Mg2+ distribution in activated sludge and its effects on the nitrifying activity and the characteristics of extracellular polymeric substances and sludge flocs

• Published in: Process biochemistry (1991) 2020-01, Vol.88, p.120-128
• Main Authors: Zhang, Lanhe, Zhao, Qiannan, Zhang, Mingshuang, Guo, Jingbo, Zheng, Jing, Chen, Zicheng, Jia, Yanping, Zhang, Jian, Li, Zheng, Zhang, Haifeng
• Format: Article
• Language: English
• Subjects: Activated sludge; Batch reactors; Bioflocculation; Cations; Cross-linkage; Crosslinking; Divalent cations; Emission spectra; Excitation spectra; Extracellular polymeric substances; Flocculation; Fluorescence; Functional groups; Humic acids; Immobilization; Magnesium; Mg2; Microorganisms; Nitrification; Nitrifying activity; Nitrogen removal; Sludge; Wastewater treatment; X ray photoelectron spectroscopy
• ISSN: 1359-5113; 1873-3298
• DOI: 10.1016/j.procbio.2019.10.002

[Display omitted] •Low concentration of Mg2+ (< 3 mmol/L) promotes nitrification activity of sludge.•The distribution of Mg2+ in the activated sludge floc was as follows: pellet > supernatant > LB-EPS > TB-EPS.•The number of groups in EPS increased with the Mg2+ concentration.•Aromatic PN-like substances and humic acid-like substances were identified in LB-EPS and TB-EPS. Divalent cations act as bridges among extracellular polymeric substances (EPS) and form cross-linkage for the self-immobilization of microbial biomass. However, their effects on the nitrification performance during the biological nitrogen removal are still unclear. In the present study, the effects of Mg2+ on the nitrifying activity, EPS and floc characteristics were investigated using a lab-scale sequencing batch reactor. The distribution of Mg2+ was quantified at different level of sludge floc. The results indicated that the nitrification activity was significantly improved when influent Mg2+ was below 1.1 mmol/L, but suppressed at 3 mmol/L. The overall performance characterized by COD, NH4+-N and TN, the particle size and sludge flocculation ability rapidly increased with the increase of Mg2+ concentration. Mg2+ was mainly distributed in the pellet and changed slightly in supernatant, LB-EPS and TB-EPS. The four fluorescence peaks detected by three-dimensional excitation-emission matrix spectra were attributed to PN-like substances and humic acid-like substances in the LB-EPS and TB-EPS. The results of XPS analysis demonstrated that LB-EPS and TB-EPS comprised similar elements. Therefore, the types of EPS functional groups was unchanged under varied Mg2+ concentrations, while their proportions changed and LB-EPS/EPS was key factor for the changes of bioflocculation.