Improving the use of granular activated carbon to control algal byproducts during drinking water treatment

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Drinking water treatment plants may use granular activated carbon (GAC) to adsorb and remove contaminants, but the GAC has a finite service life before it is exhausted and needs to be replaced. A recent trend in the industry is to use GAC in a biological mode: allowing bacteria to grow on its surface and remove contaminants through biodegradation. This allows the GAC to remain in service, avoiding costly replacement. Such "biofiltration", however, remains poorly understood and unpredictable. The proposed research aims to take advantage of recent discoveries by the proponent to make substantial gains in our understanding of biofiltration. In particular, drinking water treatment plants have been identified in Ontario that show considerable evidence of both the presence of effective biofiltration, as well as its absence, under conditions that appear on a superficial level to be relatively similar. By studying the GAC from these plants, the factors that lead to effective biofiltration can be identified. This work will be aided by a new application of a technique to study biodegradation, called compound specific isotope analysis (CSIA), which has traditionally been used to study the fate of contaminants at large concentrations. By developing a method to apply CSIA for contaminants at low levels (µg/L or ng/L), new research areas could be opened up in terms of evaluating the fate of trace contaminants in the environment. The overall goal of this research is to identify robust, effective, and reliable strategies to enhance the biodegradation of target contaminants through GAC. This will reduce the cost of GAC treatment, which in turn would allow GAC to be used by a greater number of utilities. GAC offers good broad-spectrum protection against a range of contaminants, so the ability to apply it more widely would bring corresponding public health benefits. Furthermore, GAC is a green treatment, requiring no chemicals and little energy, so its use as an alternative to other forms of treatment to destroy microcontaminants would be a move towards more sustainable drinking water treatment.