Ozonation as an efficient pretreatment method to alleviate reverse osmosis membrane fouling caused by complexes of humic acid and calcium ion

• Published in: Frontiers of environmental science & engineering Vol. 13; no. 4; p. 55
• Main Authors: Zhao, Xuehao, Wu, Yinhu, Zhang, Xue, Tong, Xin, Yu, Tong, Wang, Yunhong, Ikuno, Nozomu, Ishii, Kazuki, Hu, Hongying
• Format: Journal Article
• Language: English
• Published: Beijing Higher Education Press 01.08.2019; Springer Nature B.V
• Subjects: Acids; Atomic force microscopy; Ca 2; Calcium; Calcium ions; Control methods; Deionization; Earth and Environmental Science; Electron microscopes; Environment; Fouling; Humic acid; Humic acids; Hydroxyapatite; Membrane fouling; Membrane processes; Membranes; Molecular structure; Molecular weight; Ozonation; Ozone; Particle size; Pretreatment; Research Article; Reverse osmosis; Scanning electron microscopy; Ozone; Reverse osmosis; Membrane fouling; Humic acid; Ca
• ISSN: 2095-2201; 2095-221X
• DOI: 10.1007/s11783-019-1139-y

Humic acids (HA) didn't cause obvious reverse osmosis (RO) membrane fouling in 45 h. Osmotic pressure (NaCl) affected slightly the RO membrane fouling behavior of HA. Ca 2+ promoted aggregation of HA molecules and thus aggravated RO membrane fouling. Ozonation eliminated the effect of Ca 2+ on the RO membrane fouling behavior of HA. The change of the structure of HA was related to its membrane fouling behavior. Humic acid has been considered as one of the most significant sources in feed water causing organic fouling of reverse osmosis (RO) membranes, but the relationship between the fouling behavior of humic acid and the change of its molecular structure has not been well developed yet. In this study, the RO membrane fouling behavior of humic acid was studied systematically with ozonation as a pretreatment method to control RO membrane fouling. Furthermore, the effect of ozone on the structure of humic acid was also explored to reveal the mechanisms. Humic acid alone (10-90 mg/L, in deionized water) was found not to cause obvious RO membrane fouling in 45-h operation. However, the presence of Ca 2+ aggravated significantly the RO membrane fouling caused by humic acid, with significant flux reduction and denser fouling layer on RO membrane, as it was observed by scanning electron microscope (SEM) and atomic force microscope (AFM). However, after the pretreatment by ozone, the influence of Ca 2+ was almost eliminated. Further analysis revealed that the addition of Ca 2+ increased the particle size of humic acid solution significantly, while ozonation reduced the SUVA 254, particle size and molecular weight of the complexes of humic acid and Ca 2+ (HA-Ca 2+ complexes). According to these results and literature, the bridge effect of Ca 2+ aggregating humic acid molecules and the cleavage effect of ozone breaking HA-Ca 2+ complexes were summarized. The change of the structure of humic acid under the effect of Ca 2+ and ozone is closely related to the change of its membrane fouling behavior.