MEMBRANE BIOREACTOR INDUSTRIAL AND MUNICIPAL WASTEWATER APPLICATIONS: LONG TERM OPERATING EXPERIENCE

There has been recent widespread interest in the U.S. and other countries in the use of membranes for biomass-effluent separation as an alternative to conventional gravity separation as a component in bioreactor flowsheets for treatment of industrial and municipal wastewaters. Although membrane biological reactors (MBRs) for treatment of wastewaters were introduced over 30 years ago, published information to-date has typically been in the form of short term operational and performance results. Little information has been reported with respect to the longer term unforeseen issues arising when the two unit processes (i.e., suspended growth bioreactor and membrane component) are coupled together. Identification of the issues and their timely resolution through cost-effective engineered solutions based on demonstrated results and/or fundamental process research, are critical if the MBR technology is to represent an attractive alternative to more conventional biological systems in certain applications. The authors have been involved in a number of commercial MBR system projects for industrial and/or municipal wastewater treatment dating back to 1991. These projects resulted in the identification of a number of unanticipated operating issues resulting from the coupling of the bioreactor and the membrane unit operations. Generally the issues are specific to the membrane configuration characterizing the MBR system and the characteristics of the wastewater being treated. External membrane MBRs in which high trans membrane pressure (TMP) and liquid cross-flow velocity are utilized to effect filtration, have proven to be robust and maintenance friendly. The issues most common to internal membrane MBRs in which a low TMP and cross flow velocity are utilized to effect filtration, are generally membrane component related. Tight wastewater screening, and optimization of membrane cleaning equipment and procedures are necessary to reduce manpower maintenance requirements.