AWWA MTC64630

Nanofiltration of surface water was investigated in pilot-scale, comparing biofiltration and rapid media filtration as simple pre-treatment options. The nanofilters were operated according to the approach established in parts of Scandinavia, where pretreatment is limited and the membrane flux is low. Biofiltration resulted in feed water containing lower concentrations of bacteria, total organic carbon (TOC) and Biodegradable organic carbon (BDOC) and resulted in a profoundly decreased biofilm formation on glass slides compared to rapid media filtration. Transmembrane pressure increase was in average 5 fold lower for the nanofilter with biofiltration as pretreatment (NF-BAC) compared to the nanofilter with rapid media filtration as pretreatment (NF-DM). The NF-BAC membranes contained less biological-, organic- and inorganic fouling than the NF-DM membranes. Iron, aluminium and silica were the dominant inorganic elements, while biopolymers (polysaccharides, proteins and aminosugars) were the dominant organic fouling fraction, despite low concentrations in the feed waters. Although NF-Bio contained less fouling matter than NF-RMF, no difference in the fouling composition was observed that would point out a specific component responsible for the reduced transmembrane pressure. The results of this study indicate that biofiltration, as a simple pretreatment option, can significantly mitigate fouling problems in low flux NF installations for natural organic matter (NOM) removal from surface water. Includes 21 references, table, figures.