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.

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.

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.

Separation characteristics in dissolved air flotation - pilot and full-scale demonstration

2003 ◽  
Vol 48 (3) ◽  
pp. 89-96
Author(s):  
M. Ljunggren ◽  
L. Jönsson
Keyword(s):  
Particle Size ◽  
Contact Zone ◽  
Separation Efficiency ◽  
Particle Separation ◽  
Full Scale ◽  
Particle Sizes ◽  
Dissolved Air Flotation ◽  
Air Flotation ◽  
Practical Implications ◽  
Dissolved Air

This study presents practical implications for particle separation in Dissolved Air Flotation (DAF). The objectives were to localise where particles are separated from the water phase and to determine what particles, in terms of size, are removed by the DAF-process. Both pilot- and full-scale plants were investigated. Particle sizes were analysed with a light-blocking particle counter and an optical borescope was used for visualisation of particle-bubble aggregates. It was found that particles are preferably separated upstream in the process, i.e. close to the contact zone. Furthermore, separation efficiency for particles increased with increasing particle size.

Parameters Influencing Sludge Thickening by Dissolved Air Flotation

1993 ◽  
Vol 28 (1) ◽  
pp. 87-90 ◽  
Author(s):  
M. Sugahara ◽  
S. Oku
Keyword(s):  
Particle Size ◽  
Particle Sizes ◽  
Dissolved Air Flotation ◽  
Flotation Process ◽  
Sludge Characteristics ◽  
Factors Influencing ◽  
Air Flotation ◽  
Sludge Particle ◽  
Sludge Thickening ◽  
Dissolved Air

The purpose of this study was to investigate factors influencing sludge thickening in the dissolved air flotation process. Attention focused on the alteration of sludge characteristics as a result of coagulation and aeration. Batch thickening experiments showed that both coagulation and aeration enhanced sludge thickening. The most important parameter influencing sludge thickening appeared to be sludge particle size; larger particle sizes produced higher sludge solids concentrations in the float.

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.

Enhanced separation of water quality parameters in the DAF (Dissolved Air Flotation) system using ozone

2007 ◽  
Vol 56 (10) ◽  
pp. 149-155 ◽  
Author(s):  
Byoung-Ho Lee ◽  
Won-Chul Song ◽  
Hye-Young Kim ◽  
Jeong-Hyeon Kim
Keyword(s):  
Water Quality ◽  
Heterotrophic Bacteria ◽  
Removal Rate ◽  
Quality Parameters ◽  
Water Quality Parameters ◽  
Water And Wastewater Treatment ◽  
Dissolved Air Flotation ◽  
Micro Bubble ◽  
Air Flotation ◽  
Dissolved Air

Dissolved Air Flotation (DAF) has been used in water and wastewater treatment because it has an excellent separation capability. It was found that the separation capability of the DAF system could be even more enhanced by ozone. Ozone was applied as a substitute for air in the DAF system, so that the system was named as the DOF (Dissolved Ozone Flotation) system. Ozone not only enhances coagulation as is well known, but also provides larger micro-bubble volume because the solubility of ozone in water is much higher than that of air. Ozone enhanced the separation rate of SS by 13.6%, and turbidity by 21% in the DOF system compared to the DAF system. T-P was also removed 7.7% more in the DOF system. 41.5% of color and 7.4% of CODCr were enhanced in their removal rate. Coliform and heterotrophic bacteria were removed 54% and 57.3% more in the DOF system. Separation capability of the DOF system was greatly enhanced for most of the water quality parameters because ozone provides strong oxidation power with large volume of micro-bubbles.

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