Page 21 - Simplified Wastewater Treatment Fundementals_Preliminary Treatment.exe

Preliminary Treatment

Differential and Control

During times of low to average flow rate, the screen mechanisms should be generally set to come on

every 10 to 15 minutes.

During time of high influent flow, screens should be operated continuously so as not to risk

accumulated debris forming a dam and causing a potential overflow.

During normal operations screens will accumulate a minor obstruction of rags and debris causing the

water level elevation upstream to be slightly higher then downstream. This is known as differential.

Differential provides the Operator with valuable information as to how often to operate screens, or how

many screens should be on line.

A low differential (a few inches) should not trigger activation of the rake or cleaning mechanism.

High differential (more than 4 to 6 inches) should activate the screens to engage and remove the

accumulated material.

High flow events clean out collection systems, resulting in a surge of debris flowing downstream to the

treatment plant. During a high influent flow event, screens should be operated continuously in manual.