Development of reactive thin film polymer brush membranes to prevent biofouling

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 mu M 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 mu g/cm(2). After acrylic acid modification, the membranes were more negatively charged, while the charge reversed to positive (similar to+30 mV) after modification with AETMA. The hydrophilicity of the membranes increased upon modification for each monomer with the contact angle decreasing from 68 degrees to 54 degrees. 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. (C) 2010 Elsevier B.V. All rights reserved.