Abstract
Controlling surface–protein interaction during wastewater treatment is the key motivation for developing functionally modified membranes. A new biocatalytic thermo-responsive poly vinylidene fluoride (PVDF)/nylon-6,6/poly(N-isopropylacrylamide)(PNIPAAm) ultrafiltration membrane was fabricated to achieve dual functionality of protein-digestion and thermo-responsive self-cleaning. The PVDF/nylon-6,6/PNIPAAm composite membranes were constructed by integrating a hydrophobic PVDF cast layer and hydrophilic nylon-6,6/PNIPAAm nanofiber layer on to which trypsin was covalently immobilized. The enzyme immobilization density on the membrane surface decreased with increasing PNIPAAm concentration, due to the decreased number of amine functional sites. An ultrafiltration study was performed using the synthetic model solution containing BSA/NaCl/CaCl2, where the PNIPAAm containing biocatalytic membranes demonstrated a combined effect of enzymatic and thermo-switchable self-cleaning. The membrane without PNIPAAm revealed superior fouling resistance and self-cleaning with an RPD of 22%, compared to membranes with 2 and 4 wt % PNIPAAm with 26% and 33% RPD, respectively, after an intermediate temperature cleaning at 50 °C, indicating that higher enzyme density offers more efficient self-cleaning than the combined effect of enzyme and PNIPAAm at low concentration. The conformational volume phase transition of PNIPAAm did not affect the stability of immobilized trypsin on membrane surfaces. Such novel surface engineering design offer a promising route to mitigate surface–protein contamination in wastewater applications.
Highlights
IntroductionNon-specific surface–protein interactions at the membrane interface during ultrafiltration (UF)
Non-specific surface–protein interactions at the membrane interface during ultrafiltration (UF)leads to permanent fouling, by accumulation of protein contaminants on the surface or pores of the membrane [1]
The results revealed that the poly vinylidene fluoride (PVDF)/nylon-6,6 membrane without PNIPAAm show superior enzyme activity than further revealed that the PVDF/nylon-6,6 membrane without PNIPAAm show superior enzyme the PNIPAAm containing membranes, possibly due to high immobilization density (Figure 3)
Summary
Non-specific surface–protein interactions at the membrane interface during ultrafiltration (UF). Biocatalytic fouling resistant membranes with stable enzyme immobilization onto the surface and altered pore structure offering high permeability and long-term operational stability are desired. The thermo-switchable characteristic of PNIPAAm providing strong inherent washing force was exploited to remove the membrane foulants in UF, exhibiting self-cleaning property. The polyethylene membrane onto which PNIPAAm was grafted, showed 97% flux recovery via applying a temperature-change (25 ◦ C/35 ◦ C) cleaning method to the bovine serum albumin (BSA) fouled membranes [33]. A new biocatalytic PVDF/nylon-6,6/PNIPAAm composite UF membrane was fabricated by covalently immobilizing trypsin (TR) enzyme onto functional nanofibrous surface of PVDF/nylon-6,6/PNIPAAm membrane, to achieve dual functionality of protein-digestion and thermo-responsivity for self-cleaning effect. The impact of thermoof thermo-switchable volume-phase transition on the stability of immobilized enzymes was studied.
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