Sediments flocculation

J. Gregory, in B. M. Moudgil and P. Somasundaran, eds.. Flocculation, Sedimentation and Consolidation, American Institute of Chemical Engineers, New York, 1985, pp. 125-138. 

Precipitation is nonselective in that compounds other than those targeted may be removed. Both precipitation and flocculation are nondestructive and generate a large volume of sludge which must be disposed of. Coagulation, flocculation, sedimentation, and filtration, are typically followed by chlorination in municipal wastewater treatment processes. 

Coagulation, flocculation, sedimentation, and filtration will remove many contaminants. Perhaps most important is the reduction of turbidity. This treatment yields water of good clarity and enhances disinfection efficiency. If particles are not removed, they harbor bacteria and make fmal disinfection more difficult. 

Content uniformity and long-term stability of a pharmaceutical product are required for a consistent and accurate dosing. Aggregation of dispersed particles and resulting instabilities such as flocculation, sedimentation (in suspensions), or creaming and coalescence (in emulsions) often represent major problems in formulating pharmaceutical disperse systems. 

It should be noted that in all cases the size (and hence cost) of end-of-pipe treatment has a direct relationship to both the volume of effluent to be treated and the concentration of pollutants contained in the discharge. For example, the size of most physicochemical reactors (balancing, neutralizing, flocculation, sedimentation, flotation, oxidation, reduction, etc.) is determined by hydraulic factors such as surface loading rate and retention time. 

Pretreatment is necessary for the treatment of the food industry wastewater. Pretreatment options such as flow equalization and neutralization, screening, FOG separation, acidification, coagulation-flocculation, sedimentation, and DAF are available. Selecting the appropriate technology depends on the wastewater characteristics. 

Dow seawater A process for extracting magnesium from seawater. Calcined dolomite (CaO-MgO, dololime), or calcined oyster shell, is added to seawater, precipitating magnesium hydroxide. This is flocculated, sedimented, and filtered off. For use as a refractory it is calcined for the manufacture of magnesium chloride for the manufacture of magnesium metal, it is dissolved in hydrochloric acid. Developed by the Dow Chemical Company and later operated by the Steetly Company in West Hartlepool, UK, and Sardinia. 

Chemical coagulation — flocculation sedimentation Coalescers Membrane processes Biological processes Carbon adsorption Inorganics Organics... 

Physicochemical treatment of pharmaceutical wastewater includes screening, equalization, neutralization/pH adjustment, coagulation/flocculation, sedimentation, adsorption, and ozone and hydrogen peroxide treatment. Detailed descriptions of the various physicochemical treatment processes are described in the following sections. 

Metallic ions in soluble form are commonly removed from wastewater by conversion to an insoluble form followed by separation processes such as flocculation, sedimentation, and filtration. Chemicals such as lime, caustic soda, sulfides, and ferrous or ferric compounds have been used for metals separation. Polymer is usually added to aid in flocculation and sedimentation. 

FIGURE 4.36 Sedimentation volumes for (a) cake and (b) flocculated sediments. 

The EPA Surface Water Treatment Ruse (SWTR) requires public water supplies, under the direct influence of surface water, to be disinfected. Some disinfectants produce chemical by-products SWTR requires that their concentration remain within the MCL. Currently, one such by-product is trihalomethanes. Water disinfection is effective when combined with conventional treatment, such as coagulation, flocculation, sedimentation, and filtration. The latter is accomplished by sand or diatomaceous earth. The effectiveness of disinfection is evaluated by determining total coliform bacteria which are not pathogenic, but their presence suggests that certain pathogens may have survived. The various chemicals commonly used as disinfectants are presented below and some of their advantages and disadvantages are listed. 

Watanabe, Y., Sh. Kasahara, and Y. Iwasaki (1997). Enhanced flocculation/sedimentation process by a jet mixed separator. Water Science Technol. Proc. 1997 Workshop on lAWQ-IWSA Joint Group on Particle Separation, July 1-2, Sapporo, Japan, 37, 10, 55-67. Elsevier Science Ltd., Exeter, England. 

For CFC-based suspension formulations, a surfactant was typically included. A variety of surfactants were used in these systems, e.g., lecithin, oleic acid, sorbitan trioleate. " All these surfactants were freely soluble in the CFC propellants and allowed for a degree of control over the suspension characteristics. Rates of flocculation, sedimentation, and creaming could be controlled and deposition on the internal container components was minimized. The transition to HFA-based MDIs has created significant issues in that none of the surfactants, previously used with the CFC products are soluble in HFA propellants alone. Some formulations have still used these surfactants, but the addition of a cosolvent (ethanol) has been required to solubilize the surfactant. 

Based on laboratory jar testes, the optimum pH range for flocculation-destabilization was defined. Asbestiform fiber reduction during effluent treatment, after flocculation-sedimentation and filtration, was also evaluated. 

Mulheim, West Germany [lO] Surface water Ruhr River Ozonation (1) Flocculation Sedimentation Ozonation (2) Filtration GAC filtration Safety chlorination Adsorption of toxic organics A site for bio-oxidation of organics Carbon application 2nd stage of dual stage filter Particle size 0.5—2.5 mm Filter velocity 11—22 m/hr Bed depth 4 m... 

Choisy-le-Roi, France [8 ] Surface water Seine River Ozonation (1) Coagulation/flocculation Sedimentation Sand filtration GAC filtration Ozonation (2) Post chlorination Removal of taste Removal of organics which might form toxic chloro-compounds during post chlorination Two columns Contact time 15 miri. Vol per filter 117 m Filter velocity 9 m/hr Organics removal improved by 40%... 

When direct filtration is included in the water treatment process, disinfection credit can be taken by the filtration step for a 2-log inactivation of Giardia cysts and a 1-log inactivation of viruses. This means that the primary disinfectant must provide an additional 1-log inactivation of Giardia cysts and 3-log inactivation of viruses. In the specific instance of a conventional treatment process that includes coagulation, flocculation, sedimentation, and filtration, an inactivation credit of 2.5-logs for Giardia cysts and 2-logs for viruses may be taken. This means that the primary disinfectant must provide an additional 0.5-log inactivation of Giardia cysts but a 2-log inactivation of viruses. 

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). 

There are three processes by which the number of oil drops in an emulsion is decreased. These are Brownian flocculation, sedimentation flocculation and creaming. But it should be noted that if the absorbed film strength is quite high, flocculation may not necessarily result in coalescence. It is also important to note that flocculation which may be due to any of above three reasons is reversible, but coalescence which follows flocculation is irreversible. 

As described earlier, flocculation is a physical process used to encourage small particles to aggregate into larger particles or floe. It is an essential component of most water treatment plants in which flocculation, sedimentation, and filtration processes are integrated to effectively remove suspended particles from water. Chemicals (such as alum, polyelectrolytes, etc.) are usually added to achieve agglomeration among small particles in water. 

Moudgil, Brij M., and Somasundaran, P. (eds.). Flocculation, Sedimentation, and Consolidation, Proceedings of Engineering Foundation Conference, United Engineering Trustees, Inc., USA, 1986. 

Moudgil, B. and Somasundaran, R, in Flocculation, Sedimentation and Consolidation, AIChE, New York, 1987. 

Protozoa may become another problem of water treatment. Usually, removal or inactivation of Entamoeba has been the central problem, but recent investigations also concerns Giardia [43]. Proper coagulation, flocculation, sedimentation, and filtration can remove up to 99% of protozoan cysts slow sand filtration can remove Giardia cysts [16]. Improper operation of treatment facilities can cause outbreaks of water-borne illnesses caused by protozoa [44]. Chlorination and disinfectants such as chloramines and ozone can further reduce levels of protozoa [45-47]. 

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