Evaluation of nanofiltration pretreatments for flux loss control

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.