Nitrobacteria community structure during the startup in a submerged biofilters for in-situ remediation of contaminated stream

The performance and nitrobacteria population dynamics were evaluated in a pilot-scale submerged biofilter (SB) for landscape river water purification during the startup period over 45 days. During the operation, the secchi depth (SD) of effluent was developed from 35 cm to 50 cm, and suspended solid (SS) of effluent was reduced from 31.8 mg/L to 23.0 mg/L. The NH ₄ ⁺-N removal efficiency was improved gradually, however, the TN removal was not perfect due to saturated DO conditions, and its maximum removal rate was only 28.7%. The results also suggested that the water temperature had important impact on NH ₄ ⁺-N removals. Nitrobacteria community analysis indicated that the population of ammonia oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) increased gradually during the startup. Real-time PCR results showed that bacterial 16S rRNA gene increased gradually from 4.04×10 ⁸ to 1.51×10 ⁹ copies per liter of liquor, while CTO gene copies increased from 8.62×10 ⁵ to 9.65×10 ⁶copies per liter of liquor. FISH results suggested that AOB increased from 5.0% to 10.2% and NOB stabilized around 3.5%, suggesting that AOB might be more important for nitrification. FISH analysis also revealed that Nitrospira was the dominant member of NOB in the biofilms. High-density microarray analysis further confirmed that Nitrosomonas and Nitrospira were the predominant AOB and NOB, respectively. The general nitrobacteria population coupled with the performance of the SB indicated that the dynamics of nitrobacteria was important indicator to evaluate the effect of the biofilter system.