Treatment flotation sludge

Water Treatment. Flotation in water treatment is used both for the removal of dissolved ions such as Cu ", Cr ", or (PO or surfactants and suspended soHds as in the case of sludge treatment. The final product in this case is purified water rather than a mineral concentrate. Furthermore, water is treated either for drinking purposes (potable water preparation) or safe disposal to the environment. 

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

Dissolved Air Flotation. Dissolved air flotation (DAF) is used to separate suspended soflds and oil and grease from aqueous streams and to concentrate or thicken sludges. Air bubbles carry or float these materials to the surface where they can be removed. The air bubbles are formed by pressurizing either the influent wastewater or a portion of the effluent in the presence of air. When the pressurized stream enters the flotation tank which is at atmospheric pressure, the dissolved air comes out of solution as tiny, microscopic bubbles. Dissolved air flotation is used in many wastewater treatment systems, but in the United States it is perhaps best known with respect to hazardous waste because it is associated with the Hsted waste, K048, DAF flotation soflds from petroleum refining wastewaters. Of course, the process itself is not what is hazardous, but the materials it helps to remove from refining wastewaters. 

Conventional treatment The preliminary treatment, sedimentation, flotation, trickling filter, rotating biological contactor, activated sludge and chlorination of wastewater. 

Different technologies have been developed in recent years to treat the wastewaters contaminated with heavy metals. Chemical precipitation, coagulation-flocculation, flotation, ion exchange, and membrane filtration can be employed to remove heavy metals from contaminated wastewater.6 However, they have inherent limitations in application mainly due to the lack of economical feasibility for the treatment of large volumes of water with a low metal concentration. Furthermore, the major disadvantage of conventional technologies is the production of sludge.9... 

In Section 27.2, the principles of a DAF unit and the entire improved activated sludge wastewater treatment system are disclosed in detail. The economic use of secondary flotation in the improved system requires only a relatively inexpensive high-rate DAF cell that is commercially available. The consulting engineers should understand such principles for the selection of an appropriate DAF unit and for the optimization of the entire improved wastewater treatment system. 

Figure 27.12 shows the improved activated sludge process in which a new secondary flotation is applied in series between the aeration basin and the final sedimentation clarifier for increasing the overall treatment performance and hydraulic capacity of an originally overloaded existing plant. 

A typical overloaded conventional complete-mix activated sludge treatment plant (shown in Figure 27.11) has been described in Section 27.3.3. The same conventional treatment plant can be improved by the addition of a secondary flotation clarifier (shown in Figure 27.12). Some advantages of the improved activated sludge system are mathematically presented below. 

Many pilot-scale and full-scale trials involving the use of secondary flotation (Krofta Supracell) in activated sludge treatment plants were conducted by KEC and Lenox Institute of Water Technology (LIWT) (formerly Lenox Institute for Research). Only partial operational data are selected for presentation in this chapter. The readers are encouraged to contact the authors for details. In the illustration of each case history, the true names of the company and its resident engineer involved are omitted for the protection of the Company s privacy. 

A conventional activated sludge treatment plant in Flouston, Texas, is heavily overloaded. KEC and the LIWT evaluated the flotation characteristics of MLSS in the Krofta Supracell... 

Another alternative involves the addition of a secondary flotation clarifier that parallels the existing secondary sedimentation clarifier in a conventional existing activated sludge wastewater treatment plant. 

Sepaflot A process for removing solids and oil from wastewater by a combination of Activated Sludge treatment and dissolved air flotation. Offered by Lurgi. 

In addition, oily sludge from a wastewater treatment facility that results from treating sour wastewaters may be a hazardous waste (unless recycled in the refining process). These include API separator sludge, primary treatment sludge, sludge from various gravitational separation units, and float from dissolved air flotation units. 

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