MBR's Ability to Disinfect - Pathogen Removal for Discharge and Reuse

Membrane Bioreactor (MBR) technology combines secondary and tertiary wastewater treatment in one compact step. This technology has been used to treat wastewater for over 35 years and is considered the best available technology for achieving high quality effluent. MBR has demonstrated a significant degree of bacterial rejection, which provides potential cost savings opportunities to utilities by reducing or eliminating additional disinfection steps. Demonstrated removal of viral and protozoan pathogens also makes MBR a strong choice for utilities that may want to reuse the treated water for non-potable or potable purposes, either now or in the future.

This paper and presentation will share data collected from more than 10 MBR facilities to provide a benchmark of the long term microbial and pathogen removal performance of full scale MBR installations. The facilities all use ZeeWeed 500D* ultrafiltration membranes and were selected to include varying membrane age, hydraulic capacity and geographical location. Almost 3000 data points were collected to provide an aggregate view of treatment efficacy, measuring total coliforms, fecal coliforms, and E.Coli bacteria in the raw wastewater and MBR treated effluent (both pre and post-disinfection).

The geometric mean concentrations in the effluent prior to disinfection across all the plants examined in this study for E. coli, fecal coliforms, and total coliforms were 1.1 CFU/100mL, 1.6 CFU/100mL, and 2.6 CFU/100mL, respectively. 95th—percentile values were 3.4CFU/100mL for E.Coli, 10CFU/100mL for fecal coliforms, and 34CFU/100mL for total coliforms. These results, summarized in Table 1, demonstrate the ability of MBR technology to produce effluent that meets typical regulatory limits for surface water discharge and some non-potable reuse.

There are numerous facilities, listed in Table 2, located in both the US and Canada, that are utilizing the ability of MBR to achieve their required disinfection, meeting effluent discharge requirements for surface water discharge or non-potable reuse without further chlorination or UV. Some of these sites were originally constructed to include downstream disinfection in the form of either chlorine or UV, and have since taken this offline, while some sites were constructed with the MBR as the sole technology for meeting effluent coliform limits. This paper will look at case studies of these MBR facilities, including data from these sites and the regulatory allowances to bypass or remove downstream disinfection.

Removal of virus and protozoa is critical in flowsheets deployed for potable reuse applications. This paper will also address the efficacy of removal of these pathogens through MBR systems. Empirical data of virus and giardia removal from operating facilities, showing high removal of these pathogens will be presented. This data demonstrates a benefit of MBR technology in advanced reuse applications, or for utilities that want to be prepared for potential reuse needs.