Pretreatment chemicals flocculants

Filtration is often referred to as mechanical separation because the separation is accompHshed by physical means. This does not preclude chemical or thermal pretreatment used to enhance filtration. Although some slurries separate well without chemical conditioning, most pulps of a widely varying nature can benefit from pretreatment (see Flocculating agents). 

Pretreatment Chemicals Even though the suspended solids concentration of the slurry to be tested may be correct, it is frequently necessary to modify the sluriy in order to provide an acceptable filtration rate, washing rate, or final cake moisture content. The most common treatment, and one which may provide improvement in all three of these categories, is the addition of flocculating agents, either inorganic chemicals or natural or synthetic polymers. The main task at this point is to determine which is the most effective chemical and the quantity of chemical which should be used. 

Chemical pretreatment is often used to improve the performance of contaminant removal. The use of chemical flocculants is based on system efficiency, the specific DAF application and cost. Commonly used chemicals include trivalent metallic salts of iron, such as FeClj or FeSO or aluminum, such as AISO. Organic and inorganic polymers (cationic or anionic) are generally used to enhance the DAF process. 

Chemical-oxidation treatments of wood preserving wastewaters containing phenols have been successfully conducted on both a laboratory and commercial scale using either chlorine or a chlorine compound, principally calcium hypochlorite. Its effectiveness varies with the type of phenolic compound in the effluent, either cresols from creosote treatments or pent achlorophenol from treatments enploying that chemical. Also influential in this regard are effluent pH, the effectiveness of pretreatment, particularly flocculation and filtration, and the amount and type of organic materials other than phenols present in the wastewater. 

Other pretreatment chemical feeds These include coagulants and flocculants. What is the nature of the chemical(s) being fed, the dosage, and how is the dosage controlled ... 

Continuous DAF system may not need the air saturation tank. The compressed air is injected in the recycle stream of the treated effluent. In this case, the control valve settings are done on basis of an almost constant characteristic of incoming effluent. This needs a sufficiently large equalisation tank and may also need chemical pretreatment by flocculants. 

A large number of commercial coagulants and synthetic flocculants are available with which to pretreat suspensions. While newer products have displaced the use of more traditional chemicals in recent years, few have been eliminated completely from the marketplace. The more important and widely used pretreatment chemicals are described here. 

Add flocculants or pretreatment chemicals as necessary (more information on the choice of pretreatment chemicals can be found in... 

Keywords Additional discharge streams Antisealants Chemical treatment Coagulation/flocculation Concentration factor Dechlorination Filtration High recovery Membrane cleaning Pretreatment Recovery rate... 

The purification operation starts with addition of chemicals to precipitate arsenic and sulfate in a pretreatment step. The acid is then cooled and left for an appropriate aging time. A flocculent is added and the solid content is allowed to flock (precipitate) in a clarifier. 

Traditional pretreatments make an extensive use of chemicals (NaCIO as disinfection, FeCl3 as flocculants, H2S04 as antiscaling agent) and mechanical filtration units (sand filtration, media filtration, cartridge filtration). 

Depending on the nature of the product, pretreatment of the feed material may be desirable to improve the separation characteristics. Possible techniques are based on chemical or physical treatment and include thickening, flocculation, and coagulation. A simple heat treatment process where the temperature of the broth is elevated and held for a period of time can reduce... 

After a pretreatment step, followed by a preozonation, a physico-chemical process (coagulation-flocculation, settling and sand filtration) removes the suspended solids and colloids of water. Then the dissolved organic compounds are oxidised and adsorbed with their by-products on active carbon. Before leaving the plant, a last oxidation step allows the disinfection of the produced water and to assure its sanitary protection along the distribution network, until its consumption. 

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