Use of photosynthetic bacteria for hydrogen sulfide removal from anaerobic waste treatment effluent

The feasibility of using photosynthetic bacteria to remove H₂S from anaerobic waste treatment effluent was investigated by growing fixed films of photosynthetic bacteria in a packed column or in a submerged tube system (“phototube”). Growth and enrichment for these organisms depended on constant illumination, anaerobic conditions and a substratum for attachment of the bacteria. Both systems were operated as flow-through processes using effluent from anaerobic (upflow) filters.Results showed that photosynthetic bacteria in fixed films can be effectively used for H₂S removal. Removal efficiencies of 81–95% were obtained on a 24-h retention time. Residual H₂S remained in the process effluent. The submerged “phototube”, showed dramatic improvement over the column, yielding a final effluent completely devoid of H₂S, at significantly shorter retention times and higher loading rates than the column. Performance appeared dependent on cell-H₂S contact and adequate illumination. The green photosynthetic sulfide-oxidizing bacterium, Chlorobium, was identified as a common organism in this phototube.This biological sulfide removal process offers the following advantages over currently used physical-chemical techniques: simplicity, no need for aeration or chemical additives and odor-free. Much research in process design is necessary before pilot or full scale application of the technique is possible.