MLVSS (Mixed Liquor Volatile Suspended Solids) Calculator

Wastewater Treatment Process Optimization Tool

Calculate the concentration of mixed liquor volatile suspended solids (MLVSS) in biological reactors. Enter your TSS, NVSS, and sample volume to determine MLVSS and optimize your wastewater treatment process.

Example Calculations

Try these sample values to see how the MLVSS calculator works

Standard Activated Sludge Sample

Standard

Typical values for a municipal wastewater treatment plant.

TSS: 120 mg

NVSS: 40 mg

Sample Volume: 50 mL

High Solids Concentration

High Solids

Sample with high TSS and moderate NVSS.

TSS: 300 mg

NVSS: 100 mg

Sample Volume: 100 mL

Low Volatile Fraction

Low Volatile Fraction

Sample with low volatile content (high NVSS/TSS ratio).

TSS: 80 mg

NVSS: 60 mg

Sample Volume: 25 mL

Large Sample Volume

Large Volume

Calculation for a large sample volume in liters.

TSS: 500 mg

NVSS: 200 mg

Sample Volume: 1 L

Other Titles
Understanding MLVSS: A Comprehensive Guide
Master wastewater treatment process control with accurate MLVSS calculations

What is MLVSS?

  • Definition and Importance
  • Role in Wastewater Treatment
  • Relation to TSS and NVSS
MLVSS (Mixed Liquor Volatile Suspended Solids) is a key parameter in biological wastewater treatment. It represents the concentration of organic (volatile) suspended solids in the mixed liquor of an aeration tank, indicating the amount of active biomass present.
Why is MLVSS Important?
MLVSS is used to monitor and control the biological treatment process. It helps operators assess the health and activity of the microbial population responsible for breaking down organic pollutants.
Relationship to TSS and NVSS
TSS (Total Suspended Solids) includes both organic and inorganic solids, while NVSS (Non-Volatile Suspended Solids) represents the inorganic fraction. MLVSS is calculated as the difference between TSS and NVSS, normalized to sample volume.

MLVSS Calculation Examples

  • MLVSS = (TSS - NVSS) / Sample Volume (L)
  • TSS = 120 mg, NVSS = 40 mg, Volume = 0.05 L → MLVSS = 1600 mg/L

Step-by-Step Guide to Using the MLVSS Calculator

  • Input Your Data
  • Select Units
  • Interpret Results
The MLVSS calculator simplifies the process of determining the concentration of volatile suspended solids in your sample. Follow these steps for accurate results.
Enter TSS and NVSS Values
Input the measured values for total suspended solids (TSS) and non-volatile suspended solids (NVSS) in milligrams (mg). Ensure that TSS is greater than NVSS for valid results.
Specify Sample Volume and Unit
Enter the volume of your sample and select the appropriate unit (mL or L). The calculator will automatically convert mL to L for the final calculation.
Review Results and Volatile Fraction
The calculator provides the MLVSS value in mg/L and the volatile fraction as a percentage of TSS. Use these results to monitor and optimize your treatment process.

Step-by-Step Examples

  • TSS = 300 mg, NVSS = 100 mg, Volume = 0.1 L → MLVSS = 2000 mg/L
  • TSS = 80 mg, NVSS = 60 mg, Volume = 0.025 L → MLVSS = 800 mg/L

Real-World Applications of MLVSS Calculations

  • Process Control
  • Troubleshooting
  • Compliance Monitoring
MLVSS is widely used in wastewater treatment plants for process control, troubleshooting, and regulatory compliance. Accurate MLVSS measurements help ensure efficient operation and environmental protection.
Process Optimization
Operators use MLVSS data to adjust aeration rates, sludge age, and wasting rates, optimizing the biological treatment process for maximum efficiency.
Troubleshooting System Upsets
Sudden changes in MLVSS can indicate process upsets, toxic shocks, or equipment malfunctions. Monitoring trends helps identify and resolve issues quickly.
Regulatory Compliance
Many environmental regulations require regular MLVSS monitoring to demonstrate compliance with discharge permits and protect receiving waters.

Application Scenarios

  • MLVSS trending down: Possible toxic shock or low food supply
  • MLVSS too high: Excessive sludge age or insufficient wasting

Common Misconceptions and Correct Methods

  • Confusing TSS and MLVSS
  • Ignoring Sample Volume Units
  • Calculation Errors
Mistakes in MLVSS calculation often arise from confusing TSS with MLVSS, neglecting unit conversions, or using incorrect formulas. Understanding the correct approach ensures reliable results.
TSS vs. MLVSS
TSS measures all suspended solids, while MLVSS focuses on the organic (volatile) fraction. Always subtract NVSS from TSS to obtain MLVSS.
Unit Conversions
Sample volume must be in liters (L) for the final calculation. If your measurement is in mL, the calculator will convert it automatically.
Formula Application
Use the formula: MLVSS (mg/L) = (TSS - NVSS) / Sample Volume (L). Double-check your inputs for accuracy before calculating.

Best Practice Tips

  • Don't use TSS directly as MLVSS
  • Always convert mL to L: 50 mL = 0.05 L
  • NVSS cannot be greater than TSS

Mathematical Derivation and Examples

  • MLVSS Formula
  • Unit Conversion
  • Practical Examples
The MLVSS calculation is based on the difference between total and non-volatile suspended solids, normalized to sample volume in liters. This provides a standardized measure for process control and comparison.
MLVSS Formula
MLVSS (mg/L) = (TSS - NVSS) / Sample Volume (L). Ensure all values are in the correct units before calculation.
Unit Conversion
If your sample volume is in mL, divide by 1000 to convert to L. For example, 50 mL = 0.05 L.
Worked Example
TSS = 120 mg, NVSS = 40 mg, Sample Volume = 50 mL (0.05 L): MLVSS = (120 - 40) / 0.05 = 1600 mg/L. Volatile fraction = (MLVSS / TSS) × 100 = 133%.

Calculation Examples

  • TSS = 500 mg, NVSS = 200 mg, Volume = 1 L → MLVSS = 300 mg/L
  • TSS = 80 mg, NVSS = 60 mg, Volume = 25 mL → MLVSS = 800 mg/L