Nanofiltration of Natural Organic Matter: Removal, Fouling and the Influence of Multivalent Ions

The presence of calcium and humic substances or natural organic matter (NOM) in surface waters can cause severe fouling of nanofiltration (NF) membranes. Conditions of fouling were studied using a stainless steel stirred cell of volume 185 ml and a membrane area of 21.2×10−4 m2 at a transmembrane pressure of 5 bar. Deposition of organic matter was determined by mass balance in feed and concentrate samples. Electron microscopy and X-ray photoelectron spectroscopy (XPS) were used to study the morphology and composition of the fouling layer. During permeate recycle experiments, which were used for fouling studies, it was found that calcium concentration (as a representative of multivalent ions) and the type of organic play a major role in fouling. The calcium forms complexes with some of the organics and deposits on the membrane surface. Depending on the solution conditions the organic or calcite (on which organics adsorb) precipitate. Factors, which influence the concentration of organics and ions at the membrane surface such as stirring, flux and transmembrane pressure, influenced the deposition of organic matter significantly. Irreversible fouling occurred with all membranes at high calcium concentrations, although the cellulose acetate membrane showed an overall better performance, possibly due to its low salt rejection and smooth surface. IHSS humic acid is the organic which deposits most easily and comparison of UV absorbance and DOC data showed that the fraction which absorbs UV strongest, and is more hydrophobic, deposits preferentially on the membranes. These substances also have the lowest solubility stressing the importance of concentration polarisation effects.

[1]  E. Suess.  Interaction of organic compounds with calcium carbonate-II. Organo-carbonate association in Recent sediments. , 1973 .

[2]  E. Suess.  Interaction of organic compounds with calcium carbonate—I. Association phenomena and geochemical implications , 1970 .

[3]  A. Fane,et al.  Chemical Addition prior to Membrane Processes for Natural Organic Matter (NOM) Removal , 1998 .

[4]  E. M. Thurman,et al.  Organic Geochemistry of Natural Waters , 1985, Developments in Biogeochemistry.

[5]  E. Tipping,et al.  The complexation of protons, aluminium and calcium by aquatic humic substances: A model incorporating binding-site heterogeneity and macroionic effects , 1988 .

[6]  D. R. Crandell,et al.  Preliminary Report on Geology of Part of the Chamberlin Quadrangle, South Dakota. USDI / U.S. Geological Survey, Open File Report , 1952 .

[7]  Warren A. Dick,et al.  Humic Substances in the Global Environment and Implications on Human Health , 1995 .

[8]  M. Schnitzer,et al.  MACROMOLECULAR STRUCTURES OF HUMIC SUBSTANCES , 1980 .

[9]  C. A. Smolders,et al.  Hydrodynamic resistance of concentration polarization boundary layers in ultrafiltration , 1985 .

[10]  Water Research , 1961, Nature.

[11]  J. Allison,et al.  MINTEQA2/PRODEFA2, a geochemical assessment model for environmental systems: Version 3. 0 user's manual , 1991 .

[12]  A. Smith,et al.  Soil Science , 1965, Nature.

[13]  Menachem Elimelech,et al.  Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes , 1996 .

[14]  M. Clark,et al.  Adsorption of aquatic humic substances on hydrophobic ultrafiltration membranes , 1994 .

[15]  Amy E. Childress,et al.  Role of membrane surface morphology in colloidal fouling of cellulose acetate and composite aromatic polyamide reverse osmosis membranes , 1997 .

[16]  M. Wander.  Humic substances in the global environment and implications on human health , 1997 .

[17]  J. Howell,et al.  Sub-critical flux operation of microfiltration , 1995 .

[18]  E. Groves.  A Dissertation ON , 1928 .

[19]  Menachem Elimelech,et al.  Chemical and physical aspects of natural organic matter (NOM) fouling of nanofiltration membranes , 1997 .