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5.2.3 Effluent Sewer System
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5.2.3 Effluent Sewer System

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Description:
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Septic tank effluent pump (STEP) and septic tank effluent gravity sewers (STEG) systems are widely used in rural area. Effluent from septic tanks flows into the sewer system using either a pump (STEP) or gravity (STEG). STEG systems operate totally via gravity owing to a higher elevation relative to the treatment facility. STEP systems operate via pressure owing to a lower elevation or complex topography relative to the treatment facility. Thus, a typical effluent sewer is a mixture of STEP and STEG depending upon the location of the service lines.

 

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Figure 5.3 Schematic of a STEP/STEG system

(Source: WERF, 2010)

 

As solids have been removed in the septic tank, the pipe slope requirement of the STEG systems is reduced, and the width and depth of the required excavation for piping is also reduced compared to conventional gravity sewers. This results in lower installation cost and less community disruption. Furthermore, effluent from the septic tank has relatively lower strength than raw wastewater. Costs of downstream treatment components may thus be reduced.

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