What are Volatile Suspended Solids (VSS)?

Volatile Suspended Solids (VSS) represent the organic fraction of the Total Suspended Solids (TSS) in a water or wastewater sample. By heating a dried sample in a muffle furnace at high temperatures (typically 550°C), the organic matter is oxidized and ignited, leaving behind only the inorganic, fixed solids. The weight lost during this combustion process is the volatile portion.

How to Calculate VSS

The standard laboratory procedure involves three primary weights. First, you measure the total suspended solids by drying the sample at 105°C. Second, you ignite that same filter in a furnace at 550°C. The difference between these two weights represents the organic matter that escaped as gas. The formula used by this calculator is:

VSS (mg/L) = [(Dry Weight - Ignited Weight) × 1,000,000] / Sample Volume (mL)

Significance in Wastewater Treatment

In environmental engineering and wastewater management, VSS is a critical parameter. It is often used as a proxy for the biological concentration in activated sludge systems, specifically known as Mixed Liquor Volatile Suspended Solids (MLVSS). Unlike TSS, which includes grit and minerals, VSS gives operators a better estimate of the active microbial population responsible for treating the waste.

Frequently Asked Questions

Q: Why use 550°C?
A: This temperature is high enough to ensure complete combustion of organic carbon without causing significant decomposition of inorganic salts like calcium carbonate.

Q: What is the difference between TSS and VSS?
A: TSS is the total amount of solids trapped by a filter. VSS is only the organic part of those solids that burns away at high temperatures.

Q: Can VSS be higher than TSS?
A: No, by definition, VSS is a component of TSS. If your calculations show a higher VSS, there is likely a weighing error or a data entry mistake.