Dissolved air flotation-filtration

Additional research conducted by LIWT88 91 has shown that the wastestreams, such as those shown in Figure 21.11, can be effectively treated by the two-stage biological-physicochemical process system or two-stage DAF-DAFF (dissolved air flotation-filtration) process system. The readers are referred to the literature88-91 for details. 

Section 27.3 introduces the improved activated sludge systems involving the use of either a DAF clarifier or a dissolved air flotation-filtration (DAFF) clarifier as the secondary flotation clarification unit. 

Most of the pollutants may be effectively removed by precipitation of metal hydroxides or carbonates using a reaction with lime, sodium hydroxide, or sodium carbonate. For some, improved removals are provided by the use of sodium sulfide or ferrous sulfide to precipitate the pollutants as sulfide compounds with very low solubilities. After soluble metals are precipitated as insoluble floes, one of the water-solid separators (such as dissolved air flotation, sedimentation, centrifugation, membrane filtration, and so on) can be used for floes removal.911 The effectiveness of pollutant removal by several different precipitation methods is summarized in Tables 5.15-5.17. 

Krofta, M. and Wang, L.K., Development of innovative flotation-filtration systems for water treatment, part B dissolved-air flotation plants for small communities, Proc. American Water Works Association Water Reuse Symposium III, San Diego, CA, 3, 1238-1250, 1984. 

Krofta, M. and Wang, L.K., Potable Water Pretreatment for Turbidity and Color Removal by Dissolved Air Flotation and Filtration for the Town of Lenox, Massachusetts, Krofta Engineering Corporation, Lenox, MA, Report No. KEC-10-81/3, 84pp., October 1981. 

Wang, L.K. Potable water treatment by dissolved air flotation and filtration. J. AWWA 1982, 74 (6), 304-310. 

M. Krofta, L. K. Wang, L. L. Spencer, and J. Weber, Separation of algae from lake water by dissolved air flotation and sand filtration. Proceedings of the Water Quality and Public Health Conference, Worcester Polytechnic Institute, Worcester, MA, USA, pp. 103-110, 1983 (NTIS-PB83-219550). 

PAC can be fed in the dry state using volumetric or gravimetric feeders or can be fed in slurry form. There are at least three major PAC producers, more than 50 manufacturers of volumetric and gravimetric feeders, and more than 50 manufacturers of slurry feeders (24-26). Additionally, there are many manufacturers of sequencing batch reactors (SBR) (22), dissolved air flotation (DAP) clarifiers (36), and membrane filtration (ME) reactors (31). 

Both insoluble Mn02 and Fe(OH)3 are then removed by one or more solid-water separation processes, such as sedimentation (1,14,28), dissolved air flotation (16,22), filtration (23,26), membrane filtration (20,21,25,26), electroflotation (17), physicochemical sequencing batch reactor (18,19), or precoat filtration (29,46). 

An innovative potable filtration plant with a design capacity of 1.2 MGD has been reliably serving 10,000 residents and tourists in the town of Lenox, Massachusetts, USA, since July 1982. Its process system consists of chemical flocculation, dissolved air flotation, and automatic backwash and sand filtration. It substantially improves upon the conventional flocculation, sedimentation, and filtration system in performance, capability, operation, maintenance, and energy use (19 2). 

Like all unit chemical processes, the RO is usually not capable of standing entirely by Itself. The important thing to remember is that a system must be developed to give a complete product. In the case of Cummins, the complete system includes dissolved air flotation, anthracite/sand filtration, activated carbon filtration and RO. In the case of Whitestone Chemical, the complete system includes RO and a cleaning regimen to maintain the RO at the required permeate flow rate. Time will tell which of these alternatives has the best economics. The economics and the proper system using RO are both dependent on the problem that requi res a solution. 

Until recently, the standard method for treatment of these wastes consisted of lime coagulation and flocculation with clarification by dissolved air flotation. Subsequently, the underflow is polished with sand or diatomaceous earth filtration. Finally, the sludge is dewatered by vacuum filtration. The effluent quality is variable and does not always meet discharge standards. 

Oil and grease - induced gas flotation (IGF), dissolved air flotation (DAF), membrane filtration... 

Sim et al. used centrifugation, dissolved air flotation and drum filtration techniques for harvesting sewage-grown algae.Centrifugation was found to be effective... 

The most straightforward means of physical treatment involves phase separation of the components of a mixture that are already in two different phases. Sedimentation and decanting are easily accomplished with simple equipment. In many cases, the separation must be aided by mechanical means, particularly filtration or centrifugation. Flotation is used to bring suspended organic matter or finely divided particles to the surface of a suspension. In the process of dissolved air flotation (DAF), air is dissolved in the suspending medium under pressure and comes out of solution when... 

Stock usually the best dewatering stock component used at the paper machine is selected in order to Hmit the size of the disc filter. In addition to cloudy and clear filtrate, disc filter save-aU applications also produce a superclear filtrate with very low solids content This superclear filtrate is used as a fresh water substitute for spray apphcations in the paper machine. The clear filtrate is stored in a buffer tank. The cloudy filtrate is usually fed directly back to the inlet of the disc filter, the used sweetener, including the recovered stock, is fed back to the thick stock in the approach flow system. DAF (dissolved air flotation) type save-alls are used in older machines and nowadays when a certain degree of ash and fines removal from the process is demanded. In this case, the sludge of the DAF is rejected. The advantages of a disc filter save-all compared to a DAF save-all are higher filtrate quahty, no chemical consumption and less space requirements (see Sections 4.2.62 and 4.2.9). 

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