Mixed culture hydrogenotrophic nitrate reduction in drinking water.

Isolation and identification of the bacteria from a hydrogenotrophic reactor for the denitrification of drinking water revealed that several microorganisms are involved. Acinetobacter sp., Aeromonas sp., Pseudomonas sp. and Shewanella putrefaciens were repeatedly isolated from the hydrogenotrophic sludge and postulated to be of primary importance in the process. Nitrate reduction to nitrite appears to be a property of a diverse group of organisms. Nitrite reduction was found to be stimulated by the presence of organic growth factors. Thus, in a mixed culture, hydrogenotrophic denitrification reactor, NO inf2 (sup-) formed by NO inf3 (sup-) -reducers can be converted by true denitrifiers thriving on organic growth factors either present in the raw water, or excreted by the microbial community. Mixotrophic growth also contributes to NO inf2 (sup-) reduction. Finally, chemolithotrophic bacteria participate in the nitrite to nitrogen gas conversion.