The effect of fine bubble aeration intensity on membrane bioreactor sludge characteristics and fouling.

While most membrane bioreactor (MBR) research focuses on improving membrane filtration through air scour, backwashing and chemical cleaning to physically counteract fouling, relatively few studies have dealt with fouling prevention, e.g. minimizing the impact of operational settings that negatively impact sludge filterability. To evaluate the importance of those settings, the effects of bioreactor aeration intensity variations on membrane fouling have been studied in a lab-scale MBR setup while simultaneously monitoring a unique set of key sludge parameters. In particular, this paper focuses on the impact of shear dynamics resulting from fine air bubbles on the activated sludge quality and flocculation state, impacting membrane fouling. When augmenting the fine bubble aeration intensity both the total and irreversible fouling rate increased. Major indications for sludge filterability deterioration were found to be a shift in the particle size distribution (PSD) in the 3-300 µm range towards smaller sludge flocs, and increasing concentrations of submicron particles (10-1000 nm), soluble microbial products and biopolymers. When lowering the aeration intensity, both the sludge characteristics and fouling either went back to background values or stabilized, respectively indicating a temporary or more permanent effect, with or without time delay. The shift in PSD to smaller flocs and fragments likely increased the total fouling through the formation of a less permeable cake layer, while high concentrations of submicron particles were likely causing increased irreversible fouling through pore blocking. The insights from the performed fouling experiments can be used to optimize system operation with respect to influent dynamics.

Large-vessel vasculitis: interobserver agreement and diagnostic accuracy of 18F-FDG-PET/CT.

INTRODUCTION: (18)F-FDG-PET visualises inflammation. Both atherosclerosis and giant cell arteritis cause vascular inflammation, but distinguishing the two may be difficult. The goal of this study was to assess interobserver agreement and diagnostic accuracy of (18)F-FDG-PET for the detection of large artery involvement in giant cell arteritis (GCA). METHODS: 31 (18)F-FDG-PET/CT scans were selected from 2 databases. Four observers assessed vascular wall (18)F-FDG uptake, initially without and subsequently with predefined observer criteria (i.e., vascular wall (18)F-FDG uptake compared to liver or femoral artery (18)F-FDG uptake). External validation was performed by two additional observers. Sensitivity and specificity of (18)F-FDG-PET were determined by comparing scan results to a consensus diagnosis. RESULTS: The highest interobserver agreement (kappa: 0.96 in initial study and 0.79 in external validation) was observed when vascular wall (18)F-FDG uptake higher than liver uptake was used as a diagnostic criterion, although agreement was also good without predefined criteria (kappa: 0.68 and 0.85). Sensitivity and specificity were comparable for these methods. The criterion of vascular wall (18)F-FDG uptake equal to liver (18)F-FDG uptake had low specificity. CONCLUSION: Standardization of image assessment for vascular wall (18)F-FDG uptake promotes observer agreement, enables comparative studies, and does not appear to result in loss of diagnostic accuracy compared to nonstandardized assessment.

In-situ biofilm characterization in membrane systems using Optical Coherence Tomography: formation, structure, detachment and impact of flux change.

Biofouling causes performance loss in spiral wound nanofiltration (NF) and reverse osmosis (RO) membrane operation for process and drinking water production. The development of biofilm formation, structure and detachment was studied in-situ, non-destructively with Optical Coherence Tomography (OCT) in direct relation with the hydraulic biofilm resistance and membrane performance parameters: transmembrane pressure drop (TMP) and feed-channel pressure drop (FCP). The objective was to evaluate the suitability of OCT for biofouling studies, applying a membrane biofouling test cell operated at constant crossflow velocity (0.1 m s(-1)) and permeate flux (20 L m(-2)h(-1)). In time, the biofilm thickness on the membrane increased continuously causing a decline in membrane performance. Local biofilm detachment was observed at the biofilm-membrane interface. A mature biofilm was subjected to permeate flux variation (20 to 60 to 20 L m(-2)h(-1)). An increase in permeate flux caused a decrease in biofilm thickness and an increase in biofilm resistance, indicating biofilm compaction. Restoring the original permeate flux did not completely restore the original biofilm parameters: After elevated flux operation the biofilm thickness was reduced to 75% and the hydraulic resistance increased to 116% of the original values. Therefore, after a temporarily permeate flux increase the impact of the biofilm on membrane performance was stronger. OCT imaging of the biofilm with increased permeate flux revealed that the biofilm became compacted, lost internal voids, and became more dense. Therefore, membrane performance losses were not only related to biofilm thickness but also to the internal biofilm structure, e.g. caused by changes in pressure. Optical Coherence Tomography proved to be a suitable tool for quantitative in-situ biofilm thickness and morphology studies which can be carried out non-destructively and in real-time in transparent membrane biofouling monitors.

Effect of dissolved oxygen concentration on the bioflocculation process in high loaded MBRs.

High-loaded membrane bioreactors (HL-MBRs), i.e. MBRs which are operated at extremely short sludge and hydraulic retention times, can be applied to flocculate and concentrate sewage organic matter. The concentrated organics can be used for energy recovery, or for the production of more valuable organic chemicals. Little is known about the effect of the dissolved oxygen concentration (DO) on this bioflocculation process. To examine this effect, two HL-MBRs were operated, respectively at a low (1 mg L(-1)) and a higher (4 mg L(-1)) DO. The higher DO resulted in a better flocculation efficiency, i.e. 92% of the colloidal COD in the sewage flocculated compared to 69% at the lower DO. The difference was attributed to a higher microbial production of extracellular polymeric substances at a DO of 4 mg L(-1) and to more multivalent cations (calcium, iron and aluminium) being distributed to the floc matrix. In addition, the HL-MBR that was operated at a DO of 4 mg L(-1) gave a bigger mean floc size, a lower supernatant turbidity, better settleability and better membrane filterability than the HL-MBR that was operated at a DO of 1 mg L(-1).

Salt stress in a membrane bioreactor: dynamics of sludge properties, membrane fouling and remediation through powdered activated carbon dosing.

Membrane bioreactors are a well-established technology for wastewater treatment. However, their efficiency is adversely impacted by membrane fouling, primarily inciting very conservative operations of installations that makes them less appealing from an economic perspective. This fouling propensity of the activated sludge is closely related to system disturbances. Therefore, improved insight into the impact of fouling is crucial towards increased membrane performance. In this work, the disturbance of a salt shock was investigated with respect to sludge composition and filterability in two parallel lab-scale membrane bioreactors. Several key sludge parameters (soluble microbial products, sludge-bound extracellular polymeric substances, supramicron particle size distributions (PSD), submicron particle concentrations) were intensively monitored prior to, during, and after a disturbance to investigate its impact as well as the potential governing mechanism. Upon salt addition, the supramicron PSD immediately shifted to smaller floc sizes, and the total fouling rate increased. Following a certain delay, an increase in submicron particles, supernatant proteins, and polysaccharides was observed as well as an increase in the irreversible membrane fouling rate. Recovery from the disturbance was evidenced with a simultaneous decrease in the above mentioned quantities. A similar experiment introducing powdered activated carbon (PAC) addition used for remediation resulted in either no or less significant changes in the above mentioned quantities, signifying its potential as a mitigation strategy.

High loaded MBRs for organic matter recovery from sewage: effect of solids retention time on bioflocculation and on the role of extracellular polymers.

High loaded MBRs (HL-MBR) can concentrate sewage organic matter by aerobic bioflocculation for subsequent anaerobic conversion to methane or volatile fatty acids. In the range of very short solid retention times (SRT), the effect of SRT on bioflocculation and EPS production in HL-MBR was investigated. This short SRT range was selected to find an optimum SRT maximising recovery of organics by aerobic bioflocculation and minimizing losses of organics by aerobic mineralization. Bioflocculation was studied in five HL-MBRs operated at SRTs of 0.125, 0.25, 0.5, 1 and 5 d. The extent of flocculation, defined as the fraction of suspended COD in the concentrate, increased from 59% at an SRT of 0.125 d to 98% at an SRT of 5 d. The loss of sewage organic matter by biological oxidation was 1, 2, 4, 11 and 32% at SRT of 0.125-5 d. An SRT of 0.5-1 d gave best combination of bioflocculation and organic matter recovery. Bound extracellular polymeric substances (EPS) concentrations, in particular EPS-protein concentrations, increased when the SRT was prolonged from 0.125 to 1 d. This suggests that these EPS-proteins govern the bioflocculation process. A redistribution took place from free (supernatant) EPS to bound (floc associated) EPS when the SRT was prolonged from 0.125 to 1 d, further supporting the fact that the EPS play a dominant role in the flocculation process. Membrane fouling was most severe at the shortest SRTs of 0.125 d. No positive correlation was detected between the concentration of free EPS and membrane fouling, but the concentration of submicron (45-450 nm) particles proved to be a good indicator for this fouling.

Impact of biofilm accumulation on transmembrane and feed channel pressure drop: effects of crossflow velocity, feed spacer and biodegradable nutrient.

Biofilm formation causes performance loss in spiral-wound membrane systems. In this study a microfiltration membrane was used in experiments to simulate fouling in spiral-wound reverse osmosis (RO) and nanofiltration (NF) membrane modules without the influence of concentration polarization. The resistance of a microfiltration membrane is much lower than the intrinsic biofilm resistance, enabling the detection of biofilm accumulation in an early stage. The impact of biofilm accumulation on the transmembrane (biofilm) resistance and feed channel pressure drop as a function of the crossflow velocity (0.05 and 0.20 m s(-1)) and feed spacer presence was studied in transparent membrane biofouling monitors operated at a permeate flux of 20 L m(-2) h(-1). As biodegradable nutrient, acetate was dosed to the feed water (1.0 and 0.25 mg L(-1) carbon) to enhance biofilm accumulation in the monitors. The studies showed that biofilm formation caused an increased transmembrane resistance and feed channel pressure drop. The effect was strongest at the highest crossflow velocity (0.2 m s(-1)) and in the presence of a feed spacer. Simulating conditions as currently applied in nanofiltration and reverse osmosis installations (crossflow velocity 0.2 m s(-1) and standard feed spacer) showed that the impact of biofilm formation on performance, in terms of transmembrane and feed channel pressure drop, was strong. This emphasized the importance of hydrodynamics and feed spacer design. Biomass accumulation was related to the nutrient load (nutrient concentration and linear flow velocity). Reducing the nutrient concentration of the feed water enabled the application of higher crossflow velocities. Pretreatment to remove biodegradable nutrient and removal of biomass from the membrane elements played an important part to prevent or restrict biofouling.

Definitions and incidence of cardiac syndrome X: review and analysis of clinical data.

There is no consensus regarding the definition of cardiac syndrome X (CSX). We systematically reviewed recent literature using a standardized search strategy. We included 57 articles. A total of 47 studies mentioned a male/female distribution. A meta-analysis yielded a pooled proportion of females of 0.56 (n = 1,934 patients, with 95% confidence interval: 0.54-0.59). As much as 9 inclusion criteria and 43 exclusion criteria were found in the 57 articles. Applying these criteria to a population with normal coronary angiograms and treated in 1 year at a general hospital, the attributable CSX incidence varied between 3 and 11%. The many inclusion and exclusion criteria result in a wide range of definitions of CSX and these have large effects on the incidence. This shows the need for a generally accepted definition of CSX.

Association between anxiety disorder and the extent of ischemia observed in cardiac syndrome X.

BACKGROUND: A possible link between the heart and brain has been reported for cardiac syndrome X. Anxiety disorder could be a pathophysiological mechanism for this cardiac chest pain. To the authors' knowledge, a quantitative analysis correlating anxiety with the extent of ischemia has not been done. METHODS AND RESULTS: In this pilot study, we evaluated 20 patients with typical chest pain and completely normal coronary angiograms. These patients were screened with the State Scale and Trait Scale of the State-Trait Anxiety Inventory (STAI). All patients underwent myocardial perfusion scintigraphic imaging. The scintigrams were scored by three experienced readers having no knowledge of the STAI screening results. Patients with a low trait anxiety had significantly less ischemic segments on the myocardial perfusion imaging than patients with a high trait anxiety (1.8 +/- 1.9 vs 3.5 +/- 0.6, P < .05). For state anxiety, no significant differences could be found. CONCLUSION: Cardiac syndrome X patients with high trait anxiety are at risk of having more ischemia.

Outside-in trimming of humic substances during ozonation in a membrane contactor.

This paper addresses the change of molecular size distribution of humic substances (HS) during ozonation in a membrane contactor. It focuses on the characterization and identification of some small ozonation products. The membrane contactor setup allows very precise control of ozone transfer into the solution as well as precise sampling of the products in time. The molecular size distribution was followed by gel permeation chromatography (GPC). Characterization and identification of small ozonation products was performed by membrane nanofiltration and high-performance liquid chromatography (HPLC). Measurements on molecular size distribution indicate that during the ozonation process the size of the HS molecules decreases slowly and only small highly oxidated compounds are being split off the larger molecules. Pyruvic acid, formic acid, methylglyoxal, and acetaldehyde could be identified by substantial peaks. Glyoxilic acid and glyoxal were identified to a lesser extent. This suggests that HS molecules consist of a relatively stable backbone network structure and that the HS molecule degrades according to an outside-in trimming mechanism.

The effect of colloid stability of wastewater treatment plants effluent on nanofiltration performance.

Laboratory-scale filtration tests utilizing wastewater treatment plants (WWTP) effluent were conducted to investigate fouling and filtration behaviour, especially the influence of colloidal stability on nanofiltration performance. Acidification and coagulant dosage were used to create unstable colloidal conditions. Colloidal stability of the effluent was analysed on by zeta potential measurements. A statistical design method, full factorial design with blocking, has been used to account for effluent composition variations and to account for interaction between experimental parameters. The results show a high correlation between unstable colloidal natural organic matter and the formation of dense fouling layers. The reversibility of the fouling process was shown to be independent from colloidal stability. Irreversible fouling was show to be promoted by mild acidic (pH 5) effluent conditions, whereas coagulant addition showed an increase in the reversibility of the fouling.

Interobserver variability in assessment of signs of TMD.

PURPOSE: The aim of this report was to study the ability of examiners to measure reliably the clinical signs of temporomandibular disorders (TMD). Four examiners participated in this study of 11 TMD patients and 25 nonpatients. MATERIALS AND METHODS: Vertical and lateral excursions of the jaw were measured using a millimeter ruler. Joint sounds during vertical jaw movements were assessed using digital palpation. The reliability of delivering appropriate degrees of digital pressure to assess masticatory muscle pain was assessed using a manometer after training examiners to exert specified pressures. RESULTS: Intraclass correlation coefficients for the measurement of vertical and protrusive jaw movements were > or = 0.87, which was considered excellent. The intraclass correlation coefficient for measurements of left and right lateral jaw excursions varied between 0.73 and 0.85, which was considered acceptable. The interobserver agreement for detecting the joint sounds showed overall agreement across examiners of 78%. Kappa for every possible pair of examiners varied between .52 and .86 (median .75, interquartile range .18). Reliability for diagnostic categories from the Helkimo index and Research Diagnostic Criteria for Temporomandibular Disorders involving joint noises showed modest reliability. CONCLUSION: Point estimates and measures of spread for reliability measures of single clinical TMD signs as well as combinations of signs into diagnostic categories from the Helkimo index and Research Diagnostic Criteria for Temporomandibular Disorders involving joint noises were sufficient in a group of four examiners.

Functional subdivision of the human masseter and temporalis muscles as shown by the condylar movement response to electrical muscle stimulation.

In previous studies from our laboratory, a functional subdivision of the human temporalis and masseter muscles was demonstrated by means of opto-electronic recordings of the lower incisal point movement responses to electrical muscle stimulation. In the present study, it was examined whether this subdivision was also reflected in different movement responses of the mandibular condyle. To that end, the condylar movement responses to unilateral stimulation of four masseter muscle parts and three temporalis muscle parts were studied in four different jaw positions. The kinematic centre was used for condylar reference point. For both the amplitude and the direction of the movement responses, the effects of stimulation location and jaw position were studied using multivariate ANOVA and contrast analyses. It was found that for both outcome variables, the functional subdivision of the masseter and temporalis muscles was also reflected in some, but not all, of the movement responses of the mandibular condyles. The deep masseter muscle part and the (anterior) temporalis muscle part responded similarly to electrical stimulation.

Mandibular movements in response to electrical stimulation of superficial and deep parts of the human masseter muscle at different jaw positions.

Anatomical and electromyographical evidence suggests a compartmentalized function of the human jaw-closing muscles during both static and dynamic motor tasks. However, the voluntary nature of these tasks hampers unequivocal interpretation of this evidence, because it is impossible to activate voluntarily a single part of a muscle exclusively. Activation of discrete, localized regions can be accomplished with electrical stimulation. A previous study confirmed a functional subdivision of the temporalis muscle into at least three parts. Here, differences in the direction of the lower incisal-point (IP) movement in response to electrical stimulation of four different parts of the masseter muscle were examined in five healthy men. The deep masseter muscle and the anterior, middle, and posterior parts of the superficial masseter muscle were stimulated with monopolar wire electrodes in four different jaw positions (resting position; 50% maximum mouth opening; and 10-mm right and left lateral excursions, both with respect to resting position). Electrode-insertion depth was measured from magnetic resonance images. Movement responses to stimulation were recorded with the OKAS-3D jaw-movement analysis system. The variation in the direction of the IP movement in response to stimulation of parts of the masseter was partly explained by the effects of stimulus location and jaw position. The response to stimulation of the deep masseter was mainly laterovertically directed, whereas the response to stimulation of each of the superficial parts had a mainly anterovertical direction, the responses being most pronounced with the mandible in its resting position. These results provide further evidence for a functional subdivision of the masseter into a superficial part and a deep part, but not for a further subdivision of the superficial part into an anterior, middle, and posterior part.

Movements of the mandibular condyle kinematic center during jaw opening and closing.

Little is known about the detailed kinematics of the human temporomandibular condyle during jaw opening and closing. According to the rotate and swing model by Osborn (1989), the condyle is kept in close contact with the articular eminence during opening. Whether the condyle is in closer contact with the articular eminence during opening than during closing is unknown. Another consequence of the model is that the opening condylar movements are less variable than the closing movements. In this study, the hypothesis that the opening condylar path is closer to the articular eminence and also less variable than the closing condylar path is tested. Twenty subjects (10 males and 10 females with a mean age of 22) without signs or symptoms of a craniomandibular disorder performed 2 series of 4 protrusive movements and 2 series of 4 empty opening-closing movements. The movements were recorded by a six-degrees-of-freedom opto-electronic jaw movement recording system (OKAS-3D). The kinematic center of the condyle was used as a reference point for the reconstruction of condylar movement paths. Characteristics of the opening and closing paths were investigated by means of a displacement index (DI). This index is the quotient between the three-dimensional path length and the three-dimensional path distance between the start and the end point of an opening or closing movement of the kinematic center. The DI was smaller (p < 0.0001) and also less variable (p < 0.0001) during opening than during closing. The smaller DI value, in combination with the concave nature of the movement path, indicates that the opening path of the kinematic center lies above the closing path and thus closer to the articular eminence.

Influence of choice of reference point on the condylar movement paths during mandibular movements.

Series of four open-close, protrusive and lateral movements were recorded by the six degrees of freedom jaw movement recording system OKAS-3D in 20 healthy subjects. Consequently the movement paths of nine condylar points, the palpated lateral pole and eight points located on a square parallel to the sagittal plane with an edge of 10 mm and centred around the lateral pole were calculated. For all movements except the protrusive movements, the 3-D excursions of the condylar points strongly depended upon the choice of condylar reference point (ANOVA, P < 0.001). During laterotrusive movements the Bennett angle and the Bennett shift also varied significantly according to the position of the reference point (ANOVA, P < 0.001). The results of this study underline that comparison of condylar movements between different studies is only possible when the same condylar reference point is used. General consensus on the choice of condylar reference point is thus needed.

Jaw movement responses to electrical stimulation of different parts of the human temporalis muscle.

Previous EMG studies have provided indications for the differential activation of the human temporalis muscle. However, in these studies the contribution of different parts of the temporalis muscle could not be separated from the contributions of other muscles, since contraction was performed by voluntary activation. Therefore, the aim of this study was to examine functional differences among various parts of the human temporalis muscle by means of recording the incisal point movement response to electrical stimulation of parts of the muscle. Five healthy male subjects participated in this study. Three locations (anterior, middle, and posterior temporalis muscle) were stimulated, by means of monopolar wire electrodes and rectangular pulses. The insertion depths of the stimulation electrodes were determined by means of magnetic resonance images. Stimulation was performed in four jaw positions (resting position, 50% maximum mouth opening, 1 cm to the left, and 1 cm to the right). Movement responses to stimulation of the different muscle parts were recorded with the OKAS-3D jaw movement analysis system. The movement responses were expressed in polar coordinates. The variation in the direction of the jaw movement response was partly explained by the factors 'stimulation location' and 'jaw position' (ANOVA, p < 0.001). When the stimulation location shifted in an antero-posterior direction, the response changed from a vertical-lateral incisal point movement to a lateral-posterior movement with a smaller vertical component. The jaw position during stimulation also influenced the movement response. A functional subdivision of the temporalis muscle into at least three parts is favored.

Relationship between condylar and incisor point displacement during habitual maximum open-close movements.

The relationship between condylar movements and incisor point movements during habitual maximum open-close movements were studied in 10 healthy male and 10 healthy female subjects. Jaw movements were recorded by means of an opto-electronic jaw movement recording system, OKAS-3D, capable of recording the six degrees of freedom at a sample frequency of 300 Hz. The lower jaw position of the lateral pole of the condyles was found by means of palpation. In order to analyse the movements, the opening and closing path of the incisor point were divided into ten equal intervals and the corresponding condylar displacement in each interval was calculated. A displacement index was obtained by normalizing the condylar displacement with respect to the maximum condylar displacement. Due to the normalization, the displacement index is not sensitive to possible errors in the location of the lateral condylar point. A clear condylar displacement was already recorded in the first movement interval, right at the start of opening (average displacement index in the first opening interval was significantly greater than zero, P < 0.0005). The condylar displacements in the start and the end interval of opening and closing were smaller than in the intermediate movement intervals (P < 0.00005).

The kinematic center: a reference for condylar movements.

The kinematic center of the temporomandibular condyle is that condylar point which follows as much as possible the same movement path during different types of mandibular movements. In this study, the location of the kinematic center with respect to the palpated lateral pole of the condyle was investigated. Also, the lengths of the condylar movement path reconstructed by means of the kinematic center and the palpated condyle were compared. Mandibular movements were recorded with 6 degrees of freedom in 20 healthy subjects. A software procedure calculated the location of the kinematic center as that mandibular point for which the protrusive and opening movement path showed a minimal difference. For each subject, its average location was calculated on the basis of 16 pairs of protrusive and opening movements. The kinematic center was located posteriorly and superiorly with respect to the palpated condylar point (p < 0.0001). The standard deviation in the anterior-posterior coordinate of the average kinematic center was smaller than that in the superior-inferior coordinate (p < 0.0001). During opening, the path length of the kinematic center is longer than that of the palpated lateral pole of the condyle (p < 0.0001). In contrast to left-right differences found in the path lengths of the lateral pole of the condyle, no left-right differences were found for the kinematic center.