Vacuuming settled solids from quiescent zones is one of the most common and effective methods for solids removal. Similar to vacuuming debris from swimming pools, suction is provided by head pressure from the water depth of the raceway or by a pump. Usually, a standpipe in each quiescent zone connects to a common pipe that carries the slurry mixture to the off-line settling basin. A flexible hose and a swivel joint are used to connect the vacuum head to the standpipe. Vacuum heads are commercially available, but most designs are homemade. Designs include slotted pipes, triangular heads, open hoses, and rectangular vacuum heads mounted on wheels. Where lift is required, it’s usually more efficient and cost effective to connect the pipes from the quiescent zones by gravity flow to a sump or lift station with a stationary pump, than to use a portable pump that is moved from one quiescent zone to another. One hundred gallons per minute is desirable to operate a 12 to 18-inch-wide vacuum head. Pump and pipe sales representatives can assist in proper sizing of pipes and pumps to ensure adequate suction at the vacuum head. Inadequate suction causes resuspension of the solids before they can be vacuumed and increases cleaning time.

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