The membrane process is a widely used separation process in wastewater treatment technology, which leads to an efficient treatment technology along with excellent performance and process economics. Generally, membrane-based technologies primarily rely on secondary treatment to produce high-quality effluent suitable for recycling and various applications. However, over the years, membrane-based reactors (MBRs) have proven to be quite effective in secondary treatment technology; typically, the membranes’ range of application is between microfiltration (MF) and ultrafiltration (UF). Researchers have developed numerous membrane processes and are actively working on improving others. Many researchers proved that the MBR process offers excellent performance in removing inorganic contaminants, organic compounds, and biological entities from wastewater. Except for the separation of suspended microorganisms and treated wastewater, the MBR technology is like the activated sludge process. The MBR type of system separates suspended growth and treated water simultaneously, whereas the separation occurs in the conventional system’s second stage. MBR has numerous benefits, comprising better control over biochemical activity, excellent effluent that is free of microbes, a smaller footprint, and the ability to handle variable organic load rates. Aside from municipal wastewater treatment, the MBR method makes it simple to treat a variety of industrial wastewater, from olive oil mill wastewater containing phenolic chemicals to refinery wastewater containing oil.