Advanced Oxidation and Biodegradation

Detoxifying recalcitrant organic contaminants to promote biodegradability

Recalcitrant organics have chemical structures that render them non-biodegradable.  Examples include many pesticides, pharmaceuticals, petrochemicals, dyes, and energetics.  Because they do not decompose in wastewater treatment systems or in nature, humans and aquatic organisms can be exposed to them, resulting in health and ecological risks.  

Swette Center researchers are developing means to give bacteria a “little help” so that they can fully biodegrade the recalcitrant molecules.  The “help” comes in the form of a small dose of photocatalysis, in which UV light activates titanium dioxide (TiO2) to form highly reactive free radicals that powerfully attack the recalcitrant chemical structures, creating small chemical “dings” that make the molecules biodegradable.  With this help to get them started, the bacteria are able to mineralize the organic molecules, totally eliminating the health and ecological risks.



Photograph of a cellulosic macroporous carrier cut in half to show the protected biofilm on the inside


Dr. Rittmann and colleagues developed, tested, and patented a novel means to link photocatalysis to biodegradation.  Called intimately coupled photobiocatalysis, the novel system allows the bacteria to be present at the same time and place as the photocatalysis.  As soon as a biodegradable molecule is produced by photocatalysis, the bacteria biodegrade it.  The bacteria are “standing by” inside special macroporous biofilm carriers that protect them from UV light and free radicals.  Intimate coupling makes biodegradation of recalcitrant organics simple, reliable, and efficient.  Swette Center researchers have proven intimate coupling for chlorinated phenols, dyes, heterocyclic aromatics, and other recalcitrant organic chemicals.


Scanning electron micrograph of bacteria on the inside surface of a plastic macroporous carrier


Photograph of the plastic carriers before (left) and after (right) being coated with titanium dioxide