The Gravity Belt Thickeners are designed to thicken the waste activated sludge (WAS) which comes from the final clarifiers. To aid in de-watering the sludge, a chemical called "polymer" is added to the sludge at the front of the GBT. The sludge and the polymer become bonded to each other thus causing "flocculation," where the solids start to separate from the liquid. The sludge and polymer flow onto a moving belt where the water and sludge start to separate. The water falls through the porous weave of the belt leaving the sludge behind. The water drains to a pan below the belt and is pumped back to the beginning of the treatment process. The sludge moves with the belt and is turned continuously by plow-like devices called chicanes. The chicanes move the sludge back and forth allowing the water to fall through the belt to the drain. Near the end of the belt a ramp contacts the belt at its leading edge, forcing the sludge to go up and over the ramp. This action causes the sludge to roll back on itself. This rolling motion cases further dewatering of the sludge. The ramp is adjustable to further enhance the thickening of the sludge. The thickened sludge is sent next to the Belt Filter Presses.