Detention Time Calculator

| Added in Construction

Understanding Detention Time

Detention time is a fundamental concept in water and wastewater treatment engineering. It represents the average time that water or wastewater remains in a treatment basin, tank, or reservoir before flowing out.

Formula

[\text{Detention Time} = \frac{\text{Total Volume}}{\text{Flow Rate}}]

This simple formula helps engineers design treatment systems that provide adequate time for physical, chemical, and biological processes to occur effectively.

Example (Gallons)

Calculate the detention time for a stormwater detention basin with a volume of 1,000 gallons and a flow rate of 50 gallons per minute.

Given:

  • Volume = 1,000 gallons
  • Flow Rate = 50 gallons/min

Calculation:

[\text{Detention Time} = \frac{1000 \text{ gallons}}{50 \text{ gallons/min}} = 20.00 \text{ minutes}]

This 20-minute detention time allows for settling of suspended solids and some pollutant removal.

Example (Liters)

Calculate the detention time for a wastewater treatment tank with a volume of 5,000 liters and a flow rate of 100 liters per minute.

Given:

  • Volume = 5,000 liters
  • Flow Rate = 100 liters/min

Calculation:

[\text{Detention Time} = \frac{5000 \text{ liters}}{100 \text{ liters/min}} = 50.00 \text{ minutes}]

This 50-minute detention time is suitable for primary sedimentation processes in wastewater treatment.

Applications

Detention time calculations are essential for:

  • Stormwater management and detention basin design
  • Wastewater treatment plant design and optimization
  • Sedimentation tank sizing and performance evaluation
  • Regulatory compliance and permit applications
  • Water quality control and pollutant removal efficiency
  • Industrial process water treatment systems

Frequently Asked Questions

Detention time is the average length of time that water remains in a treatment basin, tank, or reservoir. It is a critical parameter in water and wastewater treatment design to ensure adequate treatment and settling.

Detention time is calculated by dividing the total volume of the basin by the flow rate: Detention Time = Total Volume / Flow Rate. The result is typically expressed in minutes or hours.

Detention time determines how long water stays in a treatment process, affecting the efficiency of sedimentation, chemical reactions, and biological treatment. Insufficient detention time can result in inadequate treatment and regulatory violations.

Detention times vary by application: stormwater basins typically require 24-48 hours, sedimentation tanks need 2-4 hours, and chemical treatment basins may require 20-30 minutes depending on the process and regulatory requirements.