Wastewater treatment is the process of removing contaminants from wastewater to make it safe for disposal or reuse. It involves several stages of treatment that are carried out in a wastewater treatment plant. Here is a detailed explanation of the typical sequence of wastewater treatment:

1. Preliminary Treatment:
- Screening: Large objects and debris are removed using screens or grates.
- Grit Removal: Sand, gravel, and other heavy particles are settled and removed.

2. Primary Treatment:
- Sedimentation: Wastewater is held in large tanks where suspended solids settle to the bottom as sludge.
- Sludge Removal: The settled sludge is scraped off and sent for further treatment.

3. Secondary Treatment:
- Biological Treatment: Microorganisms are added to the wastewater to break down organic matter. This is typically done in activated sludge or trickling filter systems.
- Aeration: Oxygen is provided to support the growth of microorganisms and enhance the treatment process.
- Sedimentation: The mixture of treated wastewater and microorganisms is allowed to settle, and the clarified water is separated from the settled sludge.

4. Tertiary Treatment:
- Filtration: The remaining suspended solids and microorganisms are removed using sand filters or membrane filtration.
- Disinfection: Chemicals like chlorine or ultraviolet (UV) light are used to kill any remaining pathogens in the treated wastewater.

5. Sludge Treatment:
- Thickening: The sludge is concentrated by removing excess water.
- Digestion: Microorganisms break down organic matter in the sludge, reducing its volume and producing biogas.
- Dewatering: The digested sludge is mechanically squeezed to further reduce its moisture content.
- Disposal: The final sludge, called biosolids, can be incinerated, used as fertilizer, or disposed of in a landfill.

6. Effluent Discharge or Reuse:
- The treated wastewater, known as effluent, can be discharged into nearby water bodies or used for irrigation, industrial processes, or groundwater recharge.

It is important to note that the sequence and specific processes may vary depending on the capacity and design of the wastewater treatment plant. Additionally, advanced treatment methods like membrane bioreactors or reverse osmosis may be employed for specific applications or to meet stricter water quality standards.