Journal of Environmental Engineering

The presented modeling investigation examines the potential influence of advection-induced evaporation and condensation on bioventing, a vadose-zone remediation technology. Currently, few soil vapor extraction or bioventing models incorporate nonisothermal effects when considering system performance. Laboratory and field measurements suggest, however, that even small changes in temperature and moisture content can influence microbial activity and could thus affect the overall efficiency of a bioventing operation. The model here is a one-dimensional simulator that describes mass and energy transport under steady, gaseous phase flow conditions. The coupled mass and energy equations are solved using a sequential iterative solver with matric potential and temperature as primary variables. A literature-derived relation is used to quantify the combined effect of water potential and temperature change on biological growth rates. Simulations indicate that the injection of air at temperatures and/or water vapor concentrations different from the initial ambient soil conditions can induce changes in matric potential and local soil temperature, which could measurably impact biological activity.

Use of generic search algorithms for detection of subsurface biological activity zones (BAZ) is investigated through a series of hypothetical numerical biostimulation experiments. Continuous injection of dissolved oxygen and methane with periodically varying concentration stimulates the cometabolism of indigenous methanotropic bacteria. The observed breakthroughs of methane are used to deduce possible BAZ in the subsurface. The numerical experiments are implemented in a parallel computing environment to make possible the large number of simultaneous transport simulations required by the algorithm. Our results show that genetic algorithms are very efficient in locating multiple activity zones, provided the observed signals adequately sample the BAZ.

The study objective was to examine whether a relationship exists between the accumulation of exopolymeric substances (EPS) in landfill cover soil and the gradual decline in biotic methane oxidation observed in laboratory soil columns sparged with synthetic landfill gas. A mathematical model that combined multicomponent gas diffusion along the vertical axis of the columns with biotic methane oxidation was used to predict vertical gas gradients in the columns. An initial trial assumed methane oxidizers were embedded in a thin base layer of biofilm coating the soil, and the model predictions fit experimental data from soil columns early in their operating period. A second trial modeled the same system with a thick EPS layer coating the base biofilm and limiting diffusion of gases into and out of the cells. Predictions from the latter trials fit experimental data from soil columns later in their operating period when lower methane consumption rates were observed. The model results suggest that EPS accumulation may regulate methane oxidation rates in landfill covers.

The premise that the morphology of deposits formed from colloids, aerosols, and other particulate materials can be predicted from their transport properties and surface chemistries is explored. Universality classes that group the conditions of particles in suspension to the structure of a deposit composed of a large number of particles are considered in the context of their importance in natural and engineered systems encountered in environmental engineering. Evidence for one such “transport-morphology link” is presented, and the implications of this linkage in filter modeling, prediction of sediment characteristics, and membrane fouling are presented.

Rheological characteristics of sludge represent one of the few examples of fundamentally derivable properties that have also been successfully used for the improvement of actual sludge treatment processes. Previous research has suggested the use of certain sludge rheological parameters for polymer dose optimization and floc characterization. This research evaluated the use of rheological properties for characterization and control of sludge conditioning with polyelectrolytes. Rheological characteristics were compared with dewaterability in laboratory evaluations, utilizing both synthetic cellulose suspension and actual sludge. These experiments were designed to identify fundamental rheological parameters that may have the potential to be used for assessment and control of conditioning and dewatering processes. This paper reports and analyzes results from controlled laboratory experiments; evaluations of on-line rheology measurements for process control in a nearby sludge handing facility have been presented elsewhere. Laboratory conditioning indicators were capillary suction time, liquid stream (centrate) streaming current and viscosity, and solids measurements. Full-scale dewatering indicators were capillary suction time, liquid stream (filtrate) streaming current, and percent solids recovery. Results indicated lack of correlation between the proposed conditioned sludge rheology-control parameters and conditioning indices over a wide range of mixing conditions. Mixing parameters have a substantial effect on the rheological characteristics of the concentrated suspensions and shed some light upon floc strength as related to dewaterability.

The impact of synthetic surfactants on the aqueous phase biodegradation of benzene, toluene, and p-xylene (BTpX) was studied using two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS), and two nonionic surfactants, POE(20) sorbitan monooleate (T-maz-80) and octylphenolpoly(ethyleneoxy) ethanol (CA-620). Batch biodegradation experiments were performed to evaluate surfactant biodegradability using two different microbial cultures. Of the four surfactants used in this study, SDS and T-maz-80 were readily degraded by a microbial consortium obtained from an activated sludge treatment system, whereas only SDS was degraded by a microbial culture that was acclimated to BTpX. Biodegradation kinetic parameters associated with SDS and T-maz-80 degradation by the activated sludge consortium were estimated using respirometric data in conjunction with a nonlinear parameter estimation technique as μ_max = 0.93 h⁻¹, K_s = 96.18 mg/L and μ_max = 0.41 h⁻¹, K_s = 31.92 mg/L, respectively. When both BTpX and surfactant were present in the reactor along with BTpX-acclimated microorganisms, two distinct biodegradation patterns were seen. SDS was preferentially utilized inhibiting hydrocarbon biodegradation, whereas the other three surfactants had no impact on BTpX biodegradation. None of the four surfactants were toxic to the microbial cultures used in this study. Readily biodegradable surfactants are not very effective for subsurface remediation applications as they are rapidly consumed, and also because of their potential inhibitory effects on intrinsic hydrocarbon biodegradation. This greatly increases treatment costs as surfactant recovery and reuse are adversely affected.

Anaerobic biological wastewater treatment systems are difficult to model because their performance is complex and varies significantly with different reactor configurations, influent characteristics, and operational conditions. Instead of conventional kinetic modeling, advanced neural fuzzy technology was employed to develop a conceptual adaptive model for anaerobic treatment systems. The conceptual neural fuzzy model contains the robustness of fuzzy systems, the learning ability of neural networks, and can adapt to various situations. The conceptual model was used to simulate the daily performance of two high-rate anaerobic wastewater treatment systems with satisfactory results obtained.

Thermal waves resulting from the dynamic adsorption of organic vapor present in air on a granular activated carbon (GAC) filter were studied. An experimental design was carried out to determine the influential factors among the relative humidity of air (0–60%), the initial water content of the activated carbon (0–9.8%), and the volatile organic compound (VOC) concentration (0–50 g⋅m⁻³, i.e., 0–20,700 ppmv for acetone). The temperature increase is a function of the initial VOC concentration as well as the energy flux released. The warming of the adsorber is shown to be important for the adsorption of high VOC concentrations on a dry carbon bed, but the thermal amplitude is distinctly reduced when the GAC is initially wet because of water desorption. The moisture content of the air in the range of 0–95% is not found to be a prominent factor affecting both the adsorption capacity and the warming of the GAC bed for the high VOC concentration tested (20,700 ppmv of acetone). Temperature monitoring provides interesting information about the adsorption process, and the mechanisms involved are discussed.

An in situ trickling filter system, named Trickling Trench, is being used to treat biodegradable organic compounds at a site underlain by silt and clay. This method provides the containment advantages of pump-and-treat remediation with the low-cost benefits of in situ bioremediation. A design method is presented using a conventional trickling filter analytical model with kinetic coefficients for various organic compounds calculated from published data. Performance monitoring data obtained from the Trickling Trench bioreactor are compared to design predictions.

Chemical coagulation is a well-known method for removing colloidal particles that cause turbidity in water. In this study coagulation was used to remove emulsified petroleum hydrocarbons (PHCs) found in fuel oils from brackish water. Comparison of the total ion chromatograms of PHCs before and after coagulation clearly showed that PHCs with carbon numbers between 11 and 35 (naphthalene to pentatriacotane) with long chain alkanes were removed completely from the brackish water by coagulation followed by settling. Smaller carbon number (C7–C9) benzene derivatives were partially removed. For the PHCs with smaller carbon numbers, the removal efficiency increased with increasing carbon number.

Data collected in this study demonstrate that fecal bacteria counts in urban tributaries were much higher in sewered basins than in nonsewered basins; fecal bacteria densities were related to the density of housing, population, development, percent impervious area, and apparent domestic animal density. Preliminary fecal bacteria data collected for surface runoff samples in these urban neighborhoods indicate that a relationship may exist between various urban land uses and potential bacterial loading.