MLVSS Calculator

Calculate the organic content in your aeration tank. Use MLVSS to monitor the health of your wastewater treatment process.

MLVSS = MLSS - Fixed Solids (or MLSS × 0.8 if fixed solids unknown)
Scenario: MLSS = 3000 mg/L, Fixed Solids = 600 mg/L, Tank = 50,000 gallons.

Calculation:
1. MLVSS = 3000 - 600 = 2400 mg/L.
2. Volatile fraction = (2400/3000) × 100 = 80%.
3. Volume in m³ = 50,000 × 0.003785 = 189.3 m³.
4. Total MLVSS = (2400 × 189.3) / 1000 = 454.3 kg.

Result: MLVSS = 2400 mg/L, Total = 454.3 kg.

What is MLVSS and why is it important?

MLVSS (Mixed Liquor Volatile Suspended Solids) measures the organic portion of biomass in wastewater treatment. It represents the active microorganisms that consume pollutants. Higher MLVSS generally means better treatment efficiency, but extremely high levels can cause operational issues.

What is a typical MLVSS range for wastewater treatment?

Typical MLVSS ranges from 1,500 to 4,000 mg/L in conventional activated sludge. Extended aeration systems may have 3,000-6,000 mg/L. The MLVSS/MLSS ratio (volatile fraction) is usually 0.7-0.85. Values outside these ranges may indicate process problems.

How do I calculate MLVSS from MLSS?

MLVSS is determined by igniting the MLSS sample at 550°C for 20 minutes. The weight lost during ignition represents the volatile (organic) portion. The formula is: MLVSS = MLSS - Fixed Solids (ash remaining after ignition). The ratio MLVSS/MLSS indicates biomass health.

What affects MLVSS levels in a treatment system?

MLVSS is influenced by: food-to-microorganism ratio (F/M), hydraulic residence time, sludge age, temperature, and wastewater characteristics. Low MLVSS may indicate washout or low biomass. High MLVSS with poor treatment suggests old sludge or toxic conditions inhibiting microorganisms.