AWWA WQTC69316

The main limitation of membrane application is fouling, which causes a decrease of membrane performance and an increase of operating and maintenance costs. Biofouling is often the deposit component most resistant to chemical cleanings. Consequently, membrane pretreatment has to be optimized to minimize the biofouling potential of the feed water. This study focused on the effect of UV irradiation on NF membrane biofouling at pilot scale in Neuillysur- Marne Water Treatment Plant (WTP), operated by Veolia Water on behalf of the Syndicat des Eaux d'Ile-de- France. At this WTP, the conventional process was composed of clarification, sand filtration, ozonation, granular activated carbon (GAC) adsorption and chlorination. Two identical one-stage NF membrane pilots and a low pressure UV reactor were implemented and operated during two different tests. During Test 1, Pilot 1 was fed sand-filtered water (SFW) and Pilot 2 sand-filtered and UV irradiated water (SF+UVW). During Test 2, Pilot 1 was fed GAC-filtered water (GACW) and Pilot 2 GAC-filtered and UV-irradiated water (GAC+UVW). The UV dose was fixed at 400 J/m² by adjusting the feed flux of the UV reactor. Both NF pilots included a pretreatment step made of pH neutralization, 20 and 6 µm cartridge filtration, and antiscalant injection. At the end of both tests, NF spiral-wound modules were autopsied and analyzed. The fouling deposit was characterized by ATR-FTIR spectroscopy and by epifluorescence microscopy with different stainings (DAPI for total bacteria counts, SYTO9-propidium iodide for live/dead distinction, FTIC and TRITC-conjugated lectins for exopolysaccharides visualization). The deposit dry weight, wettability, ATP and proteins contents were also determined. Both membrane performances monitoring and foulant analysis indicated that UV irradiation was a favorable NF pretreatment. The longitudinal pressure drop increase was strongly limited by UV irradiation. The permeate flux decline was also slowed down by UV, at least after a 10 week filtration time. The deposit is quantitatively reduced and the membrane wettability is less affected when UV pretreatment is used. All the biofilm parameters (activity, cell counts, matrix exopolymers) were also decreased. Includes 21 references, tables, figures.