MLVSS Calculator
Enter your measured Mixed Liquor Suspended Solids (MLSS) concentration and the volatile solids percentage from your lab analysis to calculate MLVSS. This is a calculation aid based on the values you provide, not plant-operation guidance.
Last updated: September 25, 2026
Frequently asked questions
What is the difference between MLSS and MLVSS?
MLSS (Mixed Liquor Suspended Solids) is the total suspended solids concentration in the aeration basin, including both organic and inorganic material. MLVSS is the organic (volatile) portion of that total, commonly used as an approximation of active biomass.
How is the volatile solids fraction measured?
Typically by drying a sample to get total suspended solids, then igniting (burning off) a filtered sample in a muffle furnace: the weight lost on ignition is the volatile fraction, and what remains is the fixed (inorganic) fraction.
Why does MLVSS matter for activated sludge processes?
It is widely used as an indicator of the biomass available to treat wastewater, feeding into calculations like food-to-microorganism ratio and sludge age, though those calculations are outside the scope of this simple tool.
Can I use this for other volatile solids calculations?
The underlying math (total x fraction) is general, but the terminology and typical mg/L units here are specific to mixed liquor in wastewater treatment.
Does this tool tell me how to adjust my process?
No. It only converts the numbers you enter. Operational decisions should follow your facility's protocols and the judgment of a qualified wastewater professional or engineer.
Why do I need to enter a percentage instead of raw masses?
This simple mode assumes you already have the volatile fraction from a standard total solids/volatile solids lab procedure. If you only have raw sample, crucible, and residue masses, calculate the percentage from those first using your lab's standard method.