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OWML: Completed Projects

Project Title: Membrane Bioreactor Versus Conventional Wastewater Disinfection Study.

Project chief:  Donna Francy

Project support:  Rebecca Bushon, Erin Stelzer, Brian Mailot, Carrie Huitger, Amie Brady, Chantil Milam, Chris Kephart

Cooperators:  City of Delphos, CT Consultants, Ohio Water Development Authority, Enviroquip, Village of Gnadenhutten, and Summit County

Project duration:  January 2008 – September 2011

Introduction and problem:
Membrane bioreactors (MBRs) are a relatively new wastewater treatment technology in which the conventional secondary treatment or secondary with tertiary treatment processes are replaced by a membrane separation process. Although there is adequate information on the reduction of bacteria and protozoa concentrations through MBR processes, especially in drinking waters, manufacturers report variable success in reducing concentrations of viruses. In addition, there is little information on the efficiency of MBRs for removal of viruses from wastewaters and on comparisons to conventional secondary or secondary with tertiary wastewater treatment.

Today, Ohio has 7 operational MBR wastewater treatment plants and an estimated 20 plants under construction and (or) being designed. Wastewater treatment plants in Ohio and elsewhere in the U.S. operating with MBR systems are required to disinfect the permeate. This requirement results in an increased cost and, with chlorination, a potential increase in the formation of disinfection byproducts. Disinfection following MBR treatment may not be needed if MBR alone can remove microorganisms as well as or better than conventional technologies with disinfection.

Goals and objectives:
The overall goal of the project is to determine if disinfection following MBR treatment is needed to provide the same level of protection of public health from microorganisms as that found for conventional systems that use disinfection after secondary treatment. Specific objectives are to:

  1. compare the log reductions of enteric viruses in MBR systems to the reductions found for conventional secondary treatment before disinfection,
  2. compare the additional log reductions of enteric viruses achieved by disinfection of secondary wastewaters at conventional plants with those achieved by disinfection of MBR treated wastewaters, and
  3. compare the log reductions of indicator bacteria and indicator viruses (coliphage) in MBR and conventional systems, and identify which indicator(s) best represents the removal of enteric viruses.

The research project will be done at 3 small- to medium-sized wastewater treatment plants in Ohio that are within the range of MBR plants currently being constructed. The study will include the following:

  1. Two Kubotaź system MBR plants with UV disinfection—Cities of Delphos (medium) and Gnadenhutten (small). The Kubota system was selected due to the availability of MBR plants operating in Ohio with at least one year of experience,
  2. One conventional treatment plant—Summit County Aurora Shores (small with UV and tertiary).
  3. Samples will be collected on 5 sample dates at each MBR plant and 2 sample dates at the conventional plant throughout the recreational seasons of 2008−09 (May 15 through October 15) at a range of flow conditions.
  4. Samples will be collected (1) before conventional or MBR secondary treatment (post- preliminary), (2) after secondary or MBR treatment (pre-disinfection) and (3) after disinfection (post-disinfection). At the conventional plant, an additional sample will be collected after secondary, but before tertiary treatment (pre-tertiary).
  5. Fixed-interval samples will be collected over a 2-hour time interval. Compensation will be made for retention time between sample points within the treatment plant.
  6. Samples will be analyzed for E. coli, fecal coliforms, enterococci, somatic and F-specific coliphage, culturable viruses, and enteric viruses by qPCR (enteroviruses, noroviruses and adenoviruses). Analysis of samples for culturable viruses is included because of their ability to infect cells and potentially cause disease.