AWWA M37:2000 pdf download.Operational Control of Coagulation and Filtration Processes
The purpose of the initial mixing phase in a jar test is to completely disperse the primary coagulant into the raw water flow stream in a fast and uniform manner. This mixing makes the coagulation process as effective as possible. The term initial mixing is intended to apply to the point at which the primary coagulant is added to the water. Hydrolysis takes place almost instantaneously during the addition of the coagulant, Complete floc development, on the other hand, may take several minutes. Two commonly used terms for initial mixing- rapid mixing and flash mixing- -are often used interchangeably. When conducting a jar test, the time the mixer runs at rapid mix should be equivalent to the effective retention time of the mixing chamber in the treatment plant. If possible, Gvalues should match full-scale conditions, as well. Figure 1-1 illustrates how turbidity and TOC removal in jar testing can vary with mixing speed. Apparently, for the water supply in the figure, a G value of 90 s-l simulates the full- scale conditions best. Flocculation Flocculation refers to a gentle mixing process that occurs in the flocculation basin. A primary objective of the water treatment process is to destabilize and condition the particulate matter in water chemically and physically to encourage settling and/or filtration. Particle destabilization is caused by coagulant addition. The subsequent increase in the size of particles results in the development of floc through the process called flocculation. A properly designed and performed set of jar tests can give the operator a tremendous advantage in determining the correct coagulant and dose for developing the optimum floc. The word floc originates from the Latin root word floccus, and it describes a grouping of solid particles with a woolly appearance.AWWA M37 pdf download.