What is 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.

The wastewater treatment process is essential for reducing environmental impact and easing the burden on public treatment facilities. This process typically involves three main stages: primary, secondary, and tertiary, each providing an increased level of decontamination for the wastewater.

If you need a quick overview of the primary stage, check out our recent post - Wastewater Treatment Process: The Primary Stage - before delving into the details of the secondary stage.

Why is the Secondary Stage Important?

Without the secondary stage, your company's wastewater would essentially remain waste. This stage is crucial for biological treatment, playing a significant role in cleaning up wastewater. Read on to learn more about the biological processes involved!

Understanding the Secondary Stage

The secondary stage involves biological treatment to remove dissolved organics, measured as biochemical oxygen demand (BOD), and the separation of particulates, measured as total suspended solids (TSS).

How Does It Work?

The secondary treatment sustains numerous microorganisms within a tank filled with wastewater. These microorganisms need two things to survive: food and air. Air is supplied by large mechanical blowers and diffused into the wastewater by aeration grids installed at the bottom of the tank. This process is illustrated in Figure 1.

Aeration Grids Water Treatment
Aeration Grids

The contaminants dissolved in the water act as food for the microorganisms. These organisms metabolize the contaminants, similar to how people consume pizza at a party. The more contaminants present, the more microorganisms are needed to break them down. As microorganisms have short lifespans, they rapidly reproduce if sufficient food and air are available. Dead microorganisms must later be removed as suspended solids (TSS), commonly referred to as biological sludge.

Breakdown Methods

Secondary treatment can be accomplished through various methods, including:

  • Biofiltration Systems
  • Clarifiers
  • Dissolved Air Flotation (DAF) Units
  • Membranes
  • Aeration Tanks (see Figure 2)
Aeration Tanks for a bioFAS™ MBBR System

For more information on the types of contaminants and how they are measured, check out our blog - Do You Know What Is In Your Company's Wastewater?

Why Choose bioprocessH2O?

bioprocessH2O is equipped with a team of experts experienced in the wastewater treatment process, as well as in industries like food and beverage. Our team efficiently solves unique problems by offering innovative wastewater treatment systems custom-built to each client’s needs and specifications.

Feel free to contact us anytime to answer any questions or concerns you might have!

by Tim Burns

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