Coagulation chemicals

Foam Products. Latices are made into foams for use in cushioning appHcations. The latices are frothed with air and then chemically coagulated for thick appHcations, or heated to induce coagulation for thinner appHcations. The latter method allows for infinite pot life during production (see Foamed plastics). 

Inorganic and organic coUoidal suspensions in wastewater can be removed by chemical coagulation. Coagulation has been defined as the addition of... 

The first five of these techniques involve deformation and this has to be followed by some setting operation which stabilises the new shape. In the case of polymer melt deformation this can be affected by cooling of thermoplastics and cross-linking of thermosetting plastics and similtir comments can apply to deformation in the rubbery state. Solution-cast film and fibre requires solvent evaporation (with also perhaps some chemical coagulation process). Latex suspensions can simply be dried as with emulsion paints or subjected to some... 

Floe Clumps of bacteria and particulate impurities or coagulants that have come together and formed a cluster. Found in aeration tanks and secondary clarifiers. Flocculation The process of forming floe particles when a chemical coagulant or... 

Polymer A chemical formed by the union of many monomers (a molecule of low molecular weight). Polymers are used with other chemical coagulants to aid in binding small suspended particles to form larger chemical floes for easier removal from water. All polyelectrolytes are polymers, but not all polymers are polyelectrolytes. 

The nature of chemical coagulants are such that the macrofloc may possess certain charges for example lime (CaO), alum (A1203) and flocculating polyvalent cations cany positive charges, which interact with proteins. The interactions are simply illustrated in Figure 7.6. 

This facility produces 110 m2/h of enameled steel and operates 4000 h/yr. It uses 0.0042 m3 water/m2 of product in coating operations. Average process water flow is 1.69 m3/h for coating operations and 0.466 m3/h for metal preparation. The primary in-place treatment is chemical coagulation and clarification. Clarification can be either settling or dissolved air flotation. 

This plant produces 290 m2/h of enameled aluminum for 6400 h/yr. It uses 0.018 m3 water/m2 product for coating and ball milling purposes. The average process flow rate is 12.5 m3/h for metal preparation and 1.59 m3/h for coating and ball milling. In-place treatment consists primarily of chemical coagulation, clarification (settling), and final pH adjustment. 

This facility produces 9.1 m2/yr of porcelain enameled cast iron. The primary in-place treatment for process wastewater is chemical coagulation, clarification (settling), and skimming. 

Sedimentation and dissolved air flotation are the most common clarification processes for removal of precipitates. Either sedimentation or flotation is often preceded by chemical coagulation or precipitation, which converts dissolved pollutants to a suspended form, and by flocculation, which enhances clarification by flocculating suspended solids into larger, more easily separating particles. Simple sedimentation normally requires a long retention time to adequately reduce the solids content. The detention time of dissolved air flotation, however, is much shorter. When chemicals are used, retention times are reduced and clarification removal efficiency of either sedimentation or flotation is increased. A properly operated clarification system is capable of efficient removal of suspended solids, metal hydroxides, and other wastewater impurities.10-12... 

In this treatment process, unit operations such as chemical coagulation, flocculation, and sedimentation followed by filtration, activated carbon, ion exchange, and reverse osmosis are employed to remove significant amounts of nitrogen, phosphorus, heavy metals, organic matters, bacteria, and viruses present in wastewater.2 It is always the last process step in the wastewater treatment plant that finally renders the treated wastewater reusable and disposable into the environment without any adverse effect (Figure 22.1). 

Amoo, I.A., Amuda, O.S., Ipinmoroti, K.O., and Ajayi, O.O., Performance optimization of some chemical coagulants/flocculants in the treatment of wastewater from food industry, Science Focus, 11 (1), 38-45, 2006. 

The basic unit operations/processes required for treating the acid pickling wastewater are (a) neutralization with NaOH and/or lime to increase the pH and (b) physicochemical methods, such as chemical coagulation, precipitation, clarification (sedimentation or DAF), and filtration to remove BOD5, COD, and iron. 

Chemical processes include reduction and oxidation. Conventional chemical (coagulation-flocculation) and advanced oxidation processes (AOPs), such as chemical oxidation (ozonation, Fenton oxidation, Fe2+/H202), ultrasonic chemical oxidation, photocatalysis oxidation (UV/H2Q2, UV/O3, and W/O3/H2O2),... 

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

Design and operational variables Chemicals Coagulation aids, media size, sludge recirculation Energy input, mass transport Residence time filter length and media diameter... 

Vieno N, Tuhkanen T, Kronberg L (2006) Removal of pharmaceuticals in drinking water treatment effect of chemical coagulation. Environ Technol 27 183-192... 

Treatment of selected waste streams by activated carbon, ion exchange, electromembranes, chemical coagulation, sand, and dual and multimedia filtration. 

Several physico-chemical methods are available for the treatment of pulping and pulp bleaching effluents. The most prominent methods are membrane separation, chemical coagulation, and precipitation using metal salts and advanced oxidation processes. 

Solvents, extender oils, and insoluble monomers are used throughout the rubber industry. In addition, miscellaneous oils are used to lubricate machinery. Laboratory analysis indicates the presence of oil and grease in the raw wastewater of these plants. Oil and grease entering the wastewater streams are removed by chemical coagulation, dissolved air flotation, and, to some extent, biological oxidation. 

In the early 1900 s, the rapid sand filter was introduced, together with chemical coagulation and periodic backwashing of the filter. Effective size of the rapid sand filter media might vary from 0.3S to 1.0 mm typical size is 0.5 mm. This type of filter has demonstrated the ability to remove effectively applied suspended solids of 5 to 10 ppm at flow rates of 2 to 3 gal/min per square foot of bed area. 

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