title: Synergetic effect between photocatalytic degradation and adsorption processes on the removal of phenolic compounds from olive mill wastewater.
abstract: The photocatalytic degradation of two phenolic compounds, p-coumaric acid and caffeic acid, was performed with a suspended mixture of TiO(2) and powdered activated carbon (PAC) (at pH=3.4 and 8). Adsorption, direct photolysis and photocatalytic degradation were studied under different pH and UV light sources (sunlight vs. 365nm UV lamps). The potential for reusing this catalyst mixture in sequential photocatalytic runs was examined as well. Quantum yields for the direct photolysis of caffeic acid under solar and artificial 365nm light were calculated (for the first time) as 0.005 and 0.011, respectively. A higher removal rate of contaminants by either adsorption or photocatalysis was obtained at a low pH (pH 4). Furthermore, the addition of PAC increased the removal efficiency of the phenolic compounds. Fast removal of the pollutants from the solution over three sequential runs was achieved only when both TiO(2) and PAC were present. This suggests that at medium phenolic concentrations, the presence of PAC as a co-sorbent reduces surface poisoning of the TiO(2) catalyst and hence improves photocatalysis degradation of phenolic pollutants. The adsorption equilibrium of caffeic acid or p-coumaric acid on TiO(2), PAC and the combined mixture of TiO(2) and PAC follows the Langmuir isotherm model. Experiments with PAC TiO(2) mixture and olive mill wastewater (anaerobically treated and diluted by a factor of 10) showed higher removal of polyphenols than of chemical oxygen demand (COD). 87% removal of total polyphenols, compared to 58% of COD, was achieved after 24h of exposure to 365nm irradiation (7.6W/m(2)) in the presence of a suspended mixture of TiO(2) and PAC, indicating "self-selectivity" of polyphenols.
authors.affiliation: The Galilee Society, Institute of Applied Research, P.O. Box 437, Shefa-Amr 20200, Israel.
authors.forename: Katie
authors.initials: K
authors.lastname: Baransi
authors.forename: Yael
authors.initials: Y
authors.lastname: Dubowski
authors.forename: Isam
authors.initials: I
authors.lastname: Sabbah
mesh_terms: D000327:Adsorption / Q000528:radiation effects; D000693:Anaerobiosis / Q000528:radiation effects; D002109:Caffeic Acids / Q000737:chemistry / Q000302:isolation & purification; D002384:Catalysis / Q000528:radiation effects; D002606:Charcoal / Q000737:chemistry; D003373:Coumaric Acids / Q000737:chemistry / Q000302:isolation & purification; D004058:Diffusion / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration / Q000528:radiation effects; D007220:Industrial Waste / Q000032:analysis*; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D031658:Olea / Q000737:chemistry*; D052638:Particulate Matter / Q000737:chemistry; D010636:Phenols / Q000302:isolation & purification*; D010782:Photolysis / Q000528:radiation effects*; D016062:Porosity / Q000528:radiation effects; D011208:Powders; D011422:Propionates; D059027:Recycling; D012722:Sewage / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014025:Titanium / Q000737:chemistry; D014466:Ultraviolet Rays; D014865:Waste Disposal, Fluid; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D002109:Caffeic Acids; D003373:Coumaric Acids; D007220:Industrial Waste; D052638:Particulate Matter; D010636:Phenols; D011208:Powders; D011422:Propionates; D012722:Sewage; D014874:Water Pollutants, Chemical; C009495:titanium dioxide; D002606:Charcoal; D014025:Titanium; C495469:p-coumaric acid; C040048:caffeic acid