Ag-NPs were introduced into the OMBR system at an average concentration of 0.29 mg/L from Day 64. Nitrifying efficiency decreased from 98% to about 15% within 2 days after the addition of Ag-NPs, which resulted in significant accumulation of NH4-N within the bioreactor, and a significant drop of the overall removal efficiency from 98% to about 90% (Fig. 4). The significant deterioration in the nitrifying activity clearly manifests the inhibition effects of Ag-NPs. This corroborates a study which showed that the presence of Ag-NPs (for more than one month) led to a high degree
of nitrification inhibition and increase in NH4-N and NO2-N concentrations in the effluent (Liang et al., 2010). NH4-N removal may be affected by Ag-NPs, due to the inhibition of ammoniumoxidizing bacteria and nitrite-oxidizing bacteria activities. Studies have shown that Ag-NPs at 1.0 mg/L inhibit the respiration of autotrophic nitrifying organisms significantly (at 85%) in a continuous flow bioreactor (Choi et al., 2008). However, nitrifying activity
started to restore after 90 days, and finally recovered to almost 100% after 100 days.
Ag-NPs were introduced into the OMBR system at an average concentration of 0.29 mg/L from Day 64. Nitrifying efficiency decreased from 98% to about 15% within 2 days after the addition of Ag-NPs, which resulted in significant accumulation of NH4-N within the bioreactor, and a significant drop of the overall removal efficiency from 98% to about 90% (Fig. 4). The significant deterioration in the nitrifying activity clearly manifests the inhibition effects of Ag-NPs. This corroborates a study which showed that the presence of Ag-NPs (for more than one month) led to a high degreeof nitrification inhibition and increase in NH4-N and NO2-N concentrations in the effluent (Liang et al., 2010). NH4-N removal may be affected by Ag-NPs, due to the inhibition of ammoniumoxidizing bacteria and nitrite-oxidizing bacteria activities. Studies have shown that Ag-NPs at 1.0 mg/L inhibit the respiration of autotrophic nitrifying organisms significantly (at 85%) in a continuous flow bioreactor (Choi et al., 2008). However, nitrifying activitystarted to restore after 90 days, and finally recovered to almost 100% after 100 days.
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