Anti-Scale Effects of Select Organic Macromolecules on Gypsum Bulk and Surface Crystallization during Reverse Osmosis Desalination

Significance Statement

Reverse osmosis desalination technology is of an interest in the field of water treatment plants and systems, especially in arid and water scarce regions. However, membrane scaling as a result of salt rejection and according supersaturation of sparingly soluble salts on the semipermeable reverse osmosis membrane defies the use of this technology. Gypsum is a common scale forming salt during desalination of natural waters as both, calcium and sulfate ions, are ubiquitously present.

Gypsum scaling may occur by crystallization directly on the membrane surface or by bulk crystallization from the supersaturated feed solution. Both scaling mechanisms have been previously reported coupled with the determination of the prevailing mechanism. It’s also known that certain organic macromolecules which lead to membrane fouling may inhibit or favor gypsum scaling on reverse osmosis membranes. Hence, a profound knowledge of the interactions between organic macromolecules, gypsum scaling and scaling mechanisms would be of help to optimize scale prevention measures.

Jan Benecke and colleagues from Institute for Water Resources and Water Supply at Hamburg University of Technology (TUHH) in Germany tailored the operation of a bench-scale reverse osmosis desalination system to independently investigate the interactions between organic macromolecules such as bovine serum albumin, humic acid and sodium alginate with gypsum bulk and surface scaling mechanisms.

The research work which is now published in the journal, Separation and Purification Technology implemented a bench-scale reverse osmosis desalination system operating at two tailored degrees of concentration polarization. During permeability and retentate turbidity tests, the authors found that at the lower degree of concentration polarization, bulk crystallization of gypsum was predominant. However, at a higher degree of concentration polarization, gypsum surface crystallization occurred with the non-presence of gypsum bulk crystals. Results from scanning electron microscopy supported the predominance of each scaling mechanism.

Among the selected organic macromolecules, sodium alginate contributed mostly to permeability loss, which indicates strong membrane fouling, followed by humic acid and bovine serum albumin, respectively. At low concentration polarization and predominance of gypsum bulk crystallization, all macromolecules retarded the onset of bulk crystallization. However, it was also found that the presence of sodium alginate shifted the gypsum scaling mechanism from bulk to surface crystallization, indicating an enhancement of surface crystallization due to the deposited sodium alginate fouling layer. These conclusions were backed with scanning electron micrographs of the scaled membrane surface and complimentary results from crystallization jar tests. At high degree of concentration polarization, the coexistence of sodium alginate and humic acid slightly enhanced gypsum surface crystallization, whereas the coexistence of bovine serum albumin showed marginal effects. The authors suggest a correlation between the severity of macromolecular fouling and the enhancement of gypsum surface crystallization.

The study by Jan Benecke and colleagues enables an avenue for optimizing existing scale prevention technologies, given the ubiquitous presence of natural organic matter in natural waters. The results highlight the necessity for further research to comprehensively understand interactions between organic and inorganic membrane foulants in reverse osmosis desalination systems to develop more sustainable and green scale inhibition additives and techniques.

Anti-Scale Effects of Select Organic Macromolecules on Gypsum Bulk and Surface Crystallization during Reverse Osmosis Desalination (Advances in Engineering)

About The Author

Jan Benecke is currently working as a research fellow at the Institute for Water Resources and Water Supply (Hamburg University of Technology, Germany). His doctoral research study focuses on the interactions between natural organic macromolecules and gypsum scaling during high pressure membrane filtration. Additionally, Jan is involved in teaching undergraduate and graduate courses (membrane technology, (waste)water treatment and reuse, water resources management) and further research projects related to water quality control and treatment.

Jan graduated from Berlin Institute of Technology (Technische Universitaet Berlin, Germany) in 2012 with a diploma degree in environmental technology. Through his studies and complimentary research visits at the NSERC Chair in Water Treatment (University of Waterloo, Canada) and the NSF Engineering Research Center “ReNUWit” (Colorado School of Mines, USA), Jan has gained broad theoretical knowledge and hands-on experience in the field of (waste)water treatment and reuse, membrane processes, environmental chemistry and microbiology, as well as environmental assessment.

About The Author

Jelena Rozova received a B.Sc. (2009) and M.Sc. (2011) in Chemical and Environmental Technologies from the Tallinn University of Technology (Estonia). Jelena’s research focused on the removal of triclosan, endocrine disrupting compound, from household wastewater effluent using combination of aerobic bio-oxidation and ozonation.

Jelena joined the Hamburg University of Technology (TUHH) in 2011 as a master’s student and a research assistant in the Institute of Wastewater Management and Water Protection. She graduated in 2014 with a Master of Science in Environmental Engineering. During her time at TUHH, Jelena received an award from the German Technical and Scientific Association for Gas and Water (DVGW) for having one of the best master’s thesis in the field of water treatment in 2014.

Jelena is currently establishing her career as an engineer in Calgary (Canada) and in her spare time volunteers for a Canadian charity and engineering organization CAWST (Centre for Affordable Water and Sanitation Technologies).

About The Author

Mathias Ernst is an environmental engineer with more than 20 years experiences in water and wastewater treatment. Mathias did his PhD in 1999 in an international project on potable water recycling by membrane and oxidation treatment at Technische Universitaet Berlin, Germany. In a Marie-Curie Industrial-Postdoc fellowship with VW in Paris / Maisons-Lafitte, he developed membrane based industrial recycling processes.

He was associate professor and director of the TU Berlin internal network Centre for Water in Urban Areas before he became full Professor at the Hamburg University of Technology in 2012. Here, he chairs the Institute of Water Resources and Water Supply as well as the adjunct nonprofit DVGW-Research Institute TUHH.

Mathias has published more than 40 scientific papers, mainly in the field of water recycling, membrane technology and water quality assessment. His main fields of research interest are optimization and functionalization of membrane filtration processes, oxidation, adsorption and advanced characterization of dissolved organics in water treatment. Apart his research activities, he is study program coordinator of the International Master Program Environmental Engineering (IMPEE) at Hamburg University of Technology.

Journal Reference

Benecke, J., Rozova, J., Ernst, M. Anti-Scale Effects of Select Organic Macromolecules on Gypsum Bulk and Surface Crystallization during Reverse Osmosis Desalination,  Separation and Purification Technology, Available online 30 November 2016 . http://doi.org/10.1016/j.seppur.2016.11.068.

Institute for Water Resources and Water Supply, Hamburg University of Technology, Am Schwarzenberg-Campus 3, 21073 Hamburg, Germany.

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