Membrane bioreactor takes the proven biological process and combines it with a more recent technology: membrane filtration. The last step in the biological process is the solids-liquid separation. In this step the sludge is being removed from the water by using a settler. In an MBR the last step is replaced by an ultrafiltration membrane. This will results in a process that is able to operate at higher micro-organism concentration and thus require less space. Also the ultrafiltration membrane is superior to the settler in the quality of effluent it produces. The water that leaves the MBR is especially suitable for reuse since it has a good quality.