An initial study was conducted to assess the potential feasibility of developing an anaerobic photobiofiltration process to remove trace concentrations of H2S from gas streams such as syngas generated by coal gasification for fuel cells. Using the strain Heliobacterium chlorum, net removals of H2S by the biomass oil the order of 7-18% were obtained with a simple gas-biomass contactor energized by red light. Volumetric elimination capacities are 1-2 orders of magnitude lower than those obtained in liquid cultures under optimal conditions. This, combined with observed severe transport limitations, is an indication that the real residence time for biomass-gas contact in the photobioreactor is at least 1-2 orders of magnitude lower than the calculated value based on the ratio of the coke bed volume to gas flow rate. The quantity of aqueous medium that must be utilized to maintain active biocatalyst is shown to be quite small. Thus, the use of a gas/biocatalyst contactor should result in minimal water vapor addition to syngas streams. The challenge is designing an anaerobic photobioreactor with a significantly greater biomass surface-to-volume ratio than traditional biofiltration reactors. (c) 2005 Elsevier B.V. All rights reserved.