Elimination of persistent emerging micropollutants in a suspended-bed photocatalytic reactor: influence of operating conditions and combination with aerobic biological treatment.

A larger, lab-scale photocatalytic suspended-bed reactor using TiO2 sol-gel-coated expanded clay granules as a bed material was evaluated for oxidative removal of the persistent pharmaceuticals doxycycline, prednisolone, amoxicillin, and sulfamethizole, as well as their mixture, in ppm concentrations. The photocatalytic degradation potential of drug molecules increases as their adsorption affinity increases towards TiO2-containing coatings. The performance of the photocatalytic reactor in the removal of drugs was improved by optimizing the fluidization process parameters. The reactor operation at high bed loadings is determined by the abrasion resistance of the catalyst coating. The long-term stability of the coated bed was enhanced by optimal loading, achieving a higher removal rate while placing moderate mechanical stress on the coated granules. The photocatalytic pretreatment decreased the toxicity of doxycycline solutions to several bacterial strains, including the environmental bacterium Pseudomonas putida and bacterial strains freshly isolated from the activated sludge. The treatment of doxycycline-containing water with a combination of photocatalytic treatment and bio-oxidation resulted in 98% removal of the target in the bioreactor outlet, with no deterioration in the operation of the biological process.

Aqueous photocatalytic oxidation of sulfamethizole.

Aqueous photocatalytic oxidation (PCO) of a non-biodegradable sulphonamide antibiotic sulfamethizole was studied. The impacts of photocatalyst dose, initial pH, and substrate concentration in the range from 1 to 100 mg L(-1) were examined with a number of organic and inorganic by-products determined, suggesting the initial break-up of the SMZ molecule at the sulphonamide bond. The experiments were carried out under artificial near-UV and visible light, and solar radiation using Degussa P25 and less efficient visible light-sensitive C-doped titanium dioxide as photocatalysts.

The influence of ferrous/ferric ions on the efficiency of photocatalytic oxidation of pollutants in groundwater.

The complex influence of ferrous/ferric ions on the efficiency of aqueous photocatalytic oxidation (PCO) of 2-ethoxyethanol (2-EE), methyl tert-butyl ether (MTBE) and humic substances (HS) was established. A drastic efficiency increase at lower concentration of ferrous/ferric ions was observed to change to a sharp decrease at higher concentrations for 2-EE and MTBE, whereas for HS only an inhibitive effect of Fe2+/3+ on the PCO efficiency was noticed. The authors proposed an explanation for the observed phenomena based on the different sensitivities of pollutants towards radical-oxidation reactions and the competitive adsorption of metallic ions and pollutants on the TiO2 surface.

Photocatalytical oxidation of de-icing agents in aqueous solutions and aqueous extract of jet fuel.

Improper handling of jet fuel at abandoned military bases has resulted in heavy pollution of the soil and groundwater. Experimental research of photocatalytical oxidation (PCO) of jet fuel aqueous extract and aqueous solutions of de-icing agents was undertaken. The influence of different parameters - pH, concentration of substances to be oxidised, presence of inorganic admixtures, effect of OH. radical generators--on the PCO of solutions of de-icing agents and jet fuel aqueous extract was determined. The role of OH. radicals was found to be less important in determining the PCO rate. The PCO of organic pollutants was also investigated using a catalyst immobilised onto the surface of buoyant hollow glass microspheres. Attached titanium dioxide (TiO2) showed lower photocatalytical activity than when suspended in slurry, although it allows waters to be treated in simple shallow ponds without intensive stirring. The biodegradability of aqueous solutions of de-icing agents and jet fuel aqueous extract increased as PCO proceeded.