8 Most Common Biological Wastewater Treatment Plant Designs

Biological Wastewater Treatment Plant Design

There are many kinds of biological wastewater treatment plant designs, each with its own advantages and disadvantages. In this blog, we review eight of the most common designs and offer ways to set up your plant for success.

There’s no “one size fits all” design for biological wastewater treatment plants.

The layout for one plant may not work for another because the wastewater and other factors involved–including budget, available space, etc.–are all different.

As a result, there are multiple layout options out there, making it challenging to figure out which one is right for your plant. To help you make sense of everything, we put together this helpful list of the most common designs.

Top 8 Common Biological Wastewater Treatment Plant Designs

When it comes to biological wastewater treatment plants, there are eight common designs to consider:

  1. Facultative lagoon
  2. Activated sludge
  3. Oxidation ditch
  4. Extended aeration
  5. Membrane bioreactor (MBR)
  6. Moving bed biological reactor (MMBR)
  7. Fixed bed bioreactors (FBR)
  8. Sequencing batch reactor (SBR)

1. Facultative Lagoon

A facultative lagoon design uses a giant lagoon for aeration. The design includes a system of constructed ponds to polish the water. It’s the most common design for treatment plants because it’s the easiest to set up.

2. Activated Sludge

Activated sludge designs are also common. In this design, you return the solids settled in the secondary clarifier back to the aeration basin, providing a sludge that has already seen the wastewater.

3. Oxidation Ditch

An oxidation ditch is a modified version of the activated sludge design that uses a large holding tank in a continuous oval-shaped ditch. With an oxidation ditch, the tank removes biodegradable organics through long solids retention times (SRTs).

4. Extended Aeration

An extended aeration design is often used in prefabricated plants because it reduces design costs and is mechanically simpler than other designs. It treats wastewater with modified activated sludge procedures.

5. Membrane Bioreactor (MBR)

The membrane bioreactor (MBR) design is popular because its equipment is more affordable, takes up less space and can upgrade existing facilities. MBRs use a combination of a membrane process with the activated sludge process to clean wastewater.

6. Moving Bed Biofilm Reactor (MBBR)

The moving bed biofilm reactor (MBBR) design uses an aeration tank with plastic carriers that allow biofilm to grow on the surface. Like its name suggests, the media moves around the tank. The MBBR system takes up less space than activated sludge systems because it has more concentrated biomass.

7. Fixed-Bed Bioreactor (FBR)

The fixed-bed bioreactor (FBR) design is a variation of the MBBR. Instead of moving around the tank, the media stays in place and provides a surface area for the bacteria to attach to. That way, you can grow bacteria in high numbers with a smaller footprint.

8. Sequencing Batch Reactor (SBR)

A sequencing batch reactor (SBR) design involves tanks with a flow-through system, allowing raw wastewater to enter one end and treated water to leave through the other. If a system has multiple tanks, one tank will be in settle mode while the other aerates and fills.

Now that you know the different biological wastewater treatment plant designs, how do you decide which one to choose? Let’s look at four factors.

Deciding on a Design: 4 Factors

Each treatment plant layout has advantages and disadvantages. That’s why you need to work with experienced engineers who can offer the best design option based on four main factors:

  1. Budget
  2. Available space
  3. Type of wastewater (municipal or industrial)
  4. Available workforce

In the end, engineers will likely choose the design that’s most familiar. But even if you decide on a layout, you still must consider which treatment processes you will take.

Picking a Treatment Process: 3 Approaches

Biological wastewater treatment plants use different treatment processes to achieve certain successes. You can approach the treatment processes in three ways:

  1. Aerobic: Oxygen is added to the wastewater.
  2. Anaerobic: No oxygen is present in the wastewater.
  3. Anoxic: Some bound oxygen is present, meaning it doesn’t contain oxygen molecules, but it may have nitrates or nitrites.

The goal of each process is to grow microbes that will remove pollutants and pathogens from the wastewater. You expect each microbe to perform specific functions within each process.

Certain microbes thrive in each environment. For example, strict aerobes or anaerobes thrive in their respective environment, and there are also facultative microbes that can switch between the two. Depending on your plant, you may end up using each of the treatment processes so you can grow different kinds of microbes for several purposes.

In a treatment plant, it’s common to have a process for each approach, depending on what you’re trying to accomplish. If you aren’t sure which direction to take, get help from a bioaugmentation specialist.

Partner With a Bioaugmentation Specialist

Bioaugmentation is the addition of any beneficial microbe to enhance a biological process and achieve desirable effects (lower costs, improved performance, increased safety, reduced odors, etc.) Added microbes augment the existing biomass to make it more stable and increase its ability to produce an acceptable effluent.

In most cases, the engineers designing your treatment plant won’t be microbiology experts. Therefore, you should work with a bioaugmentation specialist to help you understand which bacteria is right for your plant. Otherwise, you could end up wasting time and money on a bioaugmentation solution that doesn’t work.

You’ll want to partner with a bioaugmentation specialist who can “seed” your wastewater with biological material when you’re ready to start up your system. The ideal partner will work with any design or processes to ensure your facility operates at an optimal level.

If any issues arise, your partner can offer solutions ranging from laboratory services to bioaugmentation products.


Every biological wastewater treatment plant has unique needs, which is why there are so many designs available. When choosing a layout that meets your needs, consider factors like budget and space to make the most impact. It’s also essential to work with a bioaugmentation specialist to determine the best treatment approach so you can keep your plant functioning properly.

Monera Technologies provides comprehensive consulting, lab services and bioaugmentation solutions for biological wastewater treatment plants. Contact us for more information on our holistic approach.