What is septicity in wastewater?

Spirochete from ucmp.berkeley.edu

We often hear that wastewater has septicity when the water has black color, high sulfides, odors, and spirochetes/spirillum when viewed under the microscope. Today I want to define the conditions that cause septicity and how it can/should be addressed.

Conditions to create septicity:

• Soluble organics (BOD5)
• Depleted free oxygen and nitrate - pushing to highly negative redox conditions
• Sulfate - is used as an electron acceptor under anaerobic conditions producing H2S
• Soluble organics become volatile organic acids that cause odors
  

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Problems with septicity in collection systems

• Dangerous H2S levels
  
• Odors
• Corrosion from H2S and sulfide oxidation
• Filament blooms from sulfides and short chain organic acids in wastewater plant influent

Controlling septicity

• Add aeration/mixing in EQ tanks
• Reduce primary clarifier residence time
• Discharge lifts-station more frequently (reduce collection system residence time)
  
• Pre-aeration before the treatment system
• Add nitrate to the collection system to increase redox and prevent true anaerobic activity