PHOTODEGRADATION OF DICHLOROMETHANE, TETRACHLOROETHYLENE AND 1,2-DIBROMO-3-CHLOROPROPANE IN AQUEOUS SUSPENSIONS OF TIO(2) WITH NATURAL, CONCENTRATED AND SIMULATED SUNLIGHT

The photodegradation of dichloromethane and of tetrachloroethylene in dilute aqueous solutions and of 1,2-dibromo-3-chloropropane (DBCP) in contaminated groundwater was carried out by illumination with natural, concentrated and simulated sunlight in the presence of air and suspended TiO2 or TiO2 Coated on silica gel. With tetrachloroethylene in homogeneous aqueous solutions, illumination with a high pressure mercury lamp resulted in photodegradation even in the absence of any additive, but the rate was significantly enhanced in the presence of powdered TiO2. The TiO2-promoted degradation of tetrachloroethylene with light of 313 nm or with natural sunlight was further increased by the addition of hydrogen peroxide. The rate of the homogeneous photolysis of tetrachloroethylene by illumination with light longer than 300 nm was not affected by the presence of nitrate ion. Using concentrated sunlight, the Tate of the photodegradation of aqueous tetrachloroethylene in the presence of H2O2 and suspended TiO2 was approximately linear with the light intensity, up to a light flux of about 80 kW m-2. With DBCP in polluted well-water from California, illumination in the presence of TiO2 resulted in a decrease in the halocarbon content of the water from the initial high concentration of 2.9 +/- 0.2 ppb to 0.4 +/- 0.1 ppb.