In septic systems, what is the function of scum?

The function of scum in septic systems is indeed to separate solids from liquids. When wastewater enters the septic tank, it undergoes a process of settling and separation. Heavier solids settle to the bottom and form sludge, while lighter materials, including fats, oils, and grease, float to the top and form the scum layer. This separation is crucial as it helps maintain the proper functioning of the septic system by keeping solids out of the drain field, where they could cause blockages and other issues.

Scum acts as a barrier that prevents some solids from re-entering the liquid effluent that flows into the leach field, thus aiding in the overall treatment of wastewater. Effective separation contributes to the decomposition processes that occur below the scum layer, supporting the biological treatment of the effluent.