Development of a new method of measuring bubble size

2002 ◽  
Vol 2 (2) ◽  
pp. 77-83 ◽  
Author(s):  
M.Y. Han ◽  
Y.H. Park ◽  
T.J. Yu
Keyword(s):  
Bubble Size ◽  
New Method ◽  
Water And Wastewater Treatment ◽  
Dissolved Air Flotation ◽  
Batch Type ◽  
On Line ◽  
Water And Wastewater ◽  
Points Of View ◽  
Traditional Image ◽  
Dissolved Air

The use of bubbles in water and wastewater treatment, including dissolved air flotation (DAF) and electro-flotation (EF), is attracting much interest recently. These flotation processes are governed by characteristics of the bubbles as well as the particles, and therefore it is necessary to investigate the size distribution of the bubbles that are generated. In this research, a new method has been developed to measure the bubble size, using commercially available batch-type and on-line particle counters. The results are compared with the traditional image analysis method. Although there are some discrepancies, the results show that an on-line particle counter can produce reasonably accurate size distributions conveniently and efficiently. The bubble size measurement technique developed in this study will assist understanding and improvement of the DAF and EF processes, from both theoretical and practical points of view.

Effect of pressure on bubble size in dissolved air flotation

2002 ◽  
Vol 2 (5-6) ◽  
pp. 41-46 ◽  
Author(s):  
M. Han ◽  
Y. Park ◽  
J. Lee ◽  
J. Shim
Keyword(s):  
Bubble Size ◽  
Critical Pressure ◽  
Theoretical Work ◽  
Particle Sizes ◽  
Water And Wastewater Treatment ◽  
Dissolved Air Flotation ◽  
Recent Theoretical Work ◽  
Water And Wastewater ◽  
Air Flotation ◽  
Dissolved Air

Although dissolved air flotation (DAF) has been successfully adopted for water and wastewater treatment, the fundamental characteristics of the process have not been fully investigated. According to recent theoretical work on DAF, bubble size is one of the most important factors that affect the efficiency of the process, with better removal efficiency when the sizes of both bubbles and particles are similar. In this study, a newly developed particle counter method (PCM) was introduced to measure particle sizes. To confirm its usefulness, the results were compared with those from image analysis. Then, using PCM, the size of bubbles in DAF was measured under various pressure conditions which are known to affect the bubble size the most (from 2 to 6 atmospheres). The bubble size decreased as the pressure increased up to a pressure of 3.5 atmospheres. Above this critical pressure, the bubble size did not decrease with further increases in pressure. According to these experimental results, it is not only costly, but also unnecessary, to maintain a pressure above 3.5 atmospheres if the goal is only to generate smaller bubbles.

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.

A kinetic model for dissolved air flotation in water and wastewater treatment

1995 ◽  
Vol 31 (3-4) ◽  
pp. 37-47 ◽  
Author(s):  
K. Fukushi ◽  
N. Tambo ◽  
Y. Matsui
Keyword(s):  
Kinetic Model ◽  
Balance Model ◽  
Rise Velocity ◽  
Water And Wastewater Treatment ◽  
Dissolved Air Flotation ◽  
Floc Size ◽  
Water And Wastewater ◽  
Bubble Number ◽  
Synthetic Clay ◽  
Attachment Process

A kinetic model for DAF is presented. The author's kinetic model consists of the equations for describing a process of bubble-floc collision and attachment in a mixing zone, and a rise velocity of bubble-floc agglomerates in a flotation tank. The attachment process is formulated on a population balance model with bubbles and flocs as a flocculation in a turbulent flow. The rise velocity of bubble-floc agglomerates is formulated with size of flocs and composition of flocs including the floc density function and attached bubble number. The experimental verification was carried out, using a batch flotation tested and a mini-plant with synthetic clay suspension and colored water. The results successfully verify the validity of the model. From a given condition such as floc size and attached bubble number, the rate and extent of removal by DAF can be readily assessed by the model. A single-collector collision model, often discussed in some occasions, seems to be not useful to describe the DAF process.

Removal of cadmium from dilute solutions by flotation

1995 ◽  
Vol 31 (3-4) ◽  
pp. 315-326 ◽  
Author(s):  
Anastasios I. Zouboulis ◽  
Konstantine A. Matis
Keyword(s):  
Sodium Dodecyl ◽  
Toxic Metal ◽  
Dilute Solutions ◽  
Water And Wastewater Treatment ◽  
Dissolved Air Flotation ◽  
Bubble Generation ◽  
Flotation Technique ◽  
Air Flotation ◽  
Ph Range ◽  
Dissolved Air

Cadmium constitutes a priority pollutant existing in waste streams from metal plating and various other industries. The removal of this toxic metal employing the dissolved air flotation technique was investigated in laboratory batch experiments; the mechanism of precipitate flotation as the respective hydroxide was followed. Main examined parameters include: recycle ratio, pH of the solution, concentrations of added surfactant (sodium dodecyl sulphate), frother (ethanol) and cadmium. Promising results have been obtained, at the pH range between 10 and 11 approximately, showing the significance of flotation as a separation process in water and wastewater treatment for dilute solutions (around 10 mg/l of metal). Under the optimum conditions removal of cadmium was near to 100%, while the remaining concentration in the solution after flotation was less than 0.10 mg/l. A comparison was also attempted between two flotation techniques applying different bubble generation methods, i.e. dissolved air and dispersed air flotation. These experiments run in parallel and under the same conditions.

Characterization of micro-bubble size distribution and flow configuration in DAF contact zone by a non-intrusive image analysis system and tracer tests

2010 ◽  
Vol 61 (1) ◽  
pp. 253-262 ◽  
Author(s):  
R. B. Moruzzi ◽  
M. A. P. Reali
Keyword(s):  
Size Distribution ◽  
Contact Zone ◽  
Bubble Size ◽  
Bubble Size Distribution ◽  
Image Analysis System ◽  
Particle Removal ◽  
Air Concentration ◽  
Dissolved Air Flotation ◽  
Micro Bubble ◽  
Dissolved Air

This paper aims to investigate the influence of some dissolved air flotation (DAF) process variables (specifically: the hydraulic detention time in the contact zone and the supplied dissolved air concentration) and the pH values, as pretreatment chemical variables, on the micro-bubble size distribution (BSD) in a DAF contact zone. This work was carried out in a pilot plant where bubbles were measured by an appropriate non-intrusive image acquisition system. The results show that the obtained diameter ranges were in agreement with values reported in the literature (10–100 μm), quite independently of the investigated conditions. The linear average diameter varied from 20 to 30 μm, or equivalently, the Sauter (d3,2) diameter varied from 40 to 50 μm. In all investigated conditions, D50 was between 75% and 95%. The BSD might present different profile (with a bimodal curve trend), however, when analyzing the volumetric frequency distribution (in some cases with the appearance of peaks in diameters ranging from 90–100 μm). Regarding volumetric frequency analysis, all the investigated parameters can modify the BSD in DAF contact zone after the release point, thus potentially causing changes in DAF kinetics. This finding prompts further research in order to verify the effect of these BSD changes on solid particle removal efficiency by DAF.

Determination of chlorine demand in water and wastewater chlorination by oxidation-reduction potential

2003 ◽  
Vol 3 (1-2) ◽  
pp. 313-320 ◽  
Author(s):  
R.F. Yu ◽  
W.P. Cheng
Keyword(s):  
Control Strategy ◽  
Reduction Potential ◽  
Wastewater Treatment Plants ◽  
Water And Wastewater Treatment ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
On Line ◽  
Water And Wastewater ◽  
Chlorine Demand

Chlorination is the most practical way for the destruction of pathogenic and other harmful organisms in water and wastewater treatment plants. However, highly erratic concentrations of ammonia is contained in most water and wastewater treatment plants, which will react to chlorine and seriously alter the required chlorine dosages in the control of chlorination. The conventional control of chlorine dosage is widely practical throughout the batch breakpoint chlorination test in the laboratory, which is not feasible for the requirement of real-time regulation of the chlorine demands. In this study, a simple automatic oxidation-reduction potential (ORP) titration system was developed for on-line determination of the chlorine demand. The experimental results showed that different decrease tendencies on ORP slope profiles were found to correlate to the ammonia concentrations in samples. In addition, the required chlorine demands were found to correlate to ammonia concentrations with a linear relationship. The ORP control strategy was, therefore, developed for on-line determination of the chlorine demands. Applying this ORP control strategy, the required chlorine demands were precisely predicted, and good disinfection efficiency was obtained in the wastewater chlorination experiments.

Collision efficiency factor of bubble and particle (abp) in DAF: theory and experimental verification

2001 ◽  
Vol 43 (8) ◽  
pp. 139-144 ◽  
Author(s):  
M. Han ◽  
W. Kim ◽  
S. Dockko
Keyword(s):  
Particle Size ◽  
Zeta Potential ◽  
Bubble Size ◽  
Efficiency Factor ◽  
Collision Efficiency ◽  
Turbidity Removal ◽  
Dissolved Air Flotation ◽  
Accepted Practice ◽  
Bubble Sizes ◽  
Dissolved Air

The collision efficiency factor of bubble and particle (αbp) in dissolved air flotation (DAF) can be calculated theoretically by trajectory analysis, which takes into account both hydrodynamics and inter-particle forces. To determine the theoretically optimum particle size for any given bubble size, a collision efficiency diagram for DAF was developed where collision efficiency is contoured on a plane of particle and bubble sizes for different conditions of particle zeta potential. A set of experiments tested the validity of the suggested collision efficiency diagram, and examined whether pretreatment is important and why slight coagulant overdosing and shorter flocculation times are generally preferred in DAF, both current accepted practice. Batch DAF reactors were used and kaolin samples were prepared from jar tests using different alum dosages and flocculation times. The particle size distribution, particle zeta potential, and turbidity removal in each experiment were measured, as were bubble size and zeta potential. The results agreed well with the predictions of the collision efficiency diagram and explained current practices. A collision efficiency diagram identifies the pretreatment goal, i.e., tailoring of the optimum characteristics required of particles (zeta potential and size) under existing operational bubble characteristic.

Modelling the global efficiency of dissolved air flotation

2001 ◽  
Vol 43 (8) ◽  
pp. 159-166 ◽  
Author(s):  
D. M. Leppinen ◽  
S. B. Dalziel ◽  
P. F. Linden
Keyword(s):  
Particle Size ◽  
Bubble Size ◽  
High Surface ◽  
Surface Loading ◽  
Dissolved Air Flotation ◽  
Loading Rates ◽  
Air Flotation ◽  
Bubble Attachment ◽  
Attachment Process ◽  
Dissolved Air

The purpose of this paper is to examine how the efficiency of dissolved air flotation is affected by the size of bubbles and particles. The rise speed of bubble/particle agglomerates is modelled as a function of bubble and particle size, while the kinematics of the bubble attachment process is modelled using the population balance approach adopted by Matsui, Fukushi and Tambo. It is found that flotation, in general, is enhanced by the use of larger particles and larger bubbles. In particular, it is concluded that for the ultra-high surface loading rates of 25 m/hr or more planned for future flotation tanks, bubble size will have to be increased by a factor of two over the size currently employed in many facilities during dissolved air flotation.

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