Kinetics and toxicity of direct reaction between ozone and 1,2-dihydrobenzene in dilute aqueous solution

The presence of toxic aromatic organic compounds in industrial wastewater a ffects the efficiency of conventional biological treatment. The oxidizing p ower of ozone represents an interesting pretreatment to reduce toxicity and increase biodegradability. At low pH, ozone is known to attack electron-ri ch structures by direct electrophilic reactions which open aromatic rings, and generate smaller oxidized compounds. This paper reports experimental re sults on kinetic and toxicity aspects of ozone direct reactions with 1,2-di hydrobenzene. This toxic compound is frequently found in cellulose bleachin g effluents. Although the reaction pathway is rather complex, 4-carbon comp ounds, such as maleic acid, are readily formed during the first stage of oz onation. These 4-carbon compounds are further oxidized to form smaller mole cules (mostly 2-carbon, such as oxalic acid). The apparent kinetics of 1,2- dihydrobenzene follows a second order law, with a rate constant around 0.36 (dm(3) mmol(-1)s(-1)), at pH 2 and 20 degreesC. Results show that the BOD: GOD ratio increase five-fold as ozonation progresses. Furthermore, the muta genicity of 1,2-dihydrobenzene totally disappears as the aromatic compound is destroyed by ozonation.