The first stage involves biological treatment, where microorganisms (bacteria, protozoa, etc.) break down organic matter present in the wastewater. This process typically occurs in an aerated tank, where oxygen is provided to support the growth of aerobic bacteria that consume organic pollutants.

In MBR systems, instead of using secondary clarifiers to separate the treated water from the biomass (sludge), membrane filtration is employed. Specialised membranes with microscopic pores act as physical barriers, allowing only clean water to pass through while retaining suspended solids, bacteria, and other contaminants. The membranes used in MBR systems can be made of various materials like polymeric or ceramic, depending on the application.

Aeration is crucial to MBR operation. It serves two purposes: providing oxygen for the biological treatment process and scouring the membrane surface to prevent fouling. Constant aeration helps maintain the effectiveness of the membrane by minimising the buildup of solids on its surface.

Over time, the membrane surface can become fouled or clogged with accumulated solids and biofilm. Periodic cleaning is necessary to maintain membrane performance. Cleaning methods include backwashing, air scouring, chemical cleaning, or a combination of these techniques.

The permeate, or treated water, that passes through the membrane is collected and can be further treated if needed for reuse or discharge.

In MBR systems, the biomass (activated sludge) remains within the system, unlike in conventional wastewater treatment plants where it’s separated in secondary clarifiers. This concentrated biomass contributes to the effectiveness of the treatment process but requires proper management, including periodic removal or wasting to maintain system efficiency