Technical Innovation of KUBOTA Submerged Membrane Unit

Increasing demand for high quality water has promoted technical innovations in wastewater treatment. A membrane bioreactor (MBR) has been selected in commercial installations as a promising process to meet the demand. The MBR technology has been enormously advanced, so that the MBR has been applied in more facilities. Recent years, several needs such as energy reduction, downsizing, and easy maintenance have become more important key words for the system using the MBR.The KUBOTA Submerged Membrane Unit (SMU) has been installed since 1991. Above needs have driven KUBOTA Corporation (KUBOTA) to create more promising membrane units, which have less footprint and operate with less energy consumption. In 2004, a new SMU was proposed, which has larger membrane area per unit footprint and less replacement parts. Additionally, the new SMU is made of more material which can be recycled in order to contribute to resource saving.Since new SMU was proposed in 2004, a basic performance test and a pilot study were carried out in Japan. In the basic performance test, upward flow velocity of new SMU showed higher value by 87 % compared to the current SMU, which could expect better air scouring efficiency. In the pilot study, the system was operated successfully with instant flux rate of 0.83 m/d and air low rate per single cartridge of 10 L/min/cart. The required air flow rate was saved by 43 % compared to the current SMU. In peak flow tests, 2.0 m/d of average flux rate could be sustained for a half day with air flow rate per single cartridge of 12 L/min/cart. As one of the possible factors for long-term stable operation, average flux rate per unit air flow rate per single cartridge of 0.07 (m/d)/(L/min/cart.) was proposed.According to the effluent water quality, it successfully met the requirement for the recycling use with Reverse Osmosis (RO) membrane.