Short circuiting in a denitrifying activated sludge tank

2005 ◽  
Vol 52 (10-11) ◽  
pp. 79-87 ◽  
Author(s):  
R. Kjellstrand ◽  
A. Mattsson ◽  
C. Niklasson ◽  
M.J. Taherzadeh
Keyword(s):  
Activated Sludge ◽  
Short Circuit ◽  
Lithium Concentration ◽  
Tracer Tests ◽  
Maximum Flow ◽  
Dead Volume ◽  
Mean Velocity ◽  
Stirred Tank Reactors ◽  
In Series ◽  
The Mean

The presence of a short circuit flow in a denitrifying activated sludge tank was identified and modelled. Tracer tests with pulse addition of lithium salt were used to investigate the hydraulics of the tank. The lithium concentration in the effluent was detected and residence time distribution (RTD) curves were generated. Hydraulic models based on completely stirred tank reactors (CSTRs) in series were generated from the RTD curves and the models were compared. The short circuit problem was successfully described using the Martin model, where the inflow is divided into two strands. Each strand was modelled as a number of CSTRs in series. At a normal flow the results of the model show that the tank has 12.8% dead volume, 85.8% main volume and 1.3% short circuiting volume. The inflow was divided into 91.9% entering the main volume and 8.1% entering the short circuiting volume. The mean velocity of the short circuiting stream was estimated to 0.4m/s. At maximum flow the short circuiting stream was even larger and handled 24.3% of the flow. The short circuiting stream was identified in the upper part of the tank due to the position of the inlet and the outlet. The configuration of a tank including the use of baffles, the geometry of the inlet and mixer configuration should be considered carefully if short circuiting is to be avoided.

TCD in Infants: A Report from the BABY HUG Trial.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 952-952 ◽  
Author(s):  
Robert J. Adams ◽  
Julio Barredo ◽  
Duane R. Bonds ◽  
Clark Brown ◽  
James Casella ◽  
...  
Keyword(s):  
Sickle Cell ◽  
Sickle Cell Anemia ◽  
Maximum Flow ◽  
Organ Damage ◽  
Sample Volume ◽  
Phase Iii ◽  
Mean Velocity ◽  
Increased Risk ◽  
The Mean ◽  
The Right

Abstract Transcranial Doppler (TCD) is useful in children with sickle cell anemia (SCA) to detect increased risk of stroke. The use of TCD in infants less than 2 years of age is less well established, but has previously been shown to be feasible. As a secondary endpoint in the BABY HUG Trial, TCD is expected to provide useful information on the possible effects of hydroxyurea (HU) in babies with SCA. BABY HUG is an NHLBI-NICHD sponsored phase III clinical trial to compare hydroxyurea to placebo to ascertain effectiveness in preventing end organ damage of the spleen and kidney. Eligible subjects underwent a baseline TCD using the Nicolet Companion (EME) 2-MHz pulsed Doppler. All infants were 8–18 months of age at enrollment, had no history of stroke and were not receiving chronic blood transfusions. Blood flow velocities were recorded using the Stroke Prevention Trial in Sickle Cell Anemia (STOP) protocol with the exception of reducing the standard sample volume to 4 mm. No sedation was used. The time averaged maximum mean was measured to determine the highest velocity on either side to categorize the study as normal (all recordings <170 cm/sec), conditional (170–199cm/sec) or abnormal (≥200 cm/sec). Recordings of the middle cerebral artery (MCA) and internal carotid artery (ICA) bifurcation defined an adequate TCD. TCD was not required for study entry but subjects with an abnormal exam were not eligible for randomization and treatment. TCD exams were read by blinded reviewers at the Medical College of Georgia. TCD results were transmitted to Clinical Trials & Surveys Corporation (C-TASC) for statistical analysis. As of June 24, 2005, 70 TCD exams had been attempted. Two exams were unsuccessful (no data) because of the children’s irritability and 1 was interpreted as inadequate. Of the remaining 67 TCD exams, 66 were normal and one baby had a high conditional TCD (190 cm/sec). No subjects were found ineligible for the study due to TCD results. The mean velocity of the left MCA was 117 cm/sec ±22.9 and that of the right MCA was 114 cm/sec ±24.9. Regression analyses were performed to examine the relationship of maximum flow velocity (VMAX) to age and total hemoglobin (Hb). VMAX was inversely correlated to Hb (left p=<0.0001, right=<0.0014) and directly associated with age (left p=<.0005, right p=<0.0022). When the mean MCA velocity was regressed against age and Hb, both age (p=0.0285) and Hb (p=.0024) were significant. Adequate baseline TCD evaluation was obtained on 67 out of 70 babies. As expected, baseline TCD velocities varied inversely with the degree of anemia and directly with age; all but one was normal by childhood sickle cell disease standards. These studies provide valuable normative data for infants with SCA, and for further assessment of the effect of HU on TCD in infants with SCA as the study progresses.

PIV-POD Investigation of the Wake of a Sharp-Edged Flat Bluff Body Immersed in a Shallow Channel Flow

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Arindam Singha ◽  
A.-M. Shinneeb ◽  
Ram Balachandar
Keyword(s):  
Velocity Field ◽  
Channel Flow ◽  
Bluff Body ◽  
Maximum Flow ◽  
Velocity Fields ◽  
Central Plane ◽  
Mean Flow ◽  
Mean Velocity ◽  
Near Surface ◽  
The Mean

This paper reports particle-image velocimetry measurements of instantaneous velocity fields in the wake of a sharp-edged bluff body immersed vertically in a shallow smooth open channel flow. The maximum flow velocity was 0.19 m/s and the Reynolds number based on the water depth was 18,270. The purpose of the present study is to show the vertical variation of the velocity field in the near region of a shallow wake. Measurements of the flow field in the vertical central plane and in the horizontal near-bed, mid-depth, and near-surface planes were taken. Then, the mean flow quantities such as the mean velocity, turbulence intensity, and Reynolds stress fields were investigated. In addition, the proper orthogonal decomposition technique was used to reconstruct the velocity fields to investigate the energetic vortical structures. The results showed that the largest recirculation zone in the mean velocity fields occurred in the mid-depth velocity field, while the smallest one occurred near the bed. Also, the fluid was entrained from the sides toward the wake central plane in the three horizontal velocity fields but with different rates. This behavior was attributed to the existence of quasi-streamwise vortices near the boundaries. In addition, patterns of ejection and sweep events near the free surface similar to the features commonly observed near the wall-bounded flows were observed.

scholarly journals Application of entropic approach to estimate the mean flow velocity and Manning roughness coefficient in a high-curvature flume

2016 ◽  
Vol 48 (3) ◽  
pp. 634-645 ◽  
Author(s):  
D. Termini ◽  
T. Moramarco
Keyword(s):  
Flow Velocity ◽  
Maximum Flow ◽  
Roughness Coefficient ◽  
Mean Flow ◽  
Mean Velocity ◽  
Bed Deformation ◽  
Side Walls ◽  
The Mean ◽  
Manning Roughness ◽  
Mean Flow Velocity

The entropy-based approach allows the estimation of the mean flow velocity in open channel flow by using the maximum flow velocity. The linear relationship between the mean velocity, umax, and the mean flow velocity, um, through the dimensionless parameter Φ(M), has been verified both in natural rivers and in laboratory channels. Recently, the authors of this study investigated the reliability of the entropy-based formula in a straight channel and under different bed and side-walls' roughness conditions. The present study aims to further validate the entropy-based approach and to explore the effectiveness of entropy-based formula in high curvature channels. Results show that as the effect of the downstream variation of the channel's curvature the value of the parameter Φ(M) varies along the bend. When the bed deformation is evident, the variation of the parameter Φ(M) is strongly reduced compared to that obtained in absence of bed deformation. Results also show that the Manning's roughness coefficients determined through entropy-based formula are in agreement with those estimated by applying other literature's expressions but, unlike the latter, through the parameter Φ(M) the entropy-based formula could account for the effects due to the advective momentum transport by cross-circulation along the strongly curved reaches of the channel.

Imbalanced flow changes of distal arteries: An important factor in process of delayed ipsilateral parenchymal hemorrhage after flow diversion in patients with cerebral aneurysms

2021 ◽  
pp. 159101992110091
Author(s):  
Wenqiang Li ◽  
Wei Zhu ◽  
Jian Liu ◽  
Xinjian Yang
Keyword(s):  
Blood Flow ◽  
Cerebral Artery ◽  
Cerebral Aneurysms ◽  
Flow Distribution ◽  
Maximum Flow ◽  
Flow Diverter ◽  
Control Group ◽  
Blood Flow Distribution ◽  
Mean Velocity ◽  
The Mean

Background and objective Hemodynamic forces may play a role in symptomatic delayed ipsilateral parenchymal hemorrhage (DIPH) of intracranial aneurysm (IA) after flow diverter placement. We aimed to investigate the hemodynamic risk factors in the postsurgical DIPH process. Methods Six patients with internal carotid artery (ICA) aneurysm developed to DIPH and 12 patients without DIPH (1:2 matched controls) after flow diverter were included between January 2015 to January 2019. Postsurgical hemodynamics of distal arteries (terminal ICA, middle cerebral artery (MCA), anterior cerebral artery (ACA)) were investigated using computational fluid dynamics, as well as the hemodynamic alteration between pre- and post-treatment. The DIPH related and unrelated distal arteries (either MCA or ACA) were discriminated and compared. Definition of imbalance index is the difference in increased velocity post-flow diverter between MCA and ACA and was used to evaluate the blood flow distribution of distal arteries. Results The mean and maximum flow velocities in the terminal ICA increased significantly after treatment in both groups. In DIPH group, the increase rate of mean velocity in the DIPH-related artery was significantly higher than that in DIPH-unrelated artery after the treatment (20.98 ± 15.38% vs −6.40 ± 7.74%; p = 0.028). Between the DIPH and control group, the baseline characteristics were well matched. However, a higher imbalance index of mean velocity was found in DIPH group (27.38 ± 13.03% vs 10.85 ± 14.12%; p = 0.031). Conclusion The mean velocity of DIPH related artery increased more, and the imbalance in increased blood flow distribution of distal arteries might play an important role in DIPH after flow diverter of IAs.

Velocity profiles assessment in natural channels during high floods

2011 ◽  
Vol 42 (2-3) ◽  
pp. 162-170 ◽  
Author(s):  
Tommaso Moramarco ◽  
Carla Saltalippi ◽  
Vijay P. Singh
Keyword(s):  
Flow Velocity ◽  
Maximum Flow ◽  
Velocity Profiles ◽  
Mean Flow ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Flow Area ◽  
The Mean ◽  
Logarithmic Law ◽  
Maximum Flow Velocity

The accuracy of three different approaches for velocity profiles assessment during high floods, when the velocity points sampling is carried out only in the upper portion of the flow area, has been investigated. The first two methods assume the classical logarithmic law with additional terms, to take account of the dip-phenomenon in the velocity profile. The third one is based on the entropy theory and uses the maximum flow velocity occurring in the flow area. A sample of velocity measurements carried out at Pontelagoscuro gauged section (Po River, Italy), has been considered for the analysis. Six flood events have been selected and the accuracy of the investigated methods has been evaluated in terms of mean error in estimating both the mean velocity along each sampled vertical and the mean flow velocity. For high floods, the logarithmic law and the entropic approach were found quite accurate; however, the ability of the latter in reproducing the velocity profiles only by sampling the maximum flow velocity has been shown. Therefore, a procedure for velocity measurements based on the entropic approach has been proposed. The procedure allows one to both to shorten remarkably the time of the velocity sampling and to quickly estimate the discharge.

Tracer test and hydraulics modeling of a large WWTP

2012 ◽  
Vol 7 (1) ◽  
Author(s):  
C. Fall ◽  
N. Flores-Alamo ◽  
M. Esparza-Soto ◽  
C. M. Hooijmans
Keyword(s):  
Activated Sludge ◽  
Treatment Plant ◽  
Tracer Tests ◽  
Tracer Test ◽  
Stirred Tank ◽  
Mixing Models ◽  
Concentration Profiles ◽  
Stirred Tank Reactors ◽  
Rhodamine Wt ◽  
Sampling Schedule

Tracer tests with rhodamine WT were performed at the biggest wastewater treatment plant of Mexico (‘Dulces Nombres’ WWTP, 5 m3/s). The aim was to develop the hydraulics sub-model to represent the aeration tanks, in the context of a project for calibrating the activated sludge model N°1 (ASM1). The planning of the experiment was performed by pre-simulation in AQUASIM, which allowed determining the quantities of dye (8 L per reactor) and sampling schedule that were required. After the tests, the rhodamine concentration profiles of the outlet mixed liquors were fit with different alternative of tank mixing models. Simulating the tracer data allowed to estimate the unknown influent flows, as well as determine the best hydraulics model: 4 completely stirred tank reactors retro-connected through the RAS (return activated sludge).

Effect of the larynx on oscillatory flow in the central airways: a model study

1985 ◽  
Vol 59 (1) ◽  
pp. 160-169 ◽  
Author(s):  
A. S. Menon ◽  
M. E. Weber ◽  
H. K. Chang
Keyword(s):  
Oscillatory Flow ◽  
Flow Distribution ◽  
Maximum Flow ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Local Velocity ◽  
Mean Velocity ◽  
Model Study ◽  
Flow Cycle ◽  
The Mean

Measurements were made of the effect of the larynx on the oscillatory flow profiles in a 3:1 scale model of the human central airways. A fixed glottic aperture corresponding to the shape and size at midinspiration was used. Oscillatory airflows at peak Reynolds numbers, similar to those obtained during spontaneous breathing and panting, were studied. The flow distribution to the five lobar bronchi was maintained by distally placed linear resistors. A hot-wire anemometer probe was used to measure the local velocity along two perpendicular diameters at six stations distributed through the model. Near the proximal end of the trachea, the flat velocity profiles at the beginning of the flow cycle peaked at maximum flow because of the jet created by the glottic aperture. This peaked structure was conserved during the latter half of the inspiratory cycle. Close to the carina, the jet had almost dissipated and the entry conditions into the main bronchi corresponded to those in the absence of the laryngeal model. The effect of the glottic aperture on the mean velocity was not felt beyond the carina, and the characteristic skewed profiles seen in oscillatory flows, in the absence of the larynx, were present in the main and lobar bronchi.

Pond Treatment of Rettery Wastewaters

1987 ◽  
Vol 19 (12) ◽  
pp. 79-83
Author(s):  
K. Bartoszewski ◽  
A. Bilyk
Keyword(s):  
Activated Sludge ◽  
Treatment Process ◽  
New Technology ◽  
Treatment Plant ◽  
Anaerobic Treatment ◽  
Cod Removal ◽  
Experimental Results ◽  
Aerobic Conditions ◽  
Aerobic Stabilization ◽  
In Series

Rettery wastewaters were treated in anaerobic and aerobic ponds. Anaerobic treatment yielded efficiencies of BOD5 and COD removal as low as 20%. The treatment process conducted under aerobic conditions in aerated and stabilizing ponds arranged in series took from 18 to 20 days and gave efficiencies of BOD5 and COD removal amounting to 90%. The experimental results were interpreted by virtue of the Eckenfelder equation. Excess activated sludge was subjected to aerobic stabilization in a separate tank. A new technology was suggested for the existing obsolete industrial treatment plant.

Comparison of Aerobic and Anoxic-Aerobic Digestion of Waste Activated Sludge

1985 ◽  
Vol 17 (8) ◽  
pp. 1475-1478 ◽  
Author(s):  
A P. C. Warner ◽  
G. A. Ekama ◽  
G v. R. Marais
Keyword(s):  
Experimental Data ◽  
Activated Sludge ◽  
Waste Activated Sludge ◽  
Activated Sludge Process ◽  
Cycle Times ◽  
Waste Sludge ◽  
Volatile Solids ◽  
In Series ◽  
Flow Through ◽  
Theoretical Simulations

The laboratory scale experimental investigation comprised a 6 day sludge age activated sludge process, the waste sludge of which was fed to a number of digesters operated as follows: single reactor flow through digesters at 4 or 6 days sludge age, under aerobic and anoxic-aerobic conditions (with 1,5 and 4 h cycle times) and 3-in-series flow through aerobic digesters each at 4 days sludge age; all digesters were fed draw-and-fill wise once per day. The general kinetic model for the aerobic activated sludge process set out by Dold et al., (1980) and extended to the anoxic-aerobic process by van Haandel et al., (1981) simulated accurately all the experimental data (Figs 1 to 4) without the need for adjusting the kinetic constants. Both theoretical simulations and experimental data indicate that (i) the rate of volatile solids destruction is not affected by the incorporation of anoxic cycles and (ii) the specific denitrification rate is independent of sludge age and is K4T = 0,046(l,029)(T-20) mgNO3-N/(mg active VSS. d) i.e. about 2/3 of that in the secondary anoxic of the single sludge activated sludge stystem. An important consequence of (i) and (ii) above is that denitrification can be integrated easily in the steady state digester model of Marais and Ekama (1976) and used for design (Warner et al., 1983).

On the Problem of “Two-Phase” Activated Sludge

1991 ◽  
Vol 24 (7) ◽  
pp. 59-64 ◽  
Author(s):  
R. W. Szetela
Keyword(s):  
Activated Sludge ◽  
Single Phase ◽  
Phase System ◽  
Two Phase ◽  
Wastewater Treatment Process ◽  
Sludge Stabilization ◽  
Technological Advantage ◽  
In Series ◽  
State Models ◽  
Activated Sludge Systems

Steady-state models are presented to describe the wastewater treatment process in two activated sludge systems. One of these makes use of a single complete-mix reactor; the other one involves two complete-mix reactors arranged in series. The in-series system is equivalent to what is known as the “two-phase” activated sludge, a concept which is now being launched throughout Poland in conjunction with the PROMLECZ technology under implementation. Analysis of the mathematical models has revealed the following: (1) treatment efficiency, excess sludge production, energy consumption, and the degree of sludge stabilization are identical in the two systems; (2) there exists a technological equivalence of “two-phase” sludge with “single-phase” sludge; (3) the “two-phase” system has no technological advantage over the “single-phase” system.

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