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T h e C a s e F o r The Case For R e m o v i n g D i s i n f e c t i o n Removing Disinfection F r o m W a s t e w a t e r T r e a t m e n t From Wastewater Treatment Membrane bioreactor (MBR) technology is proven to adequately remove microbial contaminants all on its own, eliminating the time, money, and focus spent on disinfection. By Stephen Katz A tremendous amount of pressure is put on municipalities to provide higher-quality effluent within increasingly constrained capital and operating budgets — they are required to do more with less. Wastewater treatment industry stakeholders should strive to understand and prove the capabilities of technology so as to enable the implementation of the required treatment levels within existing budgets. Membrane bioreactor (MBR) technology enables municipalities to effectively remove pathogens without the need — and cost — of an additional disinfection step. Regulatory agencies provide guidance on safe limits of pathogens in water bodies actively used by the public for recreational purposes. In 2012 the U.S. EPA published recreational water quality criteria (RWQC) for protecting human health for primary contact recreational use, and in 2006 the European Union (EU) published the new Bathing Water Directive, which member states must follow to inform the public of bathing water quality. Since wastewater treatment plants discharge directly into surface waters and can be a source of these pathogens, microbial parameters are generally among their effluent water-quality standards. Historically, regulations have been based on total coliforms, fecal coliforms, or Escherichia coli (E. coli), but have more recently moved to favor E. coli, as it is the only member of the total coliform family exclusively found in the feces of humans or other warm- blooded animals and the best indicator of possible presence of intestinal-disease-causing bacteria, viruses, and protozoa. As further protection, facilities are typically mandated to include a disinfection step to the treatment flowsheet. MBR Efficacy When considering municipal wastewater treatment by the conventional activated-sludge process (CAS) to achieve effluent quality requirements for microbial indicators, the addition of a disinfection step is required because the CAS process cannot reliably remove indicator bacteria to a low-enough level. In this treatment scheme, microbial removal is partially dependent on the settling of bacterial floc particles, a process which is subject to variability. MBR is considered the best available technology for achieving high-quality effluent, as it achieves secondary and tertiary wastewater treatment in one, compact step. When ultrafiltration membranes are incorporated into the MBR process, the dominant removal mechanism for coliforms is size exclusion. The coliforms may be directly excluded or may be indirectly blocked due to sorption to the activated sludge solids, which are themselves excluded. The presence of a dynamic filtration layer on the membrane surface can further enhance the size-exclusion capabilities of the membrane pores. To help assess the long-term viability of MBR technology to effectively remove pathogens, GE conducted an extensive multiyear study where more than 2,000 samples were taken at 10 plants of various ages, hydraulic capacities, and geographic locations. Depending on the plant's effluent requirements, 14 wateronline.com ■ Water Innovations MBR technology enables municipalities to effectively remove pathogens without the need — and cost — of an additional disinfection step.