Removal of High-Strength Ammonia Nitrogen in Biofilters: Nitrifying Bacterial Community Compositions and Their Effects on Nitrogen Transformation

Nitrosomonas

,

Nitrobacter

,

Lambdalikevirus,

and

Deinococcus

) had no relationship with N concentration in the effluent (

Nitrosomonas

and

Nitrobacter

) in DAS were not significantly related with N concentration in the effluent (

Nitrososphaera

, existed in the DAS recorded in 3−-N concentration in the effluent negatively. The low ΔNO3−-N/ΔNH4+-N ratio in the DAS caused by high AOA growth in 3−-N, rather than COD, TN, or NH4+-N, had positive effects on the relative abundance of this genus, and can be used in predicting the degree of NO3−-N accumulation from another point. In terms of AOB, two main genera were identified,

Nitrosomonas

and

Nitrosospira

. Only

Nitrosospira

was present in DAS and was not the dominant genus in CFM and DAS. Thus, underrepresentation was observed. However, the results in 4+-N, and NO3−-N removal, confirming that

Nitrosomonas

, which had the highest abundance, did not necessarily act as a crucial indicator of N variation. Compared with no significant correlation between genera and NH4+-N in CFM,

Nitrosospira

in DAS had a better prediction of NH4+-N variation because of a significant relationship between its relative abundance and NH4+-N concentration was determined. Similarly,

Nitrosospira

showed an inverse relationship with NH4+-N and NO3−-N, and the overgrowth of this genus facilitated the decrease in NH4+-N concentration at effluents via nitritation, thereby resulting in low ΔNO3−-N/ΔNH4+-N ratio in the DAS (

Nitrosospira

from the lower to the upper layer (4+-N elimination and NO3−-N accumulation. This result was in agreement with a previous finding [4+-N, and NO3−-N concentrations in the CFM–DAS system. Unexpectedly, no correlation between

Nitrobacter

and COD, TN, NH4+-N, and NO3−-N concentrations in the effluent was observed unlike in a previous study [

Nitrobacter

, which was dominant in NOB, cannot be used as an indicator of N transformation.

The significant correlation between dominant genera and N concentration in the effluents showed that some genera can be used as indicators of N transformations. Interestingly, the four genera in CFM (and) had no relationship with N concentration in the effluent ( Table 2 ) possibly because of the unique characteristics of the filter media of CFM, where the growth of bacteria was not affected by the concentrations of pollutants that produced relatively stable relationship between genera in AOB and NOB. By contrast, structures in CFM that were not subjected to space–time changes supported the relatively stable nitrifying bacterial compositions irrespective of changes in N concentration. Similarly, two of the four genera (and) in DAS were not significantly related with N concentration in the effluent ( Table 2 ). The only major AOA genus,, existed in the DAS recorded in Table 2 , which correspond with NO-N concentration in the effluent negatively. The low ΔNO-N/ΔNH-N ratio in the DAS caused by high AOA growth in Figure 3 confirmed this result. This finding revealed that NO-N, rather than COD, TN, or NH-N, had positive effects on the relative abundance of this genus, and can be used in predicting the degree of NO-N accumulation from another point. In terms of AOB, two main genera were identified,and. Onlywas present in DAS and was not the dominant genus in CFM and DAS. Thus, underrepresentation was observed. However, the results in Table 2 show the most important one that works in COD, NH-N, and NO-N removal, confirming that, which had the highest abundance, did not necessarily act as a crucial indicator of N variation. Compared with no significant correlation between genera and NH-N in CFM,in DAS had a better prediction of NH-N variation because of a significant relationship between its relative abundance and NH-N concentration was determined. Similarly,showed an inverse relationship with NH-N and NO-N, and the overgrowth of this genus facilitated the decrease in NH-N concentration at effluents via nitritation, thereby resulting in low ΔNO-N/ΔNH-N ratio in the DAS ( Figure 3 ). Furthermore, the decrease in DO along the depth gradient ( Table S4 ) in accordance with the apparent increase in the relative abundance offrom the lower to the upper layer ( Figure 5 ) caused NH-N elimination and NO-N accumulation. This result was in agreement with a previous finding [ 38 ]. Given that the rate of AOA was not significantly higher than that of AOB in N-rich environments [ 16 ], AOA was weaker than AOB in terms of the correlation between genus and COD, NH-N, and NO-N concentrations in the CFM–DAS system. Unexpectedly, no correlation betweenand COD, TN, NH-N, and NO-N concentrations in the effluent was observed unlike in a previous study [ 6 ]. Thus, the relative abundance of, which was dominant in NOB, cannot be used as an indicator of N transformation.