Flotation-filtration unit

Flotation-Filtration Systems 6.9.3.1 Combined Flotation-Filtration Unit... 

A combined flotation-filtration unit, shown in Figure 6.8, is an advanced water clarification system, using a combination of chemical flocculation, DAF, and rapid sand filtration in one unit. The average processing time from start to finish is less than 15 min.15-57-58... 

The following paragraphs briefly describe how the flotation-filtration unit shown in Figure 6.8,... 

FIGURE 6.8 Top and side views of the flotation-filtration unit. (Taken from Krofta, M. and Wang, L.K., Flotation Engineering, Technical Manual Lenox/1-06-2000/368, Lenox Institute of Water Technology, Lenox, MA, 2000.)... 

The flotation-filtration unit can be either manually operated or completely automated with a level control [17] that operates the inlet flow valve [18]. Filter backwashing can also be automated by a timer or head loss control [19]. 

It is important to note that all flotation clarifiers63,64 may be used for treatment of nickel-chromium plating wastes regardless of their shapes (rectangular or circular) or manufacturers. A filtration unit is an optional step for final polishing. The treatment efficiency of separate flotation and filtration units65 will be similar to that of a combined flotation-filtration unit (Figure 6.8). 

The first system, shown in Figure 6.6, is identical to the conventional reduction-precipitation in chemistry (i.e., neutralization, chromium reduction, pH adjustment, metal hydroxide precipitation, and so on). However, a flotation-filtration clarifier (Tank T101SF, as shown in Figure 6.6) is used. The unit consists of rapid mixing, flocculation, high-rate DAF, and sand filtration.1557... 

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. 

FIGURE 8.13 The scheme of flotation-filtration water purification process under recirculation conditions. 1 bio sand filter 2 aerator 3 bubble-film extraction unit F flow of the treated water F, recirculation flow Ki, K2, K rate constants of separate stages of water treatment AKi, AK2, AK efficiency increments of the stages at the expense of feedbacks in recirculation system. 

Chemicals can be added to the water in clarifiers, which are tanks that contain mixers that cause sufficient turbulence to create contact between the chemical and the solids. Coagulation/flocculation chemicals can also be added in flotation units to aid in attaching gas bubbles to the solid particles. Polyelectrolytes added to the feed stream to filtration units have proven effective at increasing filtration efficiency. 

The carbon black (soot) produced in the partial combustion and electrical discharge processes is of rather small particle si2e and contains substantial amounts of higher (mostly aromatic) hydrocarbons which may render it hydrophobic, sticky, and difficult to remove by filtration. Electrostatic units, combined with water scmbbers, moving coke beds, and bag filters, are used for the removal of soot. The recovery is illustrated by the BASF separation and purification system (23). The bulk of the carbon in the reactor effluent is removed by a water scmbber (quencher). Residual carbon clean-up is by electrostatic filtering in the case of methane feedstock, and by coke particles if the feed is naphtha. Carbon in the quench water is concentrated by flotation, then burned. 

The flotation unit maximum loading is 2.1 L/s/m2 (3.1 gal/min/ft2). The maximum filtration rate is 1.7 L/s/m2 (2.5 gal/min/ft2). Each filter compartment is backwashed at or more than 10.2 L/s/m2 (15 gal/min/ft2) during the backwash operation. The single-medium backwash filter consists of 28 mm (11 in.) high-grade silica sand. The effective size and uniformity coefficient for the sand are 0.35 mm and 1.55, respectively. 

The position for NOM-oxidation in water treatment schemes often is an intermediate one, e. g. between settling/flotation and rapid filtration or between rapid filtration and activated carbon filters or other post-treatment units (see Figure 3-1). 

Part II covers the unit operations of flow measurements and flow and quality equalizations pumping screening, sedimentation, and flotation mixing and flocculation filtration aeration and stripping and membrane processes and carbon adsorption. These unit operations are an integral part in the physical treatment of water and wastewater. 

Ovhemical DOSING for improvement of liquid-solid separation is traditionally designed and operated more or less independently of the geometry and hydraulic performance of the actual separation reactor. The widespread use of jar tests in the day-to-day operation of filtration and flotation plants illustrates this fact. Yet it is not difficult to visualize situations in which aggregation processes would furnish floes unsuitable for the subsequent separation unit, such as voluminous floes that do not settle out readily. 

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. 

Physical unit operations Screening Comminution Flow equalisation Sedimentation Flotation Granular-medium filtration... 

The water enters the plant and goes into accumulation tank. The treatment of water includes mechanical filtration, coagulation and flocculation, flotation, and then water is transported to biological treatment unit, where the organic impurities are decomposed due to heterotrophic... 

In the case of combined device (i.e., filtration-flotation water treatment under recirculation conditions), it is important to know the values of integrated constants of the filtration process, bioflltration process, bubble-flhn extraction process, gas exchange absorption process, and ion separation process in the functional units of combined device, that is, in the filter and in the bubble-film extractor, operating separately. The initial parameters for the device analysis are the required purification degree and treating time. And the calculated parameters are the integrated rate constants of such processes as filtration, biofiltration, flotation, bubble absorption, and dimensions of reaction spaces. 

As followed from the results, represented in Sections 8.7.1 through 8.7.5, the combination of filtration and flotation processes of water treatment under recirculation conditions has a great potential to reduce the number and size of functional units of required equipment in comparison with direct-flow devices. This is the first essential advantage of the created system. 

The second advantage is the use of positive feedbacks that are arisen in the system at the recirculation mode of action due to saturation of filtered water with oxygen of air and effective removal of products of microbial metabolism, as described in Sections 8.5 and 8.6. The scheme of combined filtration-flotation device that operates continuously, under recirculating conditions (rotating wheel), is shown in Figure 8.14. In this device, the processes of filtration, bioflltration, bubble aeration (exchange absorption), and bubble-film extraction are realized in a common reaction space, separated by the unit case 1. The centrifugal pump 2 is used to ensure the circulation of treated... 

FIGURE 8.14 The scheme of filtration-flotation device. 1 unit case 2 centrifugal pump 3 drainage device 4 sand 5 pump inlet line 6 ejector 7 bubbling compartment 8 bubble-film extractor 9 water inlet 10 UV sterilizer 11 water outlet. 

Saturation of filtered water with oxygen of air and withdrawal of surfactant inhibitors of microbial metabolism lead to growth of biomass within the filter sand, and thns the sand filter is transformed into the biofilter. Thus, the positive feedback is realized between the functional units of the complex filtration-flotation device. The contribution of these components to the efficiency of water purification under recirculation conditions depends upon the age and form of the species of biofouling and also upon the presence of impurities in the filtered water flow, which are the substrate supply for bacteria [19]. 

---