Solid/liquid separation behavior of alum and polyaluminium chloride coagulation flocs

2006 ◽  
Vol 6 (1) ◽  
pp. 87-93 ◽  
Author(s):  
B. Gorczyca ◽  
G. Zhang
Keyword(s):  
Liquid Separation ◽  
Dissolved Air Flotation ◽  
Gravity Settling ◽  
Mean Size ◽  
Air Flotation ◽  
Solid Liquid ◽  
Solid Liquid Separation ◽  
Separation Behavior ◽  
Polyaluminium Chloride ◽  
Dissolved Air

Properties of alum and polyaluminium chloride (PACl) flocs were analyzed in order to explain solid/liquid separation behavior of these aggregates in dissolved air flotation and gravity settling. PACl flocs settle better and are less sensitive to changes in water temperature than alum flocs. Therefore, PACl flocs may be more suited for gravity separation, especially in cold waters, and alum flocs may be preferred for flotation. At an optimum coagulant dose for dissolved air flotation the logarithmic mean size of alum flocs was close to the size of the air bubbles (30 μm) and the proportion of flocs smaller than 20 μm was about 30.5%.

Treatment Spent Filter Backwash Water using Dissolved Air Flotation (DAF) in Isfahan WTP

2008 ◽  
Vol 3 (3) ◽  
Author(s):  
Mohammad Hassan Mahmoodian ◽  
Mohammad Mehdi Amin ◽  
Mohammad Reza Shahmansouri ◽  
Mohammad Ghasemian
Keyword(s):  
Low Dose ◽  
Saturation Pressure ◽  
Raw Water ◽  
Dissolved Air Flotation ◽  
Air Flotation ◽  
Recycle Rate ◽  
Polyaluminium Chloride ◽  
Significant Concentration ◽  
Dissolved Air ◽  
Filter Backwash Water

Recovering spent filter backwash water is currently receiving a great deal of attention. EPA published the Filter Backwash-Recycling Rule (FBRR) in 2001. Recycle stream may contain significant concentration of pathogens, such as, cryptosporidium and Giardia. Dissolved Air Flotation (DAF) was investigated as a possible technology alternative to simple or advanced sedimentation technology. In this study with using a pilot of DAF effluent turbidities of >20NTU could be easily obtained, when raw water turbidities were in excess of 800 NTU. Chemical requirements were low with only a single low dose of polyaluminium chloride (PACl) required binding the floc particles to form a solids matrix suitable for flotation. The results showed that the efficiency of continuous flow DAF with using PACl as coagulant for removal of Turbidity, COD, HPC, SS and MPN were 97, 72, 75, 95 and 100 percent, respectively. The statistical analyses indicated that the optimum saturation pressure is 4-5 atm, during recycle rate of 20-25 percent. The removal efficiencies of turbidity and bacteria in coagulation with sedimentation were reported up to 70 and 65 percent, while in this study using DAF with coagulant PACl could remove turbidity, COD, SS and bacterial up to 97,72, 95 and, 72 percent respectively.

scholarly journals Solid–liquid Separation of Activated Sludge by Flotation Using Microporous Ceramic Diffuser

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
S. W. Hong ◽  
C. Park ◽  
T. H. Chung ◽  
Y. S. Choi
Keyword(s):  
Activated Sludge ◽  
Porous Ceramic ◽  
Operating Cost ◽  
Experimental Results ◽  
Solid Loading ◽  
Dissolved Air Flotation ◽  
Pressure Water ◽  
Solid Liquid ◽  
Solid Liquid Separation ◽  
Dissolved Air

Dissolved air flotation (DAF) is the most widely used to separate particles from liquid. However, the main disadvantage of DAF systems is the increased operating cost due to the energy requirements for the high pressure water recycling and air compressing. In this study, alumina–based porous ceramic diffusers which can produce microbubbles at low pressure regions have been developed in order to separate and thicken activated sludge solids. No bubble was generated at lower pressure (< 0.2 bar), whereas too large bubbles were generated at higher than 2.0 bar. At 1.8 bar, more than 70% of the bubbles had a diameter ranged from 20 to 60 μm. According the experimental results, the separation and thickening efficiency was mainly dependant on solid loading rate (SLR) and air to solid (A/S) ratio. When the sludge with a concentration of exceeding 5,000 mg/L was continuously fed into the flotation tank, the thickened concentration was measured to be higher than 20,000 mg/L, while SS concentrations in the clarified effluent were ranged from 5 to 10 mg/L. The experimental results revealed that the use of microporous ceramic diffusers could provide an economical, easy and reliable means of separating suspended solids (e.g., biological flocs) from liquid.

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.

Toxic metals removal from dilute solutions by biosorptive flotation

1995 ◽  
Vol 32 (9-10) ◽  
pp. 211-220
Author(s):  
A. I. Zouboulis ◽  
P. Solari ◽  
K. A. Matis ◽  
G. A. Stalidis
Keyword(s):  
Toxic Metal ◽  
Separation Process ◽  
Dissolved Air Flotation ◽  
Metals Removal ◽  
Dilute Aqueous Solutions ◽  
Flotation Technique ◽  
Solid Liquid ◽  
Solid Liquid Separation ◽  
Digested Sewage Sludge ◽  
Dissolved Air

Toxic metal ions (cadmium, nickel and zinc), considered as priority pollutants, were removed from dilute aqueous solutions by sorption onto non-living (sterilized) anaerobically digested sewage sludge. The desorption of cadmium from metal-laden sludge was also examined. Flotation was subsequently applied as an effective solid/liquid separation process. The dissolved-air flotation technique was applied for the generation of fine bubbles and, in parallel, electrokinetic measurements were carried out. Promising results were succeeded from the combined process of biosorption/flotation (termed biosorptive flotation).

Application of Chitosan in Removing Algae by Dissolved Air Flotation

2011 ◽  
Vol 347-353 ◽  
pp. 1911-1916 ◽  
Author(s):  
Yu Heng Wang ◽  
Sheng Guang Zhuo ◽  
Yi Xin Yang ◽  
Na Li
Keyword(s):  
Aluminum Concentration ◽  
Removal Rates ◽  
Dissolved Air Flotation ◽  
Treated Water ◽  
Residual Aluminum ◽  
Flotation Performance ◽  
Air Flotation ◽  
Polyaluminium Chloride ◽  
Dissolved Air

Using polyaluminium chloride (PAC) and chitosan as the main coagulant and coagulant-aid respectively, the high algae-laden water was treated by coagulation/flocculation/dissolved air flotation (C/F/DAF). When the doses of PAC and chitosan were both moderate (7.0~8.4 mg Al2O3/L of PAC and 0.6~1.0 mg/L of chitosan), the removal rates of turbidity, algae cells and TOC were all increased apparently compared with adding PAC alone. Especially, the residual aluminum concentration reduced significantly in treated water with the aid of chitosan. The structrue and strength of flocs formed by coagulation aid of chitosan were improved obviously, which proved that addition of chitosan could enhance the flocculation performance of PAC. So, in C/F/DAF process for removing algae, using chitosan as coagulant-aid can improve the flotation performance and reduce residual aluminum concentration in treated water.

Behaviour of air injection nozzles in dissolved air flotation

1995 ◽  
Vol 31 (3-4) ◽  
pp. 25-35 ◽  
Author(s):  
E. M. Rykaart ◽  
J. Haarhoff
Keyword(s):  
Bubble Coalescence ◽  
Second Phase ◽  
Initial Growth ◽  
Two Phase ◽  
Dissolved Air Flotation ◽  
Nozzle Orifice ◽  
Pressure Release ◽  
Air Volume ◽  
Air Flotation ◽  
Dissolved Air

A simple two-phase conceptual model is postulated to explain the initial growth of microbubbles after pressure release in dissolved air flotation. During the first phase bubbles merely expand from existing nucleation centres as air precipitates from solution, without bubble coalescence. This phase ends when all excess air is transferred to the gas phase. During the second phase, the total air volume remains the same, but bubbles continue to grow due to bubble coalescence. This model is used to explain the results from experiments where three different nozzle variations were tested, namely a nozzle with an impinging surface immediately outside the nozzle orifice, a nozzle with a bend in the nozzle channel, and a nozzle with a tapering outlet immediately outside the nozzle orifice. From these experiments, it is inferred that the first phase of bubble growth is completed at approximately 1.7 ms after the start of pressure release.

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