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In recent years, there have been increases in contamination of water supplies, due to the continuous discharge of wastewater from chemical and pharmaceutical industries, without them being properly treated to remove the refractory organic compound they may contain. These contaminants endanger the quality of surface and groundwater, the ecosystems, and the health of the world´s population. In view of these problems, the present work examined the effectiveness of combining ozone and ozone-UV processes with a biological treatment to increase biodegradability and reduce toxicity levels of the chlorophenolic compound, 2,5-dichlorophenol (2,5-DCP) and its oxidative intermediates. A comparative study was carried out in a glass bubble column reactor equipped with a fine-pore glass diffuser with a volumetric mass transfer kLa of 1.58 min-1. Each experiment was done using a 1.5 L volume of 2,5-DCP (3.07 mM) aqueous solution of distilled water and municipal wastewater, at pH 7 with an applied ozone dose of 22 mg min-1 and an oxygen-ozone flow rate of 0.7 L min-1. Additionally, a low mercury UV lamp with wavelength of 254 nm was used during ozone-UV treatments. The results obtained, showed that 2,5-DCP was completed degraded with an ozone dose of approximately 1.2 g h-1 in both solutions, treated with ozone and ozone-UV processes. The best results were obtained with the ozone-UV processes after 60 min of oxidation, showing that the addition of photolysis treatment (UV lamp intensity = 4 mW cm-2) to ozone, accelerated COD removal (75%), mineralization (53%) and biodegradability (BOD5/COD) of 2,5-DCP from 0.2 to 0.85 in the wastewater. The toxicity of 2,5-DCP and its oxidation by-products were monitored at different time intervals using activated sludge respiration inhibition tests. The test analyses showed that ozone and ozone-UV treatments were effective in reducing the toxicity of 2,5-DCP and its by-products, which were less toxic to the microorganisms in activated sludge (IC25 = 135 mg/L), than the untreated 2,5-DCP solutions (EC50= 50 mg/L). The results achieved in this work, showed that the presence of organic and inorganic matters in the wastewater, had a positive effect on the oxidation of 2,5-DCP, which support the potential use of ozone and ozone-UV processes for the treatment of effluent with high concentration of chlorophenols.

Degradación del 2,5-DCP en agua destilada y en agua residual por los procesos de oxidación avanzada con ozono y ozono-UV combinados con un tratamiento biológico