Long-term performance and fouling analysis of full-scale direct nanofiltration (NF) installations treating anoxic groundwater
Rietman, Bas M.
Van Den Brink, Paula J.
Vrouwenvelder, Johannes S.
Stams, Alfons JM M
Plugge, Caroline M.
KAUST DepartmentWater Desalination and Reuse Research Center (WDRC)
Environmental Science and Engineering Program
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AbstractLong-term performance and fouling behavior of four full-scale nanofiltration (NF) plants, treating anoxic groundwater at 80% recovery for drinking water production, were characterized and compared with oxic NF and reverse osmosis systems. Plant operating times varied between 6 and 10 years and pretreatment was limited to 10μm pore size cartridge filtration and antiscalant dosage (2-2.5mgL-1) only. Membrane performance parameters normalized pressure drop (NPD), normalized specific water permeability (Kw) and salt retention generally were found stable over extended periods of operation (>6 months). Standard acid-base cleanings (once per year or less) were found to be sufficient to maintain satisfying operation during direct NF of the described iron rich (≤8.4mgL-1) anoxic groundwaters. Extensive autopsies of eight NF membrane elements, which had been in service since the plant startup (6-10 years), were performed to characterize and quantify the material accumulated in the membrane elements. Investigations using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), total organic carbon (TOC) and adenosine triphosphate (ATP) measurements revealed a complex mixture of organic, biological and inorganic materials. The fouling layers that developed during half to one year of operation without chemical cleaning were very thin (<2. μm). Most bio(organic) accumulates were found in the lead elements of the installations while inorganic precipitates/deposits (aluminosilicates and iron(II)sulfides) were found in all autopsied membrane elements. The high solubility of reduced metal ions and the very slow biofilm development under anoxic conditions prevented rapid fouling during direct NF of the studied groundwaters. When compared to oxic NF and RO systems in general (e.g. aerated ground waters or surface waters), the operation and performance of the described anoxic installations (with minimal pretreatment) can be described as very stable. © 2014 Elsevier B.V.
SponsorsThis work was performed at Wetsus, Centre of Excellence for Sustainable Water Technology (www.wetsus.n1). Wetsus is funded by the Dutch Ministry of Economic Affairs, the European Union European Regional Development Fund, the Province of Fryslan, the city of Leeuwarden and by the EZ-KOMPAS Program of the "Samenwerkingsverband Noord-Nederland". The authors would like to thank the participants of the research theme "Biofouling" for the fruitful discussions and their financial support and in particular the water company "Vitens", for supply of the operational data and membrane elements and the possibility to perform the research presented in this manuscript.
JournalJournal of Membrane Science