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What Is Tertiary Wastewater Treatment, and How Does It Work?

By: Tom Frankel
Post Date: December 2nd 2020

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What Is Tertiary Wastewater Treatment, and How Does It Work?

In the wastewater industry, plants often focus on primary and secondary treatments, which do most of the work of preparing wastewater for discharge into the environment. Tertiary treatment is also critical in many situations. It affords the peace of mind of knowing that the treated wastewater is clean, sanitary, compliant with regulations and safe enough for drinking or reuse.

The guide below will discuss how tertiary wastewater treatment works and elaborate on some different types of tertiary filtration and disinfection methods.


Table Of Contents

  1. What Is Tertiary Wastewater Treatment?
  2. How Does Tertiary Wastewater Treatment Work?


What Is Tertiary Wastewater Treatment?

What is tertiary treatment in wastewater? To answer this question, let’s look into how treatment plants generally work and how the main stages of wastewater treatment progress.

Most wastewater treatment systems consist of at least two main treatment processes: primary and secondary treatment, with some additional preliminary methods. Primary treatment, which typically removes 50% to 70% of the suspended solids in wastewater, uses physical processes like filtration and settling to remove grit, debris, oil, grease and some lighter solids. Secondary treatment applies additional biological processes like aeration and activated sludge treatment to break down dissolved and suspended biosolids using good bacteria.

Tertiary treatment adds a third, more advanced and rigorous level of treatment. Primary and secondary treatment typically get wastewater only clean enough to discharge safely into the environment. Tertiary treatment, on the other hand, can achieve levels of water purification that make the water safe for reuse in water-intensive processes or even as drinking water.

Not all wastewater treatment plants use tertiary treatment. Primary and secondary treatment are often sufficient for many purposes. Those that do use tertiary treatment achieve more stringent levels of cleanliness to meet the exacting standards that govern water reuse, especially in public water supplies. Tertiary treatment is also beneficial when facilities must discharge water into sensitive aquatic ecosystems such as estuaries, sluggish rivers or waters close to coral reefs.

It is more effective than primary or secondary treatment at removing unwanted color from wastewater, so it is essential in industrial pulp and paper applications and textiles manufacturing.

How Does Tertiary Wastewater Treatment Work?

How Does Tertiary Wastewater Treatment Work?

Tertiary wastewater treatment often works by using a combination of physical and chemical processes to remove harmful microbiological contaminants from wastewater. The process usually involves filtration followed by additional disinfecting treatment. In some cases, tertiary treatment may also use other specialized treatments like lagoon storage, biological nutrient removal, and nitrogen and phosphorus removal.


Tertiary filtration components can contain a few different materials. Sand and activated carbon filters are common, and filters can also contain fine woven cloth. The filters also come in a few different types, including bag filters, drum filters and disc filters:




The process of tertiary disinfection may take a few different forms:




Once the wastewater has undergone tertiary treatment, it is ready for discharge back into the environment. Many municipalities have specific requirements about the discharge of treated water, and tertiary treatment should be sufficient to meet those standards, keep the environment clean and preserve human health.


Many treatment plants use tertiary treatment specifically to make the water safe for human ingestion. After tertiary treatment, the water has undergone sufficient purification to be clean and healthy as drinking water. Water that has received tertiary treatment is also suitable for numerous operations that require clean water, such as industrial and manufacturing processes, oil and gas extraction and refining, utilities cooling and agricultural practices like irrigation.

Contact SSI Aeration, Inc. for All Your Tertiary Treatment Needs

Contact SSI Aeration, Inc. for All Your Tertiary Treatment Needs

To receive assistance with your tertiary wastewater treatment system, make SSI Aeration your trusted source. As a full-service wastewater treatment engineering company, SSI has the experience and industry expertise to help you improve your treatment’s efficiency or meet environmental regulatory standards for your discharged wastewater. We offer comprehensive system design and engineering and are happy to assist with lab servicesfield services and treatment product selection.

Start your quote today, or contact us to learn more.