Graft Polymerization as a Route to Control Nanofiltration Membrane Surface Properties to Manage Risk of EPA Candidate Contaminants and Reduce NOM FoulingEPA Grant Number: R830909
Title: Graft Polymerization as a Route to Control Nanofiltration Membrane Surface Properties to Manage Risk of EPA Candidate Contaminants and Reduce NOM Fouling
Investigators: Kilduff, James E. , Belfort, Georges
Institution: Rensselaer Polytechnic Institute
EPA Project Officer: Lasat, Mitch
Project Period: August 25, 2003 through August 25, 2007
Project Amount: $349,000
RFA: Environmental Futures Research in Nanoscale Science Engineering and Technology (2002) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
We propose to develop new nanofiltration membranes by modifying the surface structure of commercial membranes at the molecular level via UV-assisted graft polymerization of hydrophilic monomers using our patented method. Our objective is to transfer major successful developments from biotechnology applications to environmental protection. New materials will be developed that offer high flux compared to commercial membranes (by improving membrane porosity), enhanced rejection of inorganic anions and ionizable organic compounds (by controlling membrane pore size distribution and surface charge), and enhanced ability to resist fouling by natural organic matter (NOM) by reducing adhesion. We seek to understand the characteristics of natural organic matter accumulated on membrane surfaces both in terms of resistance to flow (which can influence the cost of membrane processes) and its affects on the transport and rejection of charged solutes.
Commercially-available poly(aryl sulfone) membranes will be UV-irradiated in the presence of water-soluble monomers, which chemically bond to the surface by a mechanism involving a photochemically induced free radical polymerization. Several different monomers will be evaluated to determine the effects of monomer structure on membrane properties. At least one monomer will contain a carboxylic moiety (e.g., poly(acrylic acid)). Poly(aryl sulfone) membranes offer attractive features for water treatment applications, including wide pH tolerance and good resistance to oxidants, including chlorine. The membranes will be well characterized using Fourier Transform Infrared Spectroscopy (FTIR) to assess degree of grafting, contact angle measurements to assess wetability, and atomic force microscopy to measure surface roughness. Membrane charge will be characterized by measuring salt rejection, and pore size distribution will be estimated from dextran rejection data analyzed by size-exclusion chromatography. The modified membranes will be evaluated for their flux characteristics, and their ability to reject charged solutes during cross-flow filtration. Contaminants selected for study include an ionizable aromatic (2,4-dinitrophenol), an inorganic salt (perchlorate) and a metallic oxyanion (arsenic). The rejection characteristics will be compared to a fairly large, neutral chloroacetanilide herbicide (metolachlor). Perchlorate, 2,4-dinitrophenol, and metolachlor were selected from the EPA Candidate Contaminant List (CCL), while arsenic is regulated under the Safe Drinking Water Act. Membrane tests will be performed in the presence and absence of NOM to determine the effects on the rate of flux decline (fouling) and on the rejection of target solute molecules. Kilduff, who has extensive experience conducting treatment studies and isolating, characterizing, and measuring membrane transport of NOM will team up with Belfort, who is a leading researcher in the membrane field, with expertise in the use of surface modification to tailor surfaces of synthetic membranes for specific applications.
Results from this project will provide new approaches to develop membrane materials that have superior performance characteristics in terms of both enhanced rejection of charged contaminants and resistance to fouling by natural organic matter. The proposed research will also expand our understanding of the role of membrane charge and NOM fouling layers on solute rejection by nanofiltration processes. The proposed materials and processes will provide new options for controlling risks from contaminants of water supplies. In this way we seek to protect human health, and improve the performance of membrane treatment technologies while reducing their cost.