Additives flocculants

If additional flocculation is required, use lime or calcium chloride. The water at suction should be as clean as possible. 

Partial recycling of treated water after biological treatment will usually require additional polishing (tertiary treatment). This may include chemical addition, flocculation, and DAF. This is BAT according to the EC.38... 

Polymer Concentration. The effect of polymer dosage on additional flocculation responses was measured together with adsorption... 

The optimum pH for flocculation is about 6.5 to 7.5 for aluminum salts and about 8.5 for iron salts. If the natural alkali content of the untreated water is insufficient to neutralize the acid formed, alkali has to be added (e.g. calcium hydroxide or sodium hydroxide). In addition flocculation aids such as poly(acrylamide) or starch derivatives may be added (not in the case of potable water production). When aluminum sulfate Al2(S04)3 I8H2O is used 10 to 30 g/m- is added. The very fine hydroxide flakes which precipitate are positively charged and adsorb the negatively charged colloidal organic materials and clay particles. 

Coagulants may be either organic such as polyelectrolytes or inorganic such as alum. Coagulants can be used alone or in conjunction with flocculants to improve the performance of the flocculant or reduce the quantity oF the flocculant required. In some systems, where a flocculant has been used in an upstream process, a coagulant may be needed to allow additional flocculant to be effective. 

Fig. 6 Different types of interaction between PC and PA in the presence of particles, depending on the amount of PC and the order of addition (a) low amount of polycation, (b) higher amount of PC (than in a), formation of PEC as an additional flocculant, (c) dosage of PC and PA at the same time...

Fig. 5 Effect of electrolyte addition (flocculation with NaCl) on the stability of a silicon oil emulsion (p = 30% m/m, emulsions, just prepared). Creaming kinetics at llOOg displayed as movement of the boundary separating water and creaming emulsion...

It exhibits distinctive physical properties, such as adhesive ability, the capacity to form fibers, and the capacity to form thin and biodegradable film, which is transparent and highly impermeable to oxygen [251]. Other applications of pullulan include blood plasma substitutes, food and cosmetic additives, adhesive additives, flocculants, resins, and environmental remediation agents [246, 252, 253]. 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

A fourth mechanism is called sweep flocculation. It is used primarily in very low soflds systems such as raw water clarification. Addition of an inorganic salt produces a metal hydroxide precipitate which entrains fine particles of other suspended soflds as it settles. A variation of this mechanism is sometimes employed for suspensions that do not respond to polymeric flocculants. A soHd material such as clay is deUberately added to the suspension and then flocculated with a high molecular weight polymer. The original suspended matter is entrained in the clay floes formed by the bridging mechanism and is removed with the clay. 

Addition Point. The flocculant addition point in a continuous system can also have a significant effect on flocculant performance. The turbulence as the flocculant is mixed in and the floes travel toward the point where they enter the thickener or filter causes both the formation and breakup of floes. Usually there is an optimal addition point or points which have to be determined empirically. In cases where the same polymer is being added at two or more points, the relative amounts added at each point may also affect performance. Thus providing multiple addition points in the design of new installations is recommended (56). 

In the area of municipal and iadustrial wastewater treatment, the principal environmental issue is the toxicity of residual flocculating agents ia the effluent. Laboratory studies have shown that cationic polymers are toxic to fish because of the iateraction of these polymers with giU. membranes. Nonionic and anionic polymers show no toxicity (82,83). Other studies have shown that ia natural systems the suspended inorganic matter and humic substances substantially reduce the toxicity of added cationic polymer, and the polymers have been used successfully ia fish hatcheries (84—86). Based on these results, the EPA has added a protocol for testing these polymers for toxicity toward fish ia the presence of humic acids (87). The addition of anionic polymers to effluent streams containing cationic polymers to reduce their toxicity has been mentioned ia the patent Hterature (83). 

The Vepex process developed in Hungary (Table 9) involves disintegration of plant materials followed by double screw pressing to maximize juice production. Green chloroplastic protein is removed by direct steam-injection heat treatment at 82°C with the addition of flocculents and centrifugation. The white protein fraction is separated from the chlorophyU-free process juice by direct steam injection at 80°C, followed by centrifugation and drying (94). 

In the production of opalescent or natural-type apple juice, ascorbic acid is added to the fmit pulp before pressing, or to the juice as it comes from the press, to retain more of the apple flavor (4). Ascorbic acid addition and pasteurization of the juice as soon as possible after pressing prevent polyphenol oxidation, which causes browning and contributes to pulp flocculation. 

Gums are used in industry because their aqueous solutions or dispersions possess suspending and stabilising properties. In addition, gums may produce gels or act as emulsifiers, adhesives, flocculants, binders, film formers, lubricants, or friction reducers, depending on the shape and chemical nature of the particular gum (2). Considerable research has been carried out to relate the stmeture and shape (conformation) of some gums to their solution properties (3,4). 

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