Wastewater treatment is a process used to convert wastewater, which is water no longer needed or suitable for its most recent use, into an effluent that can be either returned to the water cycle with minimal environmental issues or reused. The treatment process takes place in a wastewater treatment plant (WWTP), often referred to as a Water Resource Recovery Facility (WRRF) or a sewage treatment plant. Here are the general stages involved in wastewater treatment:

Preliminary Treatment: This is the first stage of wastewater treatment and involves the removal of large objects and debris such as rags, plastics, and metals that may have been sent down the sewer system. This is typically done using screens, grit chambers, and sometimes grinders.

Primary Treatment: In this stage, wastewater is held in a quiescent basin where heavy solids can settle to the bottom while oil, grease, and lighter solids float to the surface. The settled and floating materials are removed, and the remaining liquid may be discharged or subjected to secondary treatment.

Secondary Treatment: This stage uses biological processes to remove dissolved and suspended organic compounds. The most common method is activated sludge, where microorganisms are cultivated and mixed with the wastewater to consume the organic material.

MBR (Membrane Bioreactor):
This is a combination of a membrane process like microfiltration or ultrafiltration with a suspended growth bioreactor. It's a highly efficient, compact method of achieving high-quality effluent. The membrane component uses low pressure filtration to separate the treated solid waste from the ater. This process results in a high level of pollutant removal, and the treated water is often of high enough quality to be reused.

MBBR (Moving Bed Biofilm Reactor):
This is a type of biological process used for the treatment of wastewater. Plastic carriers, which have a large surface area for biofilm growth, are used in the reactor. The carriers move freely in the reactor with the flow of the wastewater, providing excellent treatment efficiency. This process is relatively simple to operate and requires less space than other traditional treatment systems.

Tertiary Treatment: Also known as advanced treatment, this stage further treats the wastewater to remove nutrients such as phosphorus and nitrogen. It can also include disinfection processes to kill bacteria and other microorganisms.

Sludge Treatment: The solids collected during the primary and secondary treatment processes are treated and disposed of separately. This can involve processes like thickening, digestion, dewatering, and drying.

Disinfection: Before the treated wastewater is discharged back into the environment, it is often disinfected to kill any remaining pathogens. This can be done using chemical disinfectants, ultraviolet light, or other methods.
The goal of wastewater treatment is to produce an effluent that will do as little harm as possible when discharged to the surrounding environment, thereby preventing pollution compared to releasing untreated wastewater into the environment.