Enhancing degradation and mineralization of tetracycline using intimately coupled photocatalysis and biodegradation (ICPB)

Intimately coupled photocatalysis and biodegradation (ICPB) has been studied for treating bio-recalcitrant pollutants. The key principle of ICPB is that photocatalysis occurs on a porous carrier’s outer surface, and biofilms are present in the interior, where they are protected from inhibition. Little is known regarding the ability of ICPB to degrade antibiotics, and a primary issue is whether or not the bacteria in the carriers’ interior can acclimate to biodegrade the products from photocatalysis of antibiotics. This study evaluated the removal and mineralization of tetracycline hydrochloride (TCH) using visible-light-induced ICPB (called VPCB) with Ag-doped TiO2 as the photocatalyst. The biofilms inside the VPCB carriers could mineralize the photocatalytic products, which led to more than 20% enhanced removal of chemical oxygen demand (COD). By biodegrading the products of TCH photocatalysis, the biofilms lowered the competition for free radicals between TCH and its photocatalysis products; thus, VPCB accelerated TCH removal by ∼11% in the first 2 h of operation, compared with photocatalysis alone. The biofilms in the VPCB carriers evolved to being enriched in Methylibium, Runella, Comamonas, and Pseudomonas, which are known for biodegrading aromatics and being resistant to TCH. In conclusion, VPCB enhanced degradation and mineralization of TCH.