Reclamation of impacted urban phreatic water through nanofiltration technology: Insight on natural organic matter removal by fluorescence spectroscopy

Abstract

Nanofiltration (NF) is a promising technology called to play a relevant role in water reclamation, which lies in the core of circular economy in the water sector. The aim of this study was to assess two aromatic polyamide-based NF membranes (the looser NF270 and the tighter NF90 ones) for the treatment of urban impacted phreatic water. The focus was centred on the removal of dissolved inorganic and organic solutes and on the differences observed between solutes. Membrane ions rejection was modelled by the Solution-Electro-Diffusion Film Model (SEDFM). DOC was tracked by Fluorescence Excitation-Emission Matrices (FEEM) coupled to Parallel Factor Analysis (PARAFAC) to get insight into the character of DOC rejected by or permeated through the membranes. Results showed that the NF90 membrane systematically achieved upper values in the rejection of ions than the looser NF270 one. Variations between ions could be interpreted by the mechanisms ruling their rejection, i.e. Donnan and dielectric exclusion phenomena. Experimental rejections were also satisfactorily fit by the SEDFM, indicating that that the presence of DOC in the phreatic water did affect modelling of ions transport through the membranes. DOC was rejected at very high percentages (>90%) by both membranes, but FEEM-PARAFAC analysis revealed that humic- and tryptophan- like components were more rejected (>90% for both membranes) than tyrosine-like compounds (45% for NF270 and 57% for NF90). The finding is of relevance from a point of view of disinfection practices, as it has been observed that humic-like substances are strongly correlated with DBPs formation.