Abstract
ABSTRACTThe outcomes of a pilot-scale study of the rejection of trihalomethanes (THMs) precursors by commercial ultrafiltration/nanofiltration (UF/NF) spiral-wound membrane elements are presented based on a single surface water source in Scotland. The study revealed the expected trend of increased flux and permeability with increasing pore size for the UF membranes; the NF membranes provided similar fluxes despite the lower nominal pore size. The dissolved organic carbon (DOC) passage decreased with decreasing molecular weight cut-off, with a less than one-third the passage recorded for the NF membranes than for the UF ones.The yield (weight % total THMs per DOC) varied between 2.5% and 8% across all membranes tested, in reasonable agreement with the literature, with the aromatic polyamide membrane providing both the lowest yield and lowest DOC passage. The proportion of the hydrophobic (HPO) fraction removed was found to increase with decreasing membrane selectivity (increasing pore size), and THM generation correlated closely (R2 = 0.98) with the permeate HPO fractional concentration.
Highlights
It has been recognised for more than 40 years that the reaction of natural organic matter (NOM) with chlorine generates chlorinated disinfection by-products (DPBs) generally and trihalomethanes (THMs) .[1]
Whilst the residual dissolved organic carbon (DOC) level provides an indication of THM formation propensity (THMFP in μg L−1), such that DOC passage through the membrane is a useful performance indicator, the yield is subject to significant variation
The NF membranes provided similar fluxes despite differences in the rated MWCO. ● Recorded flux values were markedly higher than those previously reported in the literature for full and pilot plants. ● DOC passage decreased with decreasing MWCO, an intuitive outcome which conflicts with more unpredictable trends previously reported for NOM removal by membranes
Summary
It has been recognised for more than 40 years that the reaction of natural organic matter (NOM) with chlorine generates chlorinated disinfection by-products (DPBs) generally and trihalomethanes (THMs) .[1] In the UK the prescribed concentration value of THMs in potable water is currently 100 μg L−1.[2] An established option for addressing this issue is the removal of the NOM using membranes. Membranes of appropriate selectivity—generally in the tight ultrafiltration (UF)/loose nanofiltration (NF) region—have been shown to be reasonably effective for removing DOC, and THM precursors.[6,7]
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