In which step is most of the organic content of sewage removed?
a. Primary treatment
b. Secondary treatment
c. Tertiary treatment
d. Sludge treatment

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Understand the sewage treatment process, which typically involves multiple stages: primary, secondary, tertiary, and sludge treatment.

Primary treatment mainly involves physical processes like sedimentation to remove large solids and settleable organic matter from sewage.

Secondary treatment focuses on biological processes where microorganisms break down and remove most of the dissolved and suspended organic matter.

Tertiary treatment is an advanced step aimed at removing remaining nutrients, pathogens, or specific contaminants, but it does not remove the bulk of organic content.

Sludge treatment deals with the processing and stabilization of the solid waste (sludge) generated during earlier treatment steps, rather than removing organic content from the liquid sewage.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Primary Treatment

Primary treatment is the initial stage of sewage treatment where large solids and settleable organic matter are physically removed by screening and sedimentation. It mainly reduces suspended solids but does not significantly degrade dissolved organic material.

Secondary Treatment

Secondary treatment involves biological processes where microorganisms break down dissolved and suspended organic matter in sewage. This step removes most of the organic content by converting it into biomass, carbon dioxide, and water, making it the main phase for organic matter removal.

Tertiary Treatment

Tertiary treatment is an advanced purification step that removes remaining nutrients, pathogens, and pollutants after secondary treatment. It focuses on polishing the effluent to meet environmental standards but does not primarily target organic content removal.

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