AWWA MTC57558

Parallel experiments were conducted to determine the source of organic/biological fouling of reverse osmosis (RO) membranes when operated only under pilot-scale conditions. Testing was conducted using a 230 L/min conventional filtration (rapid mix/flocculation/sedimentation/ filtration) package plant (CPP) and a 2,000 ML/day full-scale treatment plant (FTP) as pretreatment to separate RO membrane test units. Coagulation consisted of 10 mg/L of alum and 2.0 mg/L of cationic polymer. A 2.5 to 3.0 mg/L free chlorine residual was maintained at the filter effluent and converted to chloramines through ammonium sulfate addition (3:1 chlorine to ammonia w/w ratio). Membrane performance was based on normalized flux and salt rejection data. Membrane surface analyses included scanning electron microscopy, energy-dispersive spectroscopy, and attenuated total reflectance Fourier-transform infrared spectroscopy. Microbial activity and community analyses were conducted through: fluorescence staining with 4',6'-diamidino-2-phenylindole; polymerase-chain reaction amplification of isolated bacterial DNA; and, microscopic taxonomic identification. Results indicated that the RO membrane fed by the CPP fouled at least three times faster than the RO membrane fed by the FTP. The differential fouling between the two process streams was determined to be from lack of maintenance in the CPP influent piping that lead to the establishment of biological communities consisting of algae, microbes, and potentially fresh water clams. These communities produced low levels of natural polymers that when presented to the polyamide RO membrane surface resulted in rapid fouling. Includes 21 references, tables, figures.