Infiltration and inflow: Difference between revisions

Revision as of 20:25, 8 May 2023

Revision as of 23:08, 8 May 2023

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==Significance==

Dilution of sewage directly increases costs of pumping and [[Water chlorination|chlorination]], ozonation, or [[ultraviolet disinfection]]. Physical treatment structures including screens and pumps must be enlarged to handle the peak flow. Primary clarifiers must also be enlarged to treat average flows, although [[primary treatment]] of peak flows may be accomplished in [[detention basin]]s. Biological [[secondary treatment]] is effective only while the concentration of soluble and colloidal pollutants (typically measured as [[biochemical oxygen demand]] or BOD) remains high enough to sustain a population of microorganisms digesting those pollutants. Secondary treatment is expected to remove 85 percent of soluble and colloidal organic pollutants from sewage containing 200&nbsp;mg/L BOD;<ref?<ref>EPA. "Part 133—Secondary Treatment Regulation." {{uscfr|40|133}}</ref> but BOD removal by conventional biological secondary treatment becomes less effective with dilution and practically ceases as BOD concentrations entering the treatment facility are diluted below about 20&nbsp;mg/L. Unremoved organics are potentially converted to [[disinfection by-products]] by chemical disinfection prior to discharge.

High rates of infiltration/inflow may make the sanitary sewer incapable of carrying sewage from the design service area. Sewage may back up into the lowest homes during wet weather, or street manholes may overflow.<ref name="hammer"/>