What is the KSD? Plant tour Rates News & announcements Agenda Specifications Year end report & audit Home Town of Kennebunk		Primary clarifiers This is a close-up picture taken from above the primary clarifier showing two filters the wastewater passes through before leaving the clarifier. The inner ring, called the "scum ring" skims oil and other floating matter from the top of the water, which must flow underneath it. On the edge of the clarifier are a series of gates, or weirs, that help catch other floating debris while allowing water to flow through the gaps between the teeth. Return to primary treatment