Degradation of organochlorinated pollutants in water by catalytic hydrodechlorination and photocatalysis

• Chlorophenoxy herbicides were efficiently removed by PCO.
• PCO allows achieving high mineralization efficiency.
• HDC is an efficient technology to reduce toxicity of chlorinated pollutants.
• Sequential process (HDC + PCO) did not improve photocatalytic oxidation.

The degradation of chlorinated herbicides (MCPA and 2,4-D) and 4-chlorophenol (4-CP) by photocatalytic oxidation (PCO) and the combination of catalytic hydrodechlorination (HDC) and photocatalysis, at ambient conditions, has been studied. Commercial TiO2 (P25) and Pd/Al2O3 catalysts were used for PCO and HDC, respectively. MCPA and 2,4-D were transformed upon photo-oxidation to intermediate products and almost total mineralization was achieved. However, in the case of 4-CP, a conversion of only 82% of chloride formation and 87% TOC were obtained. In spite of the fact that the HDC reaction resulted in a total dechlorination of organochlorinated pollutants combined with an important decrease of the effluent ecotoxicity, the percentage of mineralization obtained in the combined process (HDC–PCO) was slightly lower than in the PCO treatment. Thus, the HDC–PCO process is not justified versus a single PCO treatment.

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