Biomedical subjects

E Morgenroth

Publications and source records attributed to E Morgenroth.

14 recordsLinked to original sources

PubMed2006

Optical method for long-term and large-scale monitoring of spatial biofilm development.

A method was developed that allows biofilm monitoring on the square centimeter scale over extended periods of time. The method is based on image acquisition using a desktop scanner and subsequent image analysis. It was shown that results from grey level analysis are highly correlated with physical properties of the biofilm like average biomass and biofilm thickness. The scanner method was applied to monitor overall biofilm growth, detachment, and surface roughness during two 3 and 4 week long experiments. Two significantly different growth dynamics during the biofilm development could be identified, depending on the biofilm history. Surface roughness on transects in flow direction was always higher than on transects perpendicular to the flow, reflecting the anisotropic characteristics of biofilms growing in a flow field.

Bacteria↗

PubMed2006

Endogenous processes during long-term starvation in activated sludge performing enhanced biological phosphorus removal.

In many biological wastewater treatment systems, bacterial growth and the amount of active biomass are limited by the availability of substrate. Under these low growth conditions, endogenous processes have a significant influence on the amount of active biomass and therefore, the overall system performance. In enhanced biological phosphorus removal (EBPR) systems endogenous processes can also influence the levels of the internal storage compounds of the polyphosphate accumulating organisms (PAO), directly affecting phosphorus removal performance. The purpose of this study was to evaluate the significance of different endogenous processes that occur during the long-term starvation of EBPR sludge under aerobic and anaerobic conditions. Activated sludge obtained from a laboratory sequencing batch reactor was used to perform a series of batch starvation experiments. Under aerobic starvation conditions we observed a significant decay of PAO (first-order decay rate of 0.15/d) together with a rapid utilization of polyhydroxyalkanoates (PHA) and a slower utilization of glycogen and polyphosphate to generate maintenance energy. On the other hand, anaerobic starvation was best described by maintenance processes that rapidly reduce the levels of polyphosphate and glycogen under starvation conditions while no significant decay of PAO was observed. The endogenous utilization of glycogen for maintenance purposes is currently not included in available EBPR models. Our experimental results suggest that mathematical models for in EBPR should differentiate between aerobic and anaerobic endogenous processes, as they influence active biomass and storage products differently.

Aerobiosis↗

PubMed2004

Evaluation of microscopic techniques (epifluorescence microscopy, CLSM, TPE-LSM) as a basis for the quantitative image analysis of activated sludge.

Microscopic techniques ranging from epifluorescence microscopy to confocal laser scanning microscopy (CLSM) and two photon excitation laser scanning microscopy (TPE-LSM) combined with fluorescent stains can help to evaluate complex microbial aggregates such as activated sludge flocs. To determine the application limits of these microscopic techniques, activated sludge samples from three different sources were evaluated after staining with a fluorescent viability indicator (Baclight Bacterial Viability Kit, Molecular Probes). Image analysis routines were developed to quantify overall amounts of red and green stained cells, location of stained cells within the flocs, and the spatial organization in clusters and filaments. It was found that the selection of the appropriate microscopic technique depends strongly on the type of microbial aggregates being analyzed. For flocs with high cell density, the use of TPE-LSM is preferred, since it provides a clearer image of the internal structure of the aggregate. Epifluorescence microscopy did not allow to reliably quantify red stained cells in dense aggregates. CLSM did not adequately image the internal filamentous structure and the location of stained cells within dense flocs. However, for typical activated sludge flocs epifluorescence and CLSM proved adequate.

Flocculation↗

PubMed2004

International evaluation of current and future requirements for environmental engineering education.

The field of environmental engineering is developing as a result of changing environmental requirements. In response, environmental engineering education (E3) needs to ensure that it provides students with the necessary tools to address these challenges. In this paper the current status and future development of E3 is evaluated based on a questionnaire sent to universities and potential employers of E3 graduates. With increasing demands on environmental quality, the complexity of environmental engineering problems to be solved can be expected to increase. To find solutions environmental engineers will need to work in interdisciplinary teams. Based on the questionnaire there was a broad agreement that the best way to prepare students for these future challenges is to provide them with a fundamental education in basic sciences and related engineering fields. Many exciting developments in the environmental engineering profession will be located at the interface between engineering, science, and society. Aspects of all three areas need to be included in E3 and the student needs to be exposed to the tensions associated with linking the three.

Curriculum↗

PubMed2004

Introduction to the IWA task group on biofilm modeling.

An International Water Association (IWA) Task Group on Biofilm Modeling was created with the purpose of comparatively evaluating different biofilm modeling approaches. The task group developed three benchmark problems for this comparison, and used a diversity of modeling techniques that included analytical, pseudo-analytical, and numerical solutions to the biofilm problems. Models in one, two, and three dimensional domains were also compared. The first benchmark problem (BM1) described a monospecies biofilm growing in a completely mixed reactor environment and had the purpose of comparing the ability of the models to predict substrate fluxes and concentrations for a biofilm system of fixed total biomass and fixed biomass density. The second problem (BM2) represented a situation in which substrate mass transport by convection was influenced by the hydrodynamic conditions of the liquid in contact with the biofilm. The third problem (BM3) was designed to compare the ability of the models to simulate multispecies and multisubstrate biofilms. These three benchmark problems allowed identification of the specific advantages and disadvantages of each modeling approach. A detailed presentation of the comparative analyses for each problem is provided elsewhere in these proceedings.

Bacteria↗

PubMed2004

Biofilm modeling with AQUASIM.

AQUASIM is a computer program for the identification and simulation of aquatic systems. The program includes a one-dimensional multisubstrate and multispecies biofilm model and represents a suitable tool for biofilm simulation. The program can be used to calculate substrate removal in biofilm reactors for any user specified microbial system. One-dimensional spatial profiles of substrates and microbial species in the biofilm can be predicted. The program also calculates the development of the biofilm thickness and of the substrates and microbial species in the biofilm and in the bulk fluid over time. Detachment and attachment of microbial cells at the biofilm surface and in the biofilm interior can be considered, and simulations of sloughing events can be performed. Furthermore, AQUASIM allows pseudo two-dimensional modeling of plug flow biofilm reactors by a series of biofilm reactor compartments. The most significant limitation of the model is that it only considers spatial gradients of substrates and microbial species in the biofilm in the direction perpendicular to the substratum.

Bacteria↗

PubMed2004

Comparing biofilm models for a single species biofilm system.

A benchmark problem was defined to evaluate the performance of different mathematical biofilm models. The biofilm consisted of heterotrophic bacteria degrading organic substrate and oxygen. Mathematical models tested ranged from simple analytical to multidimensional numerical models. For simple and more or less flat biofilms it was shown that analytical biofilm models provide very similar results compared to more complex numerical solutions. When considering a heterogeneous biofilm morphology it was shown that the effect of an increased external mass transfer resistance was much more significant compared to the effect of an increased surface area inside the biofilm.

Bacteria↗

PubMed2004

Modelling a spatially heterogeneous biofilm and the bulk fluid: selected results from benchmark problem 2 (BM2).

The numerical simulation of mass transfer and conversion in spatially heterogeneous biofilms on the meso-scale requires an accurate description of the hydrodynamics in the biofilm systems and of spatial effects. This leads to systems of three-dimensional nonlinear partial differential equations that are numerically very expensive to solve and to data requirements that are not easy to meet. In this paper several modeling approaches to reduce the physical complexity and, hence, accelerate the computation are compared. They range from a mere reduction of dimensionality by lumping the problem along a secondary flow direction to global mass balances or empirical correlations, at the core of which a one-dimensional boundary value problem must be solved. It is found that even strongly simplified models can describe the qualitative behaviour of the model with regard to variations in the geometrical and hydrodynamic model parameters quite well. In order to obtain also quantitatively reliable results the hydrodynamics must be considered in an appropriate manner.

Bacteria↗

PubMed2004

Results from the multi-species benchmark problem (BM3) using one-dimensional models.

The IWA's Biofilm Modeling Task Group created a multi-species benchmark problem in which heterotrophic bacteria, nitrifying bacteria, and inert biomass coexist in a biofilm. Members of the Task Group submitted solutions from nine different one-dimensional models. The most important distinctions among the models were (1) whether the model required a full numerical solution or was solved with a spreadsheet, and (2) the way the biomass types were distributed in the biofilm. The models that protected the slow-growing species by having them accumulate away from the outer surface always had the largest surface coverage by nitrifiers and inerts, but the heterotroph coverage declined to compensate. Coverage by heterotrophs and removal of substrate COD were most strongly affected by dilution from nitrifiers and inerts near the outer surface. Models that did not allow the nitrifiers and inerts to dilute the heterotrophs significantly in the outer layer predicted more removal of COD than did the other models. The choice of the model to use depends on the user's needs and the relative importance of including protection of slow-growing species and/or dilution of fast-growing species.

Bacteria↗

PubMed2003

Monitoring biofilm detachment under dynamic changes in shear stress using laser-based particle size analysis and mass fractionation.

Biofilm detachment under a dynamic change in shear stress was monitored using Focused Beam Reflectance Measurements (FBRM, LASENTEC) and mass fractionation. An annular reactor was used to grow biofilm with glucose as substrate. Changing the rotational speed on the inner cylinder of the annular reactor from 150 RPM to 420 RPM induced a step increase in shear stress. It was observed that the rate of detachment increased rapidly after increasing shear stress and then returned to the previous level. Erosion was the dominant process of detachment under steady state operation, whereas sloughing was dominant following the sudden increase in shear stress. After reaching steady state detachment under high shear conditions, the rotational speed was decreased for a 12-hour period. During this brief period of lower shear, the biofilm adjusted to this new condition. When the shear stress was increased again, another sharp increase in effluent solids concentration was observed. A decrease in density indicates that the biofilm became more vulnerable to shear stress after being subjected to this short period of low shear.

Biofilms↗

PubMed2002

Oligonucleotide probe hybridization and modeling results suggest that populations consuming readily degradable substrate have high cellular RNA levels.

Analyses based on ribosomal RNA (rRNA)-targeted hybridization performed in our laboratory identified two types of bacterial populations: a population with a high RNA level per biomass and a population with a low level of RNA per biomass. To extend these descriptions, the diurnal dynamics of the RNA pool were monitored by rRNA-targeted oligonucleotide probe membrane hybridization. Under the typical diurnal variation in COD loading rate experienced by municipal wastewater treatment plants, the RNA level of the bacterial population with a high level of RNA per biomass varied with changes in the COD loading rate. Under the same conditions, the RNA level of the population with low RNA level per biomass remained constant. A structured biomass model was developed to describe these data. Substrate COD was divided into a readily biodegradable and a slowly biodegradable COD fraction. It was assumed that two specialized populations coexist in municipal activated sludge treatment systems. One population consumes readily degradable COD and the other consumes slowly degradable COD. According to model simulations, the population consuming readily degradable COD has a high level of RNA per biomass under variable substrate concentrations. Comparatively, the population consuming slowly degradable COD has a low level of RNA level per biomass. Furthermore, model simulations reproduced the two diurnal RNA profiles observed in a full-scale municipal activated sludge system. Therefore, we suggest that two populations can be distinguished in municipal activated sludge systems: a population consuming readily degradable substrate and a population consuming slowly degradable substrate.

Bacteria↗

PubMed2002

The use of mathematical models in teaching wastewater treatment engineering.

Mathematical modeling of wastewater treatment processes has become increasingly popular in recent years. To prepare students for their future careers, environmental engineering education should provide students with sufficient background and experiences to understand and apply mathematical models efficiently and responsibly. Approaches for introducing mathematical modeling into courses on wastewater treatment engineering are discussed depending on the learning objectives, level of the course and the time available.

Curriculum↗

PubMed2002

Processes and modeling of hydrolysis of particulate organic matter in aerobic wastewater treatment--a review.

Carbon cycling and the availability of organic carbon for nutrient removal processes are in most wastewater treatment systems restricted by the rate of hydrolysis of slowly biodegradable (particulate) organic matter. To date, the mechanisms of hydrolysis are not well understood for complex substrates and mixed populations. Most mathematical models use a simple one-step process to describe hydrolysis. In this article, mechanisms of hydrolysis and mathematical models to describe these processes in wastewater treatment processes are reviewed. Experimental techniques to determine mechanisms of hydrolysis and rate constants are discussed.

Bacteria, Aerobic↗

PubMed2001

The mechanism and design of sequencing batch reactor systems for nutrient removal--the state of the art.

The Sequencing Batch Reactor (SBR) process for carbon and nutrient removal is subject to extensive research, and it is finding a wider application in full-scale installations. Despite the growing popularity, however, a widely accepted approach to process analysis and modeling, a unified design basis, and even a common terminology are still lacking; this situation is now regarded as the major obstacle hindering broader practical application of the SBR. In this paper a rational dimensioning approach is proposed for nutrient removal SBRs based on scientific information on process stoichiometry and modelling, also emphasizing practical constraints in design and operation.

Biodegradation, Environmental↗