Chemical treatment for clarifiers

Chemical addition is typically used with clarification to improve both the utility and performance of the unit operation. Coagulants and flocculants are generally used to improve the ability to settle particles in the clarifier. Jar tests are used to determine the proper dosage of chemicals and streaming current detectors or turbidity monitors are used to monitor performance and control chemical dosage. Chlorine is often used to improve the removal of organics and color in the clarifier. Chlorine also provides disinfection of the make-up water to prevent the clarifiers from going septic. 

The performance of inorganic coagulants depends on pH. The performance of alum is optimum at pH 6.0 - 7.0 (with an optimum at PH = 6), while ferric coagulants can be used over a broader pH range, from 5.0 -11.0 (with an optimum at pH = 8). 

Flocculation is the agglomeration of charge-neutralized particles into larger particles. Unlike coagulation, rapid mixing is not required for flocculation to take place. It typically occurs in the reaction chamber or slow mix zone of the clarifier. 

Chlorine is usually added upstream of a clarifier to oxidize organics, to improve the removal of color in the clarifier, and to control 

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Points of Chemical Addition In independent physical-chemical treatment or in phosphate removal in the primary clarifier ahead of biological treatment, chemicals are added to raw sewage. In tertiary treatment for phosphate removal and suspended solids (SS) reduction, they are added to secondary effluent. In both cases, proper mixing and flocculation units are needed. For phosphate removal or improvement of SS capmre in biological secondary treatment, chemicals are often added directly to aeration units or prior to secondary settling units, without separate mixing and flocculation. In some phosphate removal applications coagulants are added at... 

Conventional chemical treatment of metal finishing wastes will usually produce clarified effluent acceptable for discharge however, in those applications where it is desirable or necessary to recover the clarified rinse water for re-use, the technologies are utilized to purify or "desalt" the effluent for re-use. 

Another chemical treatment that has resurged recently due to improvements made in its formulation is the hydroxymethylated resorcinol (HMR). HMR has been used successfully with several timbers and adhesives, to promote the exterior durability of their bonded joints [65, 71]. Consequently, this technique seems ready for industrial application, at least for the species and adhesives tested. Nevertheless, studies to clarify some aspects of its action mechanism are still needed [20]. 

Alternative Clarification Processes. The discussion so far has assumed the use of a single conventional clarifier, with a cylindrical body and conical bottom with a thickening rake, in continuous operation. In small plants, the rake may be eliminated the use of a conical bottom for easy removal of the sludge is then very important. In very small plants, clarification may be a batch process, often in the same tanks used for chemical treatment. Very large clarifiers, on the other hand, are sometimes rectangular... 

The first two categories, clarifying and crossflow filters, have been very well developed and optimized for use in biotechnology and standard wastewater treatment applications. Equipment is easily available for these applications, whether as small 0.2 micron sterilizing filter used to terminally sterilize 100 ml of product solution, or a small 500 ml crossflow filter used to concentrate a small amount of antibody solution. Many vendors of this equipment to wastewater treatment applications have their origins in the CPI (Chemical Process Industries), and have incorporated many of the scale-up and optimization properties developed in much larger units used in large scale chemical production. As a result, these two filtration unit operations are one of the most optimized and efficient used in wastewater treatment. 

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