A modified coagulation-ultrafiltration process for silver nanoparticles removal and membrane fouling mitigation: The role of laminarin

• Published in: International journal of biological macromolecules 2021-03, Vol.172, p.241-249
• Main Authors: Zou, Zhangjian, Gu, Yingqiu, Yang, Weihua, Liu, Minjie, Han, Jing, Zhao, Shuang
• Format: Article
• Language: English
• Subjects: Adsorption; Aluminum Hydroxide - chemistry; Coagulant aid; Coagulation-ultrafiltration; Flocculation; Fresh Water - chemistry; Glucans - chemistry; Humans; Humic Substances - analysis; Laminarin; Membranes, Artificial; Metal Nanoparticles - chemistry; Metal Nanoparticles - ultrastructure; Porosity; Silver - isolation & purification; Ultrafiltration - methods; Water Pollutants, Chemical - isolation & purification; Water Purification - methods
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2021.01.034

Silver nanoparticles (AgNPs) in surface water are highly toxic to humans and difficult to remove due to their adsorption to humic acid (HA). In this study, laminarin (LA) was used as a coagulant aid in a coagulation-ultrafiltration (C-UF) system to improve AgNPs-HA removal efficiency. C-UF efficiency, membrane flux, and flocs properties were investigated to explore the AgNPs-HA removal mechanism and membrane fouling. Results showed that when poly aluminum chloride (PAC) was dosed with LA, AgNPs-HA removal was 10–15% higher than when using PAC alone. The C-UF system using only PAC improved the AgNPs-HA removal efficiency through increased coagulation but resulted in membrane fouling. LA application helped mitigate membrane fouling, and the highest normalized permeate flux and smallest resistance values (0.573 and 2.180 × 1010 m−1, respectively) were achieved when 0.1 mg/L of LA was applied with 5 mg/L of PAC. The alleviating mechanism was related to flocs with large sizes and small fractal dimension (Df) values, generating a cake layer with porous morphology. This cake layer was easily removed by flushing and backwashing, which resulted in minimal resistance and fouling of the UF membrane. [Display omitted] •Silver nanoparticles (AgNPs) could be effectively removed by C-UF technology.•Membrane flux restored availably after backwashing due to laminarin (LA) addition.•LA addition improved AgNPs removal and meanwhile mitigated membrane fouling.•Flocs possess big sizes and loose structure under the action of LA.•The formation of a porous cake layer brought low membrane resistance and fouling.