Removal of trace organic substances from river bank filtrate – performance study of RO and NF membranes

Producing drinking water from raw waters like river bank filtrate nowadays requires the safe removal of ever new emerging organic substances. At present, in Germany perfluorinated organic compounds are heavily discussed. When it comes to trace organics removal, reverse osmosis (RO) and nanofiltration (NF) are alternatives to conventional bank filtrate treatment technologies like ozonation and activated carbon adsorption. However, the trace organics removal capabilities of dense membranes are still under investigation. Questions about concentrate disposal strategies are still open. The paper presents results from lab-scale and pilot studies which were conducted for the project planning of a 1,100 m³/h NF plant treating river Rhine bank filtrate. Membranes from loose NF to dense RO were investigated spiking the raw waters with trace organic substances which usually pass the soil passage and to some extent even the conventional treatment process. The results showed high retention capabilities of the more dense membranes, even under ageing conditions.