The phenomenon of granulation of anaerobic sludge

Successful high-rate anaerobic wastewater treatment can only be accomplished when the slowgrowing anaerobic biomass is efficiently held back in the anaerobic treatment system. This biomass retention can be achieved in various ways including immobilization of the organisms on fixed materials and immobilization on mobile support materials: in the latter case, combined with settling of the anaerobic sludge aggregates.This dissertation focuses on the phenomenon of flocculent anaerobic sludge transferring into highly active well-settling sludge granules under specific conditions. A high level of sludge retention can be achieved with granular anaerobic sludge under conditions of high gas production and turbulence in the digester, and consequently, the anaerobic treatment system accommodating high loading rates. This sludge granulation phenomenon proceeds in treatment systems operated in an upflow mode; the Upflow Anaerobic Sludge Bed (UASB) reactor being the main reactor system supporting this phenomenon. The UASB system is in fact nowadays, the most widely applied high-rate anaerobic treatment system in the world. One of the reasons for the UASB system's popularity is undoubtedly this granulation phenomenon.The work presented in this thesis is focused on the study of the various operational factors that effect the granulation process. This study was conducted in small-scale UASB reactors using well defined feed stocks. The main objective of this work was to develop useful guidelines for operators of full-scale UASB reactors for cultivating granular sludge in their systems.Chapter I reviews the present knowledge on relevant factors related to the granulation of anaerobic sludge. Important factors discussed regarding the formation of granular sludge include: the mechanisms governing bacterial adhesion and the production and role of extracellular polymers as "sticking" agents, the role of Ca 2+, and the effect of the seed sludge. The ideas of the various researchers are often contradictory, emphasizing the fact that the fundamental mechanism of granulation is a very complex and still only partially understood process.Considerable emphasis has recently been directed to the characterization of granular sludge, particularly with respect to the chemical and microbiological composition of the granules. The chemical composition varies considerably and depends on the composition of the wastewater. As far as the microbiological composition is concerned, it is commonly agreed that the acetate utilizing methanogen Methanothrix soehngenii is the predominant organism, although various other methanogenic and acetogenic organisms are always present, as well as, depending on the composition of the wastewater, a certain population of acidogenic bacteria. The specific methanogenic activity of the granular sludge is a useful tool for characterizing the sludge. The high methanogenic activities generally found with granular sludges demonstrate their ability to be excellent micro- ecosystems with a good micro-environment for all kinds of organisms, including the syntrophically-growing organisms involved in the anaerobic degradation process.For the physical characterization of granules, factors of specific importance are size,. size distribution, density, settleability and granule strength.And finally, presented in Chapter 1 is our hypothesis of the granulation mechanism. In our opinion, the selection pressure plays a key role in the granulation process. It is a result of the hydraulic surface-load and the gas surface-load, and is required for accomplishing the necessary separation of lighter and heavier sludge fractions. Almost all growth should eventually concentrate on or in the heavier particles which can be accomplished by allowing all finely dispersed sludge to wash out of the system. The first generations of granules will be fairly open and fluffy in nature, but as a result of a maturation process the granules will gradually become more compact, and filamentous Methanothrix bacteria will be overgrown by the shortchained Methanothrix cells.For the proper separation of dispersed sludge and agglomerated sludge, it is important that the sludge bed is kept at a level that leaves an area of free space between the sludge bed and the gas collector.Chapter 3 describes the experimental results concerning granulation on volatile fatty acid (VFA) mixtures (acetate, propionate and butyrate) with digested sewage sludge as seed material. Various relevant parameters were investigated such as the sludge loading rate, substrate concentration, the effect of Ca 2+and NH4+, pH and temperature. The results demonstrate that granulation with a simple VFA substrate proceeds very well. The granules developed on VFA substrates with VFA concentrations below 150 mg/l consisted mainly of filamentous Methanothrix.In all the granulation experiments, including those discussed in Chapters 4 and 5, independent of the type of substrate used, a very similar pattern of retained sludge amounts in relation to the imposed space load could be observed. Initially, the amount of sludge diminishes as a result of wash-out of finely dispersed sludge ingredients from the system. In this initial phase of the start-up process, to prevent overloading of the system, the space loading rates should not be further increased. As a result of wash-out of inert organic sludge ingredients and the continuous accumulation of new bacterial matter, the specific methanogenic degradation capacity of the sludge (based on overall VSS) will show a distinct continuous increase until a steady state with respect to sludge composition is established.Generally after a period of 40 to 50 days, sludge granules up to a size of 0.5 mm can be observed in the sludge bed. From then onward, the total amount of sludge in the reactor will again gradually increase, while the space loading rate can usually be increased without further stagnation in the digestion process.With increasing loading rates, the fraction of granular sludge will increase in the sludge bed.The importance of imposing and maintaining a proper selection pressure has been demonstrated in the following ways:- if the system remains underloaded for a long period of time, a bulking type of anaerobic sludge, which is very hard to retain in the reactor, will develop;- at a given space loading rate, which is determined by the degradation capacity of the sludge present in the reactor, granulation proceeds clearly faster with less concentrated wastewaters.The influent VFA concentration is also of importance with respect to the ultimate bacterial. composition of the granular sludge. When using a concentrated VFA solution as feed, i.e. 10.000 mg VFA-COD/l, a granular sludge will develop consisting mainly of Methanosarcina rather than Methanothrix. With lower substrate concentrations, Methanosarcina may develop under conditions of continuous overloading. Fluidized bed systems are usually started up under such conditions, however they are kinetically unfavorable to growth of the desired wellattaching Methanothrix organism, and may therefore lead to an unwanted accumulation of less well-attaching Methanosarcina sludge in the system.The Methanosarcina granules remain very small (Dp Methanothrix granules rather than Methanosarcina granules.The granulation process can be enhanced significantly by increasing the temperature in the mesophilic range to values near 40 °C. At this temperature however, the process will also become more unstable.We have found clear evidence indicating that granulation also proceeds well at reduced pH values. At a pH level of 6, start-up and granulation proceeded surprisingly well. Quite interestingly, we also found that the Methanothrix -like organism cultivated in the sludge had a much lower pH optimum than that of the Methanothrix strains described in the literature so far.Chapter 4 describes the results of experiments investigating the effects of specific additives to the seed sludge. Again, digested sewage sludge was utilized as seed sludge.In a number of experiments (gently) crushed granular sludge was introduced to the reactor, adding a large number of small granular nuclei to the seed. We observed that with this addition (only a few percent on VSS basis), a distinct enhancement of the granulation occurred.Moreover, and of great importance, we also observed a clear difference in the type of granule cultivated. On mere digested sewage sludge, granules consist mainly of Methanothrix- like organisms in a filamentous state, whereas in the experiment with digested sewage sludge enriched with a small amount of crushed granular sludge, all of the granules consisted of Methanothrix- like organisms present as short chains of 4 to 6 cells. Both granules exert excellent settling properties and are highly active. Organic loading rates up to 50 kg COD/m 3.day could be very well accommodated in reactors containing 20-25 kg VSS/m 3. The so-called "filamentous" granules have a more open structure, while the first generation granules contain inert support particles originating from the seed sludge. The so-called "rod type" granules are significantly more compact and generally do not contain inert support particles.Experiments with hydro-anthracite as an additional inert support particle reveal its presence to have a positive effect on the granulation speed. Removal of inert particles from the digested sewage sludge contrarily results in poor granulation. The results of these experiments clearly demonstrate the importance of inert support particles generally present in digested sewage sludge.We also observed that inert particles with a filamentous nature have a negative effect on the sludge characteristics by reducing the sludge settleability and promoting excessive wash-out of sludge. Seed sludges with a high fibrous material content are therefore not recommended for inoculating the anaerobic system.The granulation process was also studied on a more complex substrate (Chapter 5). Sucrose was selected for these experiments; its investigations indicating that a stable granular type of sludge could be cultivated on this carbohydrate, and at a faster rate than on VFA substrates.The experimental results also revealed the importance of imposing proper selection pressure with more complex soluble substrates, in order to avoid the accumulation of fast-growing voluminous and dispersed acidogenic biomass. We wish to emphasize however, that it is not necessary to apply hydraulic retention times lower than the maximum specific growth rate, sometimes considered a prerequisite for the successful start-up of a fluidized bed system.In Chapter 6 the results of preliminary work on the physical characterization of granular sludge is discussed. Tools for characterization used were:- a modificated sedimentation balance for the determination of the settling characteristics and particle size distribution;- an apparatus to measure the resistance against compression forces.Both methods, combined with a picnometric density measurement, are considered useful tools for the characterization of granular sludge. With the aid of these techniques we were able to demonstrate that a substrate shift from a VFA mixture to a sucrose solution will lead to the formation of weaker and bigger granules. Furthermore, a positive correlation between ash content and granule density could also be demonstrated.Based on the insights obtained from our investigations, we can conclude that the sludge granulation process, as it occurs in upflow reactors such as the UASB system, originates from:- the strong tendency of anaerobic organisms to stick together;- the fact that a complex community is required for the anaerobic degradation of organic substrates, which forces the system to grow in the form of a micro-ecosystem;- the fact that growth of bacterial matter is stimulated to take place on and in immobilized aggregates (nuclei) present and formed in the sludge, by imposing the proper selection pressure to the system.We believe that the results of the experiments presented in this thesis provide strong evidence in support of our hypothesis of the granulation phenomenon.Summarizing the results of the present investigations, the following practical guidelines can be provided for the start-up of full-scale reactors.I Seed sludge1. The presence of "proper" carrier materials for bacterial attachment is important for the initiation and stimulation of bacterial aggregation.2. The specific methanogenic activity of the seed sludge is not the only factor of importance. Thicker types of digested sewage sludge, i.e.>60 kg TSS/m 3, are preferred over thinner types, despite their lower methanogenic activity.3. The addition of a small amount of (crushed) granular sludge to seed sludge enhances the granulation process.II The mode of operation of the processIt is essential to sufficiently and continuously remove the lighter sludge fractions from the reactor to retain the heavier sludge ingredients and to promote bacterial growth in/on the heavier sludge ingredients. To achieve this, we recommend the following:1. Washed out dispersed sludge should not be returned.2. Apply effluent recycle or dilution at an influent COD of more than 5,000 mg/l.3. Increase the organic loading rate step-wise, always after at least an 80% reduction in the biodegradable COD has been achieved.4. Maintain a low acetate concentration (5. Start with 12-15 kg sludge VSS/m 3with thick seed (>60 kg TSS/m 3) and approximately 6 kg sludge VSS/m 3with thin seed sludge (3).III Wastewater characteristics1. A general observation is that the lower the strength of the wastewater the faster the granulation will proceed. The strength however, should be high enough to maintain good conditions for bacterial growth. The minimum COD level is presumably approximately 500 mg/l.2. Dispersed solids, such as acidogenic biomass and fibrous matter, retard or may even prevent granulation.3. Granulation will more quickly occur on mainly soluble unacidified wastewaters than on acidified wastewaters.4. High ion concentrations (e.g. Ca 2+, Mg 2+) will lead to chemical precipitation (CaCO 3 , CaHPO 4 , MgNH 4 PO 4 ) resulting in the formation of a granular sludge with a high ashcontent.IV Environmental factors1. The optimal temperature for mesophilic treatment is in the range of 30-38 °C and for thermophilic treatment in the range of 50-60 °C.2. The pH should always be maintained above 6.3. All essential growth factors such as N, P, S and trace elements (Fe, Ni, Co) should be present in sufficient amounts and in available form.4. Toxic compounds should not be present at inhibitory concentrations. If they are present, sufficient time should be allowed for bacterial acclimatization

Normalized Cut Group Clustering of Resting-State fMRI Data

BACKGROUND: Functional brain imaging studies have indicated that distinct anatomical brain regions can show coherent spontaneous neuronal activity during rest. Regions that show such correlated behavior are said to form resting-state networks (RSNs). RSNs have been investigated using seed-dependent functional connectivity maps and by using a number of model-free methods. However, examining RSNs across a group of subjects is still a complex task and often involves human input in selecting meaningful networks. METHODOLOGY/PRINCIPAL FINDINGS: We report on a voxel based model-free normalized cut graph clustering approach with whole brain coverage for group analysis of resting-state data, in which the number of RSNs is computed as an optimal clustering fit of the data. Inter-voxel correlations of time-series are grouped at the individual level and the consistency of the resulting networks across subjects is clustered at the group level, defining the group RSNs. We scanned a group of 26 subjects at rest with a fast BOLD sensitive fMRI scanning protocol on a 3 Tesla MR scanner. CONCLUSIONS/SIGNIFICANCE: An optimal group clustering fit revealed 7 RSNs. The 7 RSNs included motor/visual, auditory and attention networks and the frequently reported default mode network. The found RSNs showed large overlap with recently reported resting-state results and support the idea of the formation of spatially distinct RSNs during rest in the human brain

Genetic correlations between brain volumes and the WAIS-III dimensions of verbal comprehension, working memory, perceptual organization, and processing speed

We recently showed that the correlation of gray and white matter volume with full scale IQ and the Working Memory dimension are completely mediated by common genetic factors (Posthuma et al., 2002). Here we examine whether the other WAIS III dimensions (Verbal Comprehension, Perceptual Organization, Processing Speed) are also related to gray and white matter volume, and whether any of the dimensions are related to cerebellar volume. Two overlapping samples provided 135 subjects from 60 extended twin families for whom both MRI scans and WAIS III data were available. All three brain volumes are related to Working Memory capacity (r = 0.27). This phenotypic correlation is completely due to a common underlying genetic factor. Processing Speed was genetically related to white matter volume (

Reduced resting state functional connectivity in the hippocampus-midbrain-striatum network of schizophrenia patients

Contemporary preclinical models suggest that abnormal functioning of a brain network consisting of the hippocampus, midbrain and striatum plays a critical role in the pathophysiology of schizophrenia. Previous neuroimaging studies examined individual aspects of this model in schizophrenia patients and individuals at clinical high risk for psychosis. However, this exact preclinical brain network has not been translated to human neuroimaging studies with schizophrenia patients and therefore it is currently unknown how functioning of this network is altered in patients. Here we investigated resting state functional connectivity in the hippocampus-midbrain-striatum network of schizophrenia patients, using functional Magnetic Resonance Imaging. Based on preclinical models, a network of functionally validated brain regions comprising the anterior subiculum (SUB), limbic striatum (LS), ventral tegmental area (VTA) and associative striatum (AS) was examined in 47 schizophrenia patients and 51 healthy controls. Schizophrenia patients demonstrated significantly lower functional connectivity in this hippocampus-midbrain-striatum network compared with healthy controls (p = 0.036). Particular reductions in connectivity were found between the SUB and LS (0.002 +/- 0.315 and 0.116 +/- 0.224, p = 0.040) and between the VTA and AS (0.230 +/- 0.268 and 0.356 +/- 0.285, p = 0.026). In patients, functional connectivity was not significantly associated with positive, negative or general symptom scores. Reduced connectivity is consistent with the concept of functional brain dysconnectivity as a key feature of the disorder. Our results support the notion that functioning of the hippocampus-midbrain-striatum network is significantly altered in the pathophysiology of schizophrenia

Диагностика заболеваний сердечно-сосудистой системы и ишемии миокарда с помощью магниторезонансной визуализации с контрастным усилением

Показана возможность выявления патологических изменений в миокарде (инфаркт, ишемия) и сосудистой системе (стеноз) с помощью магниторезонансной визуализации с контрастным усилением.The possibility to reveal pathological changes in the myocardium (infarction, ischemia) and vascular system (stenosis) using magnetic resonance imaging with contrast enhancement is shown

Impaired Cerebellar Functional Connectivity in Schizophrenia Patients and Their Healthy Siblings

The long-standing notion of schizophrenia as a disorder of connectivity is supported by emerging evidence from recent neuroimaging studies, suggesting impairments of both structural and functional connectivity in schizophrenia. However, investigations are generally restricted to supratentorial brain regions, thereby excluding the cerebellum. As increasing evidence suggests that the cerebellum contributes to cognitive and affective processing, aberrant connectivity in schizophrenia may include cerebellar dysconnectivity. Moreover, as schizophrenia is highly heritable, unaffected family members of schizophrenia patients may exhibit similar connectivity profiles. The present study applies resting-state functional magnetic resonance imaging to determine cerebellar functional connectivity profiles, and the familial component of cerebellar connectivity profiles, in 62 schizophrenia patients and 67 siblings of schizophrenia patients. Compared to healthy control subjects, schizophrenia patients showed impaired functional connectivity between the cerebellum and several left-sided cerebral regions, including the hippocampus, thalamus, middle cingulate gyrus, triangular part of the inferior frontal gyrus, supplementary motor area, and lingual gyrus (all p < 0.0025, whole-brain significant). Importantly, siblings of schizophrenia patients showed several similarities to patients in cerebellar functional connectivity, suggesting that cerebellar dysconnectivity in schizophrenia might be related to familial factors. In conclusion, our findings suggest that dysconnectivity in schizophrenia involves the cerebellum and that this defect may be related to the risk to develop the illness

Self-regulation in the pre-adolescent brain

Self-regulation refers to the ability to monitor and modulate emotions, behavior, and cognition, which in turn allows us to achieve goals and adapt to ever changing circumstances. This trait develops from early infancy well into adulthood, and features both low-level executive functions such as reactive inhibition, as well as higher level executive functions such as proactive inhibition. Development of self-regulation is linked to brain maturation in adolescence and adulthood. However, how self-regulation in daily life relates to brain functioning in pre-adolescent children is not known. To this aim, we have analyzed data from 640 children aged 8–11, who performed a stop-signal anticipation task combined with functional magnetic resonance imaging, in addition to questionnaire data on self-regulation. We find that pre-adolescent boys and girls who display higher levels of self-regulation, are better able to employ proactive inhibitory control strategies, exhibit stronger frontal activation and more functional coupling between cortical and subcortical areas of the brain. Furthermore, we demonstrate that pre-adolescent children show significant activation in areas of the brain that were previously only associated with reactive and proactive inhibition in adults and adolescents. Thus, already in pre-adolescent children, frontal-striatal brain areas are active during self-regulatory behavior

Genetic Influences on the Development of Cerebral Cortical Thickness During Childhood and Adolescence in a Dutch Longitudinal Twin Sample:The Brainscale Study

Previous studies have demonstrated that cortical thickness (CT) is under strong genetic control across the life span. However, little is known about genetic influences that cause changes in cortical thickness (ΔCT) during brain development. We obtained 482 longitudinal MRI scans at ages 9, 12, and 17 years from 215 twins and applied structural equation modeling to estimate genetic influences on (1) cortical thickness between regions and across time, and (2) changes in cortical thickness between ages. Although cortical thickness is largely mediated by the same genetic factor throughout late childhood and adolescence, we found evidence for influences of distinct genetic factors on regions across space and time. In addition, we found genetic influences for cortical thinning during adolescence that is mostly due to fluctuating influences from the same genetic factor, with evidence of local influences from a second emerging genetic factor. This fluctuating core genetic factor and emerging novel genetic factor might be implicated in the rapid cognitive and behavioral development during childhood and adolescence, and could potentially be targets for investigation into the manifestation of psychiatric disorders that have their origin in childhood and adolescence

Development of image analysis techniques as a tool to detect and quantify morphological changes in anaerobic sludge : I. application to a granulation process

Image analysis techniques were developed and applied to quantify the process of anaerobic granulation in an expanded granular sludge blanket reactor (EGSB) fed with a synthetic substrate based on glucose [60-30% COD chemical oxygen demand)] and volatile fatty acids (40-70% COD) over 376 days. In a first operation period that lasted 177 days, the aggregation of dispersed sludge was quantitatively monitored through the recognition and quantification of aggregates and filaments. A parameter defined as the ratio between the filaments' length and the aggregates projected area (LfA) has proven to be sensitive to detect changes in the aggregation status of the anaerobic sludge. The aggregation time-defined as the moment when a balance between filaments' length and aggregates' size was establishe-was recognized through the LfA. The percentage of projected area of aggregates within three size ranges (0.01 -0.1 mm, 0.1 - 1 mm, and >1 mm, equivalent diameter) reflected the granular size spectrum during the aggregation process. When sudden increases on the upflow velocity and on the organic loading rate were applied to the previously formed granules, the developed image analysis techniques revealed to be good indicators of granular sludge stability, since they were sensitive to detected filaments release, fragmentation, and erosion that usually leads to washout. The specific methanogenic activities in the presence of acetate, propionate, butyrate, and H2/CO2 increased along the operation, particularly relevant was the sudden increase in the specific hydrogenophilic activity, immediately after the moment recognized as aggregation time.Instituto Cooperação Científica e Tecnológica Internacional (ICCTI), Ambassade de France in Portugal - Project 203 B4.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/3187/2000, PRAXIS XXI/BD/20325/99, POCTI/1999/CTA736524