Mlvss Calculator
Mixed liquor volatile suspended solids & tank inventory
Illustrative presets — replace with measured VSS/TSS.
Mixed liquor inputs
Solids analysis
Step-by-step solution
Suspended solids composition
Tank solids inventory
At 1,000 m³
Tank inventory assumes uniform concentration throughout the entered volume.
Solids balance table
| Material | Concentration | Fraction | Tank mass |
|---|
Understand the solids balance
MLSS includes both fractions
Mixed liquor suspended solids (MLSS) contains both volatile and fixed solids. MLVSS is the volatile portion estimated here using the entered ratio.
Volatile does not mean living biomass
Volatile solids include living and nonliving material. Ignition-based measurements are not a direct count of active microorganisms or treatment performance.
Concentration versus tank inventory
Concentration is measured in mg/L or g/L. Tank inventory is the total mass (kg or lb) based on concentration and the entered volume.
Frequently asked questions
What is MLVSS?
Mixed Liquor Volatile Suspended Solids is the volatile portion of the suspended solids in mixed liquor. This calculator estimates it from MLSS and the entered VSS/TSS fraction.
Does MLVSS measure active biomass?
MLVSS measures the volatile fraction of suspended solids. It includes living microorganisms and nonliving volatile material. It is used as an approximate biomass indicator, not a direct measurement of active cells.
Can I use an assumed ratio?
Presets are illustrative examples only. Use a representative measured VSS/TSS fraction for your sample. Process type alone does not establish the fraction.
How are tank solids masses calculated?
For a uniformly mixed tank, mass in kg equals concentration in mg/L multiplied by tank volume in m³ and divided by 1,000. US gallons convert using 0.003785411784 m³ per gallon. Empty volume inputs do not produce a mass estimate.
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Can I enter the ratio as a percentage?
Yes. A ratio of 0.80 is the same as 80%. Switch between Ratio and Percent; the calculator converts the input without changing its physical meaning.
What MLSS range is appropriate?
The appropriate concentration depends on process design, sludge age, loading, settling and operating objectives. This calculator does not grade plant health or recommend a universal operating range.
What is the difference between MLSS and MLVSS?
MLSS is all suspended solids in mixed liquor. MLVSS is the volatile fraction; the remaining fixed fraction is MLFSS. The two fractions sum to MLSS.
What does the Mlvss calculate?
Mlvss Calculator Calculate Mixed Liquor Volatile Suspended Solids (MLVSS) from MLSS and the VSS/TSS ratio in a wastewater aeration basin. — free online calculator.
Which values should I enter?
Enter MLSS Concentration, VSS/TSS Ratio using the units and format shown beside each field.
What formula does this calculator use?
The calculator uses the following relationship: MLVSS = MLSS × (VSS/TSS fraction).
Why might my result differ from another source?
Results can differ when another source uses different units, rounding rules, conventions or assumptions. Compare the inputs and definitions before comparing results.
Does the result update automatically?
Yes. Changing an input updates the result using the same calculation engine shown on this page.
Formula & worked example
MLVSS = MLSS × volatile fraction
MLFSS = MLSS − MLVSS
Tank mass (kg) = concentration (mg/L) × volume (m³) ÷ 1,000
Displayed values are rounded; intermediate calculations retain full precision. US gallon = 0.003785411784 m³.
Sources & References
Primary references · no institutional endorsement.
Mlvss Calculator Calculate Mixed Liquor Volatile Suspended Solids (MLVSS) from MLSS and the VSS/TSS ratio in a wastewater aeration basin. — free online calculator.