Effect and mechanism of nitrification inhibitors on the activity of nitrifying bacteria

The effects of different concentrations of biological nitrification inhibitors(methyl p-hydroxyphenylpropionate(MHPP), syringic acid(SA)) and chemical nitrification inhibitors(dicyanediamine(DCD), 3, 4- dimethyl-1H-pyrazole(DMPP)) on nitrifying bacteria were compared by sequential batch experiments. The results showed that these four nitrification inhibitors significantly inhibited the treatment efficiency of nitrite-oxidizing bacteria(NOB) at the optimal concentration, thereby reducing the nitrous nitrogen conversion rate by 71.31%-87.38%. The two chemical inhibitors(DCD and DMPP) had a certain inhibitory effect on the conversion rate of ammonia nitrogen, while the two biological inhibitors(MHPP and SA) did not significantly affect the conversion of NH4+-N by ammonia-oxidizing microorganisms(AOB). The abundance of AOB(Nitrosomonas), the main functional bacterium in the nitrosation process, was not significantly affected, and the relative abundance of NOB(Nitrospira) was significantly suppressed, which was only 0.17%- 0.47%. Metagenomic analysis revealed that the molecular mechanism studies showed that the four inhibitors significantly inhibited the expression of nxrAB, a key gene closely related to NOB, and MHPP, SA and DCD did not significantly inhibit the key genes of AOB(amoCAB and hao). In addition, inhibitors further weakened the metabolic activity of NOB by reducing the abundance of pathways such as glyoxylate metabolism and amino acid transport(such as ABC transporters). The results showed that the nitrification inhibitor dosing strategy effectively achieved the directional inhibition of NOB,which laid a foundation for the stable operation of the subsequent low ammonia nitrosation process.