“Membrane Bioreactors” are often discussed in the context of:

The correct option is Wastewater treatment technologies.

Membrane Bioreactors (MBRs) are advanced systems that combine biological wastewater treatment processes (typically activated sludge) with membrane filtration processes (such as microfiltration or ultrafiltration).
In traditional wastewater treatment, biological decomposition is followed by secondary clarification in settling tanks to separate solids from liquid. MBRs replace this secondary clarification step with physical membrane barriers, which effectively filter out suspended solids, bacteria, and other pathogens. This results in high-quality treated water that can often be recycled or reused directly, making MBR technology highly efficient and widely adopted in modern municipal and industrial wastewater treatment plants.