(91a) Reduction of Perchlorate and Other Micropollutants in a Hydrogen-Based, Hollow-Fiber Membrane Biofilm Reactor

Perchlorate (ClO4-) contamination of surface and ground waters is a significant environmental concern in the United States. Unfortunately, perchlorate is very soluble and stable in water, and it is not removed by conventional drinking water treatment processes (i.e., flocculation, coagulation, sedimentation, and filtration). Advanced treatment processes, such as reverse osmosis, ion exchange, membrane filtration, and electrodialysis, can remove perchlorate, but are costly and generate perchlorate-containing wastes.

Biological treatment is a promising treatment approach, as perchlorate can be reduced to chloride and water by dissimilatory (per)chlorate-reducing bacteria (PCRB), i.e., bacteria that reduce perchlorate and chlorate (ClO3-) as electron acceptors for growth. PCRB are ubiquitous in the environment, and perchlorate is a highly energetic electron acceptor, with a redox potential similar to that of nitrate. All PCRB are facultative aerobes or microaerophiles, and most can also use nitrate and nitrite as electron acceptors.

For biological reduction in drinking water, an electron donor typically must be added. Ethanol, methanol, and acetate are common electron donors used in wastewater treatment, but these are not desirable for the drinking water setting due health, aesthetic, and regulatory concerns. Hydrogen is an ideal electron donor because (1) it is inexpensive; (2) it is non-toxic, increasing public acceptance for its use for water treatment; (3) it is sparsely soluble, so it is not possible to ?overdose? the system and cause re-growth downstream of the treatment process; and (4) it can be generated on-site. The historic disadvantage is that hydrogen is difficult to deliver without sparging, which is wasteful and potentially dangerous.

A novel hydrogen-based bioreactor, the hydrogen-based, hollow-fiber membrane biofilm reactor (MBfR), can deliver hydrogen safely and efficiently without sparging. The MBfR consists of a bundle of composite, hydrophobic hollow-fiber membranes collected into a hydrogen-supplying manifold at one end and sealed at the other. Pressurized hydrogen is supplied to the interior of the fibers and diffuses through the wall to a biofilm growing on the fiber surface. The biofilm consumes hydrogen as it reduces oxidized contaminants present in the water. No hydrogen bubbles are produced, and the bulk liquid may have a negligible hydrogen concentration, providing utilization efficiencies approaching 100%. The MBfR is different from ?membrane bioreactors? used in wastewater treatment. Membrane bioreactors use porous, hydrophilic membranes to separate particles from permeating water, while the MBfR uses composite microporous/non-porous membranes to deliver hydrogen gas to bacteria.

This presentation center on the MBfR and its application to perchlorate removal. It also will briefly address the MBfR's use for several other oxidized micropollutants.