Assembled denitrifying consortia for efficient nitrate removal under low-COD/N conditions

Abstract

The low denitrification efficiency of wastewater under a low COD/N ratio is an intractable barrier in the nitrate contamination remediation field. In response to this predicament, the present study enriched a high-efficiency denitrification community with the selection pressure of gradually shifting the COD/N ratio from 8.0 to 3.2 and then assembled a simplified denitrification microbial consortium based on representative species isolated from this community. The continuous culture resulted in a novel consortium consisting of Acinetobacter sp., Pseudomonas stutzeri, Paracoccus sp. and Comamonas nitrativorans, which achieved a 98.4% total nitrogen (TN) removal rate at a COD/N ratio of 3.2. Selectively culturing three of the four species indicated that delicate interspecies cooperation occurred among the four species. P. stutzeri and Paracoccus sp. were found to be the key to NOx reduction. Acinetobacter sp. could drive the co-aggregating of other species, and C. nitrativorans provided the other three microorganisms with electron donors (3-hydroxybutyric acid and succinic acid) after the depletion of acetate at COD/N 3.2. Further bioaugmentation studies showed that the assembled consortium could effectively enhance the denitrification performance of simulated nitrate-contaminated groundwater under low COD/N ratios. Overall, this study not only assembled an excellent four-species denitrifying consortium for nitrate removal and explored the interspecies cooperation in detail but also provided a novel approach to develop bioaugmentation technology in the future.