When you flush the toilet, wash your hands, or take a shower, do you ever wonder what happens to all that waste? Here’s a brief overview of the sewage treatment process, and what happens to the leftover sewage sludge.

The Process of Sewage Treatment

1. Preliminary Treatment: In the preliminary treatment stage, the sewage undergoes screening to remove large objects like rags, sticks, and other debris. It then proceeds to a grit chamber, where sand, gravel, and other heavy materials can settle out.
2. Primary Treatment: The screened and degritted sewage undergoes sedimentation, which allows the solids (known as primary sludge) to settle at the bottom of the tank. The clarified liquid, or effluent, is then transferred to the next stage.
3. Secondary Treatment: This stage involves biological treatment, usually using activated sludge or trickling filters. Bacteria consume the organic matter in the sewage, removing contaminants and impurities. The treated effluent is then disinfected and released into waterways or further treated for reuse.

What Happens to the Leftover Sewage Sludge?

The solid material that settles out during the primary treatment stage is referred to as sewage sludge. This sludge contains a mixture of organic matter, bacteria, and other solids.

• Land Application: Some sewage sludge is applied to the land as fertilizer, after undergoing additional treatment to reduce pathogens and heavy metals.
• Incineration: Sludge can also be incinerated, turning it into ash that can be disposed of in landfills or used for other purposes.
• Anaerobic Digestion: In anaerobic digesters, bacteria break down organic matter in sludge, producing biogas and a stabilized sludge that can be used as a fertilizer or soil amendment.

Sewage treatment plays a crucial role in protecting public health and the environment by removing harmful contaminants from wastewater before it is released back into the ecosystem.