Developing a More Fundamental Understanding of Drinking Water Biofiltration

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***In the last decade, the interest in using biological processes as part of drinking water treatment has increased substantially. This is driven by their ability to biodegrade portions of the natural organic matter (NOM) in water that can interfere with good treatment. A classical issue associated with NOM is the formation of potentially harmful disinfection byproducts.***Of particular interest is rapid biofiltration, which takes place in filters normally used for particle and pathogen removal. In the absence of a disinfectant residual, the very high surface area in the filters allows for the development of biofilm that can undertake biodegradation. In the last several years, research has shown that such biofilters can also effectively reduce the concentrations of biopolymers, the high molecular weight fraction of the NOM. Biopolymers have been shown to be critical in fouling low-pressure membranes such as ultrafiltration that are increasingly being used for pathogen and particle removal in drinking water treatment. This defines a potential new application for biofiltration, i.e. as a "green" membrane pretreatment. In the last several years, a significant portion of the applicant's research has been directed towards this.***In the conduct of this research several important issues have arisen that require more fundamentally-oriented investigation. These research questions form the basis of this application and are important for the understanding and successful application of biofiltration, regardless of its treatment objective.***The first issue is that conflicting information has appeared in the literature regarding the appropriate macronutrient ratio for biofilters so that nitrogen or phosphorus are not limiting. This is of important practical significance, because if, for example, phosphorus were to be supplemented, it could potentially need to be removed at the downstream wastewater treatment plants. Additionally, the role of extracellular polymeric substances (EPS) in biofiltration has not been properly addressed. Further, commonly used parameters to quantify biomass such as adenosine triphosphate (ATP) have been shown not to have a unique relationship with biofilter performance.***A second research question is that in terms of biofiltration as a membrane pretreatment, the biodegradability of the biopolymer fraction appears to be different for different waters. Ozonation prior to biofiltration assists in reducing membrane fouling, but appears to negatively impact the removal of biopolymers by biofiltration.*** ***Because biofiltration can also remove the easily biodegradable NOM that contributes to biofouling in reverse osmosis (RO) membranes used for desalination, a third need is to explore biofiltration's potential in RO applications, where it could reduce chemical usage for membrane cleaning.*** **