title: Chemically induced alterations in the characteristics of fouling-causing bio-macromolecules - Implications for the chemical cleaning of fouled membranes.
abstract: Chemical cleaning is an essential process for the permeability recovery of fouled membranes, which is highly related to the interactions between chemicals and bio-macromolecules in fouling layers. In this study, three bio-macromolecules (i.e., effluent biopolymers (i.e., 0.45 μm-100 kDa) from a full-scale municipal wastewater treatment plant, bovine serum albumin (BSA) and dextran) were exposed to different chemicals (i.e., NaClO, H2O2, NaOH, and HCl) with varied concentrations to understand the changes in their properties and functional groups. The results showed that exposure to oxidants and alkali decreased the consistency index of all bio-macromolecules. With an increased oxidant dose, the molecular sizes of effluent biopolymers and dextran continuously reduced because of the oxidative cleavage of the long molecule chains. However, the molecular size of BSA sharply increased after being treated with oxidants and alkali, likely due to the cross-linkage of protein molecules. Three-dimensional fluorescence excitation-emission matrix (3D-EEM) spectra showed that the aromatic protein-like and humic substances in the effluent biopolymers were destructed readily during the treatments of oxidants and alkali. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyse further confirmed that exposures to NaClO, H2O2and NaOH led to the destruction of protein structures (i.e., amide I, II and III), the increase of carbonyl and carboxyl groups, and the decrease of fatty acids/lipids, all of which could make the bio-macromolecules more hydrophilic. Most importantly, the bio-macromolecules exposed to chemicals had better filterability, and their permeability through membranes also significantly increased, which could be explained well by the above analysis. The chemical cleaning mechanisms of fouled membranes are understood in depth in this study, and all of the results shed light on the implementation of on-line chemical enhanced backwashing in membrane processes.
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-sen University), Guangzhou 510275, China.
authors.forename: Zhongbo
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-sen University), Guangzhou 510275, China.
authors.forename: Xiang
authors.initials: X
authors.lastname: He
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-sen University), Guangzhou 510275, China.
authors.forename: Minghao
authors.initials: M
authors.lastname: Zhou
authors.affiliation: School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-sen University), Guangzhou 510275, China. Electronic address: mengfg@mail.sysu.edu.cn.
authors.forename: Fangang
authors.initials: F
authors.lastname: Meng
mesh_terms: D006861:Hydrogen Peroxide; D008567:Membranes, Artificial; D056951:Photoelectron Spectroscopy; D017550:Spectroscopy, Fourier Transform Infrared; D062065:Wastewater
chemical_list: D006861:Hydrogen Peroxide; D008567:Membranes, Artificial; D062065:Wastewater
keywords: Biopolymers; Chemical backwashing; Functional groups; Membrane cleaning; Membrane fouling