1. What is WAS Pumping Rate from Return Line?

Definition: This calculator determines the waste activated sludge (WAS) pumping rate from the reactor based on MLSS, sludge concentration, influent flow rate, and return activated sludge (RAS) rate.

Purpose: It helps wastewater treatment plant operators control the sludge age and maintain proper biomass concentration in the aeration tank.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q_w \) — WAS Pumping Rate from Reactor (m³/s)
• \( X \) — MLSS concentration (kg/m³)
• \( X_r \) — Sludge concentration in return line (kg/m³)
• \( Q_a \) — Average daily influent flow rate (m³/s)
• \( RAS \) — Return Activated Sludge flow rate (m³/s)

Explanation: The formula calculates the waste sludge flow needed to maintain the desired solids balance in the activated sludge system.

3. Importance of WAS Calculation

Details: Proper WAS control ensures optimal treatment efficiency, prevents sludge bulking, and maintains the desired food-to-microorganism ratio.

4. Using the Calculator

Tips: Enter MLSS concentration, return sludge concentration, influent flow rate, and RAS rate. All concentration values must be > 0, flow rates can be ≥ 0.

5. Frequently Asked Questions (FAQ)

Q1: What is MLSS?
A: Mixed Liquor Suspended Solids (MLSS) is the concentration of suspended solids in the aeration tank, representing the active biomass.

Q2: Why subtract RAS at the end?
A: The subtraction accounts for the portion of flow that is being recycled rather than wasted.

Q3: What are typical values for Xr?
A: Typically 5-10 kg/m³ for conventional activated sludge systems, but can vary based on settling characteristics.

Q4: How does this relate to sludge age?
A: The WAS rate directly affects the solids retention time (sludge age) in the system.

Q5: What if my WAS rate is negative?
A: A negative value suggests you may need to increase MLSS concentration or decrease RAS rate to achieve proper wasting.