Densification of activated sludge for better settling performances: experimental characterization in batch column and model parameters calibration.

Conventional activated sludge (CAS) and densified sludge obtained using hydro-cyclone selective wasting were compared at a full-scale water resources recovery facility. The densified tested sludge, containing around 30-50% of aerobic granules, showed enhanced settleability with low and stable sludge volume index (SVI) compared to CAS, which suffered recurrent filamentous bulking. Further in-depth batch settling tests were carried out using a 40 cm diameter column fitted with ultrasonic transducers to monitor both sludge blanket height and vertical velocity profiles. Hindered settling and compression parameters were calibrated from the experiment for latter modelling use. Test sludge displayed more than doubled settling velocities compared to CAS, with hindered settling velocities remaining >3 m·h-1 even at high solids concentrations of 6.85 g·L-1. The compression regime was attained at much higher critical concentration for the test sludge. It also displayed enhanced thickening properties, with concentrations obtained after 30 min of settling being 20.9 and 8.5 g·L-1 respectively for test and control sludge. This allows for a substantial reduction of recirculation rates in practice. These results open perspectives in optimizing existing plant operation as well as clarifier design and modelling using densified sludge.

Human placental perfusion measured using dynamic contrast enhancement MRI.

OBJECTIVES: To evaluate the feasibility of dynamic contrast enhanced magnetic resonance imaging (DCE MRI) and measure values of in vivo placental perfusion in women. METHODS: This study was part of the Placentimage trial (NCT01092949). Gadolinium-chelate (Gd) enhanced dynamic MRI was performed two days before termination of pregnancies at 16 to 34 weeks gestational age (GA). Quantitative analysis was performed using one-compartment intravascular modeling. DCE perfusion parameters were analyzed across GA and were compared in IUGR and AGA fetuses. RESULTS: 134 patients were enrolled. After quality control check, 62 DCE MRI were analyzed including 48 and 14 pregnancies with normal and abnormal karyotypes, respectively. Mean placental blood flow was 129±61 mL/min/100ml in cases with normal karyotypes. Fetuses affected by IUGR (n = 13) showed significantly lower total placental blood flow values than AGA fetuses (n = 35) (F total = 122±88 mL/min versus 259±34 mL/min, p = 0.002). DCE perfusion parameters showed a linear correlation with GA. CONCLUSIONS: Measuring placental perfusion in vivo is possible using DCE MRI. Although this study has many limitations it gives us the first DCE MRI values that provide a potential standard for future research into placental perfusion methods and suggests that placental functional parameters are altered in IUGR pregnancies.

MRI based morphological examination of the placenta.

Ultrasound is widely used as the initial diagnostic imaging modality during pregnancy with both high spatial and temporal resolution. Although MRI in pregnancy has long focused on the fetus, its use in placental imaging has greatly increased over recent years. In addition to the possibilities of evaluating function, MRI with a wide field of view and high contrast resolution allows characterization of placental anatomy, particularly in situations that are difficult to specify with ultrasound, especially for suspected placenta accreta. MRI also appears to be a particularly useful examination for the anatomical evaluation of the placenta independent of maternal body habitus or fetal position. Indeed, surprisingly little attention is paid to the placenta in MRI when the indication for the examination is fetal. Thus, some aspects of the placenta seem to us to be important to be recognized by the radiologist and to be described on the MRI report. In this review, we will describe MRI sequences used for, and common features seen in, imaging of i) the normal placenta, ii) abnormal aspects of the placenta that should be identified on MRI performed for fetal reason, and iii) placental anomalies for which placental MRI may be indicated.

Distribution and degradation trend of micropollutants in a surface flow treatment wetland revealed by 3D numerical modelling combined with LC-MS/MS.

Conventional wastewater treatment plants are not designed to treat micropollutants; thus, for 20 years, several complementary treatment systems, such as surface flow wetlands have been used to address this issue. Previous studies demonstrate that higher residence time and low global velocities promote nutrient removal rates or micropollutant photodegradation. Nevertheless, these studies were restricted to the system limits (inlet/outlet). Therefore, detailed knowledge of water flow is crucial for identifying areas that promote degradation and optimise surface flow wetlands. The present study combines 3D water flow numerical modelling and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS/MS). Using this numerical model, validated by tracer experimental data, several velocity areas were distinguished in the wetland. Four areas were selected to investigate the waterflow influence and led to the following results: on the one hand, the number and concentration of micropollutants are independent of the waterflow, which could be due to several assumptions, such as the chronic exposure associated with a low Reynolds number; on the other hand, the potential degradation products (metabolites) were also assessed in the sludge to investigate the micropollutant biodegradation processes occurring in the wetland; micropollutant metabolites or degradation products were detected in higher proportions (both number and concentration) in lower flow rate areas. The relation to higher levels of plant and microorganism metabolites suggests higher biological activity that promotes degradation.

Kinesiotaping for the Rehabilitation of Rotator Cuff-Related Shoulder Pain: A Randomized Clinical Trial.

BACKGROUND: Kinesiotaping (KT) has been widely used in clinical practice. Current evidence is insufficient to support the use of KT for treating rotator cuff-related shoulder pain (RCRSP), as its mid- and long-term effects have not been investigated. HYPOTHESES: Individuals using KT will achieve faster improvements in symptoms and functional limitations compared with those not using it. They will also present a greater increase in pain-free range of motion (ROM) and acromiohumeral distance (AHD) at the end of the treatment. STUDY DESIGN: Randomized controlled trial (NCT02881021). LEVEL OF EVIDENCE: Therapy, level 1b. METHODS: A total of 52 individuals with RCRSP, randomly assigned to 1 of 2 groups (experimental: KT; control: no-KT), underwent a 6-week rehabilitation program composed of 10 physical therapy sessions. KT was added to the treatment of the KT group. Symptoms and functional limitations were assessed using the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire (primary outcome); Brief Pain Inventory (BPI); and Western Ontario Rotator Cuff (WORC) index at baseline, 3 weeks, 6 weeks, 12 weeks, and 6 months. AHD, pain-free ROM, and full ROM were measured at baseline and at week 6. The effects of KT were assessed using a nonparametric analysis for longitudinal data. RESULTS: No significant group × time interactions (0.112 ≤ P ≤ 0.726) were found for all outcomes. Time effects were observed as both groups showed significant improvements for all studied outcomes (DASH, BPI, and WORC, p < 0.0001; AHD, p = 0.017; pain-free ROM, p < 0.0001; and full ROM abduction, p ≤ 0.0001). CONCLUSION: Whereas symptoms, functional limitations, ROM, and AHD improved in both groups, the addition of KT did not lead to superior outcomes compared with exercise-based treatment alone, in the mid and long term, for individuals with RCRSP. CLINICAL RELEVANCE: Clinicians should not expect supplementary mid- or long-term gains with KT to reduce pain, improve shoulder function and ROM, or increase AHD if a rehabilitation program focusing on shoulder neuromuscular control is concurrently provided as treatment for individuals with RCRSP.

Safety, Tolerability, Pharmacokinetics, Target Occupancy, and Concentration-QT Analysis of the Novel BTK Inhibitor Evobrutinib in Healthy Volunteers.

Bruton's tyrosine kinase (BTK) is a key regulator of B cell receptor and Fc receptor signaling, and a rational therapeutic target for autoimmune diseases. This first-in-human phase I, double-blind, placebo-controlled trial investigated the safety, tolerability, pharmacokinetics (PK), target occupancy, and effects on QT interval of evobrutinib, a highly selective, oral inhibitor of BTK, in healthy subjects. This dose escalation trial consisted of two parts. Part 1 included 48 subjects in 6 ascending dose cohorts (25, 50, 100, 200, 350, and 500 mg) randomized to a single dose of evobrutinib or placebo. Part 2 included 36 subjects in 3 ascending dose cohorts (25, 75, and 200 mg/day) randomized to evobrutinib or placebo once daily for 14 days. Safety and tolerability, as well as PK and target occupancy (total and free BTK in peripheral blood mononuclear cells), were assessed following single and multiple dosing. PK parameters were determined by noncompartmental methods. QT interval was obtained from 12-lead electrocardiogram recordings and corrected for heart rate by Fridericia's method (QTcF). Treatment-emergent adverse events (TEAEs) were mostly mild, occurring in 25% of subjects after single dosing, and 48.1% after multiple dosing. There was no apparent dose relationship regarding frequency or type of TEAE among evobrutinib-treated subjects. Absorption was rapid (time to reach maximum plasma concentration (Tmax ) ~ 0.5 hour), half-life short (~ 2 hours), and PK dose-proportional, with no accumulation or time dependency on repeat dosing. BTK occupancy was dose-dependent, reaching maximum occupancy of > 90% within ~ 4 hours after single doses ≥ 200 mg; the effect was long-lasting (> 50% occupancy at 96 hours with ≥ 100 mg). After multiple dosing, full BTK occupancy was achieved with 25 mg, indicating slow turnover of BTK protein in vivo. Concentration-QTcF analyses did not show any impact of evobrutinib concentration on corrected QT (QTc). In summary, evobrutinib was well-tolerated, showed linear and time-independent PK, induced long-lasting BTK inhibition, and was associated with no prolongation of QT/QTc interval in healthy subjects. Evobrutinib is, therefore, suitable for investigation in autoimmune diseases.

Effects of acute nitric oxide precursor intake on peripheral and central fatigue during knee extensions in healthy men.

NEW FINDINGS: What is the central question of this study? What is the effect of acute NO precursor intake on vascular function, muscle and cerebral oxygenation and peripheral and central neuromuscular fatigue during knee-extension exercise? What is the main finding and its importance? Acute NO precursor ingestion increases the plasma concentrations of NO precursors (nitrate, arginine and citrulline) and enhances post-ischaemic vasodilatation, but has no significant effect on muscle and cerebral oxygenation, peripheral and central mechanisms of neuromuscular fatigue and, consequently, does not improve exercise performance. ABSTRACT: Nitric oxide (NO) plays an important role in matching blood flow to oxygen demand in the brain and contracting muscles during exercise. Previous studies have shown that increasing NO bioavailability can improve muscle function. The aim of this study was to assess the effect of acute NO precursor intake on muscle and cerebral oxygenation and on peripheral and central neuromuscular fatigue during exercise. In four experimental sessions, 15 healthy men performed a thigh ischaemia-reperfusion test followed by submaximal isometric knee extensions (5 s on-4 s off; 45% of maximal voluntary contraction) until task failure. In each session, subjects drank a nitrate-rich beetroot juice containing 520 mg nitrate (N), N and citrulline (6 g; N+C), N and arginine (6 g; N+A) or a placebo (PLA). Prefrontal cortex and quadriceps near-infrared spectroscopy parameters were monitored continuously. Transcranial magnetic stimulation and femoral nerve electrical stimulation were used to assess central and peripheral determinants of fatigue. The post-ischaemic increase in thigh blood total haemoglobin concentration was larger in N (10.1 ± 3.7 mmol) and N+C (10.9 ± 3.3 mmol) compared with PLA (8.2 ± 2.7 mmol; P < 0.05). Nitric oxide precursors had no significant effect on muscle and cerebral oxygenation or on peripheral and central mechanisms of neuromuscular fatigue during exercise. The total number of knee extensions did not differ between sessions (N, 71.9 ± 33.2; N+A, 73.3 ± 39.4; N+C, 74.6 ± 34.0; PLA, 71.8 ± 39.9; P > 0.05). In contrast to the post-ischaemic hyperaemic response, NO bioavailability in healthy subjects might not be the limiting factor for tissue perfusion and oxygenation during submaximal knee extensions to task failure.

Fetal MRI findings in a retrospective cohort of 26 cases of prenatally diagnosed CHARGE syndrome individuals.

"CHARGE syndrome" (CS) is a multifaceted syndrome associated with a poor prognosis. The prenatal diagnosis remains challenging especially as the fetal anomalies that may evoke suspicion of CS are not comprehensively described. OBJECTIVE: This study aims to identify the anomalies in MRI with suspected CHARGE syndrome and to propose a possible standardization in the image-based prenatal diagnosis of CS. METHODS: This was a retrospective study of 26 fetuses who underwent MRI and had a confirmed diagnosis of CS, as proven by histopathological and/or neonatal examinations and/or the presence of the CHD7 gene mutation. RESULTS: The three most frequent MRI anomalies confirmed at histopathological and/or neonatal examinations were arhinencephaly in 100% (26 of 26), dysplasia of the semicircular canals agenesis (SCA) in 100% (24 of 24), and posterior fossa anomalies in 100% (22 of 22). Our study also revealed short petrous bones with a particular triangular shape in 24 of 24 cases of SCA. Other relevant findings included external ear anomalies in 36% (9 of 25), cleft lip and palate (9 of 9), ventriculomegaly (VMG) (6 of 6), short corpus callosum (3 of 3), and ocular asymmetry in 36.6% (4 of 11). CONCLUSION: Our study emphasizes the interest of fetal MRI in the diagnosis of CS with an adapted knowledge of semiology.

Seasonal and ageing effect on the behaviour of 86 drugs in a full-scale surface treatment wetland: Removal efficiencies and distribution in plants and sediments.

The presence of human drugs in the aquatic environment is partly due to an incomplete and insufficient removal process of wastewater treatment plants (WWTPs). Thus, drug traces are observed at different concentrations in water bodies, sediments and aquatic plants all over the world. At the same time, Surface Flow Treatment Wetlands (SFTWs) at the outlet of WWTPs are commonly observed in small municipalities as complementary treatment. However, little is known regarding the role of SFTWs in the complementary mitigation of emerging contaminants, such as drugs, and the interactions between drugs, plants and sediment throughout the seasons. For that reason, we conducted sampling sessions over a period of two years on a full-scale SFTW downstream of a vertical-flow constructed wetland. At each session, the SFTW influent and effluent, as well as five different plant species and one composite sediment sample, were sampled. We detected more than fifty pharmaceutical compounds in the inflow and outflow water. The compounds most frequently detected were bisoprolol and ketoprofen. We emphasized that the SFTW removal ability was better in the summer than in the winter, due to the impact of weather on physicochemical parameters. Large variations of removal efficiencies were also observed when considering all of the detected compounds. Large seasonal variations were also observed for each compound. In addition, the study of the five plants showed their ability to uptake drugs from water and soil to the leaves in a species-specific manner. The pharmaceutical composition of the sediment was also correlated with the season: the maximum occurrence was reached in summer, and the minimum was reached in winter. Finally, the continuous decrease in removal efficiencies highlights the ageing effect on SFTW removal ability.

Assessment of Placental Perfusion in the Preeclampsia L-NAME Rat Model with High-Field Dynamic Contrast-Enhanced MRI.

PURPOSE: To evaluate placental function and perfusion in a rat model of preeclampsia infused with L-nitro-arginine methyl ester (L-NAME) by dynamic contrast-enhanced (DCE) MRI using gadolinium chelates. METHODS: Pregnant female Sprague-Dawley rats were fitted on embryonic day 16 (E16) with subcutaneous osmotic minipumps loaded to deliver, continuously, L-NAME (50 mg/day per rat; case group) or saline solution (control group). DCE MRI was performed on E19 using gadolinium chelates and a 4.7-T MRI apparatus for small animals. Quantitative analysis was performed using an image software program: placental blood flow (perfusion in mL/min/100 mL of placenta) and fractional volume of the maternal vascular placental compartment (ratio between the placental blood volume and the placental volume, Vb in %) were calculated by compartmental analysis. RESULTS: A total of 176 placentas (27 rats) were analyzed by DCE MRI (97 cases and 79 controls). The model was effective, inducing intrauterine growth retardation, as there was a significant difference between the two groups for placental weight (p < 0.01), fetal weight (p = 0.019), and fetal length (p < 0.01). There was no significant difference in placental perfusion between the L-NAME and control groups (140.1 ± 74.1 vs. 148.9 ± 97.4, respectively; p = 0.496). There was a significant difference between the L-NAME and control groups for Vb (53 ± 12.9 vs. 46.7 ± 9%, respectively; p < 0.01). CONCLUSION: In the L-NAME preeclampsia model, placental perfusion is normal and the fractional blood volume is increased, suggesting that preeclampsia is not always expressed as a result of decreased placental perfusion. This highlights the usefulness of MRI for investigating the physiopathology of preeclampsia.

Effects of Acute Salbutamol Intake on Peripheral and Central Fatigue in Trained Men.

PURPOSE: Ergogenic effect in physically active subjects has been reported after acute salbutamol (SAL) intake. ß2-Agonists have potential stimulant effects within the central nervous system that could be involved in this ergogenic effect. We hypothesized that acute SAL intake would induce changes in cerebral responses during exercise, with significant improvement in cerebral oxygenation and voluntary activation (VA) contributing to an increase in muscle performance. METHODS: Fourteen trained male subjects (25 ± 5 yr) performed repeated isometric knee extensions until task failure (TF) after 4 mg (oral) SAL, 800 µg (inhaled) SAL, or placebo intake. VA, corticospinal excitability, and inhibition assessed by transcranial magnetic stimulation and changes in hemoglobin concentrations assessed by near-infrared spectroscopy were measured before and during the fatiguing task. RESULTS: SAL had no significant effect both at rest and during exercise on prefrontal cortex oxygenation (e.g., changes in oxyhemoglobin concentration at TF: 11.4 ± 11.1 (4 mg SAL) vs 10.4 ± 10.6 (800 µg SAL) vs 10.8 ± 8.1 µmol (placebo); P = 0.314) and neuromuscular function (e.g., VA measured by TMS at TF: 90.2% ± 6.6% vs 92.6% ± 5.0% vs 90.1% ± 7.0%; P = 0.760). SAL had no effect on the number of contractions until TF (95 ± 51 vs 100 ± 52 vs 93 ± 47; P = 0.629). CONCLUSIONS: These results indicate that acute SAL intake had no effect on central and peripheral mechanisms of neuromuscular fatigue and did not improve quadriceps endurance.

Is combining gait retraining or an exercise programme with education better than education alone in treating runners with patellofemoral pain?A randomised clinical trial.

DESIGN: Single-blind randomised clinical trial. OBJECTIVE: To compare the effects of three 8-week rehabilitation programmes on symptoms and functional limitations of runners with patellofemoral pain (PFP). METHODS: Sixty-nine runners with PFP were randomly assigned to one of three intervention groups: (1) education on symptoms management and training modifications (education); (2) exercise programme in addition to education (exercises); (3) gait retraining in addition to education (gait retraining). Symptoms and functional limitations were assessed at baseline (T0), and after 4, 8 and 20 weeks (T4, T8 and T20) using the Knee Outcome Survey of the Activities of Daily Living Scale (KOS-ADLS) and visual analogue scales (VASs) for usual pain, worst pain and pain during running. Lower limb kinematics and kinetics during running, and isometric strength were also evaluated at T0 and T8. The effects of rehabilitation programmes were assessed using two-way analysis of variance. RESULTS: No significant group × time interactions (p<0.447) were found for KOS-ADLS and VASs. All three groups showed similar improvements at T4, T8 and T20 compared with T0 (p<0.05). Only the exercises group increased knee extension strength following rehabilitation (group × time: p<0.001) and only the gait retraining group (group × time: p<0.001) increased step rate (+7.0%) and decreased average vertical loading rate (-25.4%). CONCLUSION: Even though gait retraining and exercises improved their targeted mechanisms, their addition to education did not provide additional benefits on symptoms and functional limitations. Appropriate education on symptoms and management of training loads should be included as a primary component of treatment in runners with PFP. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov (NCT02352909).

Effects of kinesiotaping added to a rehabilitation programme for patients with rotator cuff tendinopathy: protocol for a single-blind, randomised controlled trial addressing symptoms, functional limitations and underlying deficits.

INTRODUCTION: Rotator cuff tendinopathy (RCTe) is the most frequent cause of shoulder pain, resulting in considerable losses to society and public resources. Muscle imbalance and inadequate sensorimotor control are deficits often associated with RCTe. Kinesiotaping (KT) is widely used by clinicians for rehabilitation of RCTe. While previous studies have examined the immediate effects of KT on shoulder injuries or the effects of KT as an isolated method of treatment, no published study has addressed its mid-term and long-term effects when combined with a rehabilitation programme for patients with RCTe. The primary objective of this randomised controlled trial (RCT) will be to assess the efficacy of therapeutic KT, added to a rehabilitation programme, in reducing pain and disabilities in individuals with RCTe. Secondary objectives will look at the effects of KT on the underlying factors involved in shoulder control, such as muscular activity, acromiohumeral distance (AHD) and range of motion (ROM). METHODS AND ANALYSIS: A single-blind RCT will be conducted. Fifty-two participants, randomly allocated to one of two groups (KT or no-KT), will take part in a 6-week rehabilitation programme. The KT group will receive KT added to the rehabilitation programme, whereas the no-KT group will receive only the rehabilitation programme. Measurements will be taken at baseline, week 3, week 6, week 12 and 6 months. Primary outcomes will be symptoms and functional limitations assessed by the Disabilities of the Arm, Shoulder and Hand questionnaire. Secondary outcomes will include shoulder ROM, AHD at rest and at 60° of abduction, and muscle activation during arm elevation. The added effects of KT will be assessed through a two-way analysis of variance for repeated measures. ETHICS AND DISSEMINATION: Ethics approval was obtained from the Ethics Committee of Quebec Rehabilitation Institute of the Centre Integrated University Health and Social Services. Results will be disseminated through international publications in peer-reviewed journals, in addition to international conference presentations. TRIAL REGISTRATION NUMBER: Protocol was registered at ClinicalTrials.gov (NCT02881021) on 25 August 2016. The WHO Trial Registration Data Set can also be found as an online supplementary file.

Pilot Study of a Software-Supported Protocol for Second-Trimester Ultrasound Screening.

OBJECTIVES: To evaluate the feasibility and impact of using a software-supported protocol for routine second-trimester ultrasound scanning. METHODS: We conducted a comparative observational study of 2 sets of 25 randomly selected normal routine second-trimester examinations performed by the same expert sonographer before and 1 year after the introduction of a software-supported protocol. The scanning protocol was identical during both periods and conformed to International Society of Ultrasound in Obstetrics and Gynecology guidelines. Two independent expert sonographers reviewed the temporal sequences of fetal anatomic visualization. The examination duration, number of images, time per stored image, and number of recorded anatomic features according to the International Society of Ultrasound in Obstetrics and Gynecology guidelines were compared between the periods. RESULTS: The mean examination duration and the number of images stored ± SD were both significantly higher during the period with the software-supported protocol than during the previous period (18.9 ± 5.3 versus 15.3 ± 2.8 minutes, respectively; P = .005; and 52.0 ± 2.4 versus 35.2 ± 3.4; P < .001). The mean time per image was also shorter with the software-supported protocol (19 ± 7 versus 26 ± 4 seconds; P < .001). Recording of the placental location, amniotic fluid quantification, cavum septi pellucidi, thoracic shape, both kidneys, both arms, and genitalia was significantly more consistent with the software-supported protocol (P < .001; P = .001; P = .022; P = .050; P = .022; P < .001; and P = .048). CONCLUSIONS: This pilot study suggests that a software-supported protocol standardizing image acquisition may improve operator efficiency during second-trimester ultrasound scans.

Electromyographic analysis of rotator cuff muscles in patients with rotator cuff tendinopathy: A systematic review.

The shoulder is inherently an unstable joint which heavily relies on the neuromuscular activation of the rotator cuff (RC) complex for stability during movement. Currently, there is no consensus regarding how the activity of RC muscles is affected among individuals with a RC tendinopathy (RCTe). This study reviewed the evidence of studies comparing the electromyographic (EMG) activity of any RC muscle of shoulders with a symptomatic RCTe to asymptomatic shoulders. Eight databases were searched. Data from 343 participants (201 symptomatic and 209 asymptomatic shoulders) were analyzed from 10 out of 402 included studies. Strong evidence for the infraspinatus and supraspinatus during isometric contractions and limited evidence for the supraspinatus and infraspinatus during isokinetic contractions suggest that the muscular activity is not altered among individuals with a RCTe during these types of contraction. Very limited evidence indicates reduced muscle activity for the infraspinatus and subscapularis in the presence of a RCTe during isotonic contractions, and no alterations for the supraspinatus or teres minor were identified. Lastly, conflicting to moderate evidence suggests alterations in RC muscle activity during unrestrained movements and swimming. These findings indicate that EMG deficits associated with a RCTe can best be appreciated during unrestrained movements.

Concentration-driven models revisited: towards a unified framework to model settling tanks in water resource recovery facilities.

A new perspective on the modelling of settling behaviour in water resource recovery facilities is introduced. The ultimate goal is to describe in a unified way the processes taking place both in primary settling tanks (PSTs) and secondary settling tanks (SSTs) for a more detailed operation and control. First, experimental evidence is provided, pointing out distributed particle properties (such as size, shape, density, porosity, and flocculation state) as an important common source of distributed settling behaviour in different settling unit processes and throughout different settling regimes (discrete, hindered and compression settling). Subsequently, a unified model framework that considers several particle classes is proposed in order to describe distributions in settling behaviour as well as the effect of variations in particle properties on the settling process. The result is a set of partial differential equations (PDEs) that are valid from dilute concentrations, where they correspond to discrete settling, to concentrated suspensions, where they correspond to compression settling. Consequently, these PDEs model both PSTs and SSTs.

On constitutive functions for hindered settling velocity in 1-D settler models: Selection of appropriate model structure.

Advanced 1-D models for Secondary Settling Tanks (SSTs) explicitly account for several phenomena that influence the settling process (such as hindered settling and compression settling). For each of these phenomena a valid mathematical expression needs to be selected and its parameters calibrated to obtain a model that can be used for operation and control. This is, however, a challenging task as these phenomena may occur simultaneously. Therefore, the presented work evaluates several available expressions for hindered settling based on long-term batch settling data. Specific attention is paid to the behaviour of these hindered settling functions in the compression region in order to evaluate how the modelling of sludge compression is influenced by the choice of a certain hindered settling function. The analysis shows that the exponential hindered settling forms, which are most commonly used in traditional SST models, not only account for hindered settling but partly lump other phenomena (compression) as well. This makes them unsuitable for advanced 1-D models that explicitly include each phenomenon in a modular way. A power-law function is shown to be more appropriate to describe the hindered settling velocity in advanced 1-D SST models.