What are the stages of a Wastewater Treatment Plant (WWTP)?

Do you know what the stages of wastewater treatment are?

Each stage plays a fundamental role in ensuring the efficient removal of one or more contaminants present in the wastewater. To meet legal standards, WWTPs use sequential and integrated processes.

Each stage plays a fundamental role in ensuring efficiency and safety. To meet legal standards, WWTPs use sequential and integrated processes:

Preliminary Treatment: The first stage, where coarse solids (such as plastics and fabrics) are removed by screens and grit is removed by grit chambers, protecting the subsequent stages from clogging and abrasion.

Primary Treatment: The wastewater goes on to equipment that removes settleable solids and oils and greases, in the case of primary clarifiers, or also suspended solids, through flotation. At this stage, the concentration of organic matter and nutrients is also reduced, since a large part of the particulate fraction of the wastewater is removed.

Secondary Treatment: This is the central and most complex stage, using biological processes (aerobic, such as activated sludge; anaerobic, such as UASB reactors; or stabilization ponds, among others) to degrade the remaining dissolved and suspended organic matter. At this stage, depending on the process adopted, nitrogen and phosphorus can also be removed biologically. The biomass generated (sludge) is then separated and must receive proper treatment and disposal.

Tertiary Treatment (when needed): Applied when stricter discharge standards require it. It can include filtration (sand, membranes) to remove fine residual solids, disinfection (chlorination, UV radiation, ozone) to eliminate pathogens, and advanced nitrogen and phosphorus removal to prevent eutrophication.

Choosing and optimizing these processes is essential for the operational sustainability of a WWTP and for safely returning treated water to the environment or for reuse, intrinsically aligned with the principles of the circular economy and the construction of efficient and resilient sanitation.