Journal of Environmental Engineering

Phytoremediation is an emerging technology for degradation of organic chemicals. The potential of phytoremediation in the cleanup of contaminated sites and prevention of non-point-source pollution was examined with the pesticide atrazine in two experimental systems. Uptake was determined in batch experiments with ¹⁴ C ring-labeled atrazine and hybrid poplar trees grown in two soil types. Mineralization was studied utilizing soil microcosms with the addition of root exudates. Results indicate that poplar cuttings were able to uptake the majority of applied atrazine that was not tightly sorbed to the organic fraction of the soil, with no detectable adverse effects to the trees. The addition of root exudate to microcosms showed slight stimulation and the addition of ground-up root biomass revealed large stimulation of mineralization to ¹⁴ CO ₂ . From experimentally acquired data, a mathematical model was developed to obtain kinetic rate constants. This research indicates that vegetative uptake and degradation in the rhizosphere can play a major role in remediation at hazardous waste sites.

Landfills can be regarded as uncontrolled anaerobic digestors. An increasingly popular landfill management technique involves moisture addition and/or leachate recycle which can enhance stabilization, increase gas production, and improve leachate quality. Leachate recycle operations have not been guided by theory. In this paper, the optimal control theory is applied to managing waste decomposition in landfills through leachate recycle. The technique minimizes net present value cost of landfill postclosure operations while satisfying landfill liner safety constraints. The optimal control method specifies leachate recycle rates through the landfill lifetime and the optimal leachate collection and distribution system capacities. The approach is applied to a simplified model of waste decomposition in a typical excavated cell landfill with composite liner.

Oil-contaminated soil (2.3–17 g/kg), even soil with high clay and silt content, was remediated microbiologically in a slurry reactor. The presence of soil, however, limits the degradation rate of oil. In contrast with results from experiments using oil dispersed in water, the relative composition of the oil components in a soil slurry after degradation was about the same as that of the original oil. Thus the composition of the degraded oil is the same as that of the original oil, which is indicative for a physical, rather than a (bio)chemical, limitation on the oil degradation rate. About 70% of the contaminant was readily available and was degraded in less than eight days. The dual injected turbulent suspension (DITS) reactor is able to combine remediation of part of the contaminated (polydisperse) soil with separation of the soil into a heavily and a lightly polluted fraction. In continuous operation, lowering the overall soil residence time from 200 to 100 h did not significantly increase the oil concentration in the effluent soil. Therefore a soil residence time of less than 100 h is feasible. With a residence time of 100 h, overall oil degradation rates at the steady state were more than 70 times faster than in a comparable land farm. After treatment in a DITS reactor, the remaining oil in the contaminated soil fraction is slowly released from the soil. From a batch experiment it was found that another 10 weeks were needed to reach the Dutch reference level of 50 mg/kg. This can be done in a process with a low energy input, such as a landfarm.

Three urban wet detention ponds in the Piedmont of North Carolina were monitored to investigate long-term pollutant removal as a function of surface to area ratios. Eleven storm events were monitored over a sampling period of 13 months. Urban runoff originating from the study area was characterized by event-mean concentrations for total suspended solids (135 mg/L), total Kjeldahl nitrogen (0.88 mg/L), total iron (6.11 mg/L), and total zinc (66 ug/L). Concentrations of copper and lead were consistently below the detection limits of 30 ug/L and 100 ug/L, respectively. The observed event-mean concentrations were generally lower than the national values reported by the Nationwide Urban Runoff Program. Particle sizes of sediment discharged in runoff were much finer than the national averages due to the predominant clayey soils in the region. This study demonstrates that surface to area ratio can be a useful predictor of wet pond performance. Utilizing 1–2% of the watershed area for the development of wet detention ponds at strategic locations could reduce pollutant loadings to meet targeted requirements of water quality improvement.

Modified biological methane-potential tests were used to study the treatment of wastewater with a chemical oxygen demand (COD) concentration of 40,000 mg/L and a sulfate concentration of 5,000 mg/L. The effects of wastewater concentrations on biodegradation and substrate interactions between sulfate reducers and methanogens were studied. Isopropanol (IPA) degradation was studied since isopropyl acetate was the major organic component in the wastewater. Six sets of batch tests were done, including a series of tests with varying concentrations of wastewater; wastewater and glucose; glucose and sulfate; IPA; IPA and glucose; and IPA, glucose, and sulfate. Sulfur and electron balances were used to analyze data to determine the extent of biodegradation from both methanogenesis and sulfate reduction. IPA did not appear to be inhibitory to methanogenesis or sulfate reduction. In comparison to glucose, the presence of wastewater or isopropanol stimulated greater sulfate-reduction efficiency. Evidence for IPA degradation was observed, and IPA degradation was stimulated in the presence of sulfate. Continuous feed-reactor results corroborated batch-test observations.

The simultaneous sludge digestion and metal leaching (SSDML) process can leach out heavy metals, achieve sludge solids reduction, and eliminate sludge pathogens. The potential for application in the wastewater treatment industry requires a sound knowledge of the system kinetics. The present work targets a better understanding of the qualitative as well as quantitative relationships between solids reduction rate and other parameters such as sludge pH, initial MLSS concentration, and availability of oxygen during the SSDML process. Experiments were carried out in laboratory batch reactors (20 L working volume) as well as in a 4,000 L capacity pilot facility. Based on the results of these experiments, it was concluded that degradation rate of sludge volatile matter is influenced by (1) sludge pH; (2) availability of oxygen; and (3) initial mixed liquor suspended solids (MLSS) concentration of the sludge. The degradation rate constant for biodegradable fraction of the mixed liquor volatile suspended solids [MLVSS(B)] was computed for various initial MLVSS concentration and sludge pH ranges. The value of k _d decreased with decreasing pH in all cases. Effect of initial MLSS concentration on the value of k _d was found to be minimal for the sludge studied. The relation between the sludge pH and k _d for this sludge was expressed in the form of two polynomials. The relations developed were used in conjunction with previous results on the SSDML process kinetics to simulate the overall SSDML process. Results of these simulation studies were found satisfactory when compared to actual experimental results.

A three-dimensional finite difference model for simulation of bioventing is presented. The model incorporates three-phase (gas-water-organic) flow with equilibrium interphase mass transfer and dispersive transport of organic compounds, oxygen, and carbon dioxide. Growth of microorganisms, substrate and oxygen consumption, and carbon dioxide production due to microbial activity are included. Biodegradation limitations due to both substrate and oxygen availability are modeled using the dual Monod formulation. The model is applied to predict the fate of a spill of toluene in the vadose zone under natural conditions and with various configurations of air injection and vapor extraction wells. Configurations of wells are determined that maximize biodegradation and minimize both the amount of toluene withdrawn in extraction wells and the amount lost to the atmosphere.

The homogeneous surface-diffusion model (HSDM) and the pore-surface-diffusion model (PSDM) for adsorption on granular activated carbon in a completely mixed batch reactor are examined in the near-equilibrium regime. In this asymptotic regime, linearized model equations yield analytic solutions for the measurable rate of adsorbate uptake involving effective diffusion coefficients. The theoretical asymptotic analysis is verified by numerical simulation of the complete equations. A basis is therefore provided for a method of determining diffusion coefficients from batch experiments that is simpler, more flexible, and more robust than those presently used. The present work also clarifies differences in the qualitative effects of pore and surface diffusion and suggests a preliminary graphical criterion for assessing directly from experimental data the possible importance of surface diffusion relative to other possible intraparticle transport mechanisms. A method for determining both poreand surface-diffusion coefficients when the pore-surface-diffusion model is appropriate and the appropriate data available are described. The proposed approach is illustrated by the analysis of two data sets available in the literature, and the resulting estimates are compared with those obtained by a more conventional method.

Reliable estimates of effective diffusivities in biofilms are required to calculate the combined diffusion and biotransformation of soluble substrates. For aerobic biofilms, effective diffusivities have been previously correlated empirically to the biofilm dry densities. Biofilms consist primarily of microbial cells, insoluble extracellular polymeric substances (EPS), and interstitial water. Biofilms are therefore a natural, heterogeneous, multiphasic material. Effective diffusive properties of such materials, both biological and nonbiological, have historically been correlated to the phase-volume fractions and diffusive properties of the individual phases. This paper presents a conceptually similar model for effective diffusivities in aerobic biofilms. The model predicts separate effects for increasing concentrations of microbial cells and insoluble EPS. Predicted effective diffusivities are expressed as a fraction of the corresponding dilute aqueous values.

An inverse model of an estuarine eutrophication model with eight state variables is developed. It provides a framework to estimate parameter values of the eutrophication model by assimilation of concentration data of these state variables. The inverse model using the variational technique in conjunction with a vertical two-dimensional eutrophication model is general enough to be applicable to aid model calibration. The formulation is illustrated by conducting a series of numerical experiments for the tidal Rappahannock River, a western shore tributary of the Chesapeake Bay. The numerical experiments of short-period model simulations with different hypothetical data sets and long-period model simulations with limited hypothetical data sets demonstrated that the inverse model can be satisfactorily used to estimate parameter values of the eutrophication model. The experiments also showed that the inverse model is useful to address some important questions, such as uniqueness of the parameter estimation and data requirements for model calibration. Because of the complexity of the eutrophication system, degrading of speed of convergence may occur. Two major factors which cause degradation of speed of convergence are cross effects among parameters and the multiple scales involved in the parameter system.

High-voltage transmission lines can pose an environmental problem, especially in countries where the electricity production is at a distance from the demand location. Planning, construction, and operation of high voltage transmission lines should be conducted within a comprehensive environmental policy, which may include assessment of visual impact, landscape and wildlife protection, and reduction of health risks. This paper reviews the environmental policies and action in planning, construction, and operation as developed by the utilities members of the Union Internationale des Producteurs et Distributeurs d'Energie Electrique (UNIPEDE). The paper also presents a brief outline of the health issues associated with the effects of electromagnetic fields to humans.

On account of reliability and absence of external power source, baffled channel-type flocculating devices are preferred for class-II settling. In the present practice a feasible design is obtained by trial and error to satisfy the design constraints. There is no consideration of economy in such a design. In this paper, the design of flocculating baffled channel has been formulated as a geometric programming problem with zero degree of difficulty. The solution of such a problem yields the optimal design expressed as the closed form equations for the optimal cost and the corresponding cost dimensions.