Development of reactive thin film polymer brush membranes to prevent biofouling

Abstract

In an effort to reduce biofouling and enhance membrane cleaning and flux recovery, a positively charged polymer was grafted onto a membrane surface in order to inhibit bacterial growth. This modified membrane was compared to a negatively charged polymer and the native membrane surface with respect to potential to reduce bacterial growth and biofouling of a microfiltration membrane. Monomer units were grafted on 0.1 μM pore size polyethersulfone (PES) microfiltration membrane with [2-(acryloyloxy)ethyl] trimethyl ammonium chloride (AETMA) (positively charged, hydrophilic) and acrylic acid (AA) (negatively charged, hydrophilic) by initiating the co-polymerization reaction using ultraviolet radiation. Variation of reaction times from 5 to 15 min yielded grafted amounts ranging from 50 to 350 μg/cm2. After acrylic acid modification, the membranes were more negatively charged, while the charge reversed to positive (∼+30 mV) after modification with AETMA. The hydrophilicity of the membranes increased upon modification for each monomer with the contact angle decreasing from 68° to 54°. For all modified membranes, the initial membrane permeability decreased with increasing degree of grafting, however the flux in presence of Escherichia coli was 30–200% higher for the AETMA-modified membranes when compared to the unmodified membrane flux. AA-modified membranes had relatively low flux when compared to the AETMA-modified membranes and did not exhibit significant flux decline during the E. coli filtration. The flux recovery after chemical cleaning was greater than 80% for AETMA-modified membranes, suggesting that most of the fouling is reversible, whereas recovery of unmodified membrane flux was <10% even after chemical cleaning. AETMA-modified membranes were found to have a measurable antibacterial effect, whereas the AA-modified and unmodified membranes do not.