Influence of laccase treatment on fouling layer formation in ultrafiltration of birch hot-water extract

Fouling problems caused by lignin have been limiting the use of membranes in the recovery of value-added materials from biorefinery streams. Fortunately, laccase-based catalytic pretreatments enable modification of lignin to the less fouling form. Because the mechanisms behind the fouling caused by ligneous compounds in wood-based streams are still not deeply understood, the aim of this study was to find out how laccase oxidation affects membrane fouling caused by pressurized hot-water extract. The effect of laccase on the fouling tendency of birch extract was explored both with adsorptive and pressure-driven experiments. The results suggested that laccase treatment increased the molar mass of lignin and improved significantly filtration capacity of commercial polyethersulphone membrane, possibly due to formation of less dense foulant layer during the filtration. Based on FTIR and BET results laccase oxidation decreased both adsorptive and pressure-driven fouling caused by lignin. However, decreases in pure water permeabilities were higher for the samples that were fouled with laccase treated extract. This may have originated from the transformation in the fouling mechanism from the pore narrowing to the pore blocking and could be prevented by the selection of a membrane with a different pore size.