Intensive coagulation of secondary effluent to mitigate reverse osmosis membrane fouling at low temperatures: Strategies of pre-oxidation and coagulant aids addition

• Published in: Journal of water process engineering Vol. 66; p. 106071
• Main Authors: Yang, Qiang, Wei, Xiaohan, Hu, Tengfei, Wang, Jie, Li, Peizhuo, Gao, Aili, Wang, Jinlong, Cheng, Lihua, Huang, Shujuan, Bi, Xuejun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2024
• Subjects: Coagulant aid; Enhanced coagulation; Membrane fouling; Pre-oxidation; Reverse osmosis; Enhanced coagulation; Reverse osmosis; Coagulant aid; Pre-oxidation; Membrane fouling
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2024.106071

Conventional coagulation-sedimentation, typically used as a pretreatment for ultrafiltration-reverse osmosis, is ineffective in solving the problem of reverse osmosis membrane fouling at low temperatures. In this study, the coagulation enhancement effect of pre-oxidation and the addition of coagulant aids on conventional coagulation with polyaluminum chloride as a coagulant was investigated. The results showed that the addition of fly ash, powdered activated carbon, or diatomite as coagulant aids improved the reduction of turbidity, dissolved organic carbon (DOC), and ultraviolet absorbance at 254 nm (UV254), and also reduced the residual content of dissolved aluminum ions. Among them, diatomite was superior. Pre-oxidation before conventional coagulation increased the reduction of turbidity and UV254 by about 50 % and doubled the removal of proteins, polysaccharides, and DOC compared to conventional coagulation. Ozone was superior to sodium hypochlorite. The combination of ozone pre-oxidation and diatomite addition with conventional coagulation further increased the pollutant removal rate, with the removal rates of turbidity, UV254, polysaccharides, proteins, and DOC reaching 82.20 %, 52.35 %, 26.34 %, 24.89 %, and 26.38 %, respectively. In addition, the residual content of dissolved aluminum ions decreased to 0.84 mg/L. The reverse osmosis filtration simulation test showed that pretreating the feed water with the enhanced coagulation by the combination of ozone pre-oxidation and diatomite addition resulted in a slower decrease in membrane flux, reduced foulant content on the membrane surface, and the smallest increase in contact angle. The results of this research may offer a viable pretreatment method to reduce fouling in reverse osmosis membranes operating at low temperatures. [Display omitted] •Diat-CGG is more effective in removing turbidity, DOC, and reducing the residual Al.•Pre-oxi-CGG with NaClO or O3 as oxidant improve turbidity and organic matter removal.•O3-diat-CGG further increase coagulation efficiency and had the lowest residual Al.•O3-diat-CGG can remove more macromolecular hydrophobic organic matters.•O3-diat-CGG effectively alleviate RO membrane performance degradation during operation.