Comparative study of in-line coagulation and/or ozonization pre-treatment for drinking-water production with spiral-wound ultrafiltration membranes

• Drinking water production by spiral-wound membranes requires feed-water treatment.
• Ozonation is not recommended as a pre-treatment for spiral-wound PVDF membranes.
• Pre-coagulation-ozonation does not improve single pre-coagulation water quality.
• Fouling can be successfully controlled combining pre-coagulation and ozonation.

The application of pre-treatments is a common approach for improving ultrafiltration membrane limitations. However, most studies have been performed for lab-scale hollow-fibre or flat-sheet membrane modules. The present study was conducted to test the performance of fullscale spiral-wound ultrafiltration (UF) membranes for potabilization of influents rich in humic and fulvic acids under different scenarios: (i) direct UF, (ii) with in-line pre-coagulation, (iii) with pre-ozonation, and (iv) with both pre-treatments combined. The membranes were polyvinylidene fluoride with 0.03 μm effective pore size. Permeate flow rate was fixed, 1.0 m3/h, equivalent to 48 LMH flux. Membrane performance was compared for the aforementioned cases with the following results: feed water pretreatment was required since the effluent quality achieved with direct ultrafiltration was poor and fouling increased. Between pre-ozonation and pre-coagulation, the former was disregarded given the negligible improvement achieved with respect to single ultrafiltration. By contrast, coagulation-flocculation results were remarkably better for both organic matter removal and fouling control. The application of the two pretreatments in series resulted in effluent qualities comparable to those achieved with coagulation-flocculation but fouling rates were much lower and transmembrane pressure growth was minimal, this constituting a promising option for fouling control.