Ultrafiltration (UF) is a reliable technology for water treatment, which can effectively remove a wide range of contaminants including suspended solids, biopolymers, etc. However, UF performance can be limited by the effect of membrane fouling. According to a study led by researchers at Nanjing Normal University, an assessment of both the additional costs and environmental implications demonstrated the feasibility of the MHC-based UF process as a novel approach for enhancing the performance of the UF process in the treatment of water, and to further the knowledge about approaches for the control of membrane fouling.
The researchers reported in the Journal of Membrane Science, Jun.18 edition, that membrane fouling is a major obstacle for ultrafiltration (UF) in water treatment. Here, a strategy for fouling mitigation by applying an ultra-low concentration of moderately-hydrophobic chitosan (MHC) and using a mildly elevated backwash temperature was proposed. The effects of MHC type, concentration, and backwash temperature were investigated in continuous-flow tests using PVDF hollow fiber membranes and model raw water. Compared to the process without MHC, or with the addition of chitosan or conventional coagulant polyaluminum chloride, the MHC-based UF system under optimal conditions (MHC: 0.01 mg/L; backwash water temperature: 40 °C) demonstrated its superiority with reduction of ~55% reversible fouling (RR) and ~80% irreversible fouling (IRR), as well as improved effluent quality. A mechanistic study by experimental analyses and theoretical computations revealed that the improved performance of the MHC-based UF process was attributed to the following: (1) MHC inhibited contaminant accumulation on the membrane through a hydrophilization surface-modification effect on the PVDF; (2) increased backwash temperature promoted fouling release (by destabilizing the cake layer structure) and enhanced the surface-modification effect. The additional cost of MHC dosing and backwash water heating was estimated at ~0.126 Chinese Yuan per ton of produced water, and the environmental risk of applying MHC was lower than that of conventional water treatment chemicals. In summary, the MHC-based process has the potential to be a feasible and cost-effective approach for UF fouling control.
Min Hu (first author) worked with authors Lina Zhao, Ningbo Yu, Zhonglong Yin, Zhen Yang (corresponding author), and Weiben Yang from School of Chemistry and Materials Science, the Jiangsu Provincial Key Laboratory of Material Cycling and Pollution Control, Nanjing Normal University, Ziqi Tian from the Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, and Nigel J.D. Graham from the Department of Civil and Environmental Engineering, Imperial College.
The study, “Application of ultra-low concentrations of moderately-hydrophobic chitosan for ultrafiltration membrane fouling mitigation” was published in the Journal of Membrane Science in the Jun.18 edition. This work was completed by the School of Chemistry and Materials Science, the Jiangsu Provincial Key Laboratory of Material Cycling and Pollution Control, Nanjing Normal University, the Department of Civil and Environmental Engineering, Imperial College, Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, and was supported by the National Natural Science Foundation of China, the Natural Science Foundation of Jiangsu Province of China, the Foundation of Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), and the Scientific Computing Centre of NNU.