Experimental characterization and numerical simulation of the anti-biofuling activity of nanosilver-modified feed spacers in membrane filtration

The antibiofouling activity of nanosilver-coated feed spacers was investigated in a crossflow membrane filtration-cell system simulating the conditions in spiral wound modules. Silver ions distribution in the feed channel and near the membrane was estimated by numerical simulation. Nanosilver was embedded into the polypropylene network using sonochemical deposition. The ability of the modified spacer to hinder biofilm development on the adjacent membranes was studied at 0.15ms^-1 crossflow velocity, using polysulfone ultrafiltration membrane exposed to a mixed microbial enrichment. The physical properties of the modified spacer and biofilm development were evaluated using scanning electron microscopy and confocal laser scanning microscopy imaging (HRSEM and CLSM). HRSEM images depicted significantly less bacteria attached to the membranes near the modified spacer, mainly scattered with a sporadic monolayer structure. Dead/live staining assay by CLSM indicated a significantly higher percentage of dead bacteria cells attached to the membranes adjacent to the modified spacer in comparison to untreated spacers (control). The silver modified spacers displayed improved and steadier permeate flux along the 10 days of the run compared to the control. Flow and mass transfer simulations showed increased silver ions concentration near the membrane as a function of the spacer configuration. The life span of the modified spacer was evaluated as well.