Natural Organic Matter (NOM) reacts with Cl<sub>2 </sub>and other disinfectants to form potentially carcinogenic disinfection byproducts (DBPs) in drinking water. NOM can be effectively removed by nanofiltration (NF) and reverse osmosis (RO), but NOM fouling on the membrane is the major challenge for applying membrane processes to natural waters. Furthermore, the presence of divalent cations has been shown to increase fouling associated with NOM. Therefore, pretreatment for the removal of cations prior to NF or RO could provide a cost-effective membrane system that allows for control of the final effluent water composition as well as extends the operation period for NF. The key to this hybrid approach is that electrodialysis (ED) can be used as pretreatment option to remove most ions while achieving minimal removal of NOM. In the hybrid process, the diluate from the ED system, containing few inorganic ions but NOM at nearly the influent concentration, is treated with NF. Subsequently, the concentrate from ED is mixed with the NF permeate to yield a water with nearly the original ion concentration and dramatically lowered NOM. To make this dual-membrane (ED-NF) system viable as a full-scale treatment process, a thorough understanding of the membrane fouling processes is required. Thus, the objective of this study was to provide that understanding through a systematic study of the ED/NF process with several sources of NOM and varying solution conditions (ion makeup and concentrations). Operational characteristics of both membrane processes were monitored, and NF membranes were autopsied to characterize fouling. The hybrid system removed 70-80% of the NOM, depending on the type of NOM, and provided an effluent water that was within 15% of the initial inorganic ion composition after mixing. ED pretreatment of the more hydrophobic NOM source provided a more significant delay in the onset and degree of fouling of the NF membranes. The characteristics of NOM fouling were examined using surface techniques including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy (ATR-FTIR); these tools made it possible to observe the build-up of NOM on the surface of the membranes. The more hydrophobic NOM without ED pretreatment created the thickest fouling layer on the membrane, and the depth of the fouling layers decreased with ED pretreatment.

Characteristics of natural organic matter foulants on nano-filtration surfaces: The effect of electrodialysis pretreatment

2019 Spring National Meeting

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