Wastewater Treatment Stages and the Water Line

The Water Line in Wastewater Treatment

a) The water line. It is the road that runs the wastewater from its arrival at the facility, going through various treatments, until its final discharge receptor. The constituent treatments are:

Pretreatment: Initial Solid Separation

It is the separation of suspended solids and floating material of large size and density reaching the intake manifold of the treatment plant, whose presence in water can cause large changes in pipes and pumps and affect the installation or other phases of treatment. The following processes are performed:

• Roughing or retention: Through thick or thin bars, bulkier material is deposited in containers for transport to municipal landfills or incinerators.
• Desanding: Performed in chambers at controlled speeds to cause the deposition of sand at the bottom and its subsequent removal and disposal.
• Degreasing: It is done through the same processes as in the desanding; since fat is less dense, it stays on the surface. Both processes are often conducted together.

Primary Treatment: Sedimentation and pH

This is the separation of suspended solids and floating material that were not retained in the pretreatment. It occurs in round or rectangular settling tanks with drag mechanisms and sludge removal. After the rendering process is completed, flocculation facilitates sedimentation. Finally, there are processes of neutralization or pH adjustment to allow further processing.

Secondary Treatment: Biological Processes

A set of biological processes complemented by a secondary decanting system whose purpose is to remove the organic matter present in wastewater.

Tertiary Treatment: Nutrient Removal

These are made of advanced methods to extract additional organic matter previously not eliminated or to reduce nutrients like Nitrogen (N), Phosphorus (P), and their compounds. They are expensive and are applied in some sewage treatment plants. Their use would allow the reuse of treated water.

Disinfection: Eliminating Pathogens

This final treatment is designed to prevent health problems due to the existence of pathogenic bacteria and viruses in water. Chlorination is usually used, which uses chlorine as a gas, along with ozonation and ultraviolet lamps employment, although it increases the treatment cost.