data selection would result in different stream classifications. Results indicate if the bacterial indicator samples are near the regulated limits for water contact recreational use, temporal bias could sway impairment classification decisions. To reduce the temporal bias, sampling data submitted for stream classification should include several sampling groups within the recreational season, particularly for sites near point sources of pollution or with low fecal indicator contamination.

Traditionally, dissolved oxygen (DO) fluxes have been calculated using the thin-film theory with DO microstructure data in systems characterized by fine sediments and low velocities. However, recent experimental evidence of fluctuating DO concentrations near the sediment-water interface suggests that turbulence and coherent motions control the mass transfer, and the surface renewal theory gives a more mechanistic model for quantifying fluxes. Both models involve quantifying the mass transfer coefficient $\left(k\right)$ and the relevant concentration difference $\left(\Delta C\right)$ . This study compared several empirical models for quantifying $k$ based on both thin-film and surface renewal theories, as well as presents a new method for quantifying $\Delta C$ (dynamic approach) that is consistent with the observed DO concentration fluctuations near the interface. Data were used from a series of flume experiments that includes both physical and kinetic uptake limitations of the flux. Results indicated that methods for quantifying $k$ and $\Delta C$ using the surface renewal theory better estimated the DO flux across a range of fluid-flow conditions.

A general and integrated approach to parameter identification, model calibration, and estimation of predictive uncertainty in water-quality models is proposed and validated. The proposed approach determines the maximal conditional likelihood functions of each of the model parameters using a transformation that forces the model errors to be normally distributed, with predictive uncertainty characterized by random normally distributed and homoscedastic model errors in the transform space. The proposed approach is demonstrated using a watershed-scale model to predict the fecal coliform levels in a third-order stream within the Little River Experimental Watershed in Georgia. Maximal conditional likelihood functions were identified for all parameters in the log, square root, and no-transformation cases. The key results are: (1) the number of sensitive parameters and the optimal parameter values can depend on the transformation; (2) only in the case of the log-transformation are the errors normally distributed and consistent with the assumed Gaussian likelihood function; (3) the standard error in the model is least for the no-transform case and highest for the log-transform case; and (4) the observed model errors are most predictable using the log-transform and least predictable using the no-transform approach.

Excess heat is an unavoidable by-product of electricity generation from fossil and nuclear fuels. In most cases, excess heat is transferred to a cooling water stream and discharged to a local receiving water body, or processed through on-site cooling towers. In many cases existing discharges are potentially responsible for significant ecological impacts, and regulatory authorities are mandating the construction of cooling towers, often at significant expense. Most existing cooling water discharges are designed to reduce excess temperatures through rapid dilution. Enhanced surface cooling is an alternative approach which involves the development of a thin surface plume, while limiting mixing of the discharge with ambient waters. This process encourages rapid transfer of heat to the atmosphere while limiting impacts to sensitive benthic environments and most of the volume of the receiving water body. This discharge approach may be particularly effective for receiving water bodies which have limited natural flushing, such as enclosed bays, estuaries, reservoirs and some river environments. A preliminary case study of a thermal discharge into Mt. Hope Bay (Massachusetts/Rhode Island) is discussed.

The 2007 edition of the ASCE MOP 60-WEF FD 5 Manual recommends the tractive force (TF) method for self-cleansing design for gravity sanitary sewers. TF design is a major improvement over traditional methods to achieve self-cleansing in gravity sewers. This approach results in a self-cleansing pipe slope value $\left(S_{\text{min}}\right)$ for the design minimum flowrate $\left(Q_{\text{min}}\right)$ in each sewer reach. $Q_{\text{min}}$ is the predicted largest 1-h flowrate in the reach during the lowest flow week over the sewer design life. Past design practices seldom included accurate estimation of $Q_{\text{min}}$ values, but good estimates of $Q_{\text{min}}$ are crucial for TF design. Design equations and plots have been developed to assist in obtaining $S_{\text{min}}$ values for given $Q_{\text{min}}$ values. As compared to traditional minimum slopes, $S_{\text{min}}$ slopes via the TF method are flatter for sewers carrying typical to larger $Q_{\text{min}}$ values and steeper for sewers carrying smaller $Q_{\text{min}}$ values.

The influence of the presence of Cr (III) on the biosorption of Pb (II) by three olive wastes (olive stone, the two-phase olive mill solid, and olive tree pruning) was investigated in a batch system in terms of equilibrium isotherm and adsorption yield. The results show that the three olive wastes have greater affinity for lead than for chromium and the best results are achieved at $\text{pH}=5$ . The presence of chromium in the solution reduces the percentage of lead removal suggesting that there is a competition between the two metals for the binding sites, and that the biosorbent retains both species presenting more affinity for lead. Simultaneous biosorption phenomena of Pb (II) and Cr (III) on the three solid wastes were expressed by multicomponent isotherms. The extended Freundlich-type and Sips-type models were found to exhibit good fit to the experimental data for olive stone and olive tree pruning, respectively.

Advanced oxidation of simazine in aqueous solution by the peroxone (hydrogen peroxide/ozone) treatment was investigated using Box-Behnken statistical experiment design and response surface methodology. Effects of pH, simazine and ${\text{H}}_2{\text{O}}_2$ concentrations on percent simazine and total organic carbon (TOC) removals were investigated. Ozone concentration was kept constant at $45\text{mg}{\text{L}}^{-1}$ . The optimum conditions yielding the highest simazine and TOC removals were also determined. Both simazine and peroxide doses affected simazine removal while pH and pesticide dose had more pronounced effect on mineralization (TOC removal) of simazine. Nearly 95% removal of simazine was achieved within 5 min for simazine and peroxide concentrations of 2.0 and $75\text{mg}{\text{L}}^{-1}$ , respectively at $\text{pH}=7$ . However, mineralization of simazine was not completed even after 60 min at simazine doses above $2\text{mg}{\text{L}}^{-1}$ indicating formation of some intermediate compounds. The optimum ${\text{H}}_2{\text{O}}_2/\text{pH}/\text{Simazine}$ ratio resulting in maximum pesticide (94%) and TOC removal (82%) was found to be $75/11/0.5\left(\text{mg}{\text{L}}^{-1}\right)$ .

The toxicity of several metallic/oxide nanoparticles ( ${\text{TiO}}_2$ , CuO, ZnO, and Ag) to nitrifying bacteria was evaluated individually or in combination in batch studies. Except for the mixture of ZnO and Ag, the mixture inhibition of nanoparticles was roughly the sum of individual inhibition among the nanoparticles studied. Although there was no inhibitory effect of ${\text{TiO}}_2$ nanoparticles under ambient light or dark conditions, nitrification inhibition was significantly increased when ${\text{TiO}}_2$ nanoparticles were exposed to ultraviolet (UV) for 30 min. Under UV exposure, both ${\text{TiO}}_2$ nanoparticles (anatase) and bulk amorphous ${\text{TiO}}_2$ generated the same amount of reactive oxygen species (ROS) in the bacterial cell although ${\text{TiO}}_2$ nanoparticles were more toxic than the bulk counterpart. While the inhibition was well correlated to intracellular ROS concentration, the ROS correlations were different for the different forms of ${\text{TiO}}_2$ or for the different nanoparticles (e.g., Ag versus ${\text{TiO}}_2$ ). ROS is therefore not a good chemical marker to indicate the toxicity of common metallic/oxide nanoparticles.

A mathematical model is developed to predict continuous adsorption-regeneration cycling of volatile organic compounds (VOCs) on activated carbon fiber cloth (ACFC) at the indoor VOC concentration levels. The adsorption-regeneration model incorporates both the adsorption equilibrium and mass transfer fundamentals. It assumes local equilibrium between the gas-phase and the solid-phase, and axially dispersed-flow, film transfer, and intraparticle transport by surface and pore diffusion. Successful agreement between model simulations and experimental data was obtained and the kinetic properties of the adsorption/regeneration cycling on the ACFC were characterized. For the adsorption process, the film transfer is the dominant factor for mass transfer at low flow rates (45–184 L/min), and the intraparticle mass transfer rate controls over the gas-phase rate as the flow rates increase. The regeneration concentration profiles are most sensitive to the adsorption isotherms at the temperatures of interest, especially as desorption is initiated. The surface diffusivity also contributes to the shape of the regeneration profile: the tailing of desorption profile shifts up with the increase of surface diffusivity.

Biological sludge contains a large quantity of water and the decrease of its content constitutes one of the main issues for wastewater treatment plant operation. Laboratory tests to estimate the sludge dewaterability, i.e., its capability of being dehydrated, have been developed in the past, but there is no evidence of the tests’ direct correlation with the behavior of the real-scale dewatering devices. Different methods (specific resistance to filtration at different pressure, capillary suction time, expression tests, and drying test) have been applied on civil sludge conditioned with ferric chloride/lime or polymer/ferric chloride and results have been compared with operational data obtained from a full scale plant. The results presented in this paper highlight the role of the expression phase in the sludge dewatering using frame filter presses. To predict the sludge behavior and then to optimize the conditioning step, the laboratory procedure used for selecting the chemicals and doses has also to consider the effect of the expression of the cake.

Ionic liquids have become leading candidates for replacing many common organic solvents used in the chemical process industry. There is, however, a general lack of toxicology data relevant to wastewater treatment facility microbes for these compounds. In this study, we performed three bacterial-based toxicity assays on several imidazolium-derived compounds as well as the precursor compound 1-methylimidazole. Two of the assays, the Shk1 and Microtox assays, are used as surrogate assays for toxicity to bacterial respiration in activated sludge wastewater treatment plants. The third assay was a direct measure of the effect of toxicity on mixed bacterial culture respiration, using a commercially available consortium of naturally occurring bacteria to obtain $I{C}_{50}$ values for direct comparison to the $E{C}_{50}$ values from the surrogate assays. The Shk1 assay is based on a genetically engineered bioluminescent Pseudomonas bacterium and is more highly correlated with the respiration inhibition than the Microtox assay. The Shk1 assay gave $E{C}_{50}$ values more similar to $I{C}_{50}$ values from the bacterial respiration inhibition assay for the compounds tested in this work. The Shk1 $E{C}_{50}$ values were similar to that of 1-butanol, an alcohol with an alkyl chain length similar to that of the cation of the tested compounds, which were 1-butyl-3-methylimidazolium bromide ([bmim][Br]), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim] $\left[{\text{PF}}_6\right]$ ), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ([bmim] $\left[{\text{Tf}}_2\text{N}\right]$ ), and the precursor compound 1-methylimidazole, and were generally smaller than those typical of aromatic organic solvents.

The adsorption of two reactive dyes, Reactive Black 5 and Reactive Red E, onto palm kernel shell-activated carbon (PKSAC) was studied. The effect of the presence of more than one dye in solution on the equilibrium and kinetics of adsorption was investigated. Equilibrium isotherm models were applied to describe the adsorption capacities of single and binary systems. Adsorption of reactive dyes for single system can be represented by the Freundlich and the Redlich-Peterson models. For binary system, the equilibrium was described successfully by the modified extended Freundlich model. Experimental data showed that competitive adsorption for active sites on the carbon surface resulted in a reduction in the overall uptake capacity of the reactive dyes. The rates of adsorption in single system were found to agree well with the pseudosecond-order kinetic model. Finally, the chemical oxygen demand (COD) of the treated reactive dye solutions from single and binary systems showed that a minimum of 4 g/L dosage of PKSAC was needed to reduce the COD to an acceptable level according to the Water Quality Guidelines and the Pollutant Fact Sheets Guidelines.

In this study, the sonophotocatalytic process, i.e., combination of ultrasonic irradiation (US) and photocatalytic reaction, was proposed as a pretreatment process for the anaerobic digestion of organic sludge in order to drastically reduce the amount of sludge and promote the recovery of methane and phosphorus. Several series of experiments employing different techniques, i.e., sonophotocatalysis (SPC), US, photocatalysis (PC), and thermal treatment, were conducted by using a batch type apparatus. The results of the SPC treatment showed a decrease in sludge volume by about 50% and the synergetic effects of US and PC treatments which were clearly observed as increases in dissolved chemical oxygen demand of sludge filtrate and in phosphorus compounds dissolution from sludge particles. In the SPC process of sewage sludge, the photocatalytic reaction was enhanced by the sufficient disintegration of sludge flocks due to the US treatment. Any pretreatments applied promoted the anaerobic digestion process, however, there was little synergetic effect and the long time SPC treatment resulted in a decrease in the reaction rate.