NAMS 2002 Workshop - ICOM 2008

Drinking and Wastewater Applications IV – 7
Thursday July 17, 12:00 PM-12:30 PM, Honolulu/Kahuku
Mechanisms governing the effects of membrane fouling on the
nanofiltration of micropollutants
L. Nghiem (Speaker), University of Wollongong, Wollongong, Australia - longn@uow.edu.au
C. Espendiller, University of Wollongong, Wollongong, Australia
G. Braun, University of Applied Science Cologne, Cologne, Germany
The influence of membrane fouling on the retention of five micropollutants
namely sulfamethoxazole, ibuprofen, carbamazepine, bisphenol A, and triclosan
by nanofiltration membranes was investigated in this study. Humic acid, alginate,
bovine serum albumin, and silica colloids were selected as model foulants to
simulate various organic fractions and colloidal matter that are found in
secondary treated effluent and surface water. Membrane fouling was achieved
with foulant cocktails containing individual model organic foulants in a
background electrolyte solution. The effects of membrane fouling on the
separation process was delineated by comparing retention values of clean and
fouled membranes and relate them to the membrane properties (under both
clean and fouled conditions) as well as physicochemical characteristics of the
micropollutants. Results reported here indicate a strong correlation between
membrane fouling, foulant characteristics, and membrane properties. The effects
of fouling on retention were found to be membrane pore size dependent. It was
probable that the influence of membrane fouling on micropollutant retention could
be governed by four distinctive mechanisms: modification of the membrane
charge surface, pore constriction, cake enhanced concentration polarisation, and
modification of the membrane hydrophobicity. The presence of the fouling layer
could affect the retention behavior of charged solutes by altering the membrane
surface charge density. While the effect of surface charge modification was clear
for inorganic salts, it was less obvious for the negatively charged pharmaceutical
species (sulfamethoxazole and ibuprofen) examined in this investigation,
possibly due to the interference of the pore constriction mechanism. Behavior of
the very loose TFC-SR2 membrane was found dominated by pore constriction
and this membrane consistently showed an increase in retention under fouled
conditions. In contrast, evidence of the cake enhanced concentration polarisation
effect was observed with the smaller pore size NF-270 and NF-90 membranes,
particularly under colloidal fouling conditions. In addition, the fouling layer could
also interfere with the solute membrane interaction, and therefore, exerted
considerable influence on the separation process of the two hydrophobic
micropollutants bisphenol A and triclosan used in this study.