REMOVAL OF BENZENE FROM WASTEWATER BY ENZYME-CATALYZED OXIDATIVE POLYMERIZATION COMBINED WITH A MODIFIED FENTON REACTION

A two-step process for the removal of benzene from wastewater, pretreatment by modified Fenton reaction coupled with enzyme-catalyzed polymerization of the resulting phenolic compounds, is presented. Two oxidoreductase enzymes, namely laccase and soybean peroxidase (SBP), were investigated for their capacity to catalyze the oxidative polymerization of the phenolic compounds generated during Fenton pre-treatment. In the benzene pre-treatment step, the effect of pH, hydrogen peroxide and ferrous iron concentrations and reaction time for the Fenton reaction were studied to maximize the conversion of benzene to phenolic compounds without causing significant mineralization. Under optimum Fenton reaction conditions, conversion of benzene generated a mixture containing phenol, benzenediols (hydroquinone, catechol and resorcinol), biphenyl and benzoquinone. Most of the identified products generated after benzene pre-treatment are priority pollutants themselves. Biphenyl and benzoquinone were outside the scope of enzymatic treatment due to their chemical structure. In order to remove the rest of the Fenton products by the enzymatic process, their individual treatabilities by enzymes were explored. The effectiveness of removing 1 mM phenol and benzenediols by using a laccase from Trametes villosa, was investigated. Factors of interest were pH, enzyme concentration, effect of polyethylene glycol (PEG), effect of substrate concentration on enzyme demand, and enzyme inactivation over reaction period. Previous studies have demonstrated that SBP could also be used to treat phenol and benzenediols. As phenol and benzenediols can co-exist in wastewater, treatability of a composite wastewater containing an equimolar mixture of phenol and benzenediols was examined as well. During the enzymatic treatment of phenolic products from benzene, both laccase and SBP were successful in polymerizing the phenolic compounds. Factors of interest for the three-hour enzymatic step were pH, enzyme and hydrogen peroxide concentration. Biphenyl was removed from the solution due to its poor solubility. The benzoquinone generated was removed by employing additives like chitosan or polyethyleneimine (PEI). Alum was used for color removal of the reaction mixture