RESUMO
This study investigated the activity of partial denitrification (PD) biomass/key enzymes, functional gene expressions in response to 0 ~ 50 mg/L hydroxylamine (NH2OH) addition. Results indicated that NH2OH contributed to nitrite (NO2--N) production, facilitating the maximum increase of nitrate (NO3--N) to NO2--N transformation ratio to 80.47 ± 2.82%, leading to 2.56-fold NO2--N higher than those of control. The observed transient inhibitory effect on NO3--N reduction process was attributed by high-level NH2OH (35 ~ 50 mg/L). Enzymatic assays revealed the enhanced activity of both NO3--N and NO2--N reductase while the former showed obvious superiority which led to high NO2--N accumulation. These results were further confirmed by the corresponding functional genes (narG, napA, nirS and nirK). Besides, negative influence of NH2OH addition was limited to PD aggregates, due to the increasing secretion of extracellular polymeric substances (EPS) as well as proteins/polysaccharides ratios in tightly-bound structure of EPS.
