spread on the media plates through sludge inlet line valved discharge ports. Prior
to this discharge, polymer is injected into the sludge and rapidly mixed at the
begins as the bed is filling. The clear liquid, separated from the flocculated
solids flows down through the porous media, through the support plenum and out of the bed
After the bed is filled to maximum liquid level,
the conditioned sludge feed is shut off.
The vacuum pump is started creating a vacuum in the
plenum and media causing a uniform pressure on top of the cake.
Motorized filtrate drain valves automatically
controlled by level sensors discharge the filtrate from the plenum of the VSDB.
Typically, filtrate suspended solids are less than 30 mg/l, indicating very high solids
capture in the dewatered sludge.
As the sludge continues to consolidate and shrink,
the resulting cake will start to crack. This will continue until the bed is
uniformly cracked and the vacuum gradually lost. As the plenum area loses vacuum the
vacuum pumps shut down.
The stop-gates can now be removed to allow a
front-end loader access to the bed to remove the dewatered sludge. The surface is
then washed down with high pressure, low volume water. This washdown water is
discharged to the sewer or directed back to the head of the plant.
Following cleaning, the stop-gates are placed back
into position and the facility is ready for another dewatering cycle. A complete
dewatering cycle is typically 24 hours.