MLVSS Calculator

Use this calculator to obtain MLVSS, the volatile part of mixed-liquor suspended solids in an activated-sludge tank. Enter the MLSS concentration and the volatile percentage. MLVSS is a practical stand-in for biomass; it is not a direct cell count.

The calculation is: MLVSS = MLSS × (volatile percent ÷ 100). Use the same concentration unit for MLSS and MLVSS, typically milligrams per litre (mg/L).

This is a laboratory split of solids into volatile and inert fractions. It does not account for inert volatile matter, measurement error, or differences between plants. Many plants operate with a volatile fraction around 70–80%.

MLSS: Mixed-liquor suspended solids concentration from the lab, typically in mg/L.

Volatile (%): The volatile share of those solids (VSS/MLSS as a percent).

MLVSS: Mixed-liquor volatile suspended solids, in the same concentration unit as MLSS.