Evaluation of Pathogens Removal Capabilities of An MBR System in a Full Scale Water Reclamation Facility in Nevada

Sampling of MBR permeate at operating reuse facilities frequently demonstrates that no coliform bacteria are present because of excellent rejection of bacteria through the membranes. In addition, virus studies conducted at reuse facilities also indicated substantial virus removal (0.5- log to as high as 6 log removal) depending upon virus types used, pore sizes of membranes (MF vs. UF) and characteristics of membranes utilized in MBR systems as well as MBR design and operating conditions. As a result, many utilities ultimately ask why stringent disinfection requirements are needed since reclaimed water pathogen limits are mainly met through MBR alone. The energy use and associated cost for UV disinfection may be an impetus for some facilities to contemplate turning their UV reactors down to a lower operating dose setting without compromising regulatory compliance. There is a “disconnect” between the bacterial discharge limits that address disinfection and the implicit regulatory goals for reuse disinfection. A study was conducted at the SWRF to determine virus removal capabilities of the MBR system and UV disinfection to address this “disconnect” at the SWRF and develop operational treatment goals that protect public health while optimizing energy and chemical usage. This paper summarizes methodology and outcome of the study.