Trench-type biobarrier is one of the commonly used in situ systems for bioremediation of contaminated aquifers. Design variables for such a system are the length of the biobarrier, $L$ , initial microbial concentration, $M_0$ , and inlet substrate concentration, $S_0$ . In this work, a procedure, based on a simple mathematical model, was developed for obtaining the interrelationship between these design variables for containing $\mathrm{Cr}\left(\mathrm{VI}\right)$ in contaminated confined aquifers. The microbial characteristics used in this study were obtained by batch and bench scale column studies. A simulation-optimization model is presented for obtaining the screening level optimal solutions, corresponding to a minimal cost. Variation of values of design variables are presented as a function of a nondimensional parameter ${\pi }_1$ , which represents the relative magnitude of microbial growth rate and aquifer flow conditions. As ${\pi }_1$ increases, the optimal length of the biobarrier and, hence, the cost of the treatment system is reduced. The screening level design procedure presented here can be the starting point for design using more sophisticated mathematical models.

The long-term operation of a methane biofilter depends on maintaining a favorable environment for methanotrophic bacteria within the porous medium supporting their growth. The concentrations of methane and oxygen, moisture content, and temperature were identified as the most important factors influencing the performance of methane biofilters (MBFs). This paper presents a comprehensive one-dimensional mathematical model capable of predicting the methane oxidation capacity of MBFs based on gas and moisture transport, and heat transfer. The finite difference method was used to spatially discretize the nonlinear partial differential equations and the equations were solved explicitly. The model was calibrated and verified using laboratory experimental data.

This paper summarizes the characteristics of chromite ore processing residue (COPR) in terms of their chemical compositions, phases, and recycling potential of iron and chromium through preliminary magnetic separation. COPR from nine hazardous waste sites in Hudson County, N.J., were analyzed using nondestructive instruments including environmental scanning electron microscope, x-ray diffraction spectrometer, and x-ray fluorescence spectrometer. The test results revealed that major phases of COPR were ${\mathrm{CaCO}}_3$ , iron/chromium containing spinel, and ${\mathrm{SiO}}_2$ . Concentrations of iron-containing phases, calculated as ${\mathrm{Fe}}_2{\mathrm{O}}_3$ , ranged from 10 to 33% by weight. The COPR samples from nine sites can be divided into two groups, one with high concentration of iron oxide (20–33%) in a form of spinel having magnetic property, and another with low concentration of iron oxide (10–15%) without magnetic property. The manual/dry magnetic separation was able to concentrate iron and chromium oxides in COPR from the former group to 34.9–40.9 and 6.3–8.6%, respectively. The morphology of COPR from a sample containing high iron content revealed that COPR is mainly the remnant of chromite ore. The characteristics of COPR are different from those chromium-contaminated soils from other sources. The study will provide essential information for further remediation and recycling potential for COPR.

Activated sludge process is the most widely used technology for municipal and industrial wastewater treatment. The microbial community of activated sludge is a mixed population of microorganisms containing many species of viruses, bacteria, protozoa, fungi, metazoa, and algae. This review focuses on the recent advances in microbiology of the activated sludge process. The bacterial population in activated sludge system is examined. The standard procedure, medium used, analytical methods and biochemical characterization techniques required for isolation, and identification of bacteria responsible for the key process of wastewater treatment systems (nutrient removal, aerobic, anaerobic, etc.) are discussed in the paper. The effect of seasonal (winter and summer) temperature variations and salinity variation on the bacterial species for wastewater treatment is examined. In addition, soluble microbial products (SMP) is one of the important factors that affects not only microbial activities, but consequently the quality of the effluents from biological wastewater treatment systems; the identification, characterization, significance, and implications of SMP in the context of activated sludge processes are also covered in this paper. Today, most modern wastewater treatment processes rely on the composition and activity of their microbial communities in activated sludges. Recent developments in molecular methods for analysis of the microbial communities have retriggered public interest in the microbiology of activated sludge. Whereas traditional approaches may have reached the point of diminishing returns, the molecular analysis has the potential to increase our understanding of the activated sludge process, and thereby improve the process control.

This paper presents a kinetic model for the remediation of soils contaminated with hydrocarbons by low-temperature oxidation (LTO). The oxidation of hydrocarbons, which consist of a mixture of straight chained, branched and ringed compounds follow a number of complex chain reactions. The investigations into the kinetics of the process are simplified by using pseudocomponents such as maltenes, asphaltenes, and coke. The mechanisms of LTO are divided into four groups: Original maltenes comprised of slow-reacting and volatile maltenes. Slow-reacting maltenes react with oxygen to produce asphaltenes and water. Asphaltenes undergo polymerization and dehydrogenation to form coke, product-volatile maltenes, and hydrogen; the volatile maltenes oxidize to form carbon oxides and water. These proposed mechanisms explain the experimental observations. The kinetic model in conjunction with a heat-transfer model can be used to determine the compositional changes when LTO is applied to remediate soils contaminated with hydrocarbons.