The loss of membrane flux due to fouling is a major impediment to the devel
opment of membrane processes for use in drinking water treatment. The objec
tive of this work was to evaluate fouling in nanofiltration (NF) pilot syst
ems fed conventionally-treated (coagulation/sedimentation/filtration) Ohio
River water (CT-ORW) with various additional levels of pretreatment. The ch
osen additional pretreatments were intended to produce waters with varying
biological-fouling potential. Five parallel membranes were fed CT-ORW, ozon
ated CT-ORW, ozonated/biofiltered CT-ORW, CT-ORW reduced to 7 degrees C, an
d chloraminated CT-ORW. All systems showed significant flux decline indicat
ing that methods beyond those needed for just biogrowth control are require
d for NF systems treating conventionally-treated surface waters. The NF sys
tems fed ozonated, ozonated/biofiltered, and untreated CT-ORW had the least
amount of flux decline over the course of the study; however, they had sig
nificant amounts of biological growth. Fouling in these systems was attribu
ted to the deposition of extracellular material (polysaccharides) in the ca
ke layer, either from the biogrowth on the membrane or carryover from the p
retreatment. The low-temperature system had greater flux decline, but it ha
d lower biogrowth than the ozonated, and ozonated/biofiltered and untreated
CT-ORW systems. Although lower in biogrowth, the deposited organic materia
l in the low-temperature system still showed a strong biological signature
(polysaccharides and aminosugars). The chloraminated system had the greates
t flux decline, but the least amount of biogrowth. The organic material dep
osited in the chloraminated system showed a high level of proteinaceous cha
racter.