Journal of Environmental Engineering

A soil-slurry washing technique to decontaminate soils containing low-solubility nonionic organic pollutants was investigated, using phenanthrene as a model pollutant. The technique is based on first transferring the sorbed phenanthrene from the soil to anionic surfactant-coated oxide particles, and then separating these anionic surfactant-coated oxide particles with the sorbed phenanthrene from the soil slurry via a magnetic separation technique. The decontamination of two soils with different particle sizes and soil organic matter content was investigated. The proposed soil-slurry washing technique was effective in removing a strongly sorbing nonionic organic contaminant from soil slurries. Various operational scenarios of multistage soil-slurry reactors were evaluated with a mathematical model.

A finite-difference model was developed to more closely examine the observation that polycyclic aromatic hydrocarbon (PAH) transfer to and from low-organic-carbon aquifer sediment and aqueous natural organic matter (NOM) apparently occurred uninhibited by kinetic limitations during facilitated-transport and enhanced-desorption experiments performed in laboratory columns. The model accounted for advection, dispersion, and mass transfer between the various phases comprising the system; i.e., distribution of PAH between water and sediment and water and NOM, and distribution of NOM between water and sediment. The model was run using mass-transfer coefficients based on the equilibrium constants derived from experimental data and compared against the literature. Successful reproduction of the experimentally observed facilitated-transport and enhanced-desorption curves indicated that our physical system was free of kinetic limitations and was describable by the equilibrium constants comprising the system.

Dissolved oxygen (DO) distributions in stratified lakes can be simulated by a one-dimensional (vertical), deterministic, unsteady (time-variant) diffusion equation with surface gas transfer as a boundary condition and photosynthetic oxygen production as an internal source. Both surface gas transfer and vertical diffusion depend on turbulence near the water surface. The interaction between these two mechanisms, and photosynthetic productivity of dissolved oxygen in lake models is therefore studied analytically and numerically. The analytical solution of the DO transport equation in a semiinfinite medium is developed. Predicted DO concentrations at depth z are shown to depend on three dimensionless parameters, and the strength of net photosynthetic oxygen production is an important parameter in this analysis. The increases of DO concentrations due to photosynthesis are modulated by surface aeration and vertical diffusion in the lake. A numerical solution of the dissolved oxygen transport equation is also obtained and used to illustrate simulated DO profiles over an entire open water season in two Minnesota lakes. The analytical solution is used to explain certain features of the numerical results.

Predicting the size of low-probability, high-consequence natural disasters, industrial accidents, and pollutant releases is often difficult due to limitations in the availability of data on rare events and future circumstances. When incident data are available, they may be difficult to fit with a lognormal distribution. Two Bayesian probability distributions for inferring future incident-size probabilities from limited, indirect, and subjective information are proposed in this paper. The distributions are derived from Pareto distributions that are shown to fit data on different incident types and are justified theoretically. The derived distributions incorporate both inherent variability and uncertainty due to information limitations. Results were analyzed to determine the amount of data needed to predict incident-size probabilities in various situations. Information re-quirements for incident-size prediction using the methods were low, particularly when the population distribution had a thick tail. Use of the distributions to predict accumulated oil-spill consequences was demonstrated.

A leachate-recycle system (LRS) consisting of four infiltration ponds was operated and monitored over a 28-month period at an active lined landfill in Florida. Ponds were constructed by excavating into the landfilled waste and by compacting lifts of solid waste to form the pond walls. A total of 36,470 m ³ of leachate were recirculated, representing 63% of the total volume of leachate generated. The entire leachate stream was not recycled because of the large volume of leachate and the low leachate infiltration rates into the landfill. Water budgets conducted on individual ponds over the first 16 months of operation revealed that the infiltration rates ranged from 6 × 10 ⁻⁶ to 9 × 10 ⁻⁶ cm/sec. The vertical saturated hydraulic conductivity of the compacted waste was estimated in the range of 3 × 10 ⁻⁶ –4 × 10 ⁻⁶ cm/sec, lower than values reported in the literature.

The paper reviews the initial attempts being made in India to establish the practice of environmental auditing, which is a fast-emerging new concept, especially in industries that cause pollution. The concept of the environmental audit is to highlight the notifications issued by the Government of India. A case history is included to demonstrate how the status of environmental management systems and equipments are investigated vis-à-vis the Indian regulatory requirements, and how material, energy, health, and safety audits have been conducted to identify avenues for savings in the cost of production.

Rice-husk ash (RHA) was found to be a good adsorbent for Hg(II) in aqueous solutions. Batch studies indicated that the percent adsorption decreased with increasing initial concentration of Hg(II) and particle size of adsorbent. Twenty g/L of RHA (diameter 37–50 μm) in an aqueous solution of Hg(II) with an initial concentration of 100 mg/L removed 98% of Hg(II). A contact time of 3 hr was found to be optimum. Maximum Hg(II) removal was observed near a pH of 6.0. Adsorption conformed to the Langmuir isotherm. Column experiments indicated that the adsorbed amount of Hg(II) decreased with increasing flow rate and decreasing bed height.