Journal of Environmental Engineering

A turbulence chamber designed specifically for the laboratory study of environmental scalar fluxes at sediment-water interfaces was developed and fully characterized. The turbulent flow field was documented using particle image velocimetry (PIV), with particular emphasis on turbulence characterization. The chamber is capable of reproducing a wide range of turbulence levels covering 6 orders of magnitude of the dissipation rate of turbulent kinetic energy (${10}^{-10}–{10}^{-4}{\mathrm{m}}^2{\mathrm{s}}^{-3}$). Its performance range includes conditions similar to low energy environments such as lake and reservoir bottom boundary layers (BBLs), verified by comparison to field data. The chamber is forced by three peristaltic pumps plumbed to six equispaced orifices on the top cap of the chamber, forming a closed system. The pumps drive either a momentum source (a jet) in the vertical direction or a momentum sink. The pumps operate continuously, but randomly change direction to generate a horizontally homogeneous turbulent region near the sediment-water interface. Measured turbulence intensities show a quadratic relationship with pump speed (rpm), with typical environmental BBL turbulence intensities seen at low pump speeds ($\sim 10\mathrm{rpm}$). Dissipation shows a log-linear relationship to pump speed. A field experiment in Onondaga Lake was used to characterize typical lacustrine BBL turbulence, allowing the turbulence chamber design objective of reproducing the observed range of conditions to be met. The presented chamber design is adaptable and readily optimizable by users to the specific system under study. This flexible, self-contained design was motivated by the need to handle mercury-contaminated sediments from Onondaga Lake, the initial system it was used to study. Compared to similar facilities, the presented chamber provides well-characterized turbulence which is calibrated against environmental conditions with a direct correspondence between chamber and field turbulence levels in the form of turbulence intensity and turbulent dissipation values.

Stormwater control measures (SCMs) have been employed to mitigate peak flows and pollutants associated with watershed urbanization. Downstream ecological effects caused by the implementation of SCMs are largely unknown, especially at the watershed scale. Knowledge of these effects could help with setting goals for and targeting locations of local restoration efforts. Unfortunately, studies such as these typically require a high level of time and effort for the investigating party, of which resources are often limited. This study proposes a low-cost investigation method for the prediction of ecological effects on the watershed scale with the implementation of rain garden systems by using publicly available data and software. For demonstration purposes, a typical urban watershed was modeled using Storm Water Management Model (SWMM) 5.0. Forty-five models were developed in which the percent impervious area was varied 3 to 80%, and the fraction of rain gardens implemented with respect to the number of structures was varied from 0 to 100%. The river chub fish (Nocomis micropogon) and its congeners (Nocomis spp.) were chosen as ecological indicators, as they are considered to be keystone species through interspecific nesting association. Depth and velocity criteria for successful nest building locations of the river chub were determined; these criteria can then be applied to many other watersheds. In this study, both base flow conditions and a typical summer storm event (1.3 cm, 6 h duration) were evaluated. During the simulated storm, nest-building locations were not affected in the 3 and 5% impervious cover models. Nest destruction was found to occur in approximately 54% of the original nest building sites for the 9% and 10% impervious areas. Nearly all of the nest-building locations were uninhabitable for impervious areas 20% and greater. Rain garden implementation significantly improved river chub habitat in the simulation, with greatest marginal benefit at lower levels of implementation.

This study attempted to develop an effective alternative to remove perchlorate (${\mathrm{ClO}}_4^{-}$) in water by using electrodeposited zero-valent iron (${\mathrm{Fe}}^0$) as an electron donor. Zero-valent iron was prepared on a titanium sheet as substrate through cathodic electrodeposition of ferrous ions in the presence of organic matter. It was observed that the freshly prepared ${\mathrm{Fe}}^0$ was nearly free of oxides, whereas after reductive removal of ${\mathrm{ClO}}_4^{-}$, a mixture of iron oxides (γ-${\mathrm{Fe}}_2{\mathrm{O}}_3/{\mathrm{Fe}}_3{\mathrm{O}}_4$) in a crystalline hexagonal plate shape was formed. The reaction rates of ${\mathrm{ClO}}_4^{-}$ removal relied on the dosages of ${\mathrm{Fe}}^0$. At pH 6.5, 80.9% of 1 mM ${\mathrm{ClO}}_4^{-}$ was removed in 336 h using 10 mM ${\mathrm{Fe}}^0$. This value of electrodeposited ${\mathrm{Fe}}^0$ dosage for sustaining the effective removal of ${\mathrm{ClO}}_4^{-}$ was at least 90x smaller than the ${\mathrm{Fe}}^0$ dosages previously reported. The accumulation of chloride ion, which was the only detected product containing chlorine, was detrimental to further reaction. The reduction reaction was faster at neutral pH than at acidic or basic pH. In addition, increasing the temperature and introducing Pd into the electrodeposited ${\mathrm{Fe}}^0$ to form $\mathrm{Pd}/{\mathrm{Fe}}^0$ improved the removal efficiency of ${\mathrm{ClO}}_4^{-}$.

The possibility of using a small-scale model to predict the performance of a full-size open-channel ultraviolet (UV) wastewater disinfection reactor was numerically investigated using a computational fluid dynamics (CFD) model. The CFD model consists of the volume of fluid (VOF) method for capturing the water–air interface, realizable $k\text{-}ϵ$ model for turbulence, discrete ordinate (DO) model for resolving the UV intensity field in the reactor, and Lagrangian particle tracking for calculating the microbial particle trajectory. To ensure the similarity of the hydrodynamics between the full-size and two scaled-down open-channel reactors, the Froude and Reynolds numbers were considered. Scaling methodology for the UV radiation field was formulated to ensure that the same disinfection performance can be achieved between the full-size and the scaled-down reactors. The disinfection characteristics of the full-size and scaled-down reactors predicted by the CFD model were comparable suggesting that the open-channel reactor is scalable and the behavior of a large-scale reactor can be predicted from the results of a small-scale reactor.

Manganese(II) oxidation by a new bacterium isolate, Pseudomonas putida strain EC112, was studied in batch reactors over a range of Mn(II) concentrations ($1–26\mathrm{mg}/\mathrm{L}$) in a chemically defined liquid medium (at pH 6.5 and 30°C). Bacterial Mn(II) oxidation initiated after the exponential growth phase and carbon source consumption. The best fit kinetic oxidation parameters of half-saturation coefficient $K_s=1.086\pm 0.029\mathrm{mg}/\mathrm{L}$ and maximum specific substrate utilization rate constant $k=0.180\pm 0.003\mathrm{mg}$ $\mathrm{Mn}(\mathrm{II})/(\mathrm{mg}\mathrm{dry}\mathrm{cell}\mathrm{mass}·\mathrm{h})$ were obtained using Monod-type kinetics and fitted with the Levenberg-Marquardt nonlinear least-squared algorithm. Additional experiments assessed the potential of Mn(II) oxidation by strain EC112 in the presence of the oxidation products of humic acid (HA) and manganese dioxide (${\mathrm{MnO}}_2$). Results show enhanced biological Mn oxidation and growth. This suggests ${\mathrm{MnO}}_2$ oxidizes biologically refractory organic matter to substrates that support microorganism growth.

Several biochemical and physical factors regulate phytoplankton primary productivity and algal bloom events in estuarine environments. Some of the most important factors include nitrogen, phosphorus and silica availability, light availability, and estuarine flushing potential. A better understanding of these processes is necessary to support sound management strategies that take into account the hydrological, hydraulic, and biochemical connectivity between estuaries and their watersheds. In this paper the factors controlling phytoplankton productivity in a tributary estuary of the northern Gulf of Mexico, the St. Louis Bay estuary, Mississippi, and the system responses to nutrient load alterations are studied. For this purpose a coupled hydrodynamic and water quality model based on U.S. EPA computer models was implemented. The writers present an evaluation of the model predictive capacity, and its implementation to study the processes controlling phytoplankton dynamics, nutrient cycling, and oxygen availability. The results suggest that primary productivity is limited by nitrogen availability. Under current nutrient load conditions the concentrations of nitrogen fall below $0.025\mathrm{mg}/\mathrm{L}$, and the rates of primary productivity vary between 0.5 and $1.8{\mathrm{gO}/\mathrm{m}}^2/\mathrm{day}$ with a mean of $0.65{\mathrm{gO}/\mathrm{m}}^2/\mathrm{day}$. The simulation of four different nutrient load scenarios suggests a low sensitivity of the estuary to the evaluated conditions in the watershed. The results also indicate that the coupled model is a cost-effective strategy to investigate the impacts of different management strategies. At a regional scale, the implemented approach can contribute to the design of integrated strategies to reduce hypoxia and algal bloom problems in the Gulf of Mexico.

Road runoff contains toxic heavy metals that can threaten the water quality of urban water systems. This paper characterizes the time variability of heavy metal pollution in road runoff in a 9 ha, steep (12% slope), suburban, rainy (235 rainy days; 1,120 mm per annum), cold climate catchment. Twenty-three water samples, collected during six discrete runoff events spanning 1 year, were analyzed for total and dissolved heavy metal concentrations. The most abundant pollutants were Zn ($46\mathrm{\mu g}/\mathrm{L}$), Cu ($14\mathrm{\mu g}/\mathrm{L}$), and Cr and Ni (2.3–2.5$\mathrm{\mu g}/\mathrm{L}$). Zn, As and Cd were predominantly dissolved ($>70\%$), Ni was primarily bound to particulates (68%), and Cu and Cr were equally divided between phases. Elevated dissolved and total concentrations were measured during snowmelt in correlation with high electrical conductance reflecting the use of road salt as a deicing agent. Event mean concentrations were positively correlated to wind speed and negatively correlated to rainfall depth in the two antecedent weeks. A mild first flush of dissolved metals was observed in most events, with 40–50% of pollution mass being discharged in the first 30% of runoff volume. Particulate-bound heavy metals, however, only exhibited first flush during intensive snowmelt. A strong linear correlation was observed between particulate-bound heavy metals and total suspended solids (TSS) ($R^2=0.8–0.9$), corresponding to 0.45, 0.22, 0.05, and $0.06\mathrm{\mu g}/\mathrm{mg}$ TSS slope for Zn, Cu, Cr, and Ni, respectively. Overall, the pollution levels were moderate compared with residential catchments in northern Europe and North America, which may constrain runoff treatment efficiency.

The objective of this study was to investigate the regrowth potential of E. coli and indigenous wastewater bacteria after ultraviolet (UV) disinfection in the absence of light and dark repair and under different nutrient conditions. Light repair was prevented by keeping the samples in the dark following UV exposure (15 and $40{\mathrm{mJ}/\mathrm{cm}}^2$). Dark repair was controlled for by varying the initial and surviving bacterial concentrations, and achieving complete inactivation and no growth in control samples. Net growth and die-off in samples were determined 6, 18, 24, 30, and 48 h after UV disinfection. The results of this study showed that the percent regrowth of E. coli and indigenous wastewater bacteria were higher after UV disinfection at $40{\mathrm{mJ}/\mathrm{cm}}^2$ than at $15{\mathrm{mJ}/\mathrm{cm}}^2$, and the regrowth was also sustained for a longer time. Even in the absence of any nutrients, significant regrowth of E. coli was observed in phosphate-buffered saline (PBS) indicating that the lysis of UV-damaged cells may provide a source of nutrients for the surviving bacteria. In spite of the availability of nutrients in wastewater, the presence of inhibiting and toxic substances appeared to slow down the regrowth of E. coli. Indigenous coliform bacteria in wastewater could achieve much higher regrowth compared to laboratory cultured E. coli even after a UV dose of $40{\mathrm{mJ}/\mathrm{cm}}^2$.

The development of a vertically-segmented, mechanistic mass balance model (Sed2K) for particulate organic matter (POM) diagenesis in lake sediments is described. The model is parsimonious in its requirements for input data and versatile in its accommodation of kinetic formulations. An application is provided for hypereutrophic Lake Alice, Minnesota, which includes a well-constrained calibration to downcore POM constituents (carbon, nitrogen, and phosphorus) and their efflux at the sediment-water interface. The application then considers the system response to a reduction in POM deposition to the sediments (i.e., addressing the critical “when and to what extent” question fundamental to lake restoration programs).