SLUDGE THICKENER

Sludge Thickening:

Gravity thickening is accomplished in circular sedimentation basins similar to those used for primary and secondary clarification of liquid wastes

The sludge thickener shall be used to store and gravity thicken sludges from the waste treatment processes. Settled sludges shall be mechanically raked to the center of the tank and discharged on an as needed basis to the sludge compaction system via air diaphragm sludge pumps. Water content in sludge can be reduced by mechanically compressing sludge in filter press, belt press etc. this can also be achieved by centrifuge mechanism and also by other mechanical devices.Solids coming to the thickener separate into three distinct zones. 1.The top layer is a relatively clear liquid. 2.The next layer is the sedimentation zone.3.In the thickening zone, the individual particle of the sludge agglomerate. A sludge blanket is maintained in this zone where the mass of sludge is compresses by material continuously added to the top. Excess supernatant will gravity flow from the tank with provisions for manual decanting of waters via valves located on the side of the tank.

Rack mechanism:

The equipment includes: A rotating bottom scraper arm Vertical pickets A rotating scum-collecting mechanism with scum baffle plates An overflow weir

The thickener mechanism has a shaft supported on top by bush and hung from central scrapper bridge cum walkway. Top of the shaft is connected to gearbox output by small gear. The shaft shall have rake arms on both the sides. The scrapper blades are fixed on scrapper bridge arm bottom. The blades scrape, push and demoisturize the sludge. The blades shall push the sludge to central sludge pit. The gear train with which the top of the shaft is connected shall consist of motor, gear and related drive assemblies

The design criteria for gravity thickeners include the following:

Generally, the sludge thickeners are designed with a side water of depth 3-4 m and a detention period of 24 h. The hydraulic loading rates of16-32 m3/m2.d for primary sludge, 4-8 m3/m2.d for waste activated sludge, and 6-12 m3/m2.d for combined sludge are used.

The slope of the bottom floor is generally 2:12 to 3:12, which is steeper than for standard settling tanks.