Flocculation chemicals

The degrees of clarification of both clarifiers are the same with the same flocculating chemical addition. 

Iron (II) chloride solution, for possible treatment in a pyrolysis plant or, more probably, for the production of flocculation chemicals used in sewage water treatment... 

Less coagulation or flocculation chemicals are required in the treatment processes. 

Xiao, J., and Zhou, Q. (2005). Natural Polymer Flocculants. (Chemical Industry Press, Beijing). 

Flocculation. The mechanisms involved in flocculation are quite different from those in coagulation. The flocculant chemical is a long-chain polymeric molecule and some... 

Flocculant Reagents. Natural polymer flocculants have been known and used for centuries. Some exanq>les are i glass used in beer fining, ghies, gelatin and starches in the mineral industries, and al ates, firom seaw, used in water treatment. The market for these materials has bear challenged by the rise of the flocculant chemical industry hich has produced materials which are cheaper and more reliable. 

In today s world of waste treatment, bubble and foam separations lemain lelatively little used techniques. Dissolved or induced air flotation is the most commonly used variation, havii been enqiloyed for many years in the treatment of wastewaters for the separation of suspended sc, oils, greases, fibeis, and other iow-density solids as well as fbr the thickening of activated sludge and flocculated chemical sludges. The most active commercial use was and is in ore flotation—as discussed in Chapter 16. The potential Cor the use of these separation techniques, however, is veiy high in both the areas of traditional and hazardous waste management. 

Comparative testing in the beakers of a particular jar test apparatus is, however, vahd due to the identity of stirring conditions. So the effects of various doses of flocculating chemicals, of different pH conditions, and of different types of chemicals (e.g. indifferent electrolytes, aluminium or ferric salts, various polyelectrolytes) can be determined. Usually, an optimum is required and this relates to the formation by flocculation of a separable suspension. 

There are two reasons why there is always an excess of water present in the paper machine loop. First, the paper machine loop is continuously fed with fresh water, used for spraying and chemical dilution. Secondly, the incoming water content of the stock is higher (consistency 12-30%) than the water content in the sheet after the press section (consistency up to 50% and more). This excess water is sent, in the form of clear filtrate, from the save-all unit backwards, as make-up water, to the stock preparation, thus following the counter current principle. This make-up water is often additionally treated in a DAF with coagulation and flocculation chemicals in order to remove detrimental substances before feeding it backwards. 

Figure 21.5 Examples of the effect of adding flocculation chemicals, (a) Before using flocculants (compliments of Ten Cate) (b) After using flocculants (compliments of Ten Cate) (c) Flocculated versus nonflocculated sediments (authors).

The raw water, enriched with flocculant chemicals, flows into the bottom part of the reaction tank, causing an upward spiral current. The settled matter in the form of a sludge is periodically removed from the reaction tank by means of a ring conduit placed near the bottom of the settling tank. The pre-clarifled water then flows down into the automatic gravity filter from the top of the water surface level of the reaction tank. By its own head the water moves down through the Alter layer and out to service. 

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. 

Korpijarvi, J,Laine,E and Alhstedt,H,Eds. (2000). Using CFD in the study of mixing in coagulation and flocculation. Chemical Water and Wastewater Treatment VI. Berlin, Springer-Verlag. 

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