Chemical Addition Prior to Membrane Processes for Natural Organic Matter (NOM) Removal

  • A. I. Schäfer
  • A. G. Fane
  • T. D. Waite
Conference paper

Abstract

Membrane processes for surface water treatment include microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF), depending on the target material to be removed and the limiting process economics. MF will remove turbidity, but no dissolved compounds, unless associated with colloids, UF will, depending on the molecular weight cut off (MWCO), partially remove NOM, and NF will remove NOM almost completely, but for a price often considered as uneconomic due to energy costs. Chemical addition prior to MF or UF may enhance the NOM removal capacity of these processes to a comparable range as achieved with NF. In this work the improvement of NOM removal by MF with chemical pretreatment was investigated using FeCl3 and hematite (α-Fe2O3) addition.

The results achieved with the addition of ferric chloride as a coagulant prior to MF showed that 95 % removal of NOM can be achieved at a dosage of 25 mg L ™1. The flocs form a gelatinous deposit on the membranes and cause flux decline, however the resulting flux is still high compared to UF and NF. Higher dosage of 100 mgL™1 resulted in a very high flux decline.

The addition of hematite synthesised as monodispersed, spherical colloids in the sizes 75, 250 and 500 nm showed the importance of colloid size on MF flux. Small colloids (75 nm) are not retained by the membrane when stabilised due to the adsorption of organics, but also adsorb larger amounts of NOM than do larger hematite particles. Aggregation of these colloids increased colloid rejection with a concomitant increase (to about 20% at a low dosage of 10mgL™1 hematite) in removal of adsorbed organic matter. Aggregation of small colloids increases the adsorbant surface area significantly versus larger primary colloids. The structure of the aggregates was found to be important for membrane flux.

Alternatively, tighter membranes can be used. UF membranes showed a NOM removal of 10 to 90 % for a MWCO of 30 to 1 kDa (five membranes were investigated), respectively. NF removed > 95 % of organics, independent of solution chemistry and could remove a large fraction of multivalent ions.

The study shows that if no salt rejection (softening) but very high NOM removal (> 90 %) are required in a water treatment application, hybrid processes of MF with chemical pretreatment may be a very attractive alternative to UF or NF.

Keywords

Permeability Porosity Hydrolysis Filtration Hydroxide 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. [1]
    Crozes, G., Jacangelo, J., Anselme, C., Laîné, J.M.: Impact of Ultrafiltration Operating Conditions on Membrane Irreversible Fouling. Proc. AWWA Membrane Technology Conference, Reno, Nevada 1995, p. 457.Google Scholar
  2. [2]
    Crozes, G., White, P., Marshall, M.: Enhanced Coagulation: Its Effect on NOM Removal and Chemical Costs. J. AWWA 01/95 (1995) 78.Google Scholar
  3. [3]
    Mallevialle, J., Odendaal, P.E., Wiesner, M.R.: Water Treatment Membrane Processes. McGraw-Hill, New York 1996.Google Scholar
  4. [4]
    Vickers, J.C., Thompson, M.A., Kelkar, U.G.: The Use of Membrane Filtration in Conjunction with Coagulation Processes for Improved NOM Removal. Desalination 102 (1995) 57.CrossRefGoogle Scholar
  5. [5]
    Schäfer, A.I., Fane, A.G., Waite, A.G.: A Review on the Options for Removal of Natural Organics by Membranes. Proc. International Membrane Science and Technology Conference Sydney 2 (1996) 7.Google Scholar
  6. [6]
    Jucker, C., Clark, M.M.: Adsorption of Aquatic Humic Substances on Hydrophobic Ultrafiltration Membranes. Journal of Membrane Science 97 (1994) 37.CrossRefGoogle Scholar
  7. [7]
    Beckett, R., Jue, Z., Giddings, J.C.: Determination of Molecular Weight Distribution of Fulvic and Humic Acids Using Flow Field-Flow Fractionation. Environmental Science & Technology 21(3) (1987) 289.CrossRefGoogle Scholar
  8. [8]
    Hering, J.G., Morel, F.M.M.: Humic Acid Complexation of Calcium and Copper. Environmental Science & Technology 22(10) (1988) 1234.CrossRefGoogle Scholar
  9. [9]
    Schäfer, A.I., Mauch, R., Hepplewhite, C., Fane, A.G., Waite, T.D.: Charge Effects in the Fractionation of Humic Substances and Natural Organic Matter Using Ultrafiltration. (In preparation).Google Scholar
  10. [10]
    Amal, R., Raper, J.A., Waite, T.D.: Effect of Fulvic Acid Adsorption on the Aggregation Kinetics and Structure of Hematite Particles. Journal of Colloid and Interface Science 151(1) (1992) 244.CrossRefGoogle Scholar
  11. [11]
    Matijevic, E., Schreiner, P.: Ferric Hydrous Oxide Sols III. Preparation of Uniform Particles by Hydrolysis of Fe(III)-Chloride,-Nitrate, and-Perchlorate Solutions. Journal of Colloid and Interface Science 63(3) (1978) 509.CrossRefGoogle Scholar
  12. [12]
    Tang, H.X., Tian B.Z., Luan, Z.K., Zhang, Y.: Inorganic Polymer Flocculant Polyferric Chloride, It’s Properties, Efficiency and Production. In: Chemical Water and Wastewater Treatment III, R. Klute and H.H. Hahn (Eds.). Springer, Berlin Heidelberg New York 1994, pp. 57–69.Google Scholar
  13. [13]
    Krasner, S.W., Amy, G.: Jar Testing Evaluations of Enhanced Coagulation. J. AWWA 10(95) (1995) 93.Google Scholar
  14. [14]
    Dennett, K.E., Amirtharajah, A., Moran T.F., Gould, J.P.: Coagulation: Its Effect on Organic Matter. J. AWWA 04(96) (1996) 129.Google Scholar
  15. [15]
    Gu, B., Schmitt, J., Chen, Z., Liang, L., McCarthy, J.F.: Adsorption and Deposition of Natural Organic Matter in Iron Oxide: Mechanisms and Models. Environmental Science & Technology 28(1) (1994) 38.CrossRefGoogle Scholar
  16. [16]
    Chang, Y., Benjamin, M.M.: Iron Oxide Adsorption and UF to Remove NOM and Control Fouling. J. AWWA 12(96) (1996) 74.Google Scholar
  17. [17]
    Schäfer, A.I., Fischer, M.M., Schwicker, U., Fane, A.G., Waite, T.D.: Physicochemical Aspects on Microfiltration of Natural Colloidal Systems. (In preparation).Google Scholar
  18. [18]
    Crosby, S.A., Glasson, D.R., Cuttler, A.H., Butler, I., Turner, D.R., Whitfield, M., Millward, G.E.: Surface Areas and Porosities of Fe(III)-and Fe(II)-Derived Oxyhy-droxides. Environmental Science & Technology 17 (1983) 709.CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • A. I. Schäfer
    • 1
  • A. G. Fane
    • 1
  • T. D. Waite
    • 2
  1. 1.UNESCO Centre for Membrane Science and Technology School of Chemical Engineering and Industrial ChemistryUniversity of New South WalesSydneyAustralia
  2. 2.Department of Water Engineering School of Civil and Environmental EngineeringUniversity of New South WalesSydneyAustralia

Personalised recommendations