MLSS Returned Given Ultimate BOD Calculator

Formula Used:

\[ X_R = \frac{\frac{Q_s \times (Q_i - Q_{ub})}{\frac{BOD_5}{BOD_u}} - O_2}{1.42 \times Q_w} \]

Sewage Discharge (Qs):

m³/s

Influent BOD (Qi):

kg/m³

Effluent BOD given Ultimate BOD (Qub):

kg/m³

5 Days BOD (BOD5):

kg/m³

Ultimate BOD (BODu):

kg/m³

Theoretical Oxygen Requirement (O2):

kg/s

Volume of Wasted Sludge per day (Qw):

m³/s

MLSS in Returned or Wasted Sludge (XR):

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1. What is MLSS in Returned or Wasted Sludge?

MLSS in Returned or Wasted Sludge refers to the concentration of mixed liquor suspended solids in the returned or wasted sludge from a wastewater treatment process. It is a key parameter in activated sludge systems for maintaining proper treatment efficiency.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ X_R = \frac{\frac{Q_s \times (Q_i - Q_{ub})}{\frac{BOD_5}{BOD_u}} - O_2}{1.42 \times Q_w} \]

Where:

\( X_R \) — MLSS in returned or wasted sludge (kg/m³)
\( Q_s \) — Sewage discharge (m³/s)
\( Q_i \) — Influent BOD (kg/m³)
\( Q_{ub} \) — Effluent BOD given ultimate BOD (kg/m³)
\( BOD_5 \) — 5 days BOD (kg/m³)
\( BOD_u \) — Ultimate BOD (kg/m³)
\( O_2 \) — Theoretical oxygen requirement (kg/s)
\( Q_w \) — Volume of wasted sludge per day (m³/s)

Explanation: This formula calculates the concentration of suspended solids in returned sludge based on BOD parameters, oxygen requirement, and flow rates in the treatment system.

3. Importance of MLSS Calculation

Details: Proper MLSS control is essential for maintaining efficient biological treatment, ensuring adequate biomass for organic matter removal, and preventing system upsets in wastewater treatment plants.

4. Using the Calculator

Tips: Enter all values in the specified units. Ensure sewage discharge, BOD values, and sludge volume are positive numbers. Theoretical oxygen requirement should be non-negative.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range for MLSS in activated sludge systems?
A: MLSS typically ranges from 1500-4000 mg/L (1.5-4.0 kg/m³) in conventional activated sludge systems, though this can vary based on specific process requirements.

Q2: Why is the 1.42 factor used in the formula?
A: The factor 1.42 represents the oxygen equivalent of biomass, accounting for the oxygen demand of microbial cells during endogenous respiration.

Q3: How does MLSS affect treatment efficiency?
A: Higher MLSS concentrations generally improve treatment efficiency but require more oxygen and better settling characteristics. Too high MLSS can lead to settling problems.

Q4: What's the difference between MLSS and MLVSS?
A: MLSS measures total suspended solids, while MLVSS (Mixed Liquor Volatile Suspended Solids) measures the organic fraction of suspended solids, which represents active biomass.

Q5: How often should MLSS be monitored?
A: MLSS should be monitored daily in most treatment plants to maintain proper process control and make timely adjustments to sludge wasting rates.