Journal articles: 'Water - Purification - Dissolved air flotation'

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Es'kin, Anton Andreevich, Nadezhda Sergeevna Tkach, and Marina Sergeevna Lyagusha. "PURIFICATION OF OILY WATER BY DISSOLVED AIR FLOTATION WITH SPRAYING OF LIQUID." NEWS OF HIGHER EDUCATIONAL INSTITUTIONS. CONSTRUCTION 709, no. 1 (2018): 47–56. http://dx.doi.org/10.32683/0556-1052-2018-709-1-47-56.

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Tian, Zhuang, Can Wang, and Min Ji. "Full-scale dissolved air flotation (DAF) equipment for emergency treatment of eutrophic water." Water Science and Technology 77, no. 7 (February 23, 2018): 1802–9. http://dx.doi.org/10.2166/wst.2018.046.

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Abstract Eutrophication of urban rivers has caused severe environmental problems due to the pollution from point and diffuse sources. Although eutrophication can be alleviated by reducing the input to the river system, fast-treating terminal control technologies, especially under emergent situations, should be developed to reduce risks induced by eutrophication. The present study developed an emergency purification device based on dissolved air flotation (DAF) technology. After equipment commissioning and parameter optimization for applications in the field of engineering, the device was found to effectively remove total phosphorus, chlorophyll a, chemical oxygen demand, and turbidity in water by controlling the coagulant dosage and adjusting the gas-liquid mixing pump parameters. Dissolved air in water could enhance dissolved oxygen, and dissolved oxygen in polluted rivers could be raised from 0.2–2 mg/L to 3–3.5 mg/L. Removal of total nitrogen was poor because the majority of nitrogen contents were dissolved. Finally, DAF has been proven to be a promising technology due to its ease of implementation, low equipment investment requirement, and low operation cost.

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Mohd Arif Zainol, Mohd Remy Rozainy, Hasif Mokhtar, Syafalni Sutan, Khairy Abdul Wahab, and Mohd Mustafa Al Bakri Abdullah. "Chitosan and Bentonite as Coagulant in Dissolved Air Flotation Tank." Applied Mechanics and Materials 754-755 (April 2015): 728–32. http://dx.doi.org/10.4028/www.scientific.net/amm.754-755.728.

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The use of monocoagulants, such as Chitosan, may not be a good solution for highly turbid water purification because of its high cost. The possibility to reduce the amount of the primary coagulant at the same time keeping the removal to be in optimum may be a good strategy to reduce the operation cost. There might be another coagulant aid for example the natural clay of Bentonite to reduce the cost. The initial stage is to determine the Bentonite dosage and mixture ratio to be used with Chitosan. Coagulation of Chitosan-Bentonite had successfully removed the turbidity with the efficiency of 97%. The coagulants performed well when Chitosan-Bentonite ratio is 30:70 at concentration of 1000mg/l

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Zasadowski, Dariusz, Anders Strand, Anna Sundberg, Håkan Edlund, and Magnus Norgren. "Selective purification of bleached spruce TMP process water by induced air flotation (IAF)." Holzforschung 68, no. 2 (February 1, 2014): 157–65. http://dx.doi.org/10.1515/hf-2013-0045.

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Abstract The environmentally benign closure of water systems in paper mills leads to the problem of accumulation of dissolved and colloidal wood substances (DCS) in process water. Notably, pitch affects the pulp and paper production negatively and increases the demand for additional treatment of the process water. In the present article, the purification of thermomechanical pulping process water from the alkaline peroxide bleaching stage has been investigated, with the induced air flotation (IAF) in focus. The following parameters were considered concerning the IAF efficiency to remove detrimental substances: concentration of cationic foaming agent, pH value, calcium concentration, and temperature. The amounts and characteristics of residual DCS were determined by gas chromatography and turbidity measurements. Residual concentrations of the foaming agent dodecyltrimetylammonium chloride were determined by electrospray ionization mass spectrometry. Up to 90% of pitch was removed, whereas hemicelluloses, which are important in preventing pitch problems, remained in the waters. Up to 70% of the pectic acids accounted for the high cationic demand of the process waters were removed by optimization of the IAF parameters. The presented separation process gives new opportunities to a selective purification of the process waters.

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Wang, Yong Lei, Jun Li, Ke Feng Zhang, Rui Bao Jia, Mei Li, Wu Chang Song, An Shuang Wang, and Lin Wang. "The Optimization Design and Operating Characteristics of Vertical Flow Dissolved Air Flotation Carbon-Sand Dual Media Filter Flofilter." Advanced Materials Research 864-867 (December 2013): 2031–34. http://dx.doi.org/10.4028/www.scientific.net/amr.864-867.2031.

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Aimed at the raw water quality characterized by low temperature and low turbidity in winter,high algae and organic matters in summer, the vertical flow-carbon sand dual media filter flofilter was developed to research water purification effect.In the meantime,the pressurized dissolved air system and the filter unit were optimized.Air flotation and filtration were integrated in a structure,which could effectively save land area, and the device had advantages of operation mode flexible and purifying water collaboratively,etc..The results showed that the device could reach better results when the dissolved air pressure was 0.4 Mpa,the reflux ratio was 8% and the filter speed was 8 m/h. The averaged removal efficiency of turbidity,CODMn,the total number of algae and chlorophyll a were 86.49%,43.46%,76.30% and 71.26% by combination process respectively, so water purification effect was significant.

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Wang, Yong Lei, Ning Wang, Ruibao Jia, Kefeng Zhang, Baozhen Liu, Wuchang Song, and Junqi Jia. "Research on CFD numerical simulation and flow field characteristics of countercurrent–cocurrent dissolved air flotation." Water Science and Technology 77, no. 5 (January 2, 2018): 1280–92. http://dx.doi.org/10.2166/wst.2018.006.

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Abstract Countercurrent–cocurrent dissolved air flotation (CCDAF), the popular water purification device, which consists of collision and adhesion contact zones, showed favorable flotation conditions for micro-bubble adhesion and stability. In this study, computational fluid dynamics (CFD) numerical simulation was employed to confirm that the unique CCDAF configuration create reasonable and that the flow field characteristics were good no matter for single phase or gas–liquid two-phase conditions. In addition, the turbulence of the flow field was enhanced with the increasing influent load; the swirling was remarkably reduced with the increase of gas holdup. Meanwhile, a thick micro-bubble filter layer was formed in the separation zone, which favored bubble-flocs agglomerating and rising. The force analysis also showed that the cross section within the tank contribute to the uniformity of the bottom water collection as well as enlargement of the bottom outflow area, therefore improving the overall flotation performance. The simulation results revealed for the CCDAF process can provide technical guidance for engineering design and application.

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Misković, D., B. Dalmacija, Ž. Živanov, E. Karlović, Z. Hain, and S. Marić. "An Investigation of the Treatment and Recycling of Oil Refinery Wastewater." Water Science and Technology 18, no. 9 (September 1, 1986): 105–14. http://dx.doi.org/10.2166/wst.1986.0083.

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The objective of the present investigation was a high level of purification of the wastewater from an oil refinery achieved by using some improved methods yielding an effluent suitable for recycling into the process. All the investigations were carried out on a continuous laboratory pilot system consisting of the following units: dissolved air flotation (DAF), sedimentation, double-stage microbiological reactor, and adsorption columns filled with granular biologically activated carbon (GBAC). A high degree of COD reduction close to 100% (precisely, 99.95 %), as well as removal of nitrogen compounds of 72% was achieved during a relatively short retention time within the range of 15-16.5 hrs. The DAF technique combined with gravitational separation was used to achieve the recovery of free oil matter up to 98%, without any preliminary conditioning. After the sedimentation of coagulated and flocculated dispersed oils, the microbiological oxidation of dissolved matter was accomplished by using two kinds of activated sludge for easy and hard degradable organics. Using the continuously bioregenerating GBAC, an effluent having a lowered COD value to about 9 was obtained. At the same time, the denitrification process took place. According to the obtained results the treated oil refinery wastewater can be recycled into the process, or discharged into a water recipient of a low self-purifying capacity.

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Sarja, T., M. Zabihian, P. Kourunen, and J. Niinimäki. "New method for measuring potential secondary stickies in deinked pulp filtrates." Water Science and Technology 50, no. 3 (August 1, 2004): 207–15. http://dx.doi.org/10.2166/wst.2004.0197.

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Secondary stickies refer to sticky material in recycled fiber process streams, which has been dissolved in one part of process, but turned to solid phase due to changes in process conditions. The material that can later form secondary stickies is called potential secondary stickies. A new, fast, and simple method for measuring the amount of potential secondary stickies was developed to measure the purification result in the deinked pulp (DIP) filtrates. The new method, now called potential secondary stickies method, was tested with process waters from a recycled fiber (RCF) plant. The method was found to be reliable. Several chemicals and chemical combinations were tested in laboratory scale and compared as coagulation-flocculation agents in two dissolved air flotations (DAF) used as internal water treatment units at the RCF plant. With potential secondary stickies method, significant differences between the effectiveness of the chemicals were found, whereas no difference was seen in the quality of purified process water with traditional measuring methods. The measurement method was also used in mill during a two-week measuring period. As a conclusion, it can be said that this method can be used to monitor the quality and to predict the changes in DIP process water.

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Mohammadi, Leili, Abbas Rahdar, Edris Bazrafshan, Hamid Dahmardeh, Md Abu Bin Hasan Susan, and George Z. Kyzas. "Petroleum Hydrocarbon Removal from Wastewaters: A Review." Processes 8, no. 4 (April 10, 2020): 447. http://dx.doi.org/10.3390/pr8040447.

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Oil pollutants, due to their toxicity, mutagenicity, and carcinogenicity, are considered a serious threat to human health and the environment. Petroleum hydrocarbons compounds, for instance, benzene, toluene, ethylbenzene, xylene, are among the natural compounds of crude oil and petrol and are often found in surface and underground water as a result of industrial activities, especially the handling of petrochemicals, reservoir leakage or inappropriate waste disposal processes. Methods based on the conventional wastewater treatment processes are not able to effectively eliminate oil compounds, and the high concentrations of these pollutants, as well as active sludge, may affect the activities and normal efficiency of the refinery. The methods of removal should not involve the production of harmful secondary pollutants in addition to wastewater at the level allowed for discharge into the environment. The output of sewage filtration by coagulation and dissolved air flotation (DAF) flocculation can be transferred to a biological reactor for further purification. Advanced coagulation methods such as electrocoagulation and flocculation are more advanced than conventional physical and chemical methods, but the major disadvantages are the production of large quantities of dangerous sludge that is unrecoverable and often repelled. Physical separation methods can be used to isolate large quantities of petroleum compounds, and, in some cases, these compounds can be recycled with a number of processes. The great disadvantage of these methods is the high demand for energy and the high number of blockages and clogging of a number of tools and equipment used in this process. Third-party refinement can further meet the objective of water reuse using methods such as nano-filtration, reverse osmosis, and advanced oxidation. Adsorption is an emergency technology that can be applied using minerals and excellent materials using low-cost materials and adsorbents. By combining the adsorption process with one of the advanced methods, in addition to lower sludge production, the process cost can also be reduced.

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Baeyens, J., I. Y. Mochtar, S. Liers, and H. De Wit. "Plugflow dissolved air flotation." Water Environment Research 67, no. 7 (November 1995): 1027–35. http://dx.doi.org/10.2175/106143095x133266.

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Liers, Sven, Jan Baeyens, and Indranata Mochtar. "Modeling dissolved air flotation." Water Environment Research 68, no. 6 (September 1996): 1061–75. http://dx.doi.org/10.2175/106143096x128063.

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12

Zhu, Huan Ying, Ming Zhou, and Xiao Liu. "Dissolved Air Theory in Water Process Research Overview." Advanced Materials Research 971-973 (June 2014): 2035–38. http://dx.doi.org/10.4028/www.scientific.net/amr.971-973.2035.

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Now,accompanied by water flotation theory and technology continues to improve, sothat in all types of water feed and sewage treatment plant has been widelyapplied, the article by domestic and foreign air flotation developments intheory and its applications briefly summed and simple introduction to somebasic theoretical knowledge flotation, air flotation method focuses on thefield of application in water treatment, such as for low temperature and lowturbidity of the lake water, algae content than high water quality and watertreatment, in these respects, air flotation application advantages moreprominent.

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13

Schofield, T. "Dissolved air flotation in drinking water production." Water Science and Technology 43, no. 8 (April 1, 2001): 9–18. http://dx.doi.org/10.2166/wst.2001.0453.

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Dissolved Air Flotation (DAF) has become increasingly important in the field of potable water treatment, as a preferred option for treating upland and stored lowland waters. This paper outlines the development of dissolved air flotation (DAF) in potable water treatment, the benefits and disadvantages and the recent advances that has taken the process technology from an art to a science.

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Eades, Andrew, and W. J. Brignall. "Counter-current dissolved air flotation/filtration." Water Science and Technology 31, no. 3-4 (February 1, 1995): 173–78. http://dx.doi.org/10.2166/wst.1995.0527.

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Thames Water Utilities has developed and patented a Counter-current dissolved air flotation/filtration (COCO-DAFF) process as a compact water treatment system designed to remove particulate material from traditional water sources. In particular it has been developed to overcome operational problems with primary filters caused by seasonal blooms of filter blocking algae such as Melosira sp., Aphanizomenon sp. andAnabaena sp. The process can be run without flotation during periods when algae are not a problem, giving operational cost savings. This process differs from co-current dissolved air flotation in that the recycle water is introduced after the inlet structure, but above the filter media. This generates an even depth bubble blanket in the flotation tank through which all the flocculated water must pass. The advantages are that in moving the recycle inlet away from the flocculated water inlet the potential for floc damage by the recycle is eliminated. Also since the entire sludge blanket is supported by a deep, even, bubble blanket, on de-sludging any fall-out of sludge that occurs near the de-sludging weirs will have to go back down through the process, leading to subsequent re-floating, and a reduced potential for spiking of the floated turbidity. Process validation experiments have been carried out on a 1.4 Ml/d pilot plant based at the Kempton Advanced Water Treatment Centre, London. These tests have identified a required flocculation time of 15 minutes prior to counter-current flotation, and insensitivity to the depth of the air injection below top water level. Dissolved air distribution is achieved using a special high volume flow rate DAF nozzle designed to lower the number of nozzles required per unit area, and to maximise the spread of the bubble cloud for optimum bubble/particle contact. Computational fluid dynamics (CFD) has been used in the scale-up of the pilot plant experience into the first full scale of this design plant to be built, by PWT Projects, at the 200 Ml/d Walton AWTW, for Thames Water Utilities.

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Offringa, G. "Dissolved air flotation in Southern Africa." Water Science and Technology 31, no. 3-4 (February 1, 1995): 159–72. http://dx.doi.org/10.2166/wst.1995.0526.

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A brief review is given of the historical development and current application of flotation technology in Southern Africa. Applications in water reclamation, sludge thickening, industrial effluents and water treatment are presented on the basis of some case studies and pilot investigations. Design philosophies followed are pointed out. Research and development performed and a few innovations by local engineers and scientists are highlighted. These include combination or integration of dissolved air flotation (DAF) with filtration, presettling and powdered activated carbon, a simple aeration nozzle, surface grids for float dewatering and stabilization, and a counter-current DAF.

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Plummer, Jeanine D., James K. Edzwald, and Michael B. Kelley. "Removing Cryptosporidium by dissolved-air flotation." Journal - American Water Works Association 87, no. 9 (September 1995): 85–95. http://dx.doi.org/10.1002/j.1551-8833.1995.tb06425.x.

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Shawwa, Ayman R., and Daniel W. Smith. "Dissolved air flotation model for drinking water treatment." Canadian Journal of Civil Engineering 27, no. 2 (April 1, 2000): 373–82. http://dx.doi.org/10.1139/l99-071.

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In this study, a kinetic model that describes bubble-particle transport and attachment in the contact zone of dissolved air flotation (DAF) process is presented. The kinetic model, which is based on the assumption that the contact zone is analogous to a chemical reactor, describes the particle removal rate as a first-order reaction with respect to the concentration of particles. It identified important parameters, such as the bubble-particle attachment efficiency (αPB). The theoretical first-order particle removal rate constant (kP), based on the mathematical model, was determined by varying αPB from 0.1 to 1.0. On the other hand, the experimental kP value was determined by measuring the mean residence time, the degree of mixing of particles, and the particle removal efficiency of the contact zone by conducting pilot-scale DAF experiments at different hydraulic loading rates and recycle ratios. The experimentally determined first-order particle removal rate constant was equal to the theoretical kP value when the bubble-particle attachment efficiency (αPB) was in the range of 0.35 to 0.55, which is considered typical for water treatment applications. The kinetic model can be used to predict DAF removal efficiencies provided that αPB is determined for the system under investigation and that the operating conditions applied in this research are used. However, independent experiments are required to verify the applicability of the proposed model.Key words: algae, bubble, coagulation, dissolved air flotation, flocculation, kinetic model, particle size distribution, water treatment.

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Raeli, M. A. P., and M. Marchetto. "High-rate dissolved air flotation for water treatment." Water Science and Technology 43, no. 8 (April 1, 2001): 43–49. http://dx.doi.org/10.2166/wst.2001.0461.

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This paper presents the results of an experimental investigation about the performance of a horizontal flow high-rate pilot scale Dissolved Air Flotation (HRDAF) unit containing inclined parallel plates for treating a coloured and low turbidity raw water. Experiments were performed with the DAF unit in order to verify the influence on flotation of : (i) the water velocity (Vh) between the plates, in the range 18 to 96.5 cm.min−1 with corresponding Reynolds numbers between 240 and 1060; (ii) the supplied air (S*) value ranging from 2.2 to 8.5 g of air/m3 of water ; (iii) the angle of the plates (60° or 70°). The best pilot plant operational condition was obtained applying only 4.0 g/m3 (S*) with Vh around 18 cm.min−1 for treatment of water coagulated with a Al2(SO4)3 dosage of 40 mg.l−1. In these conditions, the unit presented very good removal efficiencies of colour (90%, residual of 10 uC), turbidity (88%, residual of 0.8 NTU ) and TSS (94%, residual of 1.8 mg.l−1). Furthermore, the unit could operate at higher Vh values up to 76 cm.min−1 and still present good results. The DAF unit thus behaved as a high rate unit presenting good performance with low air requirement.

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Edzwald, James K., John P. Walsh, Gary S. Kaminski, and Howard J. Dunn. "Flocculation and Air Requirements for Dissolved Air Flotation." Journal - American Water Works Association 84, no. 3 (March 1992): 92–100. http://dx.doi.org/10.1002/j.1551-8833.1992.tb07325.x.

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van Puffelen, Jan, Paul J. Buijs, Peter N. A. M. Nuhn, and Wim A. M. Hijnen. "Dissolved air flotation in potable water treatment: the Dutch experience." Water Science and Technology 31, no. 3-4 (February 1, 1995): 149–57. http://dx.doi.org/10.2166/wst.1995.0525.

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This paper reviews the experience the drinking water companies in The Netherlands have gained in the last twenty years in the field of dissolved air flotation. An overview of the Dutch flotation plants with their individual objectives is presented. The efficiency of flotation towards the removal of different parameters, such as turbidity, organic matter and micro-organisms is good, which is illustrated by data from the water companies. Both in the past and at present water companies compare flotation to other floc separation techniques, such as sedimentation or direct filtration. Specially for waters with (relative) low turbidity and high chlorophyll-a content, flotation proved (in combination with rapid sand filtration) to be very effective. The efficiency of the flotation process has been improved by the development of different nozzle-types. Some of these types are described here, each with their advantages and disadvantages. In general dissolved air flotation has proved to be as sturdy and reliable as sedimentation techniques, such as lamellae settling.

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Zhang, Y., D. M. Leppinen, and S. B. Dalziel. "A new nozzle for dissolved air flotation." Water Supply 9, no. 6 (December 1, 2009): 611–17. http://dx.doi.org/10.2166/ws.2009.229.

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This paper examines an experimental study of optimal nozzle design for a dissolved air flotation system. The term optimal is in reference to field studies of bubble-floc agglomeration in an actual DAF tank. The primary mechanism of floc removal has been identified as bubble clustering. By understanding the significance of bubble clustering it was possible to design a nozzle that could be successfully operated at reduced saturation pressures while still achieving improved levels of turbidity in the post-DAF water.

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Lovett, D. "Dissolved air flotation for abattoir wastewater." Water Research 20, no. 4 (April 1986): 421–26. http://dx.doi.org/10.1016/0043-1354(86)90188-0.

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23

Heinänen, J., P. Jokela, and T. Ala-Peijari. "Use of dissolved air flotation in potable water treatment in Finland." Water Science and Technology 31, no. 3-4 (February 1, 1995): 225–38. http://dx.doi.org/10.2166/wst.1995.0532.

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The basic concepts of treating humic waters with dissolved air flotation are discussed emphasizing the important role of zeta potential in the forming of floc-air-bubble-agglomerates. Then practical experiences from Finnish drinking water treatment plants are presented. When surface water is used as a raw water, it is more or less humic. Thirty-six such plants have dissolved air flotation as a clarification process, the oldest one dating from 1965. They serve about one million people. All of them are working well proving that dissolved air flotation is a suitable method in humic water treatment. Some special cases are discussed in detail. These are cases where sufficient data about design, operation and costs are available and which it is hoped can help other designers. The last plant referred to is an example of an advanced treatment process where dissolved air flotation is an integrated unit process.

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Hedberg, Torsten, Jan Dahlquist, Dick Karlsson, and Lars-Ove Sörman. "Development of an air removal system for dissolved air flotation." Water Science and Technology 37, no. 9 (May 1, 1998): 81–88. http://dx.doi.org/10.2166/wst.1998.0343.

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Dissolved Air Flotation (DAF) is often used as a separation step in drinking water treatment. An increasing use of high rate processes has become a trend in chemical treatment. When increasing the loading rate for a flotation process, an increasing head loss built up occurs in the following filter process due to dispersed air carry over. This paper describes the development of an air removal system by using a lamella plate separation system for the dispersed air. Pilot plant experiments showed that the surface load for the combination Lamella Dissolved Air Flotation, the LDAF-unit can be considerably increased in comparison with a conventional DAF-unit.

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Rykaart, E. M., and J. Haarhoff. "Behaviour of air injection nozzles in dissolved air flotation." Water Science and Technology 31, no. 3-4 (February 1, 1995): 25–35. http://dx.doi.org/10.2166/wst.1995.0513.

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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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van Vuuren, L. R. J., and P. J. van der Merwe. "Thickening of Sludges by Dissolved Air Flotation." Water Science and Technology 21, no. 12 (December 1, 1989): 1771–74. http://dx.doi.org/10.2166/wst.1989.0165.

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Edzwald, J. K. "Algae, Bubbles, Coagulants, and Dissolved Air Flotation." Water Science and Technology 27, no. 10 (May 1, 1993): 67–81. http://dx.doi.org/10.2166/wst.1993.0207.

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This paper like Ken Ives' PhD research comments upon algae and their removal from drinking water. Specifically, algal properties, difficulties in removing algae by conventional treatment, and dissolved air flotation (DAF) as a treatment method are emphasized. The stability of algal suspensions may be due to surface charge, hydrophilic effects, or steric effects. Coagulation is required as a pretreatment step in DAF to destabilize algal particles relative to the microbubbles, and thus ensure particle-bubble attachment The air supplied in DAF may be expressed fundamentally as mass, volume, and number concentrations of air bubbles. Calculations show high bubble volume concentrations compared to suspended particle volumes. The effectiveness of flotation is examined in terms of dimensionless products and compared to other particle processes. DAF is compared to settling for algal separation in experiments with DAF operating at higher overflow rates and smaller flocculation times. DAF produced clarified waters with lower turbidities and algal counts.

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Edzwald, James K. "Principles and applications of dissolved air flotation." Water Science and Technology 31, no. 3-4 (February 1, 1995): 1–23. http://dx.doi.org/10.2166/wst.1995.0512.

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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.

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Amato, T., J. K. Edzwald, J. E. Tobiason, J. Dahlquist, and T. Hedberg. "An integrated approach to dissolved air flotation." Water Science and Technology 43, no. 8 (April 1, 2001): 19–26. http://dx.doi.org/10.2166/wst.2001.0455.

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DAFRapide® techniques utilising reduced flocculation times, of the order of 5 minutes, together with flotation loading rates of up to 40 m/h, can be incorporated with conventional filtration systems operating at up to 20 m/h. Product quality of typically <1 NTU and <0.1 NTU after flotation and filtration respectively can be achieved.

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Féris, L. A., C. W. Gallina, R. T. Rodrigues, and J. Rubio. "Optimizing dissolved air flotation design and saturation." Water Science and Technology 43, no. 8 (April 1, 2001): 145–57. http://dx.doi.org/10.2166/wst.2001.0486.

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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.

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31

Folkard, Sutherland, and Jahn. "Water clarification with natural coagulants and dissolved air flotation." Waterlines 5, no. 2 (October 1986): 23–26. http://dx.doi.org/10.3362/0262-8104.1986.044.

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32

Al-Shamrani, A. A., A. James, and H. Xiao. "Separation of oil from water by dissolved air flotation." Colloids and Surfaces A: Physicochemical and Engineering Aspects 209, no. 1 (September 2002): 15–26. http://dx.doi.org/10.1016/s0927-7757(02)00208-x.

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33

Hall, T., J. Pressdee, R. Gregory, and K. Murray. "Cryptosporidium removal during water treatment using dissolved air flotation." Water Science and Technology 31, no. 3-4 (February 1, 1995): 125–35. http://dx.doi.org/10.2166/wst.1995.0523.

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The occurrence of the protozoan parasite Cryptosporidium parvum in water supplies, and the resultant outbreaks of cryptosporidiosis in the UK and USA, have led to concern over the ability of conventional water treatment processes to remove Cryptosporidia from water sources. Large scale pilot plant trials of water treatment have been carried out in the UK to establish the degree of removal that can be achieved by a range of treatment processes, including dissolved air flotation, and to compare the performance of different treatment options. Results from part of these trials are presented in this paper. These results suggest that well operated chemical coagulation based treatment, using either dissolved air flotation or floc blanket clarification, should be capable of achieving removal of Cryptosporidium oocysts of over 99%. There was no evidence of differences in performance between the different types of filter media investigated. The risk of increased Cryptosporidium concentration in the filtered water will increase as filtrate turbidity increases. However, other factors such as high coagulant metal-ion concentration in the filtered water, or a sudden increase in clarified water turbidity, without any increase in filtered water turbidity, may also indicate treatment problems and associated risk from Cryptosporidia. Recycling of backwash waters may also increase the risk.

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34

Zabel, Thomas. "The Advantages of Dissolved-air Flotation for Water Treatment." Journal - American Water Works Association 77, no. 5 (May 1985): 42–46. http://dx.doi.org/10.1002/j.1551-8833.1985.tb05537.x.

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35

Ferguson, C., G. S. Logsdon, and D. Curley. "Comparison of dissolved air flotation and direct filtration." Water Science and Technology 31, no. 3-4 (February 1, 1995): 113–24. http://dx.doi.org/10.2166/wst.1995.0522.

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Direct filtration with and without pre-ozone, and dissolved air flotation and filtration were evaluated for clarification of high quality reservoir water in Greenville, South Carolina, USA. Goals of the study included production of low turbidity filtered water and control of algae, iron and manganese, and disinfection by-product precursors. The dissolved air flotation treatment train gave much longer filter runs than direct filtration, when both processes met the 0.10 NTU goal for filtered water quality. Use of pre-ozone was beneficial for direct filtration. Removal of TOC, DBP precursors, and iron and manganese were similar for both processes.

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36

Leppinen, D. M., S. B. Dalziel, and P. F. Linden. "Modelling the global efficiency of dissolved air flotation." Water Science and Technology 43, no. 8 (April 1, 2001): 159–66. http://dx.doi.org/10.2166/wst.2001.0490.

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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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37

Gorczyca, Beata, and Paul Klassen. "Optimization of Solids Separation in Dissolved Air Flotation." Water Quality Research Journal 43, no. 2-3 (May 1, 2008): 239–47. http://dx.doi.org/10.2166/wqrj.2008.027.

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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.

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Jokela, P., and P. Keskitalo. "Plywood Mill Water System Closure by Dissolved Air Flotation Treatment." Water Science and Technology 40, no. 11-12 (December 1, 1999): 33–41. http://dx.doi.org/10.2166/wst.1999.0692.

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In plywood industry water is mainly needed for soaking the logs. Dissolved air flotation with chemical precipitation was found to be a suitable treatment method for the soaking basin overflow of a plywood mill using birch as raw material. According to pilot treatment studies over 90% reductions of the suspended solids are possible with a hydraulic surface load of 6.5 m3/(m2h). In subsequent experience in full scale following reductions have been achieved: suspended solids 93%, BOD7 50%, CODCr 57%, P 92% and N 52%. Two-thirds of the flotation treated water is led to flue gas scrubbers and circulated back to the soaking basin. Optionally water can be led to the heat recovery, too. One-third of the flotation treated water is disposed of as the mill effluent. Concentrations of organic matter in the system have been reduced after the addition of flotation indicating the possibility of further closure. However, due to the use of aluminium sulphate in coagulation, aeration is needed for sulphate reduction prevention. Further closure of the water system is possible in the future if the heat recovery is renovated, preventing the increase of the water temperature (now 37°C) which otherwise might cause occupational safety hazards.

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39

Arnold, Steven R., Thomas P. Grubb, and Peter J. Harvey. "Recent applications of dissolved air flotation pilot studies and full scale design." Water Science and Technology 31, no. 3-4 (February 1, 1995): 327–40. http://dx.doi.org/10.2166/wst.1995.0541.

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The use of Dissolved Air Flotation (DAF) as a solids/liquid separation process in water treatment has been an effective alternative to sedimentation for 70 years. The process was initially applied for removal of materials which had a specific gravity less than water, such as fats, oils, fibers, and grease. DAF installations expanded in the late 1960s to wastewater and potable water treatment. Today, Dissolved Air Flotation is utilized for a wide variety of water and wastewater applications. DAF is applied extensively for wastewater sludge thickening and it is widely accepted in Scandinavia and the United Kingdom for potable water treatment. It has also gained a foothold in the United States with the start up of a 7.5 mgd (28.4 Ml/d) potable water flotation plant at New Castle, New York. The goal of this paper is to present recent applications of Dissolved Air Flotation technology on a variety of raw water sources. Descriptions and general design parameters of a typical flotation and a proprietary combined flotation and filtration process will be discussed.

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40

Ødegaard, H. "The use of dissolved air flotation in municipal wastewater treatment." Water Science and Technology 43, no. 8 (April 1, 2001): 75–81. http://dx.doi.org/10.2166/wst.2001.0468.

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Flotation can be used in municipal wastewater treatment plants in different ways. Since the pollutants in wastewater to such a large extent are associated with particles, a very substantial treatment efficiency can be reached at a very small space, by using flotation in a chemical (or enhanced primary) treatment scheme. This is demonstrated in this paper with reference to results from small, prefabricated chemical plants based on flotation, which are frequently used in Norway. If used in connection with biological plants (for instance for nitrogen removal), the combination of biofilm reactors and flotation is especially advantageous because coagulation/flocculation/flotation can be placed directly after the bioreactor. Results from two such plants in Norway are presented. Recommendations with respect to design and operation of flotation plants in wastewater treatment are given.

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41

Sugahara, M., and S. Oku. "Parameters Influencing Sludge Thickening by Dissolved Air Flotation." Water Science and Technology 28, no. 1 (July 1, 1993): 87–90. http://dx.doi.org/10.2166/wst.1993.0023.

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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.

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42

Haarhoff, Johannes, and James K. Edzwald. "Dissolved air flotation modelling: insights and shortcomings." Journal of Water Supply: Research and Technology-Aqua 53, no. 3 (May 2004): 127–50. http://dx.doi.org/10.2166/aqua.2004.0012.

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43

Li, Yan Min, Pei Yan Wang, and Kun Li. "Study on the Flow Field of Air Floating Pool of Pressurized Dissolved-Air Floatation Water Treatment System." Advanced Materials Research 706-708 (June 2013): 565–70. http://dx.doi.org/10.4028/www.scientific.net/amr.706-708.565.

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This paper used the FLUENT software to analyze a flow field of the advection type air-float pool, the simulation analysis is applied to study of partition plates, water retaining plate and floatation pool length depth ratio and other key parameters which influence the flotation pool flotation effect .The research results provide the basis for the structure design of improving the flotation pool. It has a certain reference value for the same type of flotation pool design.

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44

Haarhoff, Johannes. "Dissolved air flotation: progress and prospects for drinking water treatment." Journal of Water Supply: Research and Technology-Aqua 57, no. 8 (December 2008): 555–67. http://dx.doi.org/10.2166/aqua.2008.046b.

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45

French, Kathy, Rodney K. Guest, Gordon R. Finch, and Charles N. Haas. "Correlating Cryptosporidium removal using dissolved air flotation in water treatment." Water Research 34, no. 16 (November 2000): 4116–19. http://dx.doi.org/10.1016/s0043-1354(00)00164-0.

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46

Multon, Lance M., and Thiruvenkatachari Viraraghavan. "Removal of Oil from Produced Water by Dissolved Air Flotation." Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management 12, no. 1 (January 2008): 25–29. http://dx.doi.org/10.1061/(asce)1090-025x(2008)12:1(25).

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47

Eades, A., B. J. Bates, and M. J. MacPhee. "Treatment of spent filter backwash water using dissolved air flotation." Water Science and Technology 43, no. 8 (April 1, 2001): 59–66. http://dx.doi.org/10.2166/wst.2001.0465.

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There is increasing interest in treating recovered spent filter backwash water in the drinking water industry. In the USA the Filter Backwash Recycling Rule will come into effect in the near future. The purpose of the Rule is to prevent the concentrated pathogenic agents, potentially in the filter backwash water, from being returned to the head of the water treatment works without some form of treatment or dilution. By treating this flow both public health and financial liability can be better managed by the operating utility. Dissolved Air Flotation (DAF) was investigated as a possible technology alternative to simple or advanced sedimentation techniques. This application is not widespread but sits somewhere in between the two normal applications of DAF as a high solids sludge thickener and a low turbidity clarification system. Given this a pilot plant program, supported by jar testing, was undertaken to determine the process capability and the design parameters for this application. DAF proved to be very suitable for backwash water recovery. DAF effluent turbidities of <1.0 NTU could be easily obtained, when raw water turbidities were in excess of 50 NTU. Chemical requirements were low with only a single low dose of polymer required to bind the floc particles to form a solids matrix suitable for flotation. Flocculation contact times ranged from 0–10 minutes depending on the nature of the raw water. Recycle rates as low as 5% performed satisfactorily with no significant improvement when increased to 20%. Sludge solids of 3.5–9.6% dry solids were found and very low volumes of sludge, <0.1% of the incoming flow make the DAF solids handling system very compact.

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48

Haarhoff, Johannes, and Lucas R. J. van Vuuren. "Design parameters for dissolved air flotation in South Africa." Water Science and Technology 31, no. 3-4 (February 1, 1995): 203–12. http://dx.doi.org/10.2166/wst.1995.0530.

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Dissolved air flotation has been used in South Africa for more than 25 years in the field of water and waste-water treatment, with practically all the development and verification done locally. This substantial body of knowledge and experience was recently condensed into a document titled A South African Design Guide for Dissolved Air Flotation. A general literature survey was combined with a detailed survey of 26 dissolved air flotation plants operating in Southern Africa, to arrive at suggested design parameters. Two broad categories of applications were covered in the guidelines - those of water clarification, and of activated sludge thickening. A clear trend emerged from the data collected. Drinking water clarification plants were generally designed within a fairly narrow range of the most design parameters, and the perception of operators and managers was that these clarification plants performed very efficiently. Sludge thickening plants, on the other hand, showed considerable variability in terms of most design parameters, and the general perception of its efficiency consequently varied from highly positive to negative. The paper includes summaries of the ranges of the actually surveyed design parameters, the suggested design values and a comparison with typical design values available from other countries.

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Kyzas, George, and Kostas Matis. "Flotation in Water and Wastewater Treatment." Processes 6, no. 8 (August 7, 2018): 116. http://dx.doi.org/10.3390/pr6080116.

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Flotation constitutes a separation process that originated from mineral processing. Nowadays, wider applications have been found and compared to flotation for water and wastewater treatment. Stress in the present review paper was mainly applied to heavy metal ions recovery by flotation and the respective mechanism followed, being either ion, precipitate, or sorptive flotation. In the latter case, the use of adsorbents is included (such as powdered activated carbon, zeolites, and goethite), as well as various biosorbents. The flotation of the following metals was reviewed: copper, zinc, nickel, lead, iron, chromium, arsenic, gold, and others. The bubble generation method could be applied for typical dispersed-air flotation column, electroflotation, or dissolved-air flotation; the latter being the most appropriate established technique in water treatment. The role of particle size (for example, studying flotation of salt-type mineral fines) was also examined.

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Officer, J., J. A. Ostrowski, and P. J. Woollard. "The design and operation of conventional and novel flotation systems on a number of impounded water types." Water Supply 1, no. 1 (January 1, 2001): 63–69. http://dx.doi.org/10.2166/ws.2001.0008.

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This paper describes the design of conventional Dissolved Air Flotation (DAF) systems, and the novel Counter Current Dissolved Air Flotation Filtration (COCODAFF®) process. The operation and performance of these plants on a variety of water types in the United Kingdom and South Africa is also described. The advantages of flotation processes for the treatment of impounded waters either high in colour, or with a high concentration of algae, is discussed. Other topics covered in this paper are hydraulic flocculation, and the application of Finite Element Analysis (FEA), to the design of flotation plants. It is concluded that the COCODAFF® process offers a number of advantages over conventional DAF systems.

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Journal articles on the topic 'Water - Purification - Dissolved air flotation'

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