Characterization of magnetite assisted anammox granules based on in-depth analysis of extracellular polymeric substance (EPS)

Magnetite can be considered as an iron-rich carrier particles that can be ionized into Fe2+ and Fe3+ which im-proves the activity and aggregation of anammox bacteria. Three samples from this carrier assisted granulation reactor with size groups including Flocs, FL (0-300 mu m), Small Granules, SG (300-500 mu m) and Large Granules, LG (500-1000 mu m) were used in this study. It was observed that as the granule size increased, the iron-rich carrier content increased, and their active crystals improved the microbial cell density. Specific anammox ac-tivity (SAA) was 34.63 +/- 5.02, 55.29 +/- 5.14, and 63.81 +/- 7.50 mg-N/g-VSS/d for FL, SG and LG, respectively. In addition, in heme c content of LG was 31.5 % higher than SG and 62.9 % higher than FL. An in-depth study into the extracellular polymeric substances (EPS) showed that the secretion intensity of essential proteins followed the order of FL < SG < LG in loosely bound EPS and FL > SG > LG in tightly bound EPS. Functional group analysis confirmed that the hydrophobic C-N and N-H stretching vibration band had almost 3.5 times higher transmittance intensity in LG than the other sizes and the corresponding ratio of alpha-helix/(beta sheet + random coil) in secondary derivative proteins analysis showed tightness in the protein structures of FL. The relative abundance of Brocadia Sinica increased from 0 % in FL to a high of 20.46 % in LG. This study aims to communicate the essence of in-depth EPS analysis beyond the usual EPS yield and major contents of proteins (PN) and poly-saccharides (PS) analysis.

Automated summary

Magnetite is an iron-rich carrier that can enhance the activity and aggregation of anammox bacteria. In this study, different-sized samples from a granulation reactor were used, and it was found that larger granules had higher iron content and improved microbial cell density. The specific anammox activity increased with granule size, and the heme c content was also higher in larger granules. The extracellular polymeric substances (EPS) analysis showed differences in secretion intensity and protein structures among the different sizes. The relative abundance of Brocadia Sinica also increased with granule size. This study highlights the importance of in-depth EPS analysis beyond traditional yield and major content analysis.