Gravity clarifier

The natural process of bringing particles and polyelectrolytes together by Brownian motion, ie, perikinetic flocculation, often is assisted by orthokinetic flocculation which increases particle coUisions through the motion of the fluid and velocity gradients in the flow. This is the idea behind the use of in-line mixers or paddle-type flocculators in front of some separation equipment like gravity clarifiers. The rate of flocculation in clarifiers is also increased by recycling the floes to increase the rate of particle—particle coUisions through the increase in soUds concentration. 

The principal advantage of the tilted-plate clarifier is the increased capacity per unit of plane area. Major disadvantages are an underflow solids concentration that generally is lower than in other gravity clarifiers and difficulty of cleaning when scahng or deposition occurs. The lower underflow composition is due primarily to the reduced com-... 

There are three basic designs for clarifiers (also known as "gravity clarifiers") solids-contact, inclined-plate settlers, and sedimentation. The advantages of each type of unit are ... 

The PAC activated slndge system is a modified activated sludge process. PAC is added to the aeration tank where it is mixed with the biological solids. The mixed liquor solids are settled and separated from the treated effluent in a gravity clarifier. Polyelectrolyte will normally be added prior to the clarification step to enhance solids-liquid separation. If phosphorus removal is necessary, alum is often added at this point. Even with polyelectrolyte addition, tertiary filtration is normally required to reduce the level of effluent suspended solids. The clarifier nnderflow solids are continuously returned to the aeration tank. A portion of the carbon-biomass mixture is wasted periodically to maintain the desired solids inventory in the system. 

For nonflocculant suspensions, gravity clarifiers are sometimes used as for solids classification. The theoretical grade efficiency curve G(x) of the clarifier can be predicted, assuming laminar flow and no end effects, by... 

The largest user of gravity clarifiers is the water industry. Figure 5.2 shows a schematic flow sheet of a typical sewage treatment plant where two stages... 

As a final note on the design of gravity clarifiers, specific guidance can be found in the literature for applications in the water industry, for example on the secondary clarifiers such as the one in Figure 5.2. 

The gravity clarifier aims to remove as mnch sohd as possible from snspension in the hquid, and to produce a sohd underflow that is as fuUy dewatered as is possible... 

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