For non-residential systems, what multiplier is used to size the septic tank relative to daily design sanitary sewage flow?

For non-residential systems, what multiplier is used to size the septic tank relative to daily design sanitary sewage flow?

• A. Twice
• B. Three times
• C. Four times
• D. One time

Answer: (B)

For non-residential systems, the septic tank is sized to provide about three days of detention for the design sewage flow. This means the tank volume equals three times the daily design sanitary sewage flow. The reason is to give more time for solids to settle and for partial digestion to occur before the effluent reaches the drain field, which is important because non-residential waste streams can vary in volume and strength and may produce more solids. So, if the daily design flow is, say, 2,000 gallons, the tank should be about 6,000 gallons in capacity. Using a smaller multiplier, like two times, would offer less detention and could lead to solids carryover. A larger multiplier, such as four times, would result in a larger tank than typically required, and one time would be insufficient detention for proper treatment.

For non-residential systems, the septic tank is sized to provide about three days of detention for the design sewage flow. This means the tank volume equals three times the daily design sanitary sewage flow. The reason is to give more time for solids to settle and for partial digestion to occur before the effluent reaches the drain field, which is important because non-residential waste streams can vary in volume and strength and may produce more solids. So, if the daily design flow is, say, 2,000 gallons, the tank should be about 6,000 gallons in capacity.

Using a smaller multiplier, like two times, would offer less detention and could lead to solids carryover. A larger multiplier, such as four times, would result in a larger tank than typically required, and one time would be insufficient detention for proper treatment.