Revolving Bridge Scrapers
Suspended solids in the influent, settle down to the bottom of the settling tank and continuously revolving peripheral drive scraper bridges move the settled sludge to the central sludge hopper. Revolving bridge scrapers shapes are designed as cage, low profile with handrail or high profile. Their lenghts are calculated based on tank diameter and they can be half bridge, extended bridge and full bridge type. Optionally, a surface skimming unit can be installed on the bridge, which moves the surface scum into a scum collecting box or trough.
Reciprocating Type Bridge Scrapers
Settling process, which is one of the most commonly used unit operation, sometimes is accoplished in rectangular shaped tanks. In such case, sludge settled on the bottom must be conveyed to the sludge hopper located at the inlet part of the tank. Scraper to be used for this purpose must be formed by a bridge which can run in both direction, scraper arm and blade which can be lowered and raised and a scum collection system. Bridge runs as bottom scraper raised when moving towards to outlet side of the tank. During the movement towards sludge hopper, scraper arm is lowered and sludge is pushed to the hopper. Operation mode of the scraper can be programed according to sludge quantity and type.
Suction Scrapers
Suspended solids in the influent, settle down to the bottom of the settling tank and settled sludge is sucked from the bottom by suction heads which are suspended from continuously revolving peripheral drive scraper bridges. Settling tanks which suction scrapers are installed in are built with flat bottom .Scrapers are suspended from a radial bridge which sometimes extends in cantilever over one third of opposite radius. The suction lift draught tubes discharge into partially submerged recovery tank mounted on the bridge. It is possible to regulate the flow from each suction lift by telescopic valves. Sludge transfer from the recovery tank to the fixed annular sludge extraction trough is equipped with a siphon system.
