Journal of Environmental Engineering

This paper presents a generalized uncertainty estimation method (GUEM) to characterize the fate and transport of petroleum-hydrocarbon contaminants in subsurface environments. Compared to the conventional methods, GUEM employs the Metropolis-Hastings sampling algorithm to replace the conventional Monte Carlo algorithm; this algorithm has the advantage of reducing computational cost in obtaining realizations of uncertain parameters. The GUEM method is applied to a hypothetical homogenous and a real-world heterogonous site for demonstration studies. The first demonstration shows that GUEM generates outputs with wider bounds than conventional uncertainty characterization methods. This avoids overestimation of lower bounds and underestimation of upper bounds of resulting modeling outputs. Results from the second demonstration implied that the groundwater would not be suitable for the drinking water source after three years of natural attenuation and remediation actions should be taken to guarantee the groundwater safety. Even after taking a three-year pump-and-treat remediation action, it would pose risks as one can conclude that the benzene concentrations would violate the regulated environmental guideline with a possibility of over 0.9, and enhanced remediation actions are still desired to be taken for improving the groundwater quality. Despite the advantages in characterizing the fate and transport of contaminants, GUEM could be improved by introducing two correlated random variables in the sampling process for enhancing simulation accuracy. It is also expected to be integrated with traditional methods such as Monte Carlo method and generalized likelihood uncertainty estimation method to deal with hybrid fuzzy-random and interval-random inputs, respectively.

This study concerns the control of movement of light nonaqueous phase liquid (LNAPL) in unsaturated zone in the presence of relatively low permeability clay lens. A two-dimensional, finite-difference numerical model for the simultaneous movement of LNAPL and water through the unsaturated zone of the soil has been developed. The system is a three fluid phase system (water, LNAPL, and air) but in the derivation of the model, air was treated as an immobile phase at constant atmospheric pressure. The flow equations for LNAPL and water were cast in terms of the wetting and non-wetting fluid pressure heads, respectively. The finite-difference equations were solved implicitly with explicitly scheme using Newton-Raphson iteration with Taylor series expansion to treat nonlinearity. A physical model to represent the infiltration of kerosene above the clay lens was constructed. The numerical results were compared with those observed experimentally. The results of all tests showed that the presence of clay lens controls the vertical movement of LNAPL in heterogeneous porous medium.

Gravitational settling regimes, most commonly discrete (Type I) or flocculent (Type II) can be hindered (Type III) in unmaintained urban drainage appurtenances. In coastal zones or in areas with deicing salt applications, high salinity may influence particulate matter (PM) settling. This study examines settling of PM with a heterodisperse particle size distribution (PSD); typical of urban runoff. For Type I settling at low concentration $\left(\sim 0.1\text{g}/\text{L}\right)$ , Newton’s and logarithmic matching models each predict measured settling velocity $\left(V_s\right)$ for PM from $2–4,750\mu \text{m}$ . For Type I $V_s$ in runoff, PM diameter dominates the influence of PM density, fluid temperature and salinity parameter ranges. Integrating Type I $V_s$ across a common heterodisperse PSD for regulatory testing, a physically validated computational fluid dynamics model of a baffled hydrodynamic separator (HS) illustrates the influence of $V_s$ parameters as PM $\text{diameter}⪢\text{PM}\text{density}>\text{temperature}\approx \text{salinity}$ . Event-based PM separation by a screened HS loaded by unsteady flows and heterodisperse PSDs is predicted by overflow rate, and integrating measured (or validated Newton’s Law) $V_s$ , flow and PSD data. For Type II settling, $V_s$ is a first-order function of PM concentration (1, 2, and 3 g/L); as well as time and settling depth. Type III $V_s$ is modeled as a power law function of PM concentration. Across the PSD tested, salinity up to 30 ppt does not have a significant (at $p=0.05$ ) role on Type I $V_s$ . However, salinity is significant (at $p=0.05$ ) in Type II settling; as well as for Type III settling below 120 g/L. For all regimes, PM concentration, PSD heterodispersivity, and time dominate salinity or temperature influences.

A numerical model was developed to calculate the rate of dissolved-oxygen (DO) diffusion across a sediment surface taking into account the surface roughness and biochemical reactions of the sediment. Estimates of DO transfer rate from the model were compared with results from laboratory experiments conducted in a rectangular flume using roughness elements. In experiments, there was maximum value for the nondimensionalized DO transfer rate (Stanton number, $\mathsf{St}$ ) in the transitional region of surface roughness, in which the mass flux was two to five times larger than that of the smooth surface. The reproducibility of the experimental results by numerical analysis was significantly improved by including terms for flushing frequency of water in cavities between the roughness elements and for nonsteady variations in the diffusion rate due to step changes in DO concentration in the flushed region. A simple method to estimate enhancement effect for $\mathsf{St}$ caused by nonsteady variations was also presented.

The objective of this research was to develop a photocatalytic reactor that will reduce the total organic carbon (TOC) concentration of a gray water influent. The system used a reactor packed with titanium dioxide $\left({\text{TiO}}_2\right)$ supported by silica gel $\left({\text{SiO}}_2\right)$ and was optimized with respect to several system parameters. The ${\text{SiO}}_2–{\text{TiO}}_2$ composites (STCs) were capable of reducing the TOC concentration from 3,000 ppb to below the targeted concentration of 500 ppb in a recirculating system. An optimum empty bed contact time of 7 min was found based on the fastest destruction rate to reach below 500 ppb of TOC. Also based on destruction rate, a STC having a ${\text{TiO}}_2$ loading of 12 g/100 mL of ${\text{SiO}}_2$ precursor and approximately 120-Å pore size was shown to have the best performance among several composites of different ${\text{TiO}}_2$ loadings and pore sizes. The addition of activated carbon to the STC was found to improve the overall performance of the system by increasing the composite’s adsorption capabilities.

Bacteria can synthesize cytoplasmic granules known as polyhydroxyalkanoates (PHAs), which are carbon and energy storage reserves, from organic carbon when subject to stressful environmental conditions. PHAs are also biodegradable thermoplastics with many potential commercial applications. The purpose of the research reported herein was to evaluate the feasibility of integrating PHA production within a municipal wastewater treatment (WWT) configured as a sequencing batch reactor (SBR). Four bench-scale WWT SBRs were tested at decreasing organic loading rates to assess the potential to enrich for microbes capable of feast/famine PHA synthesis. For each treatment SBR, sidestream batch reactors receiving higher quantities of primary solids fermenter liquor were operated to produce PHA. Results from this study demonstrate that a treatment SBR supplied moderate strength wastewater can enrich for the target microorganisms, with PHA yields of 0.23–0.31-mg PHA per mg chemical oxygen demand, and produce high quality effluent. In sidestream batch reactors, microorganisms that fed excess quantities of substrate can rapidly synthesize significant quantities of PHA. Based on the results of this study, we estimate that a 1 million gallon per day SBR WWT-PHA production system could generate 11–36 t (12–40 t) of PHA annually.

Crumb rubber media have been beneficially invented for ballast water and tertiary wastewater treatment. There is a critical need for precise prediction of clean-bed head loss for engineering design purposes. Pilot crumb rubber filters were tested to study their clean-bed head loss under the influences of three design and operational parameters (media size, media depth, and filtration rate). Data from the filtration tests were used to evaluate the application of the Kozeny and Ergun equations in crumb rubber filters and to develop a statistical model for examination of the effects of each parameter and for clean-bed head loss prediction. Results showed that both the Kozeny and Ergun equations had limitations for crumb rubber filters, especially when the data of compressed media depth were unavailable from the filtration tests. The statistical model developed by the multiplicative power-law relationship was proved to be valid, and it could be used to predict clean-bed head loss in crumb rubber filters.

The ${\text{H}}_2$ -based membrane biofilm reactor (MBfR) was shown to simultaneously reduce nitrate and selenate in flue-gas desulfurization (FGD) brines (15–33 g/L TDS). The MBfR also used polyester fibers, which differ from the composite gas-transfer fibers used in previous MBfR studies. Selenate reduction was nearly 100% in all media tested and was immediate, which suggests that selenate was coreduced with nitrate, possibly by the same microorganisms. A step increase in the nitrate removal flux was observed at a ${\text{H}}_2$ pressure greater than 20 psig (138 kPa) using polyester fibers. High concentrations of nitrate and sulfate had no inhibitory effect on selenate reduction as long as ${\text{H}}_2$ was available. In comparison with previous MBfR experiments treating ion-exchange brine, total electron equivalent fluxes were 29% lower and in contrast to earlier work on selenate reduction in fresh water, sulfate reduction was inhibited, likely due to the high total dissolved solids in the FGD brine or insufficient ${\text{H}}_2$ availability due to ${\text{CaCO}}_3$ or Se° precipitation onto the tighter polyester fibers.

Solid waste management (SWM) is increasingly becoming a challenging task for the municipal authorities due to increasing waste quantities, changing waste composition, decreasing land availability for waste disposal sites, and increasing awareness about the associated environmental risk. This paper presents a fuzzy parametric programming model for the selection of the treatment and disposal facilities and optimum capacity planning and waste allocation under uncertainty associated with the long-term planning for SWM. The model dynamically locates the facilities and allocates the waste considering fuzzy waste quantities and capacities of waste-management facility in a multiperiod planning for integrated SWM. The model addresses uncertainty in waste quantity as well as uncertainties in the operating capacities of waste-management facilities. An example problem has been presented to demonstrate the usefulness of the proposed model in making the planning decisions related to SWM and achieving an efficient plan. The model is solved at different levels of membership function for the alternative solutions with respect to objective. The example problem reveals that the uncertainty in the waste quantity is likely to affect the planning for waste treatment/disposal facilities more as compared with the uncertainty in the capacities of the waste-management facilities. The relationship between increase in waste quantity and increase in the total cost involved in waste management is found to be nonlinear. The modeling results are useful for generating a range of decision alternatives under various economic conditions. They are valuable for analyzing the existing waste-management practices, the long-term capacity planning for the city’s waste-management system, and the identification of desired policies regarding waste generation and management.

This study assessed the performance of a conventional grease abatement device and the impact of internal geometry modifications on fat, oil, and grease (FOG) removal efficiency. Analysis was performed using experimental results and computational fluid dynamics (CFD) on alternative inlet, outlet, and baffle wall designs. Numerical and experimental results indicated that the conventional two-compartment design leads to substantial FOG short circuiting when operated at a 20-min hydraulic retention time (HRT). Alterations to the inlet configuration and baffle wall arrangement yielded FOG removal enhancements with the 20-min HRT that approached removal performance levels obtained with the standard configurations at the 1-h HRT. CFD simulations effectively reproduced performance trends observed on the lab-scale with the exception of simulations using a distributive inlet tee, where CFD over predicted the removal performance.

In this note an example of modeling of biodegradation processes of an old abandoned municipal solid waste landfill for its simulation is illustrated using the landfill dynamic simulation tool MODUELO. In this program the waste biodegradation model is based on the quantification of organic matter, its chemical composition, biodegradability, accessibility to microorganisms, and the ratio nonbiodegradable leachable organic matter to gasifiable matter. Data from a characterization campaign, presented elsewhere, were used to determine these parameters. The experimental information was completed with safety factors (to compensate for sampling uncertainty) and literature values. The degradation rates were determined, after having calibrated the hydrological model, by fitting the temporal series of pollutants’ concentration measured in the leachate and the biogas composition. The achieved fit of the simulated series compared to the measured data is reported as the result of this work. Given the limited information available, the obtained simulation model is considered an acceptable tool to study the future evolution of the landfill in different circumstances.