1. What is RAS Pumping Rate using Recirculation Ratio?

Definition: This calculator determines the Return Activated Sludge (RAS) pumping rate based on the recirculation ratio and average daily influent flow rate in wastewater treatment.

Purpose: It helps wastewater treatment plant operators determine the appropriate sludge return rate to maintain proper biological treatment conditions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

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

Explanation: The recirculation ratio multiplied by the influent flow rate gives the required RAS pumping rate to maintain the desired mixed liquor suspended solids (MLSS) concentration.

3. Importance of RAS Calculation

Details: Proper RAS pumping rate ensures optimal biological treatment, maintains sludge age, and prevents sludge blanket problems in secondary clarifiers.

4. Using the Calculator

Tips: Enter the recirculation ratio (typically 0.25-1.5) and average daily influent flow rate. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical recirculation ratio?
A: Most activated sludge plants operate with recirculation ratios between 0.25 and 1.5, depending on process requirements.

Q2: Why is RAS important in wastewater treatment?
A: RAS maintains the biomass concentration in the aeration tank, ensuring effective organic matter removal.

Q3: How does recirculation ratio affect treatment?
A: Higher ratios increase solids retention time but may reduce clarifier efficiency if too high.

Q4: What units should I use for flow rate?
A: The calculator uses m³/s, but you can convert from other units (1 m³/s = 86400 m³/day).

Q5: Does this calculation account for sludge quality?
A: No, this is a basic calculation. Actual RAS rates may need adjustment based on sludge settleability.