Enzymatic oxidation and adsorption as strategies for decoloration of wastewater.

GONZÁLEZ CLAR, M.; MIRANDA, M. V.; LEVIN, G. J.; CAMPO DALL' ORTO, V.

Congreso; 1er Congreso Internacional de Ciencia y Tecnología Ambiental. 1er Congreso Nacional de la Sociedad Argentina de Ciencia y Tecnología Ambiental.; 2012

Enzyme technology has become a multidisciplinary field with applications in diverse processes based on ?green chemistry? reagents. Soybean peroxidase (SBP) is present at high concentration in the seed coat, an inexpensive source by-product of food industry, and can be extracted with a buffer solution [1]. In this work we used the SBP extract from seed coat without further purification to treat aqueous solutions of Direct blue 273, an azo dye used in paper industry. Wastewaters from this origin usually contain high concentrations of various dyes, which can produce adverse effects on the eco-environments. When hydrogen peroxide was added as oxidant to a solution of the dye at room temperature, the absorbance at 588 nm diminished in presence of SBP extract at pH values between 4.0 and 7.0. The blue solution became grey and finally pale yellow, and no other absorption band appeared in the UV-visible region of the spectrum. There was no decoloration if the SBP extract was previously boiled for two hours. The optimum concentration of hydrogen peroxide strongly depended on the ratio enzyme/H2O2. For a SBP concentration of 1.5 mg L-1, the decoloration was observed with H2O2 initial concentration between 0.1 and 3.0 mM. From 0.4 mM the enzyme was saturated in peroxide, and beyond 3.0 mM the enzyme was inhibited. The concentration of the dye was followed in time in the presence of H2O2 and the SBP extract. The experimental data fitted to the pseudo-first order kinetic model with five parameters. This model involves a fast reaction that we associated to the change from blue to grey, and a slow reaction possibly related to the change to pale yellow. The pseudo-first order kinetic constants decreased from 0.2 to 1 mM H2O2. We also tested the decoloration of dye solutions using a one-step synthesized polyampholyte as adsorbent. The equilibrium results fitted to Langmuir model with a maximum binding capacity of 450 mg of dye per gram at 24º C, and Kd 1,8 x 10-5 M. The performance of the adsorbent was optimal.