Читать книгу Automation of Water Resource Recovery Facilities - Water Environment Federation - Страница 245

Scum is typically pushed to one section of the primary tank surface by flights or a surface rake for removal. From that section, the scum drops by gravity into a scum pit. The drop may be caused by a slotted pipe (scum trough) that rotates down for the scum to enter the pit or a beach where the rake pushed the scum up and into the drop pipe during each rotation of the rake. Scum is typically pumped from the pit to the solids processing section of the facility. The scum pit might have a mixer that allows mixing of the scum before pumping. Like primary sludge, scum must be thin enough that it can be pumped, but not so thin that downstream processes are overloaded. Scum must also have a limited retention time to avoid septicity.