Mitigation of reverse osmosis membrane fouling by coagulation pretreatment to remove silica and transparent exopolymer particles

Xiaochen Sun; Liang Duan; Zhenzhong Liu; Qiusheng Gao; Jianing Liu; Dahai Zhang

doi:10.1016/j.envres.2023.117569

Mitigation of reverse osmosis membrane fouling by coagulation pretreatment to remove silica and transparent exopolymer particles

Environ Res. 2024 Jan 15:241:117569. doi: 10.1016/j.envres.2023.117569. Epub 2023 Nov 2.

Authors

Xiaochen Sun¹, Liang Duan², Zhenzhong Liu³, Qiusheng Gao⁴, Jianing Liu⁵, Dahai Zhang⁶

Affiliations

¹ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China; School of Resources & Environment, Nanchang University, Nanchang, 330031, China; Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China, Qingdao, 266000, China.
² State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China. Electronic address: duanliang@craes.org.cn.
³ School of Resources & Environment, Nanchang University, Nanchang, 330031, China; Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China, Qingdao, 266000, China. Electronic address: liuzz79@126.com.
⁴ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China; College of Water Science, Beijing Normal University, Beijing, 100875, China.
⁵ State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China.
⁶ Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China, Qingdao, 266000, China.

PMID: 37925125
DOI: 10.1016/j.envres.2023.117569

Abstract

The dissolution of silica and transparent exopolymer particles (TEP) can deposit on the membrane surface and cause serious membrane fouling in reverse osmosis (RO) technology. Coagulation, as a common pretreatment process for RO, can effectively intercept pollutants and alleviate membrane fouling. In this study, FeCl₃ and AlCl₃ coagulants and polyacrylamide (PAM) flocculants were used to explore the optimal coagulation conditions to reduce the concentration of silica and TEP in the RO process. The results showed that the two coagulants had the best removal effect on pollutants when the pH was 7 and the dosage was 50 mg/L. Considering the proportion of reversible fouling after coagulation, the removal rate of pollutants, and the residual amount of coagulation metal ions, the best PAM dosage was 5 mg/L for FeCl₃ and 1 mg/L for AlCl₃. After coagulation pretreatment, the Zeta potential decreased, and the particle size distribution increased, making pollutants tend to aggregate, thus effectively removing foulants. The removal mechanisms of pollutants by coagulation pretreatment were determined to be adsorption, electric neutralization and co-precipitation. This study determined the best removal conditions of silica and TEP by coagulation and explored the removal mechanism.

Keywords: Coagulation; Membrane fouling; Reverse osmosis; Silica; Transparent exopolymer particles.

MeSH terms

Environmental Pollutants*
Extracellular Polymeric Substance Matrix
Filtration / methods
Osmosis
Silicon Dioxide
Water Purification* / methods

Substances

Silicon Dioxide
ferric chloride
Environmental Pollutants