To allow solids to settle out, wastewater should remain in a septic tank for at least

To allow solids to settle out, wastewater should remain in a septic tank for at least

• A. 12 hours
• B. 24 hours
• C. 48 hours
• D. 72 hours

Answer: (B)

Detention time in a septic tank lets solids settle out by gravity, with heavier particles dropping to the bottom and lighter scum rising to the top while the clarified liquid leaves the tank. For this settling to occur reliably, wastewater needs to be in the tank long enough—about a full day. That 24-hour minimum gives solids time to settle and for the tank to separate sludge and scum from the effluent. If the wastewater moves through in less than a day, more solids can be carried out with the liquid, reducing the tank’s effectiveness. Longer times, like 48 or 72 hours, aren’t typically needed for standard residential systems and would just waste capacity.

Detention time in a septic tank lets solids settle out by gravity, with heavier particles dropping to the bottom and lighter scum rising to the top while the clarified liquid leaves the tank. For this settling to occur reliably, wastewater needs to be in the tank long enough—about a full day. That 24-hour minimum gives solids time to settle and for the tank to separate sludge and scum from the effluent.

If the wastewater moves through in less than a day, more solids can be carried out with the liquid, reducing the tank’s effectiveness. Longer times, like 48 or 72 hours, aren’t typically needed for standard residential systems and would just waste capacity.