If the grinder is in use it will grind any solid material entering the plant. Either of these processes ensures that large material won't block pipes or jam equipment. The next step in preliminary treatment is to remove grit. Grit contains material like sand which is abrasive to equipment and must be removed. This is accomplished by sending the wastewater to one of six grit channels.
Air is added here to reduce foul odors that are are often associated with sewage.
After grit has been removed the wastewater flow will enter the primary treatment process. This is accomplished with the six primary clarifiers at the Appleton Wastewater Treatment Plant. With this condition, settable solids will now deposit on the tank's floor while oils and scums will float. Both materials are sent to the anaerobic digesters for solids treatment. The liquid portion of the wastewater flows to secondary treatment.