The Secondary Stage in Wastewater Treatment 

The wastewater treatment process lessens the impact on both the environment and public treatment facilities. The process typically involves three main stages - the primary, the secondary, and tertiary stage - where each stage provides an added level of decontamination for the wastewater.

If you want a quick review on the primary stage check out our most recent post - Wastewater Treatment Process: The Primary Stage - before going on to learn more about the secondary stage.

Without the secondary stage, your company's wastewater would pretty much remain just that - waste. Read on to learn more about how biological treatment plays an important role in cleaning up wastewater!

Aeration Grids Provide the Oxygen Necessary for Biological Treatment

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The secondary stage involves biological treatment to remove dissolved organics, which are measured as biochemical oxygen demand, or BOD, and the separation of particulates that are left floating in the treated water, which is measured as total suspended solids, or TSS.

The Secondary Stage:

Secondary Treatment involves sustaining many microorganisms within a tank that is filled up with wastewater. These microorganisms need two things in order to survive: 1. food; 2. air. 

The air is supplied by large mechanical blowers and diffused into the wastewater by the aeration grids that are installed at the bottom of the tank. This process can be seen in Figure 1.

The food, however, is supplied by any contaminants that have been dissolved into the water. The microorganisms then metabolize the contaminants much like a large group of people would who are eating pizza together. The more contaminants that are dissolved into the water, or the more pizza present at dinner, the more microorganisms, or people, are needed to metabolize/eat it all. 

Since the microorganisms have short lifespans, they rapidly reproduce ... if there is enough food & air present! Any of the ones that die, must later be removed as suspended solids (TSS), commonly referred to as biological sludge.

Breakdown is typically accomplished by any of the following:

  • A Biofiltration System
  • Clarifiers
  • A Dissolved Air Flotation (DAF) Unit
  • Membranes
  • Aeration Tanks (which can be seen in Figure 2)

More information on the types of contaminants & how they are measured can be found in our blog - Do You Know What Is In Your Company's Wastewater?

Aeration Tanks for a bioFAS™ MBBR System

bioprocessH2O is equipped with a team of experts experienced in the wastewater treatment process, along with the food and beverage industry. The bioprocessH2O team works efficiently to solve unique problems by offering innovative wastewater treatment systems that are custom built to each client’s needs and specifications. Please feel free to contact us at any time to answer any questions or concerns you might have!


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