Solids removed form the various clarifiers must be thickened to remove excess liquid and increase the concentration of solids prior to "digestion". Sludge enters the gravity thickener . Solids begin to settle into a sludge blanket at the bottom. Moving rakes and vertical pickets, which keep the sludge moving toward the center well, where it is discharged to the digester, gently agitates the concentrated sludge.

Aerobic digestion takes place in an open tank where primary sludge is aerated. chemicals are added to coagulate the aerobically digested sludge in a conditioning tank before the filter press.

After excess water is removed by the filter press, the biosolids are stabilized and conditioned for beneficial use as a fertilizer. Approximately 75% of the biosolids produced at the Pennridge Wastewater Treatment Authority are land applied.

Sludge press.	Here is the final product. the solids are dehydrated and made into fertilizer which can be sold.