Dongdong Xu,Aqiang Ding,Yang Yu,Ping Zheng,Meng Zhang,Zhetai Hu
Magnetite (Fe 3 O 4 ) particles have been widely reported to enhance the anammox's activity in anammox granular sludge (AnGS), yet the underlying mechanisms remain unclear. This study demonstrates that both Fe 3 O 4 microparticles (MPs) and nanoparticles (NPs) at a dosage of 200 mg Fe 3 O 4 /L significantly increased the specific anammox activity (SAA) of AnGS. Additionally, the transcriptional activities of the hzs and hdh genes involved in the anammox process, as well as the heme c content in AnGS, were also notably enhanced. Notably, Fe 3 O 4 NPs were more effective than MPs in boosting anammox activity within AnGS. Mechanistically, Fe 3 O 4 MPs released free iron, which anammox bacteria utilized to promote the synthesis of key enzymes, thereby enhancing their activity. Compared to MPs, Fe 3 O 4 NPs not only elevated the synthesis of these key enzymes to a higher level but also induced a nanofluids effect on the surface of AnGS, improving substrate permeability and accessibility to intragranular anammox bacteria. Moreover, the nanofluids effect was identified as the primary mechanism through which Fe 3 O 4 NPs enhanced anammox activity within AnGS. These findings provide new insights into the effects of nanoparticles on granular sludge systems, extending beyond AnGS.
Low temperatures were a critical factor that inhibited anaerobic ammonium oxidizing bacteria (AnAOB) activity. This study demonstrated the effect of exogenous zero-valent iron (ZVI) on Anammox-hydroxyapatite (HAP) system at 17°C. The results showed that long-term addition of ZVI increased the system nitrogen removal efficiency by 8.59% and alleviated the inhibition of AnAOB by low temperature. After addition of ZVI, the activity of AnAOB and the heme c content increased by 58.20% and 4.83%, respectively. Moreover, the functional enzyme activities of NIR, HZS, and HZO increased by 94.12%, 36.36%, and 16.67%, respectively. The concentrations of quorum sensing molecules, i.e., C 6 -HSL and C 8 -HSL, increased by 191.17% and 41.54%, respectively, after ZVI addition. Metagenomic analysis revealed that the addition of 5 g/L ZVI stimulated the relative abundance relative abundance of Fe(II) metabolism-related genes in AnAOB at 17 °C, thereby contributing to the uptake, transport, utilization, and storage of Fe(II). The addition of ZVI could improve the nitrogen removal performance of the anammox-HAP system at the low temperature.
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