1. What is Detention Time?

Detention time (DT) is the theoretical time required for a given amount of water or wastewater to pass through a tank at a given flow rate. It's a key parameter in wastewater treatment system design and operation.

2. How Does the Calculator Work?

The calculator uses the detention time formula:

Where:

• \( DT \) — Detention time (hours)
• \( Volume \) — Tank or basin volume (m³ or gallons)
• \( Flow\ Rate \) — Flow rate through the system (m³/h or gallons/h)

Explanation: The equation calculates how long, on average, a particle of water remains in the treatment system.

3. Importance of Detention Time

Details: Proper detention time ensures adequate treatment by allowing sufficient contact time between wastewater and treatment processes (sedimentation, biological treatment, disinfection).

4. Using the Calculator

Tips: Enter volume and flow rate in consistent units (both metric or both imperial). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical detention times for different processes?
A: Primary settling: 1.5-2.5 hours; Activated sludge: 4-8 hours; Secondary clarifiers: 2-3 hours; Disinfection: 15-30 minutes.

Q2: How does detention time affect treatment efficiency?
A: Too short DT may reduce treatment effectiveness; too long DT may cause septic conditions or excessive energy use.

Q3: What's the difference between theoretical and actual detention time?
A: Actual DT is often less due to short-circuiting and dead zones in the tank.

Q4: How do you measure detention time in practice?
A: Tracer studies using dyes or salts provide more accurate measurements than theoretical calculations.

Q5: Does detention time vary with temperature?
A: While the calculation doesn't account for temperature, treatment efficiency often changes with temperature, which may require DT adjustments.