Review of nanofiltration membranes autopsies after nine years of operation in a drinking water plant

摘要

The Mery-sur-Oise water treatment plant (France), operated by Veolia Water on the behalf of the Syndicat des Eaux d'lle de France (SEDIF), has been using nanofiltration (NF) membranes to produce safe drinking water since 1999. However, significant fouling has been observed according to seasonal conditions, even with several pre-treatments including conventional surface water treatment followed by ozonation, acid injection, antiscalant addition and microfiltration. Fouling is a phenomenon typically caused by inorganic and organic materials present in raw water, which adhere to the surface and pores of the membrane and induce deteriorations of the membrane performances. Furthermore, fouling causes flux decline leading to an increase in cost production. The aim of our study is, on one hand, to characterize and identify the nature of foulants responsible for flux declines and higher pressure drop, and on the other, to monitor the membranes performances after 9 years of operation. Since 2002, several membranes autopsies were realised each year on NF modules extracted from the first and the third stages of the Mery-sur-Oise nanofiltration unit. Several analytical tools such as FT-IR (Fourier Transformed Infra Red) spectroscopy, LC-UV-COD (Liquid Chromatography coupled with UV_(254nm) and Organic Carbon Detectors), SEM (Scanning Electron Microscopy) and TOC (Total Organic Carbon) measurements have been used to extensively characterize the fouling layer. Feed water quality parameters (organic, inorganic and microbiological compositions) were also monitored continuously. The different analyses show that fouling results mainly from the formation of a biofilm on the membrane surface. Significant variations are observed between the two stages: the amount and the composition of the deposit differ. This study shows that autopsies are a powerful tool to understand membranes fouling in order to control it. Than, informations learned from this study will provide useful elements for the development of futures installations using membrane processes.