| New technologies are required to degrade bio-recalcitrant and toxic organic contaminants in water. Combined photocatalytic-biological degradation is a promising alternative to meet this challenge: Photocatalysis breaks down toxic organics into biodegradable products, while biodegradation efficiently mineralizes the products.; 2,4,5-Trichlorophenol (TCP) is the model compound used to evaluate the scientific basis of combined photocatalytic-biological treatment, called photobiocatalaysis. Biodegradation studies demonstrated that TCP is strongly bio-recalcitrant and inhibitory at concentrations above 40 muM, and biological treatment could not reliably remove it at any concentration.; In contrast, sequential photocatalytic-biological degradation removed TCP in continuous studies. The performance of a biological post-treatment fed effluent from photocatalysis of TCP revealed tradeoffs between steady-state performance and resistance and resilience to a spike of TCP. Photocatalytic effluents with strong aliphatic and non-chlorinated character demonstrated good steady-state performance, but were impaired by a TCP perturbation, while effluents with strong aromatic character showed good resistance and resilience, even though steady-state performance was not as good. Thus, a balance must be achieved between these conditions to provide for the optimum photocatalytic effluent for biodegradation.; Single organic substrates, chosen to mimic varying degrees of photocatalytic oxidation of TCP, were used to further explore these phenomena. A heavily oxidized organic, acetate, showed the best steady-state performance and had the most diverse community, but it had the worst resistance to TCP perturbation. The chlorinated aromatic, 4-chlorocatechol, demonstrated the worst steady-state performance, but good resistance, resilience, and community stability. An intermediate compound, 2-chloromuconic acid, provided the best balance of good steady-state performance, strong resistance and resilience, and community stability.; Photocatalysis and biodegradation were intimately coupled in a single stage for the first time. This allowed the bacteria to remove biodegradable products from bulk solution as they were formed, thereby focusing the chemical oxidant on the toxic contaminants. Intimate coupling has seemed impossible, since photocatalytic conditions are severely toxic to bacteria. However, macroporous cellulosic carriers protected the bacteria from toxic conditions, allowing both processes to occur together. This system removed TCP and acetate simultaneously, while each process individually failed for the same conditions. |
