Enrichment of nitrifying bacteria and their application in removing ammonia nitrogen pollution in an urban oligotrophic river

Abstract:

[Background] With the development of industry and agriculture, excessive ammonia nitrogen caused by sewage discharge has gradually become an important issue in water pollution, and ammonia nitrogen removal has become one of research hotspots. In previous studies, it has been reported that nitrifying bacteria were able to convert ammonia nitrogen to nitrate nitrogen, resulting in the reduction of ammonia nitrogen concentration in water. Thus the ammonia nitrogen elimination in polluted water by biological methods mainly depended on nitrifying bacteria. Currently there are more studies on heterotrophic nitrifying bacteria than autotrophic ones. However, the removal efficiency of the existing heterotrophic nitrifying bacteria for ammonia nitrogen in oligotrophic rivers is not ideal. In particular, the bioremediation in situ by nitrifying consortia from oligotrophic rivers has virtually not been reported. [Objective] We aim to enrich and characterize nitrifying consortia from oligotrophic rivers, and explore the potential of the ammonia nitrogen elimination in an oligotrophic river by in situ isolated consortia. [Methods] The mineral media for ammonia-oxidizing bacteria and nitrite-oxidizing bacteria are used to isolate ammonia-oxidizing and nitrite-oxidizing bacterial consortia from rivers. The microbial diversities of two consortia were identified according to sequences of V3-V4 region of 16S rRNA genes. The microscopic counting method was used to detect the growth of the consortia. Two consortia were inoculated into the artificial sewage together with aerating at room temperature, and the depletion of ammonia nitrogen was detected. Two consortia were together introduced into the oligotrophic river in situ, and the depletion of ammonia nitrogen was also detected. [Results] In this experiment, an ammonia-oxidizing bacterial consortium and a nitrite-oxidizing bacterial consortium were enriched and designated AOB1 and NOB1, respectively. In AOB1 and NOB1, 99.28% and 99.64% strains belong to Proteobacteria, respectively. Furthermore, the relatively dominant genera in AOB1 are Aeromonas (73.00%) and Delftia (9.17%). The relatively dominant species in NOB1 are Aeromonas (36.66%) and Pseudomonas (30.82%). After 2-3 d incubation in the mineral media, the biomasses of AOB1 and NOB1 reached to 5.23×10¹⁰ cells/L and 3.63×10¹⁰ cells/L, respectively. When AOB1 and NOB1 were introduced into artificial sewage with low organic matter (glucose concentration being 0.04 g/L), the depletion of ammonia nitrogen was 95.26% after 7 d, without accumulation of nitrite nitrogen. When AOB1 and NOB1 were introduced into water from an oligotrophic river (Taizhou city, Zhejiang province) with aerating (areation rate being 5 L/min) in the lab, and the depletion of ammonia nitrogen was 94.04% after 10 d. AOB1 and NOB1 were also together introduced into a 700-meter water area of the above river, and sewage was still discharged continuously into this river during the testing period. After 16 d, 49.19% ammonia nitrogen in the above water area were removed.[Conclusion] This study has enriched an ammonia-oxidizing bacterial consortium and a nitrite-oxidizing bacterial consortium from oligotrophic rivers, which can together remove ammonia nitrogen in artificial sewage and oligotrophic river water. This study provides microbial resources and a feasibility of using microbes to eliminate ammonia nitrogen pollution in urban oligotrophic rivers. It also has a potential application in implementing the desired goal of "The Beautiful Countryside".