Degradation of EDTA in a total chlorine free cellulose pulp bleaching effluent by UV/H2O2 treatment

Degradation of EDTA in a Total Chlorine Free (TCF) cellulose pulp bleaching effluent, using UV and UV/H2O2 in presence and absence of iron, was studied. All experiences were conducted in an annular photolytic reactor at pH 9, 20 degrees C, and 0.38 mM (110 mgL(-1)) EDTA concentration. EDTA degradation followed a first order apparent kinetics, with rate constant in the range of 0.02-0.72 min(-1), depending on the initial hydrogen peroxide concentration and iron content. UV treatment without peroxide yielded 100% degradation of Fe(III)-EDTA in 40 minutes of reaction, but low COD (8%) and TOC (13%) removal. Peroxide addition (3.3 mM) increased Fe(III)-EDTA degradation rates by UV treatment, resulting in 100% removal after 20 minutes, and greater COD (28%) and TOC (36%) reductions. In absence of iron, peroxide addition was required to obtain EDTA degradation yields above 50% after 1 h treatment. Results presented here show that UV/H2O2 treatment could be suitable as a preliminary stage before a biological treatment.