Organic Flocculants

Organic flocculants and selective flocculation technology are emphatically introduced in this chapter. 

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Organic Flocculants. The organic flocculants are all water-soluble natural or synthetic polymers. 

The same questions about the safety of organic flocculants have been raised ia other countries. The most drastic response has occurred ia Japan (7,77) and Swit2edand (77) where the use of any synthetic polymers for drinking water treatment is not permitted. Alum and PAC are the principal chemicals used ia Japan (7). Chitin, a biopolymer derived from marine animals, has been used ia Japan (80,81). Maximum allowed polymer doses have been set ia Prance and Germany (77). 

The same questions about the safely of organic flocculants have been raised in olher countries. The most drastic response has occurred in Japan and Switzerland w here the use of any synthetic polymers for drinking water treatment is not permitted... 

One of the promising new technologies for separation of very fine particles is selective flocculation. The selective flocculation process has been used effectively to separate very finely disseminated minerals from mixed ore suspensions (5.). The process is based on the preferential adsorption of an organic flocculant on the wanted minerals, thereby flocculating them, while leaving the remainder of the suspension particles dispersed. The dispersion of certain components in the suspension such as pyrite can be enhanced by using more selective or powerful dispersants. Methods for achieving selective flocculation and dispersion have been recently described by Attia (6j. 

Our results show that the adsorption on suspended matter is increased in the presence of suspended humic acid (Figure 10). This is supported by the finding of other authors (53,54) showing that organic flocculant coatings greatly affect the cation exchange capacities of sediment and suspended matter. 

Minerophilic groups of organic flocculants can be classified into the following four categories based on the interaction forces of minerophilic groups with particle surface. 

The materials being used as flocculating agents can be broadly divided into two categories, inorganic and organic. The organic flocculants include... 

Class B—organic flocculants soluble in water, adsorbed on cement grains and increasing viscosity by electrostatic attraction. To class B belong styrene copolymers with carboxylate groups, synthetic polyelectrolytes and natural rabbets. 

Other Organic Flocculants and Selective Polymer Flocculation... 

Silica is hydrophilic, although under conditions where salts cause coagulation it has been classed as somewhat hydrophobic. The terms are not of much significance in relation to silica, except when organic flocculating agents are involved, where their adsorption on the silica surface makes the surface definitely hydro-phobic. 

These fines air bubbles are produced by recycling a fraction of the water clarified by flotation (20 to 50%) at a pressure of 4 to 6 bar. Compressed air is dissolved in the water to saturation (in what is called a pressurizing drum), then the water is expanded in contact with the flocculated raw water and at flotation cell backpressure (0.2 to 0,4 bar). Expansion and mixing with flocculated water should be performed with care. The delicate floe must in no case be sheared. This is why the design of potable water flotation cells (where the use of organic flocculants is sometimes prohibited, whereas the floe is labile), is very different from the design of WW flotation cells. 

Presence of cationic or anionic surfactants, such as sulfonates in fairly low concentrations. Excessive use of demulsifying reagents or certain organic flocculants during a prior step in the treatment sequence. 

Increased surface loads for secondary settlers by making them deeper, building a degassing prechamber or using an organic flocculant. 

The most cost-effective process from the standpoint of investment consists in distributing a nonionic or cationic organic flocculant at the inlet of the existing secondary settler. 

Table 6.2 Optimal dose and optimal pH range for inorganic and organic flocculants...

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