1. What is Recirculation Ratio?

Definition: The Recirculation Ratio refers to the ratio of the Return Activated Sludge (RAS) pumping rate to the influent flow rate in a wastewater treatment process.

Purpose: It helps wastewater treatment plant operators maintain the proper balance of microorganisms in the aeration tank for effective biological treatment.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( \alpha \) — Recirculation Ratio (unitless)
• \( RAS \) — Return Activated Sludge flow rate (m³/s)
• \( Q_a \) — Average Daily Influent Flow Rate (m³/s)

Explanation: The RAS flow rate is divided by the influent flow rate to determine what proportion of the treated wastewater is being recirculated.

3. Importance of Recirculation Ratio

Details: Proper recirculation maintains the right concentration of microorganisms in the aeration tank, ensures good settling in the clarifier, and helps control sludge age.

4. Using the Calculator

Tips: Enter the RAS flow rate and average daily influent flow rate in cubic meters per second (m³/s). Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical recirculation ratio?
A: Typical values range from 0.25 to 1.5, depending on the treatment process and plant design.

Q2: Why is recirculation important in activated sludge systems?
A: It maintains sufficient biomass in the aeration tank and helps control the food-to-microorganism ratio.

Q3: What happens if the recirculation ratio is too high?
A: Excessive recirculation can overload the clarifier and cause poor settling.

Q4: How does recirculation affect sludge age?
A: Higher recirculation ratios generally result in younger sludge ages.

Q5: Can this calculator be used for other types of recirculation?
A: This specific calculator is designed for activated sludge systems, but similar principles apply to other recirculation processes.