The technology of membrane activated sludge, commonly referred to as “membrane bioreactor” (MBR), is the combination of an activated sludge treatment together with a separation of the sludge interstitial water –the permeate, or micro-filtrate– by micro- or ultra-filtration membrane with pore size of typically 10 nm to 0.5µm. After initial development started in the late 60s [1], the MBR technology for wastewater treatment has known a very quick and decisive development over the last decade, which led within few years only to the construction of the first demonstration and large full-scale plants for municipal and industrial wastewater treatment.

In 1989, the Japanese Government launched a 6-year R&D project with many large Japanese companies, in order to develop low cost treatment processes utilising MBR to produce reusable water from industrial, municipal and domestic wastewater [2]. This program led to development of systems such as the Kubota flat-sheet module and the Mitsubishi Rayon hollow fibre module, still commercialised today without much change from the initial version, and led to a major technological breakthrough of the MBR process: the conception of submerged membrane modules, working with low negative pressure (permeate section) and membrane aeration to reduce fouling [3], which paved the way towards significant reduction of capital and operation costs, due to the reduction and simplification of equipment and the abandonment of the energy demanding sludge recirculation loop.