MLVSS Calculator
Use this MLVSS calculator to estimate mixed liquor volatile suspended solids either from a wastewater loading workflow or from measured MLSS and volatile solids in a lab sample.
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Run the calculator.
What This MLVSS Calculator Helps You Do
This page supports two common wastewater workflows. Operations teams can estimate MLVSS from loading and F/M assumptions, while lab teams can derive it directly from MLSS and volatile solids data.
Using both methods together helps you see whether process assumptions and measured solids are still telling the same story.
How to Calculate MLVSS Calculator
- Choose the method: Use industrial mode when you know flow, COD, F/M ratio, and tank volume. Use lab mode when you already measured MLSS and the volatile fraction.
- Estimate biomass inventory: Multiply flow by COD and 8.34, then divide by the F/M ratio to estimate MLVSS in pounds.
- Convert to concentration: Divide the pounds result by tank volume and by 8.34 if you need MLVSS as mg/L.
- Cross-check the result: Compare the loading-based estimate with the lab result to see whether your process assumptions and solids test still align.
MLVSS Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| Flow | Aeration-tank flow rate | MGD |
| COD | Chemical oxygen demand of the wastewater | mg/L |
| F/M | Food-to-microorganism ratio | dimensionless |
| Volume | Aeration tank volume | MG |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- Flow: 0.8 MGD
- COD: 2,800 mg/L
- F/M ratio: 0.60
- Volume: 0.22 MG
Result: MLVSS ≈ 31,136 lb and 17,012 mg/L.
This is a high-strength wastewater scenario. If the concentration looks unrealistic, verify the COD basis and mixed-liquor volume.
- MLSS: 3,500 mg/L
- Volatile fraction: 72%
Result: MLVSS = 2,520 mg/L.
Lab mode is useful when you want the biological portion of suspended solids directly from measured solids data.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| Industrial and lab estimates are close | Loading assumptions and measured solids broadly agree. | Use the result for routine tracking and trend review. |
| Industrial result is much higher | The process may be carrying more load than the sampled solids suggest. | Recheck tank volume, COD basis, and sampling point. |
| Lab result is much higher | Measured biomass may exceed the loading model. | Review wasting, sludge age, and whether COD or F/M were estimated correctly. |
Frequently Asked Questions
References
Last reviewed: March 2026