A selection framework for NOM removal process for drinking water treatment

NOM (natural organic matter) is increasing in water resources worldwide and is becoming more difficult to treat. Drinking water guidelines are becoming more stringent so NOM removal is becoming more critical and requires consideration as a major treatment process, rather than just a polishing step on top of turbidity removal. In this study, a review of available methodologies to determine the required degree of NOM removal was undertaken. It is demonstrated that chlorine decay and THM (trihalomethane) formation modelling of laboratory-treated water samples provides a sound guide to determine the level of NOM removal needed for a given situation. The level of NOM removal needed is linked to a specific distribution system at given water temperature and water age profile. A sample of raw water treated by a given NOM removal process is tested for chlorine decay rates and THM formation kinetics, and these results are used to evaluate the performance of a distribution system with a given configuration. Frequently used and proven processes for NOM removal are: enhanced coagulation, granulated activated carbon, ozone with biological activated carbon and ion exchange resins. The impact of any of these processes can be predicted by the proposed methodology. General guidelines for process selection are presented.