Iron has a substantial effect on
the growth and metabolism of anammox
bacteria in anammox granular sludge (AnGS). Here, the interaction
between ferrous ions, iron nanoparticles (FeNPs), and AnGS was examined
to study the mechanism by which iron affects the spatial structure
and nitrogen removal function of the AnGS system from a morphological
and molecular biology perspective. The supply of 0.03 mM Fe2+ increased the live/dead bacterial ratio and the abundance of anammox
bacteria. The ribosome metabolism and protein synthesis of bacteria
were also promoted. However, higher microbial activity provided by
0.03 mM Fe2+ decreased the porosity and restricted the
mass transfer of the AnGS, while the addition of 0.1 mM FeNPs increased
the lysis and death of microorganisms by 12.57%, which led to an increase
in the porosity (6.05%) and mass transfer of the AnGS. FeNPs also
increased the expression of the enzymes involved in the anammox reaction
(hydrazine synthetase and hydrazine dehydrogenase) and iron storage
proteins. Thus, the increase in mass transfer and anammox-related
enzymes jointly promoted the nitrogen removal of the AnGS. These results
provided deep theoretical insights that could be used to aid the efficient
and sustainable operation of the AnGS system.
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