Sulfate-reducing bacteria (SRB) are key players in many passive and active systems dedicated to the treatment of hydrometallurgical leachates. One of the main factors reducing the efficiency and activity of SRB is the low pH and poor nutrients in leachates. We propose an innovative solution utilizing biogenic ammonia (B-NH3), produced by urea degrading bacteria, as a pretreatment agent for increasing the pH of the leachate and spontaneously stimulating SRB activity via bacterial secondary metabolites. The selected strain, Ochrobactrum sp. POC9, generated 984.7 mg/L of ammonia in 24 h and promotes an effective neutralization of B-NH3. The inferred metabolic traits indicated that the Ochrobactrum sp. POC9 can synthesize a group of vitamins B, and the production of various organic metabolites was confirmed by GC-MS analysis. These metabolites comprise alcohols, organic acids, and unsaturated hydrocarbons that may stimulate biological sulfate reduction. With the pretreatment of B-NH3, sulfate removal efficiency reached ~92.3% after 14 days of incubation, whereas SRB cell count and abundance were boosted (~107 cell counts and 88 OTUs of SRB) compared to synthetic ammonia (S-NH3) (~103 cell counts and 40 OTUs of SRB). The dominant SRB is Desulfovibrio in both S-NH3 and B-NH3 pretreated leachate, however, it belonged to two different clades. By reconstructing the ecological network, we found that B-NH3 not only directly increases SRB performance but also promotes other strains with positive correlations with SRB.
Keywords: Biogenic ammonia; Biostimulation; Secondary metabolites; Sulfate-reducing bacteria; Urea degradation.
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