title: Degradation of reactive dyes in a photocatalytic circulating-bed biofilm reactor.
abstract: Decolorization and mineralization of reactive dyes by intimately coupled TiO₂-photocatalysis and biodegradation (ICPB) on a novel TiO₂-coated biofilm carrier were investigated in a photocatalytic circulating-bed biofilm reactor (PCBBR). Two typical reactive dyes--Reactive Black 5 (RB5) and Reactive Yellow 86 (RY86)--showed similar first-order kinetics when being photocatalytically decolorized at low pH (~4-5) in batch experiments. Photocatalytic decolorization was inhibited at neutral pH in the presence of phosphate or carbonate buffer, presumably due to electrostatic repulsion from negatively charged surface sites on TiO₂, radical scavenging by phosphate or carbonate, or both. Therefore, continuous PCBBR experiments were carried out at a low pH (~4.5) to maintain high photocatalytic efficiency. In the PCBBR, photocatalysis alone with TiO₂-coated carriers could remove target compound RB5 and COD by 97% and 47%, respectively. Addition of biofilm inside macroporous carriers maintained a similar RB5 removal efficiency, but COD removal increased to 65%, which is evidence of ICPB despite the low pH. ICPB was further proven by finding microorganisms inside carriers at the end of the PCBBR experiments. A proposed ICPB pathway for RB5 suggests that a major intermediate, a naphthol derivative, was responsible for most of the residual COD, while most of the nitrogen in the azo-bonds (-N=N-) was oxidized to N₂.
authors: Swette Center for Environmental Biotechnology, Biodesign Institute at Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 85287-5701, USA. guozheng.li@asu.edu
authors: Guozheng
authors: G
authors: Li
authors: Seongjun
authors: S
authors: Park
authors: Bruce E
authors: BE
authors: Rittmann
mesh_terms: D001391:Azo Compounds / Q000737:chemistry / Q000528:radiation effects*; D001673:Biodegradation, Environmental; D018441:Biofilms; D019149:Bioreactors / Q000382:microbiology; D002021:Buffers; D002254:Carbonates; D020099:Coated Materials, Biocompatible; D004396:Coloring Agents / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D009282:Naphthalenesulfonates / Q000737:chemistry / Q000378:metabolism*; D010710:Phosphates; D038761:Photobleaching; D017319:Photosensitizing Agents / Q000528:radiation effects*; D055672:Static Electricity; D014025:Titanium / Q000528:radiation effects*; D014227:Triazines / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001391:Azo Compounds; D002021:Buffers; D002254:Carbonates; D020099:Coated Materials, Biocompatible; D004396:Coloring Agents; D009282:Naphthalenesulfonates; D010710:Phosphates; D017319:Photosensitizing Agents; D014227:Triazines; D014874:Water Pollutants, Chemical; C009495:titanium dioxide; C042516:reactive red 120 dye; C572948:reactive yellow 86; D014025:Titanium; C063421:Remazol black B