The Membrane Biofilm Reactor: The Natural Partnership Of Membranes And Biofilm

Abstract. Many exciting new technologies for water-quality control combine microbiological processes with adsorption, advanced oxidation, a membrane, or an electrode to improve performance, address emerging contaminants, or capture renewable energy. An excellent example is the H₂-based membrane biofilm reactor (MBfR), which delivers H₂ gas to a biofilm that naturally accumulates on the outer surface of a bubbleless membrane. Autotrophic bacteria in the biofilm oxidize the H₂ and use the electrons to reduce NO₃-, ClO₄-, and other oxidized contaminants. This natural partnership of membranes and biofilm makes it possible to gain many cost, performance, and simplicity advantages from using H₂ as the electron donor for microbially catalyzed reductions. The MBfR has been demonstrated for denitrification in drinking water; reduction of perchlorate in groundwater; reduction of selenate, chromate, trichloroethene, and other emerging contaminants; advanced N removal in wastewater treatment, and autotrophic total-N removal.

Introduction
A vanguard of new technologies for water-quality control combines microbiological processes with physical or chemical processes. Table 1 lists a number of combined technologies that are in use or under development today. The microbiological part of the combination most often involves a biofilm, although suspended biomass also is used. The physical or chemical part includes adsorption, advanced oxidation, a membrane, an electrode, or more than one of them. The treatment targets include removing very difficult-to-biodegrade organics that are natural or anthropogenic, reducing oxidized contaminants, and capturing the energy in wastewater.

The trend toward combined technologies began as much as three decades ago, but it is accelerating today due to three forces:
(1) A push comes from revolutionary advances in nucleic-acid-based techniques from molecular biology (Rittmann 2002) that make it possible to understand and ultimately lead to control the structure and function of microbial communities.
(2) Another push comes from new materials -- particularly including membranes and nano-based materials (e.g., TiO₂) -- that open up new avenues for overcoming the limitations of more conventional ways of using microbial communities.
(3) A pull comes from society's needs to address a large number of emerging pollutants, better performance for traditional pollutants, and better cost and energy efficiencies.

SOURCE: APTwater, Inc.