Colloidal fouling of RO membranes following MF/UF in the reclamation of municipal wastewater

Major municipal wastewater reclamation plants in California, USA, Singapore, and many built or planned for other regions of the world use the high pathogen reduction properties of microfiltration/ultrafiltration (MF/UF) membranes followed by reverse osmosis (RO) membranes. Operational experiences in these plants suggest that while MF and UF membranes encounter pore and cake fouling by colloidal particles (0.1 micron down to molecular sizes, ie. nanoparticles), a significant fraction of the smaller colloidal particles pass through the MF and UF membranes, and end up on RO membranes as cake-layer foulants. Autopsies, foulant analyses and cleaning studies performed on fouled RO membranes from the plants and pilot plants showed that colloidal natural organic matter, colloidal calcium phosphate and some times colloidal silicates are the main components. These colloidal particles have great affinity towards aggregation with each other. Due to incomplete removal by MF and even UF, fouling of RO membranes downstream becomes measurable by trend-charts of normalized values of permeate flow, differential pressure and salt passage. Normalized permeate flow is the most sensitive, and an early indicator of such fouling. In this paper we will provide some details of our studies and provide literature evidences that support the conclusion that calcium phosphate in foulants originated as nanoparticles in the wastewater.

[1]  J. Floege,et al.  Do not be misguided by guidelines: the calcium x phosphate product can be a Trojan horse. , 2005, Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association.

[2]  B. Hockey,et al.  Properties of Nanostructured Hydroxyapatite Prepared by a Spray Drying Technique , 2004, Journal of research of the National Institute of Standards and Technology.

[3]  G. Chertow,et al.  Mineral metabolism, mortality, and morbidity in maintenance hemodialysis. , 2004, Journal of the American Society of Nephrology : JASN.

[4]  C. Holt.  Structure and stability of bovine casein micelles. , 1992, Advances in protein chemistry.

[5]  G. H. Nancollas.  The involvement of calcium phosphates in biological mineralization and demineralization processes , 1992 .

[6]  Philip M. Haygarth,et al.  Size distribution of colloidal molybdate reactive phosphorus in river waters and soil solution , 1997 .

[7]  T. Morcol,et al.  Calcium Phosphate Nanoparticles Induce Mucosal Immunity and Protection against Herpes Simplex Virus Type 2 , 2002, Clinical and Vaccine Immunology.

[8]  N. Goto,et al.  Relationship between Hemolytic Activity and Adsorption Capacity of Aluminum Hydroxide and Calcium Phosphate as Immunological Adjuvants for Biologicals , 1994, Microbiology and immunology.

[9]  R. Gupta,et al.  Adjuvant properties of aluminum and calcium compounds. , 1995, Pharmaceutical biotechnology.

[10]  Thomas L. Troyer,et al.  Chemical control of colloidal fouling of reverse osmosis systems , 2005 .

[11]  Benjamin L Turner,et al.  Colloidal phosphorus in surface runoff and water extracts from semiarid soils of the western United States. , 2004, Journal of environmental quality.

[12]  J. Floege.  When man turns to stone: extraosseous calcification in uremic patients. , 2004, Kidney international.

[13]  D. Schindler,et al.  Phosphate concentrations in lakes , 2000, Nature.

[14]  A. Hassan,et al.  Changes in the proportions of soluble and insoluble calcium during the ripening of cheddar cheese. , 2004, Journal of dairy science.