Wastewater Solids (TSS or VSS)

Peter Annunziato, P.E. February 13 , 2019

Solids in your wastewater

Wastewater solids take many forms.  We can tackle this subject by classifying solids that are contained in raw wastewater and biological solids generated through the treatment process.


Raw Wastewater: Raw wastewater solids are both dissolved and suspended in water.Raw Wastewater

  • Dissolved solids are a measure of the total dissolved solids (TDS) contained in solution and are due to salts, minerals as well as organic material and compounds. 
  • Total suspended solids (TSS) encompass small organic and inorganic particles including fats, oil and grease (FOG) which are measured during the TSS analysis.  It is critical that a majority of these solids are removed during primary treatment to ensure biological treatment will perform efficiently.

Biological Solids: Biological solids are generated during the aerobic/anaerobic treatment process and are termed Volatile Suspended Solids (VSS).  VSS are organic in nature and by definition will ignite at 550 °C in a muffle furnace.  The anlytical method of igniting the VSS allows us to quantify the exact mass generated during biological treatment.  The generation of biological solids, also referred to as sludge yield, is a result of the organic material (BOD5) in the wastewater being converted to biomass, water and carbon dioxide.  These excess bio-solids generated during treatment can be thickened and ultimately hauled offsite, land applied or used as a compost amendment.


Microscopic Analysis

biomass (VFlux 2SS) during biological treatment


VSS during treatment

       Volatile Suspended Solids (VSS) in a Biological Reactor

VSS Bioreactor

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