Return Activated Sludge MLSS MLVSS is usually measured using the Cubic Meter per Day[m³/d] for Volumetric Flow Rate. Cubic Meter per Second[m³/d], Cubic Meter per Hour[m³/d], Cubic Meter per Minute[m³/d] are the few other units in which Return Activated Sludge MLSS MLVSS can be measured.