title: Interrogating chemical variation via layer-by-layer SERS during biofouling and cleaning of nanofiltration membranes with further investigations into cleaning efficiency.
abstract: Periodic chemical cleaning is an essential step to maintain nanofiltration (NF) membrane performance and mitigate biofouling, a major impediment in high-quality water reclamation from wastewater effluent. To target the important issue of how to clean and control biofouling more efficiently, this study developed surface-enhanced Raman spectroscopy (SERS) as a layer-by-layer tool to interrogate the chemical variations during both biofouling and cleaning processes. The fact that SERS only reveals information on the surface composition of biofouling directly exposed to cleaning reagents makes it ideal for evaluating cleaning processes and efficiency. SERS features were highly distinct and consistent with different biofouling stages (bacterial adhesion, rapid growth, mature and aged biofilm). Cleaning was performed on two levels of biofouling after 18 h (rapid growth of biofilm) and 48 h (aged biofilm) development. An opposing profile of SERS bands between biofouling and cleaning was observed and this suggests a layer-by-layer cleaning mode. In addition, further dynamic biochemical and infrastructural changes were demonstrated to occur in the more severe 48-h biofouling, resulting in the easier removal of sessile cells from the NF membrane. Biofouling substance-dependent cleaning efficiency was also evaluated using the surfactant sodium dodecyl sulfate (SDS). SDS appeared more efficient in cleaning lipid than polysaccharide and DNA. Protein and DNA were the predominant residual substances (irreversible fouling) on NF membrane leading to permanent flux loss. The chemical information revealed by layer-by-layer SERS will lend new insights into the optimization of cleaning reagents and protocols for practical membrane processes.
authors.affiliation: Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China. Electronic address: lcui@iue.ac.cn.
authors.forename: Li
authors.initials: L
authors.lastname: Cui
authors.affiliation: Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
authors.forename: Pengyu
authors.initials: P
authors.lastname: Chen
authors.affiliation: Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
authors.forename: Bifeng
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Centre for Biophotonics, Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: Dayi
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Centre for Biophotonics, Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: Junyi
authors.initials: J
authors.lastname: Li
authors.affiliation: Centre for Biophotonics, Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: Francis L
authors.initials: FL
authors.lastname: Martin
authors.affiliation: Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China. Electronic address: kszhang@iue.ac.cn.
authors.forename: Kaisong
authors.initials: K
authors.lastname: Zhang
mesh_terms: D018407:Bacterial Physiological Phenomena; D018441:Biofilms / Q000254:growth & development*; D057219:Biofouling / Q000517:prevention & control*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013501:Surface-Active Agents / Q000737:chemistry; D014462:Ultrafiltration; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate
keywords: Biofilm; Biofouling; Chemical composition; Cleaning efficiency; Nanofiltration membrane; Surface-enhanced Raman spectroscopy