Journal of Environmental Engineering

Recent research has proposed the use of asphalt and tall-oil-pitch emulsions for stabilizing radioactive contamination deposited on surfaces in urban areas. The objective of this project was to investigate whether surface applied emulsions could capture airborne radioactive particulate. Laboratory experiments included wind-blown particulate capture studies using an acrylic column and particulate retainment experiments using a wind box capable of producing wind speeds of $96\mathrm{km}∕\mathrm{h}$ . A probe methodology was developed to relate particulate retainment to a tack force on the emulsion surface. Experiments were also performed to determine the potential for such emulsions to absorb particulate matter into their emulsion matrix. Tall-oil-pitch emulsions outperformed asphalt emulsions in terms of particulate retention, tack force, and the ability to absorb magnesium silicate. Both tall-oil-pitch and asphalt emulsions were capable of extracting $22–24\mathrm{g}{\mathrm{m}}^{-2}$ of powder from particulate-laden airflow. Tall-oil-pitch emulsions were capable of retaining as much as 5–10% of magnesium silicate powder applied (i.e., retainment densities of $10–20\mathrm{g}{\mathrm{m}}^{-2}$ ) even after $\text{seven}\text{days}$ of curing and after applying $96.5\mathrm{km}∕\mathrm{h}$ $\left(60\mathrm{mph}\right)$ wind. Tall-oil-pitch emulsions were able to absorb surface-applied magnesium silicate (approximately $0.1–0.2\mathrm{g}$ of magnesium silicate per $1.0\mathrm{g}$ of emulsion within $\text{three}\text{days}$ ) into their emulsion matrix, preventing the magnesium silicate from being exposed to the external environment. Initial results with these five different emulsion formulations suggested particulate capture was feasible. Future emulsion formulations (i.e., longer curing times with greater acid concentrations) should be tested to optimize this postdetonation response strategy.

Combined sewer overflows (CSOs) result in hazardous and unsightly contamination of receiving waters, particularly swimming areas. The removal of suspended solids and associated biological oxygen demand (BOD) can accelerate the recovery following a CSO event. This paper presents a numerical model to simulate the solids removal efficiency of a retention treatment basin (RTB) that utilizes polymers to improve the flocculation and settling rates for the suspended solids. The model includes settleable, nonsettleable, and floatable solids. The sludge is treated as a non-Newtonian fluid. Discrete, zone, and compression settling/floatation regimes are included. In-tank flocculation and a storage zone for sludge flushing are also included in the model. The model was calibrated and validated with data from a RTB pilot plant, and was applied to evaluate preliminary designs for a prototype RTB for the City of Windsor. The calibrated model showed that the optimum location of the target baffle was approximately 30% of the distance to the scum baffle. For design flows of $20\mathrm{m}∕\mathrm{h}$ and run durations of up to $2\mathrm{h}$ , it was found that the removal was insensitive to slopes from $-1$ to $-3\%$ and depths greater than $2.5\mathrm{m}$ $(\mathrm{L}∕\mathrm{H}=10)$ . The simulations indicate that 70 to 78% of solids removal can be achieved at surface overflow rates up to $25\mathrm{m}∕\mathrm{h}$ .

Ballasted flocculation processes were studied at laboratory scale to evaluate the mode of transport of ballasting agent from bulk liquid into the chemical floc and establish a new model for assessing the mechanisms of ballasted floc formation. For this purpose, a test program consisting of bench scale observations, microscopic observations, density tests, and centrifugal settling tests was developed. Ballasted flocs were found to be formed by a mechanism in which the ballasting agent is incorporated into the floc matrix by inertial forces, and the ballasting agent taking the place of the bound water content $\left({\Phi }_W\right)$ . Bulk density of ballasted flocs $\left({\rho }_b\right)$ was found to be linearly related to the ballasting agent dose $\left(M\right)$ . This study provided a better understanding of the mechanisms controlling the interaction between ballasting agent and coagulant/polymer chemical floc.

Polychlorinated biphenyl (PCB) contamination in the United States is predominately from commercially manufactured Aroclor mixtures. These mixtures consist of approximately 150 congeners and are characterized by chlorination level and congener distribution profile, with some congeners maintaining a constant relative abundance across the chlorination levels. Once introduced into the environment, changes in congener profiles occur, in some cases altering the relative abundance of congeners correlated in the commercial Aroclors. The shifts in the relationships of the correlated congener pairs (trackers) are used to quantify the likelihood of natural remediation processes occurring in the anaerobic sediment and to identify positions where chlorine removal is likely. A numerical model for elucidating the most likely chlorine positions was developed, implemented, and tested on Hudson River sediment data. The model results show that flanked chlorines were most likely to have been removed, followed by meta chlorines. These results are consistent with those reported by laboratory investigation of Hudson River sediments. The findings suggest that the model can successfully determine the most likely positions of chlorine removal, even in the absence of a priori knowledge of the sediment contamination (source Aroclors) or the dechlorinating organisms. Thus the model can be applied, even where limited knowledge exists regarding the contamination source and the nature of the biogeochemical reactions affecting the fate of PCBs in a particular sediment system.

This paper presents the genetic algorithm (GA) solution of a gray nonlinear water environment management model we developed for the Liming River basin in Daqing, China to improve the water environment management. The model has been developed by both optimizing the operation of wastewater treatment plants and making full use of assimilative capacity of the river so that the optimum integration of these two measures can keep the water quality in the Liming River basin up to a satisfactory standard at a reasonable cost. It can be used as an example to illustrate the potential application of a GA-based gray nonlinear programming in the field of water environment management.

Adsorption equilibrium and kinetics of carbon disulfide in water by granular activated carbon (GAC), powdered activated carbon (PAC), and activated carbon fiber (ACF) were investigated and compared in an effort to elucidate the fundamentals for optimizing the control process design. It has been shown that the BET expression can satisfactorily describe the adsorption equilibrium of carbon disulfide ( $\mathrm{C}{\mathrm{S}}_2$ ) on GAC, PAC, and ACF and the corresponding kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the $\mathrm{C}{\mathrm{S}}_2$ adsorption is the rate-limiting step. A two-phase mathematical model was developed to simulate $\mathrm{C}{\mathrm{S}}_2$ transfer in fixed-bed operation filled with the GAC, PAC, and ACF, and the equilibrium and kinetics information is subsequently used in the model to characterize the dynamics of adsorption. The model includes mechanisms such as axial dispersion, advection, liquid-to-solid mass transport, and intraparticle mass transport by pore and surface diffusion. It is manifested that the model was able to predict the dynamic breakthrough curve of $\mathrm{C}{\mathrm{S}}_2$ in a fixed-bed adsorption column filled with GAC, PAC, and ACF at varied conditions (standard deviations for $1.5\mathrm{cm}∕\min$ is 12.13% and for $2.2\mathrm{cm}∕\min$ is 16.12%), based on BET-3 equilibrium and second-order kinetics, which indicates that the methodology proposed by this work could be employed for adsorbents selection, adsorption design, and process optimization for $\mathrm{C}{\mathrm{S}}_2$ waste-water emission control.

Both inherent natural variability and model parameter uncertainty must be considered in the development of robust and reliable designs for drinking water treatment. This study presents an optimization framework for investigating the effects of five variable influent parameters and three uncertain model parameters on the least-cost treatment plant configuration (contact, direct, or nonsweep conventional filtration) that reliably satisfies an effluent particulate matter concentration constraint. Incorporating variability and uncertainty within the decision-making framework generates information for investigating: (1) impacts on total cost and treatment reliability; (2) shifts on the least-cost treatment configuration for providing reliable treatment; and (3) the importance of the individual variable and uncertain parameter distributions for reliably satisfying an effluent water quality constraint. Increasing the magnitude of influent variability and model parameter uncertainty results in a greater expected design cost due, generally, to increases in process sizing required to reliably satisfy the effluent concentration constraint. The inclusion of variability and uncertainty can also produce a shift in the locations of the least-cost configuration regions, which are dependent on the expected influent water quality and the magnitude of variability and uncertainty. The additional information provided by incorporating the variable and uncertain parameters illustrates that parameter distributions related to the primary removal mechanism are critical, and that contact and direct filtration are more sensitive to variability and uncertainty than conventional filtration.

Wind produces turbulence facilitating the exchange of pollutants and other environmentally important trace gases such as oxygen and greenhouse gases between stationary water bodies and the atmosphere. Whereas wind speeds continuously vary, different wind speed monitoring and characterization procedures have been used for the gas exchange studies. We assessed the impact of measurement time intervals, logarithmic wind speed profiles, and surface roughness values on wind characterizations. The Weibull probability density function effectively characterized yearly and seasonal wind speed distributions. It was not affected by various averaging time intervals $(1–60\min )$ . However, averaging time interval of $<10\min$ was necessary for reliable characterizations of shorter-periods ( $<3–5$ days). Vertical wind speed variations were effectively described by logarithmic profile irrespective of atmospheric stability conditions. Interestingly, use of the logarithmic profile allowed the actual $U_{10}$ to be predicted with reasonable accuracy for a wide range of surface roughness values. This was true under all stability conditions. Thus, small time intervals and the logarithmic profile appear to be very robust and widely useful techniques.

A water distribution network (WDN) is designed to meet time-varying demands with sufficient pressure, taking into consideration an appropriate demand during peak hours. Therefore, a network has inherent redundancy in the sense that under abnormal conditions such as those arising due to pipe breaks or pump failures, deficiency in supply during peak hours can be met through additional supply during off-peak periods. However, this necessitates a storage facility at the consumer end of the network, which is normally available in the form of a sump or an overhead tank in developing countries. Such a storage enables the consumer to store water during the off-peak period and then use it during the peak period. Reliability of a WDN is assessed herein considering nodal storage, and an iterative method is proposed for the optimal design of Level 1 redundant WDNs, i.e., networks that can sustain a single pipe failure without affecting consumer services either in part or in full. The method is illustrated through an example and the designs of a network with and without storage are compared. Provision of a nodal storage is found to reduce the total cost of the network.

This paper presents a particle penetration model predicting particle penetration coefficient $\left(P_p\right)$ through a narrow crack of arbitrary incline angles $\left(\theta \right)$ . The objective was to simulate $P_p$ for outdoor-to-indoor particle penetration for residential infiltration conditions. This model assumes laminar infiltration flow and considers particle deposition from both gravitational sedimentation and Brownian diffusion. For micron-sized particles, modeling results indicate that gravitational sedimentation is the major deposition mechanism. $P_p$ increases monotonically with $\mid \theta \mid$ because effective particle sedimentation velocity $\left(v_s\cos \theta \right)$ decreases monotonically with $\mid \theta \mid$ . For submicron-sized particles $\left(0.1\mathrm{\mu }\mathrm{m}\right)$ , Brownian diffusion is the major particle deposition mechanism. Because Brownian diffusion is a nondirectional deposition mechanism, crack inclination did not affect $P_p$ . This study applied this model to estimate $P_p$ for $L$ -shaped cracks, and validated modeling results with experiments. Experimental results indicated that inertial impaction and crack entrance cutoff effects were not significant particle deposition mechanisms for the test micron-sized particles. Gravitational sedimentation was the major deposition mechanism. An L-shaped crack can be simulated as the combination of horizontal and vertical sections. This model agreed reasonably with experimental results.

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCP, and toxicity removal performance of the system were investigated for sludge ages between 5 and $30\text{days}$ , while the feed COD $(2600\pm 100\mathrm{mg}{\mathrm{L}}^{-1})$ , TCP $(370\pm 10\mathrm{mg}{\mathrm{L}}^{-1})$ , and the hydraulic residence time $\left(25\mathrm{h}\right)$ were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above $20\text{days}$ . Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCP, COD, and toxicity removals. More than 95% of COD, TCP, and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum $\left(120\mathrm{mg}\mathrm{TCP}\mathrm{g}{X}^{-1}{\text{day}}^{-1}\right)$ at a sludge age of $20\text{days}$ . TCP inhibition was eliminated by operation of the system at sludge age above $20\text{days}$ to obtain nearly complete COD, TCP, and toxicity removal.

This paper describes a series of laboratory tests conducted to assess the performance of a novel fluorescence-based in situ sensor for environmental contaminants. The sensor, which can be deployed downhole in a monitoring well, or incorporated into the shaft of a cone penetrometer, is less than $4\mathrm{cm}$ in diameter and uses a miniature microchip laser that produces $\sim 200\mathrm{ps}$ pulses of ultraviolet radiation at a high repetition rate $(\sim 10\mathrm{kHz})$ to excite fluorescence in a wide range of compounds. Results from laser induced fluorescence tests on single compound aqueous solutions of benzene, toluene, and o-xylene (BTX) demonstrate the sensor’s ability to perform contaminant analyses on compounds with fluorescence lifetimes on the order of $1\mathrm{ns}$ . A linear relationship between contaminant concentration and fluorescence intensity was observed for concentrations over several orders of magnitude from the sensor’s detection limit ( $<1\mathrm{ppm}$ for o-xylene) to solutions of pure BTX compounds at aqueous solubility. Owing to the microchip laser’s short pulse length, fluorescence lifetimes were obtained directly from measurements without the need for spectral deconvolution. Analysis of data from these tests highlights the importance of differentiating a sensor’s ability to detect, identify, and quantify compounds of interest—performance thresholds that ultimately define potential applications for the device.