Monofermentation of grass silage under mesophilic conditions: measurements and mathematical modeling with ADM 1

In this paper experimental data from grass fermentation and simulation results with the Anaerobic Digestion Model (ADM) No. 1 are described. Two laboratory reactors were operated under mesophilic conditions with volumetric loading rates in between 0.3 and 2.5 kg(VS)/(m(3) x d). Two different kinds of grass silage were used as substrates, resulting in an average specific biogas production of 600 L/kg(VS). The ADM 1 was calibrated both manually and with the help of a Genetic Algorithm in Matlab/Simulink. Results from calibration indicate that the NH3 inhibition constant used to model the inhibition of acetate uptake is three to five times higher compared with digested activated sludge. The hydrogen inhibition constants applied for propionate and valerate/butyrate uptake are around two orders of magnitude lower than for sludge digestion.

Combined use of confocal laser scanning microscopy (CLSM) and Raman microscopy (RM): investigations on EPS-Matrix

Confocal laser scanning microscopy (CLSM) was applied in combination with Raman microscopy (RM) for the characterization of heterotrophic biofilms. Compared to CLSM, RM allows for a deeper insight into the chemical structure of extracellular polymeric substances (EPS) of the biofilm matrix. A low load of glucose (2 g m(-2)d(-1)) was applied as substrate to ensure small growth rates of the heterotrophic biofilm. To investigate the influence of hydrodynamic conditions on the chemical composition of EPS, a three funnel flow system was used, wherein biofilms were grown at Reynolds numbers of 1000, 2500 and 4000, respectively. 31 and 92 days after inoculation with activated sludge supernatant RM was applied as an additional technique to standard CLSM measurements for a more detailed analysis of the biofilm matrix. Polysaccharide-related Raman bands are in good agreement with the lectin binding analysis from CLSM. For the older biofilm, lectin binding analysis showed no change in the composition of EPS, whereas Raman spectra pointed out a change of EPS composition from predominantly polysaccharides to predominantly (glyco) proteins. For the applied substrate condition no significant influence of the Reynolds number on the chemical properties was observed.

The impact of sunlight on inactivation of indicator microorganisms both in river water and benthic biofilms

A detailed knowledge on decay or inactivation kinetics of faecal indicator microorganism in rivers is essential for control of bathing water quality. Both reliable inactivation rate coefficients for such kinetics and the knowledge on pathogen accumulation in benthic biofilms are needed for the assessment of river self purification capability and for being able to make decisions for an optimized water management. Therefore, the inactivation kinetics for main indicator microorganisms like faecal coliforms and intestinal Enterococci in water and on stones of the river Isar (Germany) were measured at artificial sunlight radiation. A flume was built, containing Isar water and sediment. By adding a pulse of pre-treated sewage water, the subsequently change of indicator bacteria levels in the bulk and biofilm phase is measured. Bacterial inactivation was mainly dependent on sunlight intensity. Mean inactivation rate coefficients in the experimental set up with river water obtained for a radiation intensity comparable to average midday sunlight in June in 50 degrees north latitude (I((290-390nm))=40.0W/m(2)) were found to be 21.4d(-1) for faecal coliforms and 20.0d(-1) for intestinal Enterococci. For a radiation intensity conform with the annual mean radiation in Germany (I((290-390nm))=8.0W/m(2)) inactivation rate coefficients were 12.7d(-1) for faecal coliforms and 9.3d(-1) for intestinal Enterococci. A measurement without direct artificial sunlight (I((290-390nm))=0.08W/m(2)) yields inactivation rate coefficients of 3.4d(-1) for faecal coliforms and 1.7d(-1) for intestinal Enterococci, which were similar to those found in wastewater treatment ponds. Due to re-growth and better environmental conditions the concentrations of faecal coliforms and intestinal Enterococci within the biofilm were 10(2) to 10(4) fold higher compared to the bulk water depending on the exposure time.

In situ surface-enhanced Raman scattering analysis of biofilm

Biofilms represent the predominant form of microbial life on Earth. They are aggregates of microorganisms embedded in a matrix formed by extracellular polymeric substances (EPS). Detailed information about chemical composition and structure of the EPS matrix is relevant e.g. for the optimization of biocides, of antifouling strategies and for biological wastewater treatment. Raman microscopy (RM) is a capable tool that can provide detailed chemical information about biofilm constituents with spatial resolution of optical microscope. However, the sensitivity of RM is limited. Surface-enhanced Raman scattering (SERS), which enables investigations of biomolecules at very low concentration levels, allows overcoming this drawback. To our knowledge, this paper is the first report on reproducible SERS spectra from different constituents of a multispecies biofilm. We believe that the reproducibility is partly owed to the in situ measurement of the biofilm, while up to now SERS measurements of microbiological samples by RM were carried out after sample drying. We employed colloidal silver nanoparticles for in situ SERS measurements by RM. The achieved enhancement factor of up to 2 orders of magnitude illustrates a high potential of SERS for ultrasensitive chemical analysis of biofilms, including the detection of different components and the determination of their relative abundance in the complex biofilm matrix.

Experimental results and mathematical modelling of an autotrophic and heterotrophic biofilm in a sand filter treating landfill leachate and municipal wastewater

A better understanding of wastewater treatment with soil filters is important to optimise plant operation and reduce the risk of clogging. The article presents results of a treatment concept which uses a combination of SBR and vertical-flow sand filter technology. The SBR was mainly used for denitrification and sedimentation of substances in particulate form. Efficient nitrification was achieved by the planted sand filter. Degradation rates of 10gNH(4)-N/(m(2)xd) were measured for periods with peak loadings. The two-dimensional dynamic model reproduces the biofilm growth and decay of heterotrophic and autotrophic biomass. It is capable of describing the clogging of the sand filter by combining a biochemical and a geometric model. After calibration, the model was used for the calculation of maximum nitrogen degradation performances. Maximum degradation rates of 12gNH(4)-N/(m(2)xd) can be achieved if the COD/TKN ratio is reduced before to a level lower than that of municipal wastewater. The COD was further degraded in the filter than we expected comparing it with activated sludge plants. Within the soil filter a biofilm thickness of up to 110microm is simulated depending on the embankment of gravel and grains of sand. Sensitivity analysis of model parameters showed the high impact of the maximum autotrophic growth rate, the autotrophic yield, the diffusion coefficient for oxygen and the number of contact points of the single grains of sand.

Hallucinations, thought disorders, and the language domain in schizophrenia

Auditory hallucinations and formal thought disorders are major diagnostic features of schizophrenia. From a neurobiological point of view, they are of particular interest since both can be attributed to the language domain of human communication. In the last decade, brain imaging studies have contributed to the understanding of the functional dynamics underlying these phenomena. In particular, auditory hallucinations were found to involve the regions generating inner speech as well as the primary acoustical cortex and the intrahemispheric fiber bundles connecting the left frontal with the temporal lobe. In patients with formal thought disorders, on the other hand, the left temporal language area showed structural deficits and functional abnormalities, i.e., reduced reactivity to stimulation and increased activity at rest; left frontal language regions were also hyperactive at rest but showed no structural deficits. The available evidence indicates a dynamic imbalance of the language system, triggered by subtle structural changes, as the possible common neurobiological basis of hallucinations and formal thought disorders.

Optimizing sequencing batch reactor (SBR) reactor operation for treatment of dairy wastewater with aerobic granular sludge

The biological wastewater treatment using aerobic granular sludge is a new and very promising method, which is predominantly used in SBR reactors which have higher volumetric conversion rates than methods with flocculent sludge. With suitable reactor operation, flocculent biomass will accumulate into globular aggregates, due to the creation of increased substrate gradients and high shearing power degrees. In the research project described in this paper dairy wastewater with a high particle load was treated with aerobic granular sludge in an SBR reactor. A dynamic mathematical model was developed describing COD and nitrogen removal as well as typical biofilm processes such as diffusion or substrate limitation in greater detail. The calibrated model was excellently able to reproduce the measuring data despite of strongly varying wastewater composition. In this paper scenario calculations with a calibrated biokinetic model were executed to evaluate the effect of different operation strategies for the granular SBR. Modeling results showed that the granules with an average diameter of 2.5 mm had an aerobic layer in between 65-95 microm. Density of the granules was 40 kgVSS/m3. Results revealed amongst others optimal operation conditions for nitrogen removal with oxygen concentrations below 5 gO2/m3. Lower oxygen concentrations led to thinner aerobic but thicker anoxic granular layers with higher nitrate removal efficiencies. Total SBR-cycle times should be in between 360-480 minutes. Reduction of the cycle time from 480 to 360 minutes with a 50% higher throughput resulted in an increase of peak nitrogen effluent concentrations by 40%. Considering biochemical processes the volumetric loading rate for dairy wastewater should be higher than 4.5 kgCOD/(m3*d). Higher COD input load with a COD-based volumetric loading rate of 9.0 kgCOD/(m3*d) nearly led to complete nitrogen removal. Under different operational conditions average nitrification rates up to 5 gNH/(m3*h) and denitrification rates up to 3.7 gNO/(m3*h) were achieved.

Investigations and mathematical simulation on decentralized anaerobic treatment of agricultural substrate from livestock farming

Anaerobic processes are widely used for treatment of both municipal and industrial wastewater as well as agricultural substrates. In contrast to the aerobic methods, they are frequently more cost-efficient, they have a lower surplus sludge production, and the reactors can be run with higher volumetric loads and thus smaller volumes. In the paper presented both experimental data and the application of the Anaerobic Digestion Model No. 1 for agricultural substrate from livestock farming will be described. A 3,500 L reactor with mesophilic operation and loaded with cattle manure was examined with respect to its COD degradation, gas production, and gas composition. Results revealed a reduction of 30-35% COD and a biogas production of 287 L(Biogas)/kg(VS) when operated with a specific loading rate of 3.6 kg(VS)/(m(3).d).After calibration of the ADM 1, which was based predominantly on the acetate uptake rate (k(ac.m)=3.6 g/(g.d)), the disintegration constant (k(Dis)=0.05 d(-1)) and the exact determination of the influent COD fractions contained in the agricultural substrate, it was possible to simulate the measured data of the plant in excellent quality. For future application of the ADM 1 as part of control strategies a sensitivity analysis was carried out. The analysis based on the SVM slope technique has been done to identify highly sensitive biochemical parameters. These are, amongst others, the acetate uptake rate, the disintegration constant, the biomass decay rates and the half saturation constant for ammonia inhibition. Sensitivity analysis of the inflow COD fractions (proteins, carbohydrates, lipids and inert) showed the necessity of detailed measurements for the prediction of the gas flow and composition as well as for prognosis of inhibitions in the anaerobic process. For cattle manure especially the fractions of inert material and carbohydrates should be observed carefully. Due to the high content of NH(4)-N in manure the protein fraction is not as sensitive as the two mentioned above.

Modelling the energy balance of an anaerobic digester fed with cattle manure and renewable energy crops

Knowledge of the net energy production of anaerobic fermenters is important for reliable modelling of the efficiency of anaerobic digestion processes. By using the Anaerobic Digestion Model No. 1 (ADM1) the simulation of biogas production and composition is possible. This paper shows the application and modification of ADM1 to simulate energy production of the digestion of cattle manure and renewable energy crops. The paper additionally presents an energy balance model, which enables the dynamic calculation of the net energy production. The model was applied to a pilot-scale biogas reactor. It was found in a simulation study that a continuous feeding and splitting of the reactor feed into smaller heaps do not generally have a positive effect on the net energy yield. The simulation study showed that the ratio of co-substrate to liquid manure in the inflow determines the net energy production when the inflow load is split into smaller heaps. Mathematical equations are presented to calculate the increase of biogas and methane yield for the digestion of liquid manure and lipids for different feeding intervals. Calculations of different kinds of energy losses for the pilot-scale digester showed high dynamic variations, demonstrating the significance of using a dynamic energy balance model.

Selection of reference genes for normalisation of specific gene quantification data of Aspergillus niger

Aspergillus niger is a widely used expression host for homologous and heterologous protein production in biotechnological processes. In order to increase product yields, a thorough optimisation of these cultivation processes is necessary. Considering mRNA as the key molecule, which transports the genetic information between DNA and protein production side, the quantification of product specific gene expression provides useful information about product formation already on the level of transcription. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) is a powerful tool to obtain data about gene transcription. However, using this technique the choice of an appropriate reference system is a crucial aspect to provide optimal data normalisation. A prominent approach is the use of so called housekeeping genes as internal references. However, validation of the usability of these reference genes is the fundamental step before starting with qRT-PCR experiments. Adequate reference genes for A. niger have not been published so far. Therefore, 10 possible candidate genes from different functional classes were selected and their applicability as internal references validated. Transcript levels of these genes were compared in sets of 9, 41 and 19 samples from diverse cultivations of A. niger. Under the chosen experimental conditions, the genes act, sarA and cox5 have been identified as genes with the most stable gene expression. The three reference genes were used to normalise qRT-PCR data for glaA gene expression which showed a high correlation with glucoamylase production in continuous cultivations.

On-site infiltration of a copper roof runoff: role of clinoptilolite as an artificial barrier material

On-site infiltration may be considered as a promising way of managing rainwater runoffs in urban areas, provided the hydrological and ecological conditions allow infiltration, and provided there is adequate treatment of the contaminants to avoid a risk of soil and groundwater pollution. The aim of this study was to evaluate the feasibility of the application of a new technical infiltration system equipped with clinoptilolite as an artificial barrier material for the treatment of the copper roof runoff of the Academy of Fine Arts in Munich, Germany. During the 2-yr sampling period, 30 rain events were examined. The cover material of the roof and the drainage system was responsible for the high copper concentrations in the roof runoff. The rain height and the rain intensity were of great significance regarding the establishment of the copper runoff rate. The technical infiltration system applied was able to reduce the copper from the roof runoff by a factor up to 96%. The mean measured copper concentration in percolation water was lower than the critical value of 50 microg/l set by the German Federal Soil Protection Act and Ordinance, indicating no risk for soil and groundwater contamination.

Comparison of some characteristics of aerobic granules and sludge flocs from sequencing batch reactors

Physical, chemical and biological characteristics were investigated for aerobic granules and sludge flocs from three laboratory-scale sequencing batch reactors (SBRs). One reactor was operated as normal SBR (N-SBR) and two reactors were operated as granular SBRs (G-SBR1 and G-SBR2). G-SBR1 was inoculated with activated sludge and G-SBR2 with granules from the municipal wastewater plant in Garching (Germany). The following major parameters and functions were measured and compared between the three reactors: morphology, settling velocity, specific gravity (SG), sludge volume index (SVI), specific oxygen uptake rate (SOUR), distribution of the volume fraction of extracellular polymeric substances (EPS) and bacteria, organic carbon and nitrogen removal. Compared with sludge flocs, granular sludge had excellent settling properties, good solid-liquid separation, high biomass concentration, simultaneous nitrification and denitrification. Aerobic granular sludge does not have a higher microbial activity and there are some problems including higher effluent suspended solids, lower ratio of VSS/SS and no nitrification at the beginning of cultivation. Measurement with CLSM and additional image analysis showed that EPS glycoconjugates build one main fraction inside the granules. The aerobic granules from G-SBR1 prove to be heavier, smaller and have a higher microbial activity compared with G-SBR2. Furthermore, the granules were more compact, with lower SVI and less filamentous bacteria.

Thermophilic anaerobic digestion in compact systems: investigations by modern microbiological techniques and mathematical simulation

Thermophilic anaerobic digestion in compact systems can be an economical and ecological reasonable decentralised process technique, especially for rural areas. Thermophilic process conditions are important for a sufficient removal of pathogens. The high energy demand, however, can make such systems unfavourable in terms of energy costs. This is the case when low concentrated wastewater is treated or the system is operated at low ambient temperatures. In this paper we present experimental results of a compact thermophilic anaerobic system obtained with fluorescent in situ hybridisation (FISH) analysis and mathematical simulation. The system was operated with faecal sludge for a period of 135 days and with a model substrate consisting of forage and cellulose for a period of 60 days. The change in the microbial community due to the two different substrates treated could be well observed by the FISH analysis. The Anaerobic Digestion Model no. 1 (ADM1) was used to evaluate system performance at different temperature conditions. The model was extended to contribute to decreased methanogenic activity at lower temperatures and was used to calculate energy production. A model was developed to calculate the major parts of energy consumed by the digester itself at different temperature conditions. It was demonstrated by the simulation study that a reduction of the process temperature can lead to higher net energy yield. The simulation study additionally showed that the effect of temperature on the energy yield is higher when a substrate is treated with high protein content.

Development of an empirical mathematical model for describing and optimizing the hygiene potential of a thermophilic anaerobic bioreactor treating faeces

Poor sanitation and insufficient disposal of sewage and faeces are primarily responsible for water associated health problems in developing countries. Domestic sewage and faeces are prevalently discharged into surface waters which are used by the inhabitants as a source for drinking water. This paper presents a decentralized anaerobic process technique for handling of such domestic organic waste. Such an efficient and compact system for treating faeces and food waste may be of great benefit for developing countries. Besides a stable biogas production for energy generation, the reduction of bacterial pathogens is of particular importance. In our research we investigated the removal capacity of the reactor concerning pathogens, which has been operated under thermophilic conditions. Faecal coliforms and intestinal enterococci have been detected as indicator organisms for bacterial pathogens. By the multiple regression analysis technique an empirical mathematical model has been developed. The model shows a high correlation between removal efficiency and both, hydraulic retention time (HRT) and temperature. By this model an optimized HRT for defined bacterial pathogens effluent standards can be easily calculated. Thus, hygiene potential can be evaluated along with economic aspects. In this paper not only results for describing the hygiene potential of a thermophilic anaerobic bioreactor are presented, but also an exemplary method to draw the right conclusions out of biological tests with the aid of mathematical tools.

Wastewater treatment with activated pre-clarifier and planted soil filters

With a series of buffer tank, activated pre-clarifier (SBR) and planted soil filters, it is possible to get a stable degradation and good effluent values in the case of unsteady inflow and changing concentrations. In the process presented here the activated pre-clarifier is working as a denitrification tank and the soil filter as a nitrification reactor. An automatic control manages the storm-water runoff, the water-recirculation returns the nitrate and provides a minimal feed. Experiences with this plant from 1999 to 2005 are given in this paper, research has been done in the project "Planted soil filters as a Biotechnological Process", founded by the German Federal Environment Foundation (DBU). A full scale pilot plant was built to treat wastewater from composting sides, with a 42 m3 SBR and a bed area of 2 x 550 m2 of the planted soil filters. Now, after six years of operation, the results are still satisfactory. Besides this pilot plant, landfill leakage and municipal wastewater have been treated in a technical scale plant with the same process in an 80 L SBR and 0.75 m2 vertical flow soil filter with good results.

Structure and shear strength of microbial biofilms as determined with confocal laser scanning microscopy and fluid dynamic gauging using a novel rotating disc biofilm reactor

The cohesive strength of microbial biofilms cultivated on a rotating disc has been measured using fluid dynamic gauging (FDG). The thickness of heterotrophic mixed culture biofilms was found to depend on substrate concentration and shear force at the biofilm surface during the cultivation. For high substrate concentrations and low shear forces the biofilm thickness increased to several 100 microm within 7 days. Low substrate concentration and higher shear forces yielded thin biofilms of about 100 microm thickness. Independent from cultivation conditions and thickness of the biofilms their cohesive strength ranged between 6.0 and 7.7 N m(-2). The ratio between cohesive strength measured with FDG and shear forces applied during biofilm cultivation have ranged from 200 to 1,100. Higher concentrations of iron in the cultivation media has a positive effect on the stability of the biofilms cultivated. By using the CLSM technique a stable base biofilm with a high amount of stained EPS glycoconjugates could be visualized after gauging. The thickness of the base biofilm was about 100 microm for all biofilms cultivated and was not removable under the applied shear conditions used during FDG.

Sex Differences in Semantic Processing: Event-Related Brain Potentials Distinguish between Lower and Higher Order Semantic Analysis during Word Reading

Behavioral studies suggest that women and men differ in the strategic elaboration of verbally encoded information especially in the absence of external task demand. However, measuring such covert processing requires other than behavioral data. The present study used event-related potentials to compare sexes in lower and higher order semantic processing during the passive reading of semantically related and unrelated word pairs. Women and men showed the same early context effect in the P1-N1 transition period. This finding indicates that the initial lexical-semantic access is similar in men and women. In contrast, sexes differed in higher order semantic processing. Women showed an earlier and longer lasting context effect in the N400 accompanied by larger signal strength in temporal networks similarly recruited by men and women. The results suggest that women spontaneously conduct a deeper semantic analysis. This leads to faster processing of related words in the active neural networks as reflected in a shorter stability of the N400 map in women. Taken together, the findings demonstrate that there is a selective sex difference in the controlled semantic analysis during passive word reading that is not reflected in different functional organization but in the depth of processing.

Comparison of spatial and temporal pattern for fMRI obtained with BOLD and arterial spin labeling

Functional magnetic resonance imaging (fMRI) is presently either performed using blood oxygenation level-dependent (BOLD) contrast or using cerebral blood flow (CBF), measured with arterial spin labeling (ASL) technique. The present fMRI study aimed to provide practical hints to favour one method over the other. It involved three different acquisition methods during visual checkerboard stimulation on nine healthy subjects: 1) CBF contrast obtained from ASL, 2) BOLD contrast extracted from ASL and 3) BOLD contrast from Echo planar imaging. Previous findings were replicated; i) no differences between the three measurements were found in the location of the activated region; ii) differences were found in the temporal characteristics of the signals and iii) BOLD has significantly higher sensitivity than ASL perfusion. ASL fMRI was favoured when the investigation demands for perfusion and task related signal changes. BOLD fMRI is more suitable in conjunction with fast event related design.

Oxygen profiles and biomass distribution in biopellets ofAspergillus niger

Morphology of fungal pellets has a significant influence on mass transfer and turnover processes in submerged cultures. There are many reports in literature that biomass is not distributed homogeneously over the pellet radius, yet quantitative data is rare. This study presents a method for the quantification of fungal pellet structure (Aspergillus niger). Confocal laser scanning microscopy (CLSM) is used in combination with image analysis freeware (Image J). Hyphal distribution is resolved spatially in radial direction. Quantitative morphological parameters are derived from digital images especially from the peripheral regions of the pellet that are not oxygen limited. This morphological information is combined with data of microelectrode measurements in the same pellets. Results show that the morphological parameters obtained can describe the impact of pellet structure on oxygen gradients much better than average biomass density. It is concluded that CLSM and image analysis are powerful tools not only to generate valuable data for quantitative description of pellet morphology. In addition, this data may be used in mathematical models to improve predictions of mass transfer and substrate conversion in mycelial aggregates.

Influence of growth history on sloughing and erosion from biofilms

The development of biofilms is determined by the balance of growth and detachment. But while the growth of biofilms is well studied, the influence of growth history and detachment on biofilm development is not. Here we report on laboratory scale experiments where heterotrophic biofilms were grown in a tubular reactor. Biofilm detachment was categorized based on particle size as erosion or sloughing. Erosion results in small particles and was approximated by the effluent suspended solids while sloughing was determined from the larger pieces of biomass that settled in a mixing tank. It was found that for all experiments, overall detachment was a combination of erosion and sloughing where erosion had a slightly larger contribution to the overall solids removal. However, sloughing had a significant influence on the biofilm morphology. Once the smooth biofilm surface was disturbed by a sloughing event (e.g., initiated through increasing liquid shear in the reactor), the biofilm became unstable resulting in spontaneous sloughing during subsequent operation. We propose that experimental investigations should consider sloughing events as an integral part of biofilm development rather than a disturbance.

Behaviour of biofilm systems under varying hydrodynamic conditions

Heterotrophic biofilms were cultivated in long-term experiments in biofilm tube reactors. During the biofilm cultivation the substrate loading of glucose was kept constant while the hydrodynamic conditions were changed stepwise. To describe the behaviour of the biofilm structure under these varying flow conditions the mass transfer and transport at the bulk/biofilm interface and inside the biofilm was investigated with oxygen microelectrodes. Furthermore, the biofilm density was used to describe the biofilm compactness before and after the change of the hydrodynamic condition. The obtained results show that the biofilm density and also the substrate flux decreased with decreasing flow velocity in the bulk phase. Additionally the slope of the oxygen concentration profiles decreased and the thickness of the concentration boundary layer increased. On the other hand, increasing the flow velocity in the bulk phase led both to a higher biofilm density and a higher maximum substrate flux. The biofilm surface became more homogenous and the thickness of the concentration boundary layer decreased. The time for adaptation of the biofilm structure after changing the hydrodynamic conditions ranged between 1 and 3 weeks.

Growth, structure and oxygen penetration in particle supported autotrophic biofilms

Particle supported autotrophic biofilms were cultivated in external-loop airlift reactors at two different pumice concentrations. Oxygen microelectrodes were used to investigate substrate transport and conversion. A special flow cell was designed for the measurement of oxygen concentration profiles in the particle supported biofilms under defined hydrodynamic conditions. The oxygen concentration profiles inside the biofilms were found to be steeper at high flow velocities in the bulk phase of the flow cell compared to those at low flow velocities. Furthermore, the oxygen flux increased and the thickness of the concentration boundary layer decreased with increasing flow velocity. This dependence was found to be more pronounced in less dense biofilms out of airlift reactors with lower pumice concentrations. In addition confocal laser scanning microscopy (CLSM) was used to visualize the biofilm structure. The volume fractions of bacteria and extracellular polymeric substances (lectin-specific EPS-glycoconjugates) were measured in living fully hydrated biofilms. Both the microelectrode and CLSM measurement showed the influence of shear stress on particle supported biofilms. A higher particle concentration led to dense biofilms with a homogeneous surface, lower thickness of the concentration boundary layer and steeper oxygen concentration profiles. The combination of both techniques allows a detailed and quantitative characterisation of particle associated biofilm structure and function.

Volumetric measurements of bacterial cells and extracellular polymeric substance glycoconjugates in biofilms

In this study an enrichment culture developed from activated sludge was used to investigate the architecture of fully hydrated multispecies biofilms. The assessment of biofilm structure and volume was carried out using confocal laser scanning microscopy (CLSM). Bacterial cell distribution was determined with the nucleic acid-specific stain SYTO 60, whereas glycoconjugates of extracellular polymeric substances (EPS) were stained with the Alexa-488-labeled lectin of Aleuria aurantia. Digital image analysis was employed for visualization and quantification of three-dimensional CLSM data sets. The specific volumes of the polymeric and cellular biofilm constituents were quantified. In addition, gravimetric measurements were done to determine dry mass and thickness of the biofilms. The data recorded by the CLSM technique and the gravimetric data were then compared. It was shown that the biofilm thicknesses determined with both methods agree well for slow-growing heterotrophic and chemoautotrophic biofilms. In addition, for slow-growing biofilms, the volumes and masses calculated from CLSM and the biomass calculated from gravimetric measurements were also comparable. For fast-growing heterotrophic biofilms cultivated with high glucose concentrations the data sets fit to a lesser degree, but still showed the same common trend. Compared with traditional gravimetric measurements, CLSM allowed differential recording of multiple biofilm parameters with subsequent three-dimensional visualization and quantification. The quantitative three-dimensional results recorded by CLSM are an important basis for understanding, controlling, exploiting, and modeling of biofilms.

Measuring local flow velocities and biofilm structure in biofilm systems with Magnetic Resonance Imaging (MRI)

The characterization of substrate transport in the bulk phase and in the biofilm matrix is one of the problems which has to be solved for the verification of biofilm models. Additionally, the surface structure of biofilms has to be described with appropriate parameters. Magnetic resonance imaging (MRI) is one of the promising methods for the investigation of transport phenomena and structure in biofilm systems. The MRI technique allows the noninvasive determination of flow velocities and biofilm structures with a high resolution on the sub-millimeter scale. The presented investigations were carried out for defined heterotrophic biofilms which were cultivated in a tube reactor at a Reynolds number of 2000 and 8000 and a substrate load of 6 and 4 g/m2d glucose. Magnetic resonance imaging provides both structure data of the biofilm surface and flow velocities in the bulk phase and at the bulk/biofilm interface. It is shown that the surface roughness of the biofilms can be determined in one experiment for the complete cross section of the test tubes both under flow and stagnant conditions. Furthermore, the local shear stress was calculated from the measured velocity profiles. In the investigated biofilm systems the local shear stress at the biofilm surface was up to 3 times higher compared to the mean wall shear stress calculated on the base of the mean flow velocity.

Simulation of growth and detachment in biofilm systems under defined hydrodynamic conditions

Detachment from biofilms was evaluated using a mixed culture biofilm grown on primary wastewater in a tube reactor. The growth of biofilms and the detachment of biomass from biofilms are strongly influenced by hydrodynamic conditions. In a long-term study, three biofilms were cultivated in a biofilm tube reactor. The conducted experiments of biofilm growth and detachment can be divided into three phases: 1) an exponential phase with a rapid increase of the biofilm thickness, 2) a quasi-steady-state with spontaneous fluctuation of the biofilm thickness between 500 and 1,200 microm in the investigated biofilm systems, and 3) a washout experiment with increased shear stress in three to four steps after several weeks of quasi-steady-state. Whereas the biofilm thickness during the homogeneous growth phase can be regarded constant throughout the reactor, it was found to be very heterogeneous during the quasi-steady-state and the washout experiments. Growth and detachment during all three phases was simulated with the same one-dimensional biofilm model. For each of the three phases, a different detachment rate model was used. During the homogeneous growth phase, detachment was modeled proportional to the biofilm growth rate. During the quasi-steady-state phase, detachment was described by random detachment events assuming a base biofilm thickness. Finally, the washout experiment was simulated with detachment being a function of the biofilm thickness before the increase of the shear stress.

RIONET: a water quality management tool for river basins

The water quality management tool RIONET for river basins has been developed with regard to the EU Water Framework Directive. The management tool can simulate the water quality in catchment basins not only in the dimension of a single river but in whole river networks. A submodel of the IWA River Water Quality Model No. 1 is used in RIONET. The river model is based on the assumption that self purification processes in the river takes place both in the benthic biofilm and the bulk water phase. Laboratory experiments with sediment cores underline the major role of the benthic biofilm. The input parameters of the management tool such as volumetric flow rates from waste water treatment plants and flow velocities and discharge in the main river and its tributaries can be loaded directly from geographic information systems (GIS). The subcatchment basin of the river Bode in Saxon Anhalt was used for test runs of RIONET.

Influence of growth conditions on biofilm development and mass transfer at the bulk/biofilm interface

In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and substrate conversion rates. Several biofilms were cultivated under different substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured substrate conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors.

2D simulation of transport and degradation in the River Rhine

A simple 2D model has been developed for the simulation of mass transport and degradation of substances in the river Rhine. The model describes mass transport in the flow direction with a convective and a dispersive term. Transversal transport is described by segmenting the river and formulating a transversal exchange coefficient between the segments. Degradation can be formulated with any kinetics from first order to complex enzyme kinetics. The model was verified with monitoring data from the river Rhine. The hydrodynamic parameters such as dispersion coefficients and exchange coefficients were fitted to the conductivity, which was assumed to be non-degradable. The degradation term was fitted to ammonia values. The model was used to simulate measured concentrations of a readily (Aniline) and a poorly biodegradable substance (1,4-Dioxan) 10 m from the left river bank. It was the objective of this research program to develop a model which allows a realistic estimation of the locally and regionally predicted environmental concentration of chemical substances in the EU risk assessment scheme.

Simulation of biofilm growth, substrate conversion and mass transfer under different hydrodynamic conditions

The hydrodynamic conditions and the substrate load in biofilm systems are two main parameters which influence the biofilm growth in particular the structure, density and thickness. In a long term study on heterotrophic biofilms in biofilm tube reactors the investigation has focussed on mass transfer at the bulk/biofilm interface, the biofilm density and the substrate conversion rates. To study the mass transfer phenomena at the bulk/biofilm interface oxygen profiles have been measured directly in tube reactors with microelectrodes. Microelectrode studies, substrate conversion rates and biofilm densities were used to formulate model equations for the simulation of biofilm growth under different hydrodynamic and substrate conditions. It can be shown that the mass transfer at any time is strongly coupled with the growth conditions during the biofilm cultivation. On the one side the calculated Sherwood numbers were coupled to the present hydraulic conditions, on the other side in addition the growth conditions such as growth rate and Reynolds number during biofilm cultivation were considered.

FLASHFLOOD: a 3D field-based similarity search and alignment method for flexible molecules

A three-dimensional field-based similarity search and alignment method for flexible molecules is introduced. The conformational space of a flexible molecule is represented in terms of fragments and torsional angles of allowed conformations. A user-definable property field is used to compute features of fragment pairs. Features are generalizations of CoMMA descriptors that characterize local regions of the property field by its local moments. The features are invariant under coordinate system transformations. Features taken from a query molecule are used to form alignments with fragment pairs in the database. An assembly algorithm is then used to merge the fragment pairs into full structures, aligned to the query. Key to the method is the use of a context adaptive descriptor scaling procedure as the basis for similarity. This allows the user to tune the weights of the various feature components based on examples relevant to the particular context under investigation. The property fields may range from simple, phenomenological fields, to fields derived from quantum mechanical calculations. We apply the method to the dihydrofolate/methotrexate benchmark system, and show that when one injects relevant contextual information into the descriptor scaling procedure, better results are obtained more efficiently. We also show how the method works and include computer times for a query from a database that represents approximately 23 million conformers of seventeen flexible molecules.