IMPACT OF WASTEWATER DISINFECTION ON REUSE APPLICATIONS Mark LeChevallier*, Zia Bukhari, Lauren Weinrich, Patrick Jjemba American Water, Voorhees, NJ Email: mark.lechevallier@amwater.com BACKGROUND The United States does not have federal effluent quality or treatment standards for reclaimed water. Each state has adopted different regulations and guidelines, with California (under Title 22) recognized as one of the states with a comprehensive set of high effluent water quality treatment process requirements (California Department of Public Health, 2009). In terms of disinfection, the chlorine disinfection requirements in California for unrestricted reuse applications is specified as a CT value (the product of total chlorine residual and modal contact time measured at the same point) of not less than 450 mg-min/L with a modal contact time (time for highest concentration to pass through contact basin) of at least 90 minutes, based on peak dry weather design flow. Other states with well developed recycled water requirements include Florida, Washington, Arizona and Texas. Membrane bioreactors (MBRs) are often the technology of choice for water recycling facilities. This technology has the capability to produce superior effluent water quality as compared to more conventional wastewater plants with tertiary treatment, particularly with respect to ammonia, organics, particles and microorganisms. DISINFECTION OF MBR EFFLUENTS MBR effluent water quality data was collected from a wide range of satellite facilities (38 facilities) to allow proper characterization of MBR effluents with respect to inorganic, organic, physical and microbial parameters (Jacangelo et al., in press). The MBR facilities sampled during the study utilized different process configurations (submerged and external), membrane geometries (hollow-fiber, flat-sheet and tubular), fouling control strategies (relaxation and backwash) and membranes of varying ages. The MBR facilities sampled were spread across six different states and three different USEPA regions; flow-rates at these facilities ranged from 0.001 to 1.8 MGD. Results from the reconnaissance survey demonstrated, in general, that satellite MBR facilities are capable of producing oxidized, nitrified effluents that have relatively lower concentration of particles and microbial indicators (Table 1). However, some plants experienced relatively poor water quality (for an MBR) and was attributed to sampling error (there was evidence of bacterial regrowth in MBR effluents, as evidence of relatively low bacteriophage levels in Figure 1) or no effluent requirement to meet certain parameters (e.g., the permit did not require treatment of TOC or ammonia in certain circumstances, Figure 2). Bench-scale microbial inactivation experiments were conducted on the filtrate samples collected from the MBR system operating with a breached membrane to develop the residual-response curves for total coliform bacteria and seeded male specific bacteriophage. The objective of these experiments was to determine the free chlorine CTs necessary to achieve a desired level of 7924 WEFTEC 2012 Copyright ©2012 Water Environment Federation. All Rights Reserved.