Effects of Al3 +  and hydraulic characteristics on the removal and behaviour of particles in dissolved air flotation

2006 ◽  
Vol 6 (3) ◽  
pp. 89-95
Author(s):  
Jungsoo Mun ◽  
Sungwon Park ◽  
Mooyoung Han
Keyword(s):  
Turbulent Flow ◽  
Removal Efficiency ◽  
Operating Conditions ◽  
Point Of Zero Charge ◽  
Hydraulic Characteristics ◽  
Dissolved Air Flotation ◽  
Floc Size ◽  
Saturated Water ◽  
Air Flotation ◽  
Dissolved Air

The removal efficiency of the dissolved air flotation (DAF) process to separate particles from water and wastewater depends on the size and zeta potential of bubbles and particles, the solution and operating conditions, hydraulic characteristics, etc. The effects of aluminium ions and turbulent flow-produced when air-saturated water was spouted into the reactor in the DAF process, on removal and, particle behaviour were on investigated. When bubble size was similar to particle size (10–50 μm), the maximum removal efficiency was 92% in a Kaolin solution of 10−3 M Al3 +  without pre-treatment for flocculation process, and, as time passed, the floc size was observed to increase at a pH of 8, which was the condition of high removal efficiency as seen through image analysis. When the air-saturated water was spouted into the reactor, the size of particle at p.z.c. (point of zero charge) seemed to increase to form a floc due to collision effects caused by turbulent flow. Consequently, floc formation by turbulent flow in the reactor seemed to positively affect removal efficiency.

Research on the CFD numerical simulation and process optimization of countercurrent–cocurrent dissolved air flotation

2019 ◽  
Vol 68 (5) ◽  
pp. 325-336
Author(s):  
Yonglei Wang ◽  
Wei Liu ◽  
Liping Tian ◽  
Ruibao Jia ◽  
Zhenqi Du ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Contact Zone ◽  
Process Optimization ◽  
Operating Conditions ◽  
Cocurrent Flow ◽  
Dissolved Gas ◽  
Dissolved Air Flotation ◽  
Simulation Results ◽  
Air Flotation ◽  
Dissolved Air

Abstract The countercurrent–cocurrent dissolved air flotation (CCDAF) process is a new type of air flotation process integrating countercurrent collision and cocurrent flow adhesion processes. The structural form of the CCDAF tank and its process parameters are the required conditions to achieve countercurrent collision and cocurrent adhesion. In this study, eight CCDAF tank process models were established with a flow rate of 0.5 m3/h. Flow field numerical simulation and process optimization of a CCDAF tank was conducted using Fluent software. The simulation results show that the optimal conditions for the CCDAF process are as follows: contact zone ascending velocity 10 mm/s, separation zone separation velocity 1.5 mm/s, dissolved gas pressure 0.45 MPa, and recirculating dissolved-gas distribution ratio R1/R2 1:1. Under these operating conditions, the flow state in the flotation tank is the most stable and the gas in the contact zone is evenly distributed. According to the simulation results, a 5 m3/h pilot plant was built. The structural dimensions were: B × L × H = 1,020 mm × 1,300 mm × 1,350 mm. The test results show that the CCDAF has a significant decontamination effect and is clearly superior to the cocurrent flow DAF process and countercurrent flow DAF process.

The role of particle size and density in dissolved air flotation and sedimentation

1997 ◽  
Vol 36 (4) ◽  
pp. 177-189 ◽  
Author(s):  
A. Vlaški ◽  
A. N. van Breemen ◽  
G. J. Alaerts
Keyword(s):  
Kinetic Modelling ◽  
Single Cells ◽  
Process Efficiency ◽  
Laboratory Model ◽  
Reservoir Water ◽  
Dissolved Air Flotation ◽  
Floc Size ◽  
Air Flotation ◽  
G Value ◽  
Dissolved Air

Conventional (sedimentation) and advanced (dissolved air flotation) treatment were studied in the context of removal of the single cells form of the cyanobacteria Microcystis aeruginosa. This cyanobacterium species is recognised as an ideal surrogate for process removal efficiency assessment of particles of the problematic size range (3-10 m). The agglomeration (coagulation/flocculation) phase has been indicated as essential and determining the down-stream process efficiency, hence it is a prerequisite for process improvement. Relevant process parameters have been addressed on a laboratory (model water) and pilot plant (reservoir water) scale, including the influence of coagulant (FeCl3) dose, coagulation pH, flocculation time, energy input (G value), single stage versus tapered flocculation and application of cationic polymer as coagulant aid. The process efficiency was assessed as a function of the preceeding agglomeration (coagulation/flocculation) phase and the obtained particle (floc) size distributions. The particle (floc) size - density relationship was addressed in the context of more accurate process kinetic modelling.

An attempt to understand dissolved air flotation using multivariate data analysis

1995 ◽  
Vol 31 (3-4) ◽  
pp. 191-201 ◽  
Author(s):  
Milos Krofta ◽  
Banda Herath ◽  
David Burgess ◽  
Larry Lampman
Keyword(s):  
Municipal Wastewater ◽  
Suspended Solid ◽  
Operating Conditions ◽  
Effluent Water ◽  
Dissolved Air Flotation ◽  
Multivariate Technique ◽  
Operating Variables ◽  
Treatment Processes ◽  
Air Flotation ◽  
Dissolved Air

In order to optimize the dissolved air flotation (DAF) process, a mathematical relationship should be established between the operating variables and the quality of the effluent water. In this study, operating parameters, including influent wastewater characteristics, were related to suspended solid (SS), COD, BOD5 and turbidity of the effluent via an empirical mathematical model. The data presented in this study were obtained from a pilot plant DAF study carried out on municipal wastewater at Lee, Massachusetts to determine the operating conditions for the wastewater clarification. Response surface methodology was used to determine optimal conditions and to study the variations of flotation behaviour with varying operating conditions. The multivariate technique used in this study is an extremely valuable tool to analyze data obtained from actual wastewater treatment processes where the characteristics of the wastewater are constantly changing. Without such a tool it may not be possible to draw valid conclusions. In addition, this technique requires comparatively fewer experiments when compared to traditional methods. Addition of more flocculant and recycle water over what is required actually decreases the effluent water quality. Tests carried out with the same DAF unit at Little Rock, Arkansas and Birmingham, Alabama have confirmed the accuracy of the predictions from the model.

Principles and applications of dissolved air flotation

1995 ◽  
Vol 31 (3-4) ◽  
pp. 1-23 ◽  
Author(s):  
James K. Edzwald
Keyword(s):  
Bubble Formation ◽  
Treatment Plant ◽  
Drinking Water Treatment ◽  
Plant Design ◽  
Dissolved Air Flotation ◽  
Floc Size ◽  
Hydrophobic Particles ◽  
Air Flotation ◽  
The Impact ◽  
Dissolved Air

Principles of dissolved air flotation (DAF) discussed include: bubble formation and size, bubble-particle interactions, measures of supplied air, and modeling of the reaction and clarification zones of the flotation tank. Favorable flotation conditions for bubble attachment or adhesion to particles requires a reduction in the charge of particles and production of hydrophobic particles or hydrophobic spots on particle surfaces. A conceptual model for the bubble-particle reaction zone based on the single collector collision efficiency is summarized and discussed. An alternative modeling approach is considered. Clarification or separation zone modeling is based on particle-bubble agglomerate rise velocities. The application of DAF in drinking water treatment is addressed beginning with summaries of design and operating parameters for several countries. DAF should not be considered as a separate process, but integrated into the design and operation of the overall treatment plant. This concept shows that flocculation ahead of DAF has different requirements regarding floc size and strength compared to sedimentation. The efficiency of DAF in removing particles and reducing particle loads to filters needs to be integrated into DAF plant design. The impact on filtration performance is illustrated. Finally, fundamental and applied research needs are addressed.

scholarly journals Simulation and control of dissolved air flotation and column froth flotation with simultaneous sedimentation

2020 ◽  
Vol 81 (8) ◽  
pp. 1723-1732 ◽  
Author(s):  
Raimund Bürger ◽  
Stefan Diehl ◽  
María Carmen Martí ◽  
Yolanda Vásquez
Keyword(s):  
Wastewater Treatment ◽  
Steady State ◽  
Froth Flotation ◽  
Operating Conditions ◽  
Dynamic Simulations ◽  
Dissolved Air Flotation ◽  
One Dimensional ◽  
Drift Flux ◽  
Air Flotation ◽  
Dissolved Air

Abstract Flotation is a separation process where particles or droplets are removed from a suspension with the aid of floating gas bubbles. Applications include dissolved air flotation (DAF) in industrial wastewater treatment and column froth flotation (CFF) in wastewater treatment and mineral processing. One-dimensional models of flotation have been limited to steady-state situations for half a century by means of the drift-flux theory. A newly developed dynamic one-dimensional model formulated in terms of partial differential equations can be used to predict the process of simultaneous flotation of bubbles and sedimentation of particles that are not attached to bubbles. The governing model is a pair of first-order conservation laws for the aggregate and solids volume fractions as functions of height and time. An analysis of nonlinear ingredients of the governing equations helps to identify desired steady-state operating conditions. These can be chosen by means of operating charts, which are diagrams that visualize regions of admissible values of the volumetric flows of the feed input and underflow outlet. This is detailed for the DAF thickening process. Dynamic simulations are obtained with a recently developed numerical method. Responses to control actions are demonstrated with scenarios in CFF and DAF.

Effects of floc and bubble size on the efficiency of the dissolved air flotation (DAF) process

2007 ◽  
Vol 56 (10) ◽  
pp. 109-115 ◽  
Author(s):  
Mooyoung Han ◽  
Tschung-il Kim ◽  
Jinho Kim
Keyword(s):  
Bubble Size ◽  
Saturation Pressure ◽  
Collision Efficiency ◽  
Water And Wastewater Treatment ◽  
Dissolved Air Flotation ◽  
Floc Size ◽  
Recycle Ratio ◽  
Air Flotation ◽  
The 1960S ◽  
Dissolved Air

Dissolved air flotation (DAF) is a method for removing particles from water using micro bubbles instead of settlement. The process has proved to be successful and, since the 1960s, accepted as an alternative to the conventional sedimentation process for water and wastewater treatment. However, limited research into the process, especially the fundamental characteristics of bubbles and particles, has been carried out. The single collector collision model is not capable of determining the effects of particular characteristics, such as the size and surface charge of bubbles and particles. Han has published a set of modeling results after calculating the collision efficiency between bubbles and particles by trajectory analysis. His major conclusion was that collision efficiency is maximum when the bubbles and particles are nearly the same size but have opposite charge. However, experimental verification of this conclusion has not been carried out yet. This paper describes a new method for measuring the size of particles and bubbles developed using computational image analysis. DAF efficiency is influenced by the effect of the recycle ratio on various average floc sizes. The larger the recycle ratio, the higher the DAF efficiency at the same pressure and particle size. The treatment efficiency is also affected by the saturation pressure, because the bubble size and bubble volume concentration are controlled by the pressure. The highest efficiency is obtained when the floc size is larger than the bubble size. These results, namely that the highest collision efficiency occurs when the particles and bubbles are about the same size, are more in accordance with the trajectory model than with the white water collector model, which implies that the larger the particles, the higher is the collision efficiency.

Optimization of Solids Separation in Dissolved Air Flotation

2008 ◽  
Vol 43 (2-3) ◽  
pp. 239-247 ◽  
Author(s):  
Beata Gorczyca ◽  
Paul Klassen
Keyword(s):  
Bubble Formation ◽  
Particle Removal ◽  
Dissolved Air Flotation ◽  
Particle Counter ◽  
Floc Size ◽  
Treated Effluent ◽  
Air Flotation ◽  
Average Size ◽  
Solid Liquid ◽  
Dissolved Air

Abstract Sizes of flocs were analyzed to identify characteristics of the particle size distribution optimal for separation by dissolved air flotation (DAF). Optical microscopes and two particle counters were used for floc sizing. A Brightwell Technologies particle counter was found to provide floc size measurements in agreement with improved microscopic methods. The particle counter provided distribution of flocs with sizes down to 1 micron (µm). This allowed for inclusion of flocs with size ranging from 5 to 1 µm, which were excluded from the analyses in the earlier study. Four alum dosages were applied: 15, 25, 40, and 60 mg/L. The turbidity and colour of the DAF effluent at alum dosages of 25, 40, and 60 mg/L were very similar. However, the analysis of the flocs in the treated effluent revealed that, at the alum dose of 60 mg/L, particle removal was the best. Therefore, this dosage was selected as optimal for the solid/liquid separation process. The average size of coagulation flocs at 60 mg/L was approximately 30 µm, and was equal to the estimated size of air bubbles produced by the saturator. Therefore, this study confirms the finding of the earlier work claiming that the optimum DAF performance is attained when the mean floc size and the bubble size are equal. Similar size of floc and bubble indicates that flocs act predominantly as nuclei for bubble formation. This finding contributes to the knowledge of mechanisms of floc air bubble attachment in DAF.

Flow structures in a dissolved air flotation pilot tank and the influence on the separation of MBBR floc

2002 ◽  
Vol 2 (2) ◽  
pp. 69-76 ◽  
Author(s):  
M. Lundh ◽  
L. Jönsson ◽  
J. Dahlquist
Keyword(s):  
Flow Structure ◽  
Removal Efficiency ◽  
Pilot Plant ◽  
Suspended Solids ◽  
Short Circuit ◽  
Flow Structures ◽  
Dissolved Air Flotation ◽  
Air Content ◽  
Air Flotation ◽  
Dissolved Air

The objective of the study was to find ways of improvement of the dissolved air flotation process by studying the flow structure. The paper presents experimental data on flow structures and the relation between the flow structure and the removal efficiency. Measurements have been performed in a pilot plant with an Acoustical Doppler Velocimeter. The water velocity was measured in a grid net, giving insight into the flow structure. The removal efficiency was analysed at Malmö wastewater treatment plant in Sweden. The pilot plant separated biological floc from a Kaldnes Moving Bio-Bed Reactor (MBBR). The efficiency of the separation was analysed by measurements of suspended solids in the influent and the effluent. Air content was measured inside the tank and in the re-cycle. The result showed that basically two flow structures existed; the stratified and the short-circuit flow structure. The stratified flow structure seemed correlated to efficient separation of particles while the short-circuit flow structure seemed to have a negative effect, especially when the flow structure was affected by varying the re-cycle rate, i.e. the air content. Conclusively, the flow structure seemed to be correlated to type of flow structure. However, studies with higher concentration of suspended solids for verification were suggested.

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