Thomas Baumann

Temperature development in a modern municipal solid waste incineration (MSWI) bottom ash landfill with regard to sustainable waste management.

Municipal solid waste is treated in incineration plants to reduce the volume, the toxicity and the reactivity of the waste. The final product, municipal solid waste incineration (MSWI) bottom ash, was considered as a material with a low reactivity, which can safely be deposited in a MSWI bottom ash landfill, or which can be used, e.g. in road construction after further treatment. However, temperature measurements in MSWI bottom ash landfills showed temperatures up to 90 degrees C, caused by exothermic reactions within the landfill. Such high temperatures may affect the stability of the flexible polymer membrane liner (FML) and may also lead to an accelerated desiccation of the clay barrier. At the beginning of this study it was uncertain whether those reported results would be applicable to modern landfills, because the treatment techniques in MSWI and landfills have changed, bottom and fly ash are stored separately, and the composition of the incinerated waste has changed significantly since the publication of those results. The aim of this study was to gain detailed knowledge of temperature development under standard disposal conditions in relation to the rate of ash disposal, the variation of layer thickness, and the environmental conditions in a modern landfill. Temperatures were measured at nine levels within the body of a landfill for a period of nearly 3 years. Within 7 months of the start of the disposal, a temperature increase of up to 70 degrees C within the vertical centre of the disposal was observed. In the upper and central part of the landfill this initial temperature increase was succeeded by a decrease in temperature. The maximum temperature at the time of writing (May 2000) is about 55 degrees C in the central part of the landfill. The maximum temperature (45.9 degrees C) at the FML was reached 17 months after the start of the deposition. Since then the temperatures decreased at a rate of 0.6 degrees C per month. Temperature variation within each individual layer corresponds to the temperature of the underlying layer and the overall surface-to-volume ratio of the landfill. The temperatures in the uppermost layer are significantly influenced by the ambient temperatures.

Visualization and Modeling of Polystyrol Colloid Transport in a Silicon Micromodel

ventional methods to investigate colloid transport often involve column studies. Here, colloid concentrations are A new experimental approach and complementary model analysis measured at the column effluent or at selected points are presented for studying colloid transport and fate in porous media. The experimental approach combines high precision etching to create along the column length. Unfortunately, such methods do a controlled pore network in a silicon wafer (i.e., micromodel), with not clearly distinguish how spatial and temporal changes epifluorescent microscopy. Two different sizes of latex colloids were in hydrochemical and hydrodynamic conditions affect colused; each was stained with a fluorescent dye. During an experiment, loid transport. For example, breakthrough curves (BTCs) water with colloids was purged through a micromodel at different obtained from column effluent represent some average flow rates. Flow paths and particle velocities were determined and behavior of colloids in the column (Baumann et al., compared with flow paths calculated using a two-dimensional (2D) 2002). Since different heterogeneous realizations can lattice Boltzmann (LB) model. For 50% of the colloids evaluated, contribute to such BTCs, the processes that control colagreement between measured and calculated flow paths and velocities loid transport in the column are obscured. were excellent. For 20%, flow paths agreed, but calculated velocities Filtration theory (Happel, 1958; Rajagopalan and were less. This is attributed to the parabolic velocity profile across the micromodel depth, which was not accounted for in the 2D flow Tien, 1976) is often used to evaluate colloid transport. model. For 12%, flow paths also agreed, but calculated velocities were It accounts for the hydrodynamic processes that lead less. These colloids were close to grain surfaces, where model errors to a contact between particles and filter surfaces. The increase. Also, particle–surface interactions were not accounted for attachment efficiency, , describes the probability that in the model; this may have contributed to the discrepancy. For the a collision between a particle and a filter grain results remaining 18% of colloids evaluated, neither flow paths nor velocities in a permanent attachment (Elimelech and O’Melia, agreed. The majority of colloids in this last case were observed after 1990). This parameter lumps the physical and chemical breakthrough, when concentrations were high. The discrepancies may interactions between colloids and surface at the pore be due to particle–particle interactions that were not accounted for scale. Often the attachment efficiency is used as a fitting in the model. Filtration efficiencies for all colloid sizes at different parameter for the inverse modeling of colloid breakflow rates were calculated from filtration theory. Attachment rates were obtained from successive images during an experiment. With through curves (Ren et al., 2000; Huber et al., 2000). these, attachment efficiencies were calculated, and these agreed with The boundary conditions, especially the pore topolliterature values. The study demonstrates that excellent agreement ogy, the local flow velocities, and the chemical heterogebetween experimental and model results for colloid transport at the neity of the surface, can vary in the pore space. In colpore scale can be obtained. The results also demonstrate that when umn tests, the packing density and the topology of the experimental and model results do not agree, mechanistic inferences pore network are unknown, and local physical and and system limitations can be evaluated. chemical heterogeneities cannot be assessed (Sugita and Gillham, 1995). Also, preferential flow inside the column is obscured. Therefore, the inverse derivation of C are ubiquitous in many groundwater aquifiltration parameters e.g., the attachment efficiency) are fers. They originate from weathering processes of representative only for the length scale of the column. the aquifer matrix, degradation of biological material, As a result, upscaling and downscaling become difficult, and precipitation of supersaturated solutions (Buffle et and experimentally derived parameters do not always al., 1998). Under certain conditions, colloids may facilitate conform to theory. A promising approach to study porethe transport of hazardous substances such as radionuscale processes involves the use of micromodels. clides (Tanaka and Nagasaki, 1997; Kersting et al., 1999), In groundwater and vadose zone studies, micromodheavy metals (Karathanasis, 1999; Kretzschmar et al., els are representations of porous media etched into sili1999), and organic substances (Roy and Dzombak, 1998; con wafers, glass, or polymers (Soll et al., 1993). SomeVillholth, 1999). It is therefore of great interest to predict times thin layers of glass beads or sand embedded colloid transport. between glass plates are also referred to as micromodels. Colloid transport is very sensitive to hydrochemical The main purposes of micromodel experiments are to and hydrodynamic conditions (Roy and Dzombak, 1997; increase spatial and temporal resolution and to provide Bergendahl and Grasso, 2000; Bradford et al., 2002). Condirect quantitative access to processes at the pore scale. An overview of micromodel applications is docuT. Baumann, Institute of Hydrochemistry, Technische Universität mented in Table 1. Each table entry notes the experiMünchen, Marchioninistr. 17, D–81377 Munich, Germany; C.J. Werth, mental approach and objectives, associated references, Dep. of Civil and Environmental Engineering, University of Illinois, 205 N. Mathews Ave. MC-250, Urbana, IL 61801. Received 10 July and the type of porous media represented. Only two of 2003. Special Section: Colloids and Colloid-Facilitated Transport of the references involved study of colloid transport (Wan Contaminants in Soils. *Corresponding author (thomas.baumann@ and Wilson, 1994b, 1996). In one study, the role of the ch.tum.de). Abbreviations: BTC, breakthrough curve; DDI, deionized distilled; Published in Vadose Zone Journal 3:434–443 (2004).  Soil Science Society of America LB, lattice Boltzmann; PTA, particle tracking algorithm; UV, ultraviolet; 2D, two-dimensional; 3D, three-dimensional. 677 S. Segoe Rd., Madison, WI 53711 USA

In situ sensing of volatile organic compounds in groundwater: First field tests of a mid-infrared fiber-optic sensing system

A prototype mid-infrared sensor system for the determination of volatile organic pollutants in groundwater was developed and tested under real-world conditions. The sensor comprises a portable Fourier transform infrared spectrometer, coupled to the sensor head via mid-infrared transparent silver halide fiber-optic cables. A 10 cm unclad middle section of the 6-m-long fiber is coated with ethylene propylene copolymer in order to enrich the analytes within the penetration depth of the evanescent field protruding from the fiber sensor head. A mixture of tetrachloroethylene, dichlorobenzene, diethyl phthalate, and xylene isomers at concentrations in the low ppm region was investigated qualitatively and quantitatively in an artificial aquifer system filled with Munich gravel. This simulated real-world site at a pilot scale enables in situ studies of the sensor response and spreading of the pollutants injected into the system with controlled groundwater flow. The sensor head was immersed into a monitoring well of the aquifer system at a distance of 1 m downstream of the sample inlet and at a depth of 30 cm. Within one hour, the analytes were clearly identified in the fingerprint region of the IR spectrum (1300 to 700 cm−1). The results have been validated by head-space gas chromatography, using samples collected during the field measurement. Five out of six analytes could be discriminated simultaneously; for two of the analytes the quantitative results are in agreement with the reference analysis.

Migration of dissolved heavy metal compounds and PCP in the presence of colloids through a heterogeneous calcareous gravel and a homogeneous quartz sand-pilot scale experiments.

In preparation to field experiments with in situ mobilized colloids, a set of pilot scale aquifer tank experiments was performed to gain an insight into the mass transfer of several heavy metal ions and pentachlorophenol (PCP) in a heterogeneous gravel aquifer and a homogeneous sandy aquifer. The experiments simulate a spill of dissolved contaminants and their subsequent transport with in situ mobilized colloids that are not yet in equilibrium with the contaminant. Contaminants with a weak tendency to adsorb to the stationary sediment matrix, e.g., PCP, establish a dynamic equilibrium with the mobile colloidal phase. The fraction of contaminants sorbed to colloids remains constant along the observed flow path. In contrast, for contaminants that strongly sorb to the sediment matrix, the fraction associated with colloids increases with increasing flow distance. In either case, the filtration of colloids is the limiting factor for the colloidal mass transfer. It is also shown that the recovery rates decrease rapidly within both sediments, and that the transport parameters (flow velocity, dispersivity) are only representative for the mobile fraction of the contaminant. On the given experimental scale, there was no evidence of a preferred colloidal transport, or even a transport of colloids ahead of the conservative tracer.

Sorption of silver nanoparticles to environmental and model surfaces.

The fate of engineered nanoparticles in environmental systems is controlled by changes in colloidal stability and their interaction with different environmental surfaces. Little is known about nanoparticle-surface interactions on the basis of sorption isotherms under quasi-equilibrium conditions, although sorption isotherms are a valuable means of studying sorbate-sorbent interactions. We tested the extent to which the sorption of engineered silver nanoparticles (nAg) from stable and unstable suspensions to model (sorbents with specific chemical functional groups) and environmental (plant leaves and sand) surfaces can be described by classical sorption isotherms. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) qualitative and quantitative analyses were also used to assess the morphology and nanomechanical parameters of the covered surfaces. The sorption of nAg from stable suspensions was nonlinear and best described by the Langmuir isotherm. Langmuir coefficients varied with sorbent surface chemistry. For nAg sorption from an unstable suspension, the sorption isotherms did not follow any classical sorption models, suggesting interplay between aggregation and sorption. The validity of the Langmuir isotherm suggests monolayer sorption, which can be explained by the blocking effect due to electrostatic repulsion of individual nanoparticles. In unstable suspensions, aggregates are instead formed in suspension and then sorbed, formed on the surface itself, or formed in both ways.

Applications of a laser-induced fluorescence spectroscopy sensor in aquatic systems

The use of laser-induced fluorescence spectroscopy (LIFS) is fairly accepted as a fast and reliable method for the online detection of contaminations with polycyclic aromatic hydrocarbons (PAHs) and oil in groundwater and soils. Our work was focussed not only on the assessment of those contaminations, but on the use of LIFS as a generic tool to assess subsurface contaminations and aquifer properties. Pattern recognition techniques were successfully applied to map contaminant plumes surrounding waste disposal sites. Remediation activities at a former gas plant site were monitored using a sensor system based on time-resolved fluorescence spectroscopy. Tracer investigations in the saturated and unsaturated zone were enhanced due to the small time intervals between the single measurements. The determination of single analytes (e.g. pyrene, benzo(a)pyrene) out of a complex mixture of fluorescent compounds was possible by taking advantage of the fluorescence decay-times and by applying a site-specific calibration.

Oxygen determination in oxygen-supersaturated drinking waters by NMR relaxometry

In recent years, a rising number of different table waters supersaturated with oxygen have hit the market with claims of both positive health effects and an increase in athletic performance. In addition to research on the correctness of these claims and their possible physiological reasons, the appearance of oxygen supersaturation as a marketing promise also creates a need for appropriate analytical techniques allowing a rapid and reliable determination of oxygen contents in such waters. Here, we present NMR relaxometry as a possible analytical tool for such studies. NMR relaxation in oxygen supersaturated water is not only of interest in the context of monitoring the oxygen content in such drinking water products, but also might offer some interesting possibilities in medical and environmental science MRI applications. As a contact-less measuring method, NMR relaxometry avoids disturbance of the measurement due to outgassing. The method was applied in the concentration range from 10 mg l(-1) to over 100 mg l(-1) dissolved oxygen. In addition to freshly sampled drinking waters, also oxygen losses during storage of the water in open drinking vials was studied.

Colloid dispersion on the pore scale

Dispersion describes the spreading of a tracer or contaminant in an aquifer. Detailed knowledge of dispersion is the key to successful risk assessment in case of groundwater pollution or groundwater protection. The dispersion of colloids on the pore scale is controlled by flow velocity, ionic strength, colloid size, colloid concentration, and colloid-matrix interactions. The objective of this study was to provide quantitative data and to assess the scale dependency of colloid dispersion on the pore scale. The positions of carboxylated polystyrene microspheres (1 microm, 0.5 microm) were recorded during transport experiments in silicon micromodels with three pore topologies. The positions were combined into particle trajectories revealing the flow path of individual colloids. More than thousand trajectories were evaluated for each experiment to obtain the dispersivity of the colloids for flow distances between 10 and 1000 microm. All experiments were run at high Peclet numbers. The pore scale dispersivity was on the order of 8-30% of the flow distance with pure water, dependent on the heterogeneity of the pore topology. The dispersivity was positively correlated with the ionic strength and inversely correlated with the colloid size and the flow velocity. A coating of the micromodel surface with humic acid also increased dispersivity. The quantitative data set presented here supports the theoretical framework for colloid transport and allows to parametrize colloid transport on the pore scale.

Raman microspectroscopic analysis of fibers in beverages

This technical note illustrates the applicability of Raman microspectroscopy (RM) for the analysis of the synthetic fiber content in different beverages (beer and mineral water). The particles and fibers were collected by filtration on a cellulose nitrate membrane filter (pore size = 0.45 μm) and subsequently identified and quantified by RM. Our results show no significant differences (p = 0.95) in the statistical distribution of fibers in beverage and blank samples, which suggests external contamination sources. Moreover, most of the identified fibers consisted of cellulose, which is a natural fiber and harmless compared to synthetic fibers. The other fibers identified were mainly made of polyethylene, which is used as a packaging material for the cellulose nitrate filter. Our study highlights the need for spectroscopic analysis as well as the use of adequate blank samples and an almost particle-free lab environment. Spectroscopic identification is crucial for the discrimination between cellulose and synthetic fibers; otherwise artefacts cannot be recognized and the interpretation will be misleading. The qualitative and quantitative analysis performed in our laboratory could not confirm the contamination of beverages with synthetic fibers reported by previous studies which relied on optical identification alone.

MRI observation of heavy metal transport in aquifer matrices down to sub-mg quantities.

In this contribution, we report results from MRI studies of the propagation of heavy metal ions through columns packed with sandy aquifer materials. Both sorption of low concentrations of heavy metal ions from water flowing through the column and the formation of sorption traces produced from initially localized higher concentrations of heavy metal ions, and the remobilisation of adsorbed ions with time and changing hydrochemical conditions were studied. Multislice spin-echo and FLASH techniques were used for the imaging experiments. Advantages and problems of the different imaging protocols for the study of aquifer materials are discussed.