A nanofiltration membrane for the removal of color from surface water to meet Norwegian standards

Influence of colloidal iron oxide and natural organic matter fouling on nanofiltration membrane performance: role of feed composition and membrane properties

“…In summary, the flux loss data suggests that hydrophobic interactions along with the higher MWCO of cellulose acetate active layer explain the extent of organic and combined fouling for the SBNF membrane, while electrostatic interactions (modulated by NOM and Ca 2+ ) are responsible for the flux decline observed for the NF270 membranes during the combined organic–inorganic fouling in the presence of CaCl 2 . We expect that at higher pH of 6–7.5, typical for surface water, 11,12,62 the cellulose acetate membrane would remain more susceptible to fouling due to hydrophobic organic substances, as a result of its higher contact angle compared to the polypiperazine amide membrane (Fig. 1C).…”

“…In well-oxygenated surface waters, ferrous iron – Fe( ii ) – is converted to ferric, Fe( iii ), and can form insoluble colloidal (oxy)(hydro)oxide species. 14 As some membrane plants treating surface water in northern latitudes 12,15–17 do not use any form of pre-treatment ( e.g. , flocculation and sedimentation), apart from coarse screening of the feed water (50–2000 μm), iron colloidal particles (<0.45 μm) are not removed and can hence build up on the membrane over time and decrease its useful life.…”

“…In addition to inorganic colloidal foulants, natural organic matter (NOM) presents a major challenge for membrane processes in temperate regions such as North America and Northern Europe, where organic-rich soils result in moderate surface water total organic carbon (TOC) concentrations (2.2-14.6 mg C/L). 11,12,[21][22][23][24] NOM molecules (primarily composed of fulvic acids, humic acids and some polysaccharides) have an overall negative surface charge at neutral pH due to carboxylic and phenolic functional groups. 25 Consequently, NOM fouling of NF membranes is strongly dependent on the pH, type and concentration of ions in solution, owing to electrostatic double-layer interactions and specific divalent complexation.…”

“…[6][7][8][9] However, iron (Fe) and aluminium 10 (Al) colloids, which acquire a net positive surface charge at slightly acidic and near-neutral pH, have been overlooked. Despite the typically low Fe concentration in surface feed waters (0.25-3.5 mg L −1 ), [11][12][13] its environmental cycling 14 ensures the continuous exposure of the membrane to colloidal Fe. In well-oxygenated surface waters, ferrous iron -Fe(II)is converted to ferric, Fe(III), and can form insoluble colloidal (oxy)(hydro)oxide species.…”

“…In well-oxygenated surface waters, ferrous iron -Fe(II)is converted to ferric, Fe(III), and can form insoluble colloidal (oxy)(hydro)oxide species. 14 As some membrane plants treating surface water in northern latitudes 12,[15][16][17] do not use any form of pre-treatment (e.g., flocculation and sedimentation), apart from coarse screening of the feed water (50-2000 μm), iron colloidal particles (<0.45 μm) are not removed and can hence build up on the membrane over time and decrease its useful life. 18 Two previous studies investigating iron colloidal fouling in RO membranes, have directly added soluble FeCl 3 or Fe(OH) 3 to the feed at the fouling onset, and assumed iron oxide particle formation at near-neutral pH.…”