Journal of Environmental Engineering

Polychlorinated biphenyl (PCB) concentrations from an ${}^{137}\mathrm{Cs}$ age-dated core extracted from urban lake sediments in Bergen, Norway reflect the time period from the global introduction of PCB to the legal ban of their usage in Norway (1980). PCB concentrations in the sediment deposited after the ban of PCB usage strongly suggests that there are sources still active in the urban environment today. Earlier studies and results within this study imply that these sources could be standing building mass. The main pollution pathway from source to recipient is implied to be stormwater. This study presents a long-term measured amount of suspended particles in urban stormwater. An impervious, small urban catchment ($\mathrm{5,800}{\mathrm{m}}^2$) releases almost 800 kg of suspended solids per year in stormwater. This suggests that the whole drainage area of the lake potentially contributes 9.5 t of particles via stormwater into the lake each year, potentially carrying 0.4 g of ${\mathrm{PCB}}_{\mathrm{sum}7}$.

A constructed wetland type natural treatment system was built in southern Taiwan for stream water purification and natural habitat creation. The system influent (influent rate = $\mathrm{1,170}{\mathrm{m}}^3/\mathrm{d}$) was from the local stream containing secondary wastewater from hog farms. The system included a fully vegetated free-water surface basin, followed by an open-water pond, a second fully vegetated free water surface basin, and an eco-pond with isolated islands for natural habitat creation. The hydraulic loading rate, hydraulic retention time, water depth, and total volume of the wetland system were $0.27\mathrm{m}/\mathrm{d}$, 7.5 d, 0.64 m, and $\mathrm{7,800}{\mathrm{m}}^3$, respectively. In this study, surface water, sediment, and groundwater samples were collected and analyzed quarterly for each basin during the two-year investigation period. The results show that the overall removal efficiencies for biochemical oxygen demand, total nitrogen, total phosphorus, and total coliform were 71, 85, 82, and 75%, respectively. The calculated first-order decay rates for organics and nutrients ranged from 0.25 (total nitrogen) to 0.15/d (ammonia nitrogen). Thus, the system had a significant effect on water quality improvement and could remove most of the pollutants from influents through natural treatment mechanisms. The results show that the increased effluent suspended solid concentrations correlated with the increased chlorophyll a in the system, and the growth of wetland plants was an effective method for algal control. The observed high ammonia/nitrate removal indicates that nitrification and denitrification processes occurred simultaneously. An increase in pollutant concentrations in the last basin was observed because the last basin was used as a wildlife habitat. Thus, natural habitat creation might conflict with the water quality protection issue. Groundwater recharge from the wetland basins resulted in the deterioration of the downgradient groundwater quality. Contaminant adsorption onto the sediment particles was also observed. Frequent groundwater and sediment monitoring is a necessity to assess the impacts of pollutant accumulation in the ecosystem. The results from the ecological investigation show that increased biodiversity was observed. The natural treatment system has become a successful multifunction ecosystem, which could be used for stream water purification and natural habitat creation.

The floating treatment wetland (FTW) is an innovative hydroponic device which can be installed on the surface of a stormwater retention pond to improve its pollutant removal efficiency. Limited full-scale experiments have been published, and no design or maintenance guidelines have been developed to date to promote their use. This paper presents implementation and maintenance considerations developed based on the monitoring of three full-scale ponds retrofitted with FTWs. Results suggest that the size and relative surface cover of the FTW, the relative root depth, and the capability of the plants to tolerate periodic anaerobic conditions are crucial factors to promote good removal across a spectrum of pollutants. Special attention to the location and anchorage of the FTW are thought to promote good performance and facilitate FTW maintenance. While zinc and copper sediment concentrations were unlikely to cause undue aquatic impacts after 2 years of operation, more frequent sediment removal will be needed than in conventional retention ponds to maintain adequate storage capacity in the permanent pool because of enhanced sedimentation. Given proper installation and maintenance, FTWs can enhance aesthetic and water quality benefits of stormwater ponds.

The plenum-aerated biofilter (PA biofilter) is an unsaturated, single pass vertical flow biofilter with horizontal air plena within the media to enhance passive aeration. Plena enlarge the surface area of the air/media interface, increase oxygen ingress, and permit a reduction in the footprint of ammonium oxidizing biofilters. An experimental PA biofilter was operated on household wastewater pretreated in a primary settling tank. The prototype was a 7.3 cm (3 in.) inner diameter circular column, containing 61 cm (24 in.) of granular clinoptilolite media. Three 5.1 cm (2 in.) aeration plena were placed at successive 7.6 cm (3 in.) media thicknesses below the upper filter surface. The biofilter was operated for 28 weeks at hydraulic loading of $69.8\mathrm{cm}/\mathrm{day}$ ($17\mathrm{gal}\mathrm{.}/{\mathrm{ft}}^2\text{-}\mathrm{day}$) and a 60-min dosing cycle. Performance was characterized by monitoring from days 180 to 196. Influent ${\mathrm{NH}}_4^{+}-\mathrm{N}$ was reduced by 99% (mean $51.6\mathrm{mg}/\mathrm{L}$ to $0.61\mathrm{mg}/\mathrm{L}$, $n=3$), with substantial conversion to ${\mathrm{NO}}_3^{-}-\mathrm{N}$ (mean $38.4\mathrm{mg}/\mathrm{L}$, $n=3$). Solute profiling showed ammonia reduction was substantially complete after passage through 45 cm (18 in.) of porous media and nitrite accumulated between 15 and 30 cm (5.9 and 11.8 in.). This short-term study suggests that the PA biofilter can provide a compact and passive ammonium oxidation system that is suitable for on-site wastewater treatment. Further studies are needed to verify that effective nitrogen transformations can be sustained over longer periods of operation.

This research presents a combined mechanical agitation and freeze–thaw method as a simple and immediate response to recover high-viscosity crude oil from oil-wet contaminated sand following oil spill events. The effects of temperature, pH, and agitation rate were studied on the recovery of high-viscosity crude oil in a mechanically agitated cell followed by freeze–thaw. Results showed that the increase in temperature and pH to 50°C and pH 9, respectively, was optimum and led to a 58% increase in oil recovery. The optimum agitation rate of 1,000 rpm at 50°C and pH 9 was further shown to increase the oil recovery to 68%. Further increases in agitation rates, however, showed a decline in oil recovery due to the formation of oil-in-water emulsions. Results of this study suggest that the combined mechanical agitation and freeze–thaw process is a viable method for the recovery of spilled crude oil on sand.

Accelerated stormwater runoff creates environmental problems in many urban communities. Methods of reducing runoff for individual residences are available, but are often recommended without sufficient analysis. For example, many states provide guidance on creating rain gardens, but few include information about how well rain gardens actually work. An analysis algorithm is presented to evaluate rain garden effectiveness at reducing stormwater runoff by promoting infiltration, evaporation, and evapotranspiration. Example simulations are presented based on an Ohio meteorological record. Results indicate that garden effectiveness is dominated by infiltration. Evaporation and evapotranspiration play minor roles in reducing runoff. Results also indicate that current rain garden design recommendations are often too conservative. Even for low permeability soils, rain gardens can be more effective than currently assumed. Common depth recommendations are reasonable, but area recommendations are also conservative. Residential rain gardens have a much better chance of reducing stormwater runoff than rain barrels. Their design recommendations should be revised to concentrate less on garden flora and more on the properties that promote desirable hydrologic performance.

Water disinfection processes with sequential arrangements of ultrasound (US) and ultraviolet light (UV) reactors were investigated using Escherichia coli (E. coli) in a solution of 0.9% salinity. Experimental runs were carried out with reactor setups that provided sequential treatments of US followed by UV and UV followed by US. Using a mathematical model developed for three continuously stirred tank reactors in series (3-CSTR), a nonlinear regression analysis was conducted to determine the inactivation rate constants for E. coli and the formation rate constants for hydroxyl radicals. The additive, antagonistic, and synergistic effects of US (frequency 20 kHz, power density $275\mathrm{mW}/\mathrm{mL}$) and UV (irradiance $2.25\mathrm{mW}/{\mathrm{cm}}^2$) were evaluated using kinetic constants and reactor efficiencies. Results showed that the sequential irradiation of US followed by UV yielded a synergistic effect on the inactivation of E. coli and that UV followed by US produced weak synergism.

A new stochastic water quality modeling tool was applied to quantify potential climate change effects on a nutrient impaired reach in the Pacific Northwest. This tool allows for multiple stochastic inputs for steady state river water quality simulations. A previously published calibrated deterministic model of the targeted reach was adapted for this study. This model simulates steady-state nutrient, algae, and dissolved oxygen dynamics with both point and nonpoint pollutant loadings. It also includes simulation of diurnally varying water temperature, calculated as a function of air temperature, shading, and streamflow using heat budget equations. For this study, local summer air temperature and critical low flows were treated stochastically in the model. Parameterization of these inputs was based on analysis of multiple global climate model (GCM) projections for the study area corresponding to a 2060 planning horizon. Continuous probability distribution functions were fitted to ensemble GCM data sets grouped according to two different greenhouse gas emission scenarios (best case, worst case). Climate projections were translated into summer low flows using a simple empirical regression hydrologic model that was developed on the basis of observed historical data. Model outputs are provided probabilistically, helping to quantify levels of climate model consensus and capturing a portion of the large uncertainty associated with the forecasts. This type of framework is valuable in its support of planning decision making. Results specific to this study indicate that, whereas reach dissolved oxygen and algae biomass levels are relatively insensitive to projected climate change, simulated stream water temperature changes could have an adverse effect on native salmon populations in the region. The demonstrated methods are believed to be generally transferable to other river water quality studies and are recommended as an option for planning studies.

A green roof is an environmentally friendly best management practice for volume reduction, peak flow reduction, and peak delay of stormwater runoff from impervious rooftops. In this study, HYDRUS-2D was used to model the hydrologic response of a pilot green roof system. The root-mean-square deviation (RMSD) of growth media volumetric water content values between model and field measurements ranged between 0.38 and 1.74%. A method was developed to use the water content profile at three media depths to derive regression equations that predict hydrologic performance. These equations show that runoff volume reduction follows an inverse relationship between media field capacity and precipitation depth, that peak flow reduction obeys a second-order equation between media field capacity and precipitation depth, and that peak delay time can be approximated by a third-order equation that includes maximum capacity and precipitation depth. The ${\mathrm{R}}^2\mathrm{s}$ values of the regressions range between 0.87 and 0.99. These derived equations can be used for performance evaluations or design work, including determining the necessary green roof media depth to meet Leadership in Energy and Environmental Design (LEED) runoff reduction requirements.

To project the effects of climate-induced change on aquatic environments, it is necessary to know the thermal constraints affecting different fish species and to acquire time series of the current and projected water temperature (WT). A regression between the WT at individual stations and the ambient air temperature (AT) at nearby weather stations could represent the easiest practical method of estimating the WT for an entire region. Assuming that the grid-averaged observations of AT correspond to the AT output from a general circulation model (GCM) simulation, this study constructed a regression curve between the observations of the local WT and the concurrent GCM-simulated surface AT, minimizing the difference between the time series of the measured and modeled WT, which implicitly includes downscaling to local conditions. The regression model shows excellent performance in capturing the WT trend in response to the AT of the GCM. The projected WT under the global-warming scenario shows a 1.5–2.5°C increase for the period 2080–2100. The maximum/minimum WT shows an amount of change similar to that of the mean values. The results also predict that the WT will increase during most seasons by 2100 but that only minor changes will occur during the summers.

Computational fluid dynamics (CFD) methods are employed to evaluate the influence of temperature variations on the flow field in an actual sedimentation tank for potable-water treatment. A series of experimental measurements of temperature variation has been conducted in that sedimentation tank. The mixed-convection problem caused by the density variations and the horizontal stream is considered at low temperatures (0–10°C) where the variation of water density is strongly nonlinear. Three cases have been examined: (1) one in the ascending, (2) one in the descending parabolic density region, and (3) one in the linear density region. The thermophysical properties of water have been incorporated into the CFD code. All simulations have been conducted for a transient, turbulent flow field. The momentum exchange between the primary and the secondary phase (particles) is considered. The results show that in the parabolic density region, only a few particles are trapped in the bottom, whereas many of them float near the surface and escape from the tank causing a low-tank efficiency. The opposite happens in the linear-density region where the tank efficiency is much better.