All degradable organic materials are decomposed by microorganisms, and considerable amounts of nitrogen end up as gaseous metabolites. No matter what procedure is chosen for getting rid of organic wastes (wastewater treatment, landfiling, and composting), microbial communities will always be involved in the decomposition process, and hence, emissions of greenhouse gases, including nitrous oxide $\left({\text{N}}_2\text{O}\right)$ , are inevitable with these processes. ${\text{N}}_2\text{O}$ is an influential greenhouse gas, vital on climate change, and also is a depleting substance of stratospheric ozone. Any instantaneous or eventual ${\text{N}}_2\text{O}$ emissions during wastewater treatment, biosolids landfilling, and composting must be measured as anthropogenic intrusion of global ${\text{N}}_2\text{O}$ cycle, and thus plays a decisive role in ozone depletion. This paper reviews the current available literatures concerning ${\text{N}}_2\text{O}$ emissions from wastewater treatment facilities, biosolids landfilling, and composting. The outcome of this survey portrays that each process can release a huge amount of ${\text{N}}_2\text{O}$ to the atmosphere.

The definition of contaminant source release is a necessary element of contaminant mass transport simulation in the saturated zone. At many sites the release history is unknown, and there has been a significant body of research to develop inverse models to define finite release histories. Instead of rigorously defining the source history, a mass balance-based approach is tested to explicitly account for uncertainty in rectangular pulse release variables. The approach has been incorporated into a spreadsheet model which uses a one-dimensional solution to the advection dispersion equation, which readily lends itself to Monte Carlo applications. After the model was tested with synthetic data sets, the model was calibrated and verified using a concentration data set collected at a Superfund site. Model calibration with synthetic and actual data resulted in a reasonable domain of source history parameters and the model provided reasonable results when the mass of contaminant in the aquifer was assumed to be random.

Computer waste has considerable reverse flow in terms of reuse and recycles. The reuse component is particularly significant for developing nations like India. The hierarchy of prevention, reuse, recycle/treatment, and disposal in a landfill is a universally accepted approach to waste management. This approach becomes complex to practice if due considerations are given to cost, health, environment issues, and socially perceived risk in decision making. Shifting from one stage of hierarchy to another becomes an involved decision requiring an integrated approach to visualize the tradeoffs between these factors. Also, to be able to reach the best possible configuration of such waste management systems, it is necessary to consider its reappearance in future years. The present study proposes a methodology for estimating the optimum reuse span for a waste and demonstrates the same by applying the same to a personal computer. The results of the example problem clearly demonstrate the variation in optimum reuse span for different objectives/priorities. The results can help the decision makers limit the reuse of waste categories beyond a certain age.

The groundwater circulation well (GCW) is one of the important in situ techniques used for the remediation of volatile organic contaminants (VOCs) in groundwater. The hydraulic flow field of the GCW permits physical and biological remediation of the saturated as well as the unsaturated subsurface region. The GCW is designed to remove VOCs from the groundwater by transferring the contaminants from the aqueous phase to the gaseous phase and subsequently treating the resulting air stream through carbon adsorption units. As the flow phenomena surrounding a GCW in a heterogeneous aquifer are very complex, the characterization of transport is very difficult. This paper presents the analysis of experimental tracer transport in a three-dimensional (3D) flow field induced by a GCW in an artificial aquifer at the research facility for groundwater and subsurface remediation, Versuchseinrichtung zur Grundwasser und Altlastensanierung (VEGAS), at University of Stuttgart, Germany. The circulation flow field within a heterogeneous aquifer was investigated by a partial tracer injection tracing a certain stream tube of the flow field. The controlled extraction of the tracer was rather difficult because of the aquifer heterogeneity. A numerical model has been built up and simulation has been carried out for flow and transport processes. Experimental and simulated breakthrough curves were compared and the influence of aquifer heterogeneity on the transport has been brought out. The present study reveals the various flow and transport characteristics in a circulation well field giving further insight into the remediation process by the GCW.

An innovative waste-derived paste of waste tire chips and paper sludge was proposed for daily cover applications in municipal solid waste landfills. In this study, retardation and transport behaviors of lead (Pb) by the proposed paste were investigated using column tests. Breakthrough curves of 16 specimens at various design mixes and porosities were presented. A one-dimensional equilibrium deterministic transport model was used to fit the transport parameters from the breakthrough curves and to verify the homogeneity of the specimens. Analysis of the effluent concentrations from the column tests displayed a retardation effect for Pb in all cases, with fitted retardation factors ranging from 19.9 to 59.0. Lead retardation by the proposed paste was found to be sensitive to the paste’s porosity and design mix. Early arrivals of solute were observed unexpectedly in columns with high paper sludge content under high packing densities and were attributed to the possible presence of preferential flow paths. The results also suggest that an optimal porosity and design mix for the paste existed with respect to Pb retardation.

The uncertainty of the direct gamma-spectrometry method at a nondestructive assay of radioactive wastes is considered by taking into account the heterogeneity (over the container’s volume) of the activity and of the gamma-attenuation factor distributions. Since it is impossible to obtain in a real assay the estimations of the uncertainty in individual cases, the “maximal uncertainty” approach to characterize the method is introduced in this study. It is shown that the relative maximal uncertainty of the assay is comparatively small in a rather wide range of container’s volume values (at least for bulk volumes up to $5–8{\text{m}}^3$ this uncertainty does not exceed 200–400%). That uncertainty, owing to the heterogeneity of activity, gives a main contribution in the total value. Nonuniformity of the attenuation factor (i.e., waste matrix’s density and/or effective atomic number heterogeneity) gives a comparatively less contribution to the total uncertainty, the average value of measured gamma flux turns out to be positively shifted relating to the flux value for the homogeneous waste matrix, and leads to overestimating of the activity value at the assay of heterogeneous wastes.

The use of tire-derived steel, a by-product of tire recycling, for removal of ${\text{H}}_2\text{S}$ in landfill cover systems was examined through a laboratory study. Experiments under both static and dynamic conditions were conducted. Results demonstrated that tire-derived steel removed ${\text{H}}_2\text{S}$ to a greater extent relative to a control landfill cover material consisting of sandy soil. In batch experiments, over 98% ${\text{H}}_2\text{S}$ [550 parts per million (ppm) initial concentration] was removed in 2 min by 20 g of tire-derived steel, compared to only 50% ${\text{H}}_2\text{S}$ removal in 60 min by the same amount of soil. In column experiments using 100 ppm inlet ${\text{H}}_2\text{S}$ gas concentrations, after 24-h continuous operation, the outlet ${\text{H}}_2\text{S}$ concentration increased to over 90 ppm in the sandy soil columns, while it was less than 1 ppm in the tire-derived steel columns. The experimental results showed that the outlet ${\text{H}}_2\text{S}$ concentrations from the closed columns were higher than that from the open columns, indicating a potential role of oxygen in creating or regenerating reactive surfaces for ${\text{H}}_2\text{S}$ removal.

Wind tunnel experiments were conducted to evaluate the effectiveness of two commercially available fixatives in controlling the mobility of soil particles on soil mounds when exposed to wind forces. The fixatives tested included two commercially available materials: (1) RoadMaster which consists of 38% calcium chloride solution and (2) DuraSoil which consists of a solution of alkanes and alkylated saturated compounds. Soil samples were placed in an open-loop low-speed wind tunnel and exposed to wind forces ranging from 10 to 30 mi per hour (mi/h). The amount of soil loss/displaced and particulate matter (PM10) generated were monitored in relation to soil moisture content and application rate of selected fixatives. The results showed that increase in soil moisture and amount of fixative used had a significant effect in controlling the particulate matter (PM10) concentrations and the amount of soil displaced by the wind forces. The calcium chloride solution was applied by spraying onto the soil samples. However, DuraSoil mixture was applied by pouring the fixative using pipettes due to its high viscosity.