Secondary Treatment

Definition - What does Secondary Treatment mean?

Secondary treatment is a step in wastewater treatment that involves the use of biological processes in order to capture all the dissolved organic materials that were not caught during the initial treatment.

Microbes take these organic substances as food, transforming them to water, energy and carbon dioxide. Although the technologies used in secondary treatment differ, the last stage always involves extra settling to further eradicate suspended solids.

Corrosionpedia explains Secondary Treatment

Total solids in wastewater can be categorized as inorganic and organic. When it comes to the size, it can be divided into suspended, colloidal and dissolved solids. The main purpose of the initial or primary treatment is to eliminate the suspended solids as much as possible.

However, water quality and effluent standards require a higher level of eradicating organics from wastewater which cannot be accomplished by initial treatment alone. The additional removal of this organic matter can be successfully accomplished through secondary treatment. This process is composed of biological treatments that make use of various microorganisms within a strictly controlled environment.

In this stage of wastewater treatment, combined microorganisms make use of dissolved organics and colloidal that is found from the effluent of the initial treatment as their major food supply. When the organics are consumed, these microorganisms use a portion of organic matter to get energy required for their activities.

With the secondary treatment, the remaining dissolved organics and colloidal existing in wastewater is converted to a more stable form like carbon dioxide and some into beneficial biological mass.

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