Journal of Environmental Engineering

Surface soil contamination is often regulated by using guidance values that specify the maximum amount of pollutant that can be present without prompting a regulatory response. In the United States, there are at least 88 value sets, and another 35 worldwide, that provide guidance for at least one chlorinated ethene. Trichloroethene is the most commonly regulated chlorinated ethene (118 values) and may be the most commonly regulated synthetic organic surface soil contaminant. Cis- and trans-1,2-dichloroethene are the least regulated chlorinated ethenes. Overall, there are 617 guidance values for specific chlorinated ethenes plus another 32 for mixed isomers of dichlorethene. This analysis explores the origin, magnitude, and form of the variability of these values. Results indicate that values span from 4.9 to 6.6 orders of magnitude and follow distributions similar to lognormal random variables. However, distributions include value clusters similar to values advocated by the U.S. Environmental Protection Agency (USEPA) or the Canadian Council of Ministers of the Environment (CCME). Although only 9.5% of the regulatory guidance values (RGVs) are identical to USEPA or CCME values, 55% of these fall within the uncertainty bounds estimated for USEPA risk models. Results suggest that stronger national leadership and reduced risk model uncertainty could be effective in reducing the RGV variability of chlorinated ethenes.

Bioretention has significant potential for reduction of bacterial levels in urban storm-water discharge. The long-term performance of bacteria removal was evaluated using column studies over an 18-month period, during which synthetic urban storm-water runoff was loaded into conventional bioretention media (CBM) columns once every two weeks. CBM initially achieved a mean of 72% removal efficiency for Escherichia coli O157:H7 strain B6914. The removal efficiency improved over time, achieving 97% or higher efficiency after six months. The trapped B6914 cells died off rapidly between runoff application events. Mechanistic studies indicated that decreased porosity and increased hydrodynamic dispersion observed in mature CBM are favorable for improvement of physical straining of cells and for bacterial adhesion. The temporal change in surface charge on CBM may not be a key factor in the improved bacterial removal. Indigenous protozoa in the CBM grew logistically, and may play an important role in enhancement of bacterial capture and rapid decline in numbers of trapped bacteria via predation. Overall, the long-term bacterial removal process in CBM can be efficient and sustainable.

Effective simulation of the fate and transport of runoff event inflows is an important goal of many water quality modeling initiatives. The set-up and testing of a two-dimensional hydrodynamic transport model is documented for a water supply reservoir, Schoharie Reservoir, New York, that uses specific conductance (SC) as a conservative tracer and focuses on fate and transport of runoff event inputs, particularly the plunging of density currents in summer and fall. Model testing is supported by temporally detailed measurements of meteorological, operational, and tributary (temperature and SC) model drivers, and temporally and spatially replete in-reservoir patterns of SC following multiple runoff events, obtained with a combination of robotic monitoring platforms and gridding with rapid profiling instrumentation. Specific conductance is demonstrated to be an ideal tracer because of the distinct tributary signals and subsequent in-reservoir signatures imparted from runoff events and its close coupling to turbidity patterns that are primary water quality concerns for managers. The model is demonstrated to perform well in simulating in-reservoir signatures of SC following multiple runoff events over the spring to fall interval of 2003, including vertical, longitudinal, and temporal patterns, and features of the thermal stratification regime for the same interval. The validated model is applied in a probabilistic manner on the basis of a 61-year record (239 runoff events) of model drivers to provide a robust representation of the transport of runoff event inputs relative to the location of the water supply intake. This application demonstrates the entry of runoff event inflows as plunging density currents in summer and fall is a recurring phenomenon for this reservoir.

The permeability of zero-valent iron permeable reactive barriers (ZVI PRBs) may be reduced by the production of gas and solid precipitates. The reduction in permeability was examined using column experiments, which showed that permeability loss was correlated with influent oxidant concentration. The column containing $100\mathrm{mg}/\mathrm{L}$ nitrate experienced the greatest loss, approximately two orders of magnitude over the course of 200 pore volumes. However, the permeability loss owing to precipitated solids was largely independent of oxidant concentration, accounting for only 24% of the observed loss in the $100\mathrm{mg}/\mathrm{L}$ nitrate column, suggesting that the majority of loss was attributable to gas, not precipitates. Geochemical modeling corroborated these findings, indicating that precipitation of solids in the $100\mathrm{mg}/\mathrm{L}$ nitrate system does not account for more than a 10% permeability reduction. These findings suggest that in field PRBs in which a high reduction in permeability is observed, gas production may be implicated. Design choices that impede gas migration out of ZVI PRBs, such as capping, must be considered in light of the possibility of a high potential for permeability reduction.

The development of a total maximum daily load (TMDL) for water bodies impaired by elevated microbial levels (the second leading cause of impairment nationally) requires an understanding of microbial transport processes at the watershed scale. Continuous monitoring of impaired water bodies can be expensive, and models are typically employed, but most current models represent bacteria as single discrete (“free” phase) organisms with near-neutral buoyancy, subject to first-order decay resulting primarily from predation or die-off. Studies indicate, however, that a significant fraction of microbes are associated with sediment particles, both in the water column and bed-sediments, associations that can impact microbial transport behavior and survival rates. This work incorporates considerations of microbial partitioning and its impact on survival into microbial fate and transport modeling using a well-characterized watershed. Agreement between observed and modeled instream microbial concentrations is comparable to, or better than, that seen in similar studies. Nonetheless, differences in instream concentration between model runs that consider microbe-sediment association (with attendant survival differences) and those that assume all microbes exist in the free phase are relatively small. A sensitivity analysis of relevant model inputs further indicates the minor effects of incorporating these considerations. The low settling velocities of small particles with which microbes typically associate and the dominance of other inputs related to wet weather microbial loadings, when compared with resuspension, result in the reduced significance of microbial partitioning as a factor in water quality modeling.

A study was conducted in Louisburg, North Carolina, to determine the effect of level spreader–vegetative filter strip (LS-VFS) storm-water control measures (SCMs) on runoff temperature and thermal loading. Two LS-VFS systems draining an urban catchment were monitored during the summers of 2008 and 2009. The first VFS was 7.6 m wide and entirely grassed. The second was 15.2 m wide, with the first-half grassed and the second-half wooded. Runoff temperatures and thermal loads from the urban catchment tended to peak toward the beginning of a storm event. Median and maximum storm temperatures were significantly reduced across both the 7.6-m and 15.2-m LS-VFSs. However, median and maximum effluent temperatures for both filter strip lengths were significantly greater than the 21°C trout threshold. Mean and median effluent temperatures from the 15.2-m LS-VFS were slightly lower ($<1°\mathrm{C}$) than those from the 7.6-m LS-VFS, which may show the impact of increased filter strip width and/or the shading from wooded vegetation on effluent temperatures. Expected differences between influent and effluent temperatures (both median and maximum) were greater as the influent temperature increased. Substantial and statistically significant ($\alpha =0.05$) thermal load reductions were observed in both LS-VFSs because of measured reductions in both temperature and flow volume. Thermal load was eliminated in seven of 38 storm events because of infiltration of the entire runoff volume in the filter strips. The ability of LS-VFS systems to reduce storm-water temperatures and thermal loads supports their use in thermally sensitive watersheds.

Sediment oxygen demand (SOD) can be a significant oxygen sink in various types of water bodies, particularly slow-moving waters with substantial organic sediment accumulation. In most settings in which SOD is a concern, the prevailing hydraulic conditions are such that the impact of sediment resuspension on SOD is not considered. However, in the case of Bubbly Creek in Chicago, the prevailing slack water conditions are interrupted by infrequent intervals of very high flow rates associated with pumped combined sewer overflow (CSO) during intense hydrologic events. These events can cause resuspension of the highly organic, nutrient-rich bottom sediments, resulting in precipitous drawdown of dissolved oxygen (DO) in the water column. To address this issue, a new in situ experimental apparatus designed to achieve high flow velocities was implemented to characterize SOD, both with and without sediment resuspension. In the case of resuspension, the suspended sediment concentration was analyzed as a function of bed shear stress, and a formulation was developed to characterize resuspended-sediment oxygen demand (${\mathrm{SOD}}_{\mathrm{R}}$) as a function of suspended sediment concentration in a form similar to first-order biochemical oxygen demand (BOD) kinetics with the DO term in the form of Monod kinetics. The results obtained can be implemented into a model containing hydrodynamic, sediment transport, and water-quality components to yield oxygen demand varying in both space and time for specific flow events. The results are used to evaluate water quality improvement alternatives that take into account the impact of SOD under various flow conditions.

In this paper, an advective dispersive virus transport equation, including first-order adsorption and an inactivation constant, is used for simulating the movement of viruses in fractured porous media. The implicit finite-difference numerical technique is used to solve the governing equations for viruses in the fractured porous media. In this work, the focus is (1) to investigate the transport processes of the movement of viruses in both fractured rock and porous rock without fracture and (2) to simulate the experimental data of biocolloids through a fractured aquifer model. It is seen that movement of the contaminant is faster in the fractured rock than in the porous rock formation. Higher values of diffusion coefficient, matrix porosity, mass transfer constant, and inactivation rate reduce both temporal and spatial virus concentrations in the fracture. Also, experimental data of biocolloids in the fractured aquifer model with constant and time-dependent inactivation rates were simulated successfully.

This work experimentally determined the effect of microwave treatment on the disintegration and acidogenesis of waste-activated sludges (WAS) from municipal and coke wastewater treatment plants. Sludge samples (500 g) were heated for 0, 3, 5, 7, 9, 11, and 15 min in a microwave oven (2,450 MHz, 700 W). The degree of sludge solubilization [soluble chemical oxygen demand (SCOD)/COD] increased asymptotically with microwave irradiation time from 1.5% at 0 min to 22.3% at 15 min for WAS from a municipal wastewater treatment plant (${\mathrm{WAS}}_M$) and 1.5% to 5.1% for WAS from a coke wastewater treatment plant of a steel manufacturing industry (${\mathrm{WAS}}_C$). The calcium concentrations in both sludges also increased with microwave irradiation time. The biochemical acidogenic potentials (BAP) increased from 3.70 to $4.44\mathrm{g}\mathrm{COD}{\mathrm{L}}^{-1}$ for ${\mathrm{WAS}}_M$ and 1.19 to $1.67\mathrm{g}\mathrm{COD}{\mathrm{L}}^{-1}$ for ${\mathrm{WAS}}_C$. The results show that microwave irradiation increases the solubilization and BAP of sludges and that ${\mathrm{WAS}}_M$ had a higher degree of solubilization and BAP than ${\mathrm{WAS}}_C$.

Two multistaged anaerobic digestion systems, a four-stage thermophilic anaerobic digestion (4TAD), all at 55°C, and a four-stage anaerobic digestion with a tapered temperature configuration (4ADT) at 55, 49, 43, and 37°C, respectively, were studied to evaluate their solids, volatile organic sulfur compounds, and indicator organism (E. coli and fecal coliform) reduction potentials. The 4TAD system removed significantly more volatile solids from sludges than the 4ADT system (6%). However, the dewatered biosolids cakes from the 4ADT system generated fewer organic sulfur compounds than those from the 4TAD system. Both multistage systems showed better digestion efficiencies than single-stage mesophilic or single-stage thermophilic anaerobic digesters at the same overall retention time. However, the lowest organic sulfur compounds were observed from the single mesophilic system. Both multistage anaerobic digestion systems failed to dramatically remove DNA of the indicator organism, E. coli, quantified by real time polymerase chain reaction, even though the indicator organism densities measured by standard culturing methods satisfied EPA Class A biosolids requirements.

This work studies the ozonation of the pharmaceutical propranolol (PRO) in aqueous solution. Experimental results demonstrated that ozonation was an efficient method to remove PRO, achieving its complete abatement after 8 min of treatment (ozone dose of $0.47\mathrm{mmol}{\mathrm{L}}^{-1}$), starting from a PRO initial concentration of $0.38\mathrm{mmol}{\mathrm{L}}^{-1}$. The total organic carbon (TOC) analysis indicated that 1 h of ozonation (ozone dose of $3.54\mathrm{mmol}{\mathrm{L}}^{-1}$) was able to achieve only about 5% of the total organic carbon removal. The ozonation of PRO aqueous solutions has not promoted a prompt increase of the ratio of biological oxygen demand to chemical oxygen demand, thus indicating the need for higher ozone doses to initiate the biodegradability enhancement. The acute toxicity increased in the first minutes of reaction with a posterior reduction to values slightly higher than the toxicity of the PRO raw solution. Some early intermediate structures were proposed, and finally, kinetic constants for the direct attack of ozone on PRO structure were calculated. These values are in the order of magnitude of ${10}^5\mathrm{L}{\mathrm{mol}}^{-1}{\mathrm{s}}^{-1}$.