F. Beyer, B.M. Rietman, A. Zwijnenburg, P. van den Brink, J.S. Vrouwenvelder, M. Jarzembowska, J. Laurinonyte, A.J.M. Stams, C.M. Plugge
Journal of Membrane Science, volume 468, 339-348, (2014)
Nanofiltration, Anoxic groundwater, Long-term performance, Membrane autopsy, Fouling analysis
Long-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 10 µm
pore size cartridge filtration and antiscalant dosage (2–2.5 mg L−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 (≤8.4 mg L−1) anoxic groundwaters.
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.
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.