Dissolved Air Flotation with Spraying of Liquid

This paper presents a new method of dissolved air flotation with spraying of liquid. Liquid that needs cleaning is sprayed inside an overhead reservoir through a hydraulic nozzle allowing to enlarge the contact area between phases in comparison with traditional method of saturation by barbotage. Suggested method makes it possible to increase the gas content of the liquid processed for cleaning into a flotation section. This paper also contains the results of experimental investigation of the effectiveness of liquid saturation inside the overhead reservoir using spray-centrifugal and spray-percussive nozzles. Volumetric method was used to measure the amount of air escaping during dissolved air flotation and the results of the measurement were used to calculate the speed of barbotage. It was identified that when the method of spraying of liquid is applied, the amount of soluble air increases on average by 33% in comparison with overhead reservoir of bubbling type. The speed of barbotage increases with growth of saturation pressure and significantly depends on the area of the flotation section. If the saturation pressure exceeds 2 bars, the speed of barbotage in the center of the flotation cell becomes significantly higher than in the wall area.

Download Full-text

Optimizing dissolved air flotation design and saturation

Water Science & Technology ◽

10.2166/wst.2001.0486 ◽

2001 ◽

Vol 43 (8) ◽

pp. 145-157 ◽

Cited By ~ 16

Author(s):

L. A. Féris ◽

C. W. Gallina ◽

R. T. Rodrigues ◽

J. Rubio

Keyword(s):

Iron Hydroxide ◽

Minimum Energy ◽

Saturation Pressure ◽

Complete Recovery ◽

Capture Zone ◽

Dissolved Air Flotation ◽

Flotation Cell ◽

Adhesion Zone ◽

Air Flotation ◽

Dissolved Air

Dissolved air flotation (DAF) of iron hydroxide precipitates at working pressures lower than 3 atm, using modified flotation units to improve the collection of fragile coagula, was studied. Conventional DAF flotation was studied as a function of saturation pressure in the absence and presence of surfactants in the saturator. Without surfactants, the minimum saturation pressure required for DAF to occur was found to be 3 atm. But, by lowering the air/water surface tension in the saturator, DAF was possible at a saturation pressure of 2 atm. This behavior was found to occur in both batch and pilot DAF operation tests and almost complete recovery of the precipitates was attained. Results are explained in terms of the minimum “energy” which has to be transferred to the liquid phase to form bubbles by a cavity phenomenon. Further, studies were conducted changing equipment design and feed bubbles size distribution (mixing micro and “mid-sized” bubbles). Thus, bubbles entrance position in the collision-adhesion zone (“capture” zone) was compared to bubble entrance position in the water flow inlet below the floating bed. A “mushroom” type diffuser was used for the “capture zone” experiment and better performance was obtained. Results are explained in terms of different mass transfer phenomena in the collection zone and in the separation zone. Finally, results obtained with the use of a column flotation cell working as normal DAF and with a wide bubble size range are presented. Results indicate good performance and some gains in process kinetics with middle size bubbles.

Download Full-text

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

Water Practice & Technology ◽

10.2166/wpt.2008.073 ◽

2008 ◽

Vol 3 (3) ◽

Cited By ~ 1

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.

Download Full-text

KOMBINASI ULTRAFILTRASI DAN DISSOLVED AIR FLOTATION UNTUK PEMEKATAN MIKROALGA

REAKTOR ◽

10.14710/reaktor.15.1.43-50 ◽

2014 ◽

Vol 15 (1) ◽

pp. 43

Author(s):

I Nyoman Widiasa ◽

A A Susanto ◽

B Budiyono

Keyword(s):

Organic Fertilizer ◽

Saturation Pressure ◽

Raw Material ◽

Natural Food ◽

Omega 3 ◽

Dissolved Air Flotation ◽

Microalgae Biomass ◽

Air Flotation ◽

Β Carotene ◽

Dissolved Air

Abstrak Mikroalga merupakan mikroorganisme fotosintetik prokariotik atau eukariotik yang dapat tumbuh dengan cepat. Pemanfaatan mikroalga tidak hanya berorientasi sebagai pakan alami untuk akuakultur, tetapi terus berkembang untuk bahan baku produksi pakan ternak, pigmen warna, bahan farmasi (β-carotene, antibiotik, asam lemak omega-3), bahan kosmetik, pupuk organik, dan biofuel (biodiesel, bioetanol, biogas, dan biohidrogen. Studi ini bertujuan untuk menginvestigasi kombinasi ultrafiltrasi (UF) – dissolved air flotation (DAF) untuk pemekatan mikroalga skala laboratorium. Hasil penelitian menunjukkan bahwa penurunan fluks membran UF secara tajam sebagai akibat dari deposisi sel mikroalga terjadi pada 20 menit pertama proses filtrasi. Backwash pada interval 20 menit selama 10 detik dengan tekanan 1 bar memberikan pengendalian fouling yang efektif dalam nilai kestabilan fluks yang layak. Membran UF yang digunakan dapat memberikan selektivitas pemisahan biomassa mikroalga ~ 100%. Kualitas permeat sangat stabil, yaitu kekeruhan < 0,5 NTU, kandungan organik < 10 mg/L, dan warna < 10 PCU. Lebih lanjut, pemekatan retentat membran dengan DAF pada tekanan saturasi 6 bar dapat menghasilkan pasta mikroalga dengan konsentrasi 20 g/L. Koagulan PAC perlu ditambahkan kedalam umpan DAF dengan dosis 1,3–1,6 mg PAC/mg padatan tersuspensi. Kata Kunci: ultrafiltrasi; dissolved air flotation; pemanenan mikroalga; pemekatan mikroalga Abstract COMBINATION OF Ultrafiltration and Dissolved Air Flotation for Microalgae CONCENTRATION. Microalgae is a prokaryotic photosynthetic microorganism or eukaryotic microorganism that proliferate rapidly. Cultivation of the microalgae is not only oriented as natural food for aquacultures, but also developed for animal food, color pigment, pharmaceutical raw material (β-carotene, antibiotic, fatty acid omega-3), cosmetic raw material, organic fertilizer, and biofuels (biodiesel, bioethanol, biogas, and biohydrogen. This study is aimed to investigate the potential of combination of ultrafiltration (UF) and dissolved air flotation (DAF) for concentration of microalgae in laboratory scale. The experimental results showed that fluxes of the UF membrane decreased sharply due to deposition of microalgae biomass during first 20 minutes of filtration. Periodically backwash using the UF permeate (backwash interval = 20 minutes; backwash duration = 10 seconds; backwash pressure = 1 bar) gave an effective fouling control to maintain reasonable stable fluxes. In addition, the UF membrane gave separation of microalgae biomass ~ 100%. Permeate quality is strongly stable in which turbidity < 0.5 NTU, organic content < 10 mg/L, and color < 10 PCU. Moreover, concentration of the UF retentate by DAF under saturation pressure of 6 bars was able to produced microalgae feedstock having 20 g/L dry microalgae. PAC is required for DAF feed with dosage of 1.3–1.6 mg PAC/mg suspended solids.

Download Full-text

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

Water Science & Technology ◽

10.2166/wst.2007.779 ◽

2007 ◽

Vol 56 (10) ◽

pp. 109-115 ◽

Cited By ~ 21

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.

Download Full-text

Dissolved air flotation of polishing wastewater from semiconductor manufacturer

Water Science & Technology ◽

10.2166/wst.2006.217 ◽

2006 ◽

Vol 53 (7) ◽

pp. 133-140 ◽

Cited By ~ 1

Author(s):

J.C. Liu ◽

C.Y. Lien

Keyword(s):

Removal Efficiency ◽

Suspended Particle ◽

Saturation Pressure ◽

Silica Particles ◽

Ammonium Bromide ◽

Dissolved Air Flotation ◽

Recycle Ratio ◽

Semiconductor Manufacturer ◽

Air Flotation ◽

Dissolved Air

The feasibility of the dissolved air flotation (DAF) process in treating chemical mechanical polishing (CMP) wastewater was evaluated in this study. Wastewater from a local semiconductor manufacturer was sampled and characterised. Nano-sized silica (77.6 nm) with turbidity of 130±3 NTU was found in the slightly alkaline wastewater with traces of other pollutants. Experimental results indicated removal efficiency of particles, measured as suspended particle or turbidity, increased with increasing concentration of cationic collector cetyltrimethyl ammonium bromide (CTAB). When CTAB concentration was 30 mg/L, pH of 6.5±0.1 and recycle ratio of 30%, very effective removal of particles (> 98%) was observed in saturation pressure range of 4 to 6 kg/cm2, and the reaction proceeded faster under higher pressure. Similarly, the reaction was faster under the higher recycle ratio, while final removal efficiency improved slightly as the recycle ratio increased from 20 to 40%. An insignificant effect of pH on treatment efficiency was found as pH varied from 4.5 to 8.5. The presence of activator, Al3 + and Fe3 + , enhanced the system performance. It is proposed that CTAB adsorbs on silica particles in polishing wastewater through electrostatic interaction and makes particles more hydrophobic. The increase in hydrophobicity results in more effective bubble-particle collisions. In addition, flocculation of silica particles through bridging effect of collector was found; it is believed that flocculation of particles also contributed to flotation. Better attachment between gas bubble and solid, higher buoyancy and higher air to solid ratio all lead to effective flotation.

Download Full-text

Water clarification with natural coagulants and dissolved air flotation

Waterlines ◽

10.3362/0262-8104.1986.044 ◽

1986 ◽

Vol 5 (2) ◽

pp. 23-26 ◽

Cited By ~ 2

Author(s):

Folkard ◽

Sutherland ◽

Jahn

Keyword(s):

Dissolved Air Flotation ◽

Natural Coagulants ◽

Air Flotation ◽

Dissolved Air

Download Full-text

Behaviour of air injection nozzles in dissolved air flotation

Water Science & Technology ◽

10.2166/wst.1995.0513 ◽

1995 ◽

Vol 31 (3-4) ◽

pp. 25-35 ◽

Cited By ~ 12

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.

Download Full-text

Enhanced rapid gravity filtration and dissolved air flotation for pre-treatment of river thames reservoir water

Water Science & Technology ◽

10.2166/wst.1998.0098 ◽

1998 ◽

Vol 37 (2) ◽

pp. 35-42 ◽

Cited By ~ 5

Author(s):

M. J. Bauer ◽

R. Bayley ◽

M. J. Chipps ◽

A. Eades ◽

R. J. Scriven ◽

...

Keyword(s):

Water Treatment ◽

Water Supply ◽

21St Century ◽

Reservoir Water ◽

Dissolved Air Flotation ◽

Lowland Rivers ◽

Air Flotation ◽

Pre Treatment ◽

Counter Current ◽

Dissolved Air

Thames Water treats approximately 2800Ml/d of water originating mainly from the lowland rivers Thames and Lee for supply to over 7.3million customers, principally in the cities of London and Oxford. This paper reviews aspects of Thames Water's research, design and operating experiences of treating algal rich reservoir stored lowland water. Areas covered include experiences of optimising reservoir management, uprating and upgrading of rapid gravity filtration (RGF), standard co-current dissolved air flotation (DAF) and counter-current dissolved air flotation/filtration (COCO-DAFF®) to counter operational problems caused by seasonal blooms of filter blocking algae such as Melosira spp., Aphanizomenon spp. and Anabaena spp. A major programme of uprating and modernisation (inclusion of Advanced Water Treatment: GAC and ozone) of the major works is in progress which, together with the Thames Tunnel Ring Main, will meet London's water supply needs into the 21st Century.

Download Full-text