The process of coagulation is one of the most important unit processes for nearly all water treatment plants. An integral part of coagulation is flash mixing (initial mixing). Chemical pretreatment using coagulant is the standard unit process in the field of water treatment and is considered to be a part of the process for tertiary filtration of secondary effluent and the combined sewer overflow. Industrial wastes also often require coagulants to achieve treatment goals.The purpose of flash mixing is to quickly and uniformly disperse coagulant throughout the process water. Dispersion time is ideally less than 1 s for metallic coagulants such as alum and ferric salts. The jet diffusion type flash mixing system achieves this difficult task using up to 25–30% less coagulant, and significantly reduces sludge production.

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