(458f) Dynamics of Nonliving Organic Matter in Membrane Fouling

Natural nonliving organic matter (NNOM) is well known as a foulant for many types of water purification membranes. Shearing environments, pH and ionic strength modify the self-assembled forms or aggregates of this material, affecting partitioning and dynamics. The aggregates form and disperse reversibly in the presence of shear, and hydrogen bonding has been suggested as a driving force for assembly. The argument that H-bonding energetics result only from weak attractions (<4–5 kcal mol−1]) is no longer chemically complete, and in this study we explore the presence of strong hydrogen bonding in shear-induced breakup kinetics for NNOM aggregates. Increased ionic strength was found to slow the aggregation kinetics of the physical hydrogel. Two phases of NNOM hydrogels were found to coexist, however, which we term here metachemical and physical hydrogels. One implication for membranes is that breakup on the retentate side of the membrane can lead to transport and reassembly on the permeate side, with downstream issues associated with disinfection byproducts.