VSS or Volatile Suspended Solid

Volatile Suspended Solids (VSS) Calculator

Result

VSS: -- mg/L

About Volatile Suspended Solids (VSS)

Volatile Suspended Solids (VSS) represent the organic portion of suspended solids in water or wastewater that can be combusted at 550°C. This measurement is critical for assessing the amount of biologically active organic matter in water samples.

Calculation Formula

The VSS is calculated using the following formula:

VSS = (A3 weight) × 1,000,000 / Sample Volume

Where:

  • A3 weight: Weight loss of the filter residue after burning at 550°C in a muffle furnace (mg)
  • Sample Volume: Volume of the sample filtered (ml)

Importance of VSS

VSS is crucial for:

  • Measuring the organic content in wastewater
  • Assessing the biodegradability of suspended solids
  • Determining the active biomass in biological treatment systems
  • Calculating sludge activity and treatment efficiency
  • Monitoring process performance in wastewater treatment plants

Key Differences Between TSS and VSS

  • TSS (Total Suspended Solids): Measures all suspended solids (both organic and inorganic)
  • VSS (Volatile Suspended Solids): Measures only the volatile (organic) portion that can be oxidized at 550°C
  • The ratio of VSS/TSS indicates the organic fraction of the suspended solids

Typical VSS Values and Ranges

VSS concentrations vary depending on the water source:

  • Raw Domestic Wastewater: 150-350 mg/L
  • Primary Effluent: 80-200 mg/L
  • Activated Sludge Mixed Liquor: 1,500-4,000 mg/L
  • Final Effluent: 5-30 mg/L
  • Surface Waters: 1-20 mg/L

Maximum and Minimum VSS Considerations

Maximum VSS Levels:

  • In raw wastewater, VSS typically shouldn't exceed 70-80% of TSS
  • In activated sludge systems, VSS > 5,000 mg/L may indicate sludge bulking issues
  • High VSS/TSS ratios (>0.8) suggest predominantly organic solids

Minimum VSS Levels:

  • In biological treatment systems, VSS < 1,000 mg/L may indicate insufficient biomass
  • Low VSS/TSS ratios (<0.3) suggest predominantly inorganic solids
  • In final effluents, VSS < 10 mg/L is typically desirable

Process Control Applications

VSS is used to:

  • Determine the organic loading rate in treatment systems
  • Calculate the Food to Microorganism (F/M) ratio
  • Assess sludge age (Mean Cell Residence Time)
  • Monitor sludge activity and health
  • Optimize aeration and sludge wasting rates
  • Evaluate treatment process efficiency

Testing Methodology

The standard method for VSS determination involves:

  1. Filtering a known volume of sample through a pre-weighed glass fiber filter
  2. Drying the filter at 103-105°C to determine Total Suspended Solids (TSS)
  3. Igniting the filter at 550°C in a muffle furnace to burn off organic matter
  4. Measuring the weight loss to determine VSS

Quality Control Considerations

  • Ensure consistent furnace temperature (550±50°C)
  • Use proper desiccation for cooling filters
  • Account for filter blank corrections
  • Maintain consistent ignition time (minimum 15 minutes)
  • Use appropriate sample volumes to obtain measurable residues

Scroll to Top