AWWA MTC61119

This paper discusses the planning and design for a large membrane bioreactor system. Specifically, the preliminary design study, a pilot testing study, and the final design are discussed for a new 10-mgd membrane bioreactor currently under construction for the Loudoun County Sanitation Authority in Virginia. The preliminary design study compared membrane bioreactors to conventional technologies, resulting in the conclusion that membrane bioreactors are cost competitive with conventional technology for achieving high-quality effluent. The pilot testing study confirmed the results of the preliminary design study and resulted in some significant findings regarding the effects of pretreatment and coagulant addition on membrane performance. Based on the results of the pilot testing operation, a membrane-flux maintenance strategy was developed to optimize performance through a combination of pretreatment, scheduled maintenance cleaning, and coagulant addition. Throughout the pilot operating period, the pilot membrane bioreactor (MBR) was operated at an average membrane flux rate of approximately 33 percent higher than that recommended by the manufacturer. The paper discusses how the findings of the pilot testing study were incorporated into the design of the full-scale facility. The completed facility will be one of the largest MBRs in the United States. As one of the first MBR designs in the 10-mgd size range, scale up of the technology for the treatment of high flows was an important consideration. The design included features such as full preliminary and primary treatment with coarse and fine screening of MBR influent, flow equalization capabilities to address the peak flow limitations of membranes, individual membrane trains to facilitate membrane cleaning, etc. The role of a membrane vendor pre-selection program is also discussed as a means for reducing risk to the owner as means of finalizing equipment cost and for developing a partnership between the engineering consultant and the selected vendor. Includes tables, figure.