Photochemical modification of membrane surfaces for (bio)fouling reduction: a nano-scale study using AFM

Biofouling, due to microbial growth on membranes, is a common problem during the operation of water treatment membrane plants. It leads to an increase in operation and maintenance costs due to the deterioration of membrane performance and ultimately shortening membrane life. In an attempt to develop membranes with lower fouling properties in this paper we used the photoinduced grafting technique for the modification of membrane surfaces. Two different hydrophilic monomers: 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPS) and quaternary 2-dimethylaminoethylmethacrylate (gDMAEMA) were photografted to the surface of commercial polyethersulfone (PES) microfiltration membranes (Millipore). The modified membranes were characterised using atomic force microscopy (AFM) by visualisation and the measurement of pore size, pore size distribution and surface roughness. A direct quantification of the force of adhesion using silica colloid probe technique and comparisons with unmodified samples were also made. The membrane affinity to biofouling was tested in the presence of Escherichia coli bacteria. It was found that the number of bacterial cells able to proliferate from countable colonies was much less for qDMAEMA-grafted samples compared with unmodified PES membranes. Thus these modified membranes could be potentially more resistant to biofouling.