Oxidation of microcystin-LR by copper (II) coupled with ascorbic acid: Kinetic modeling towards generation of H2O2

Abstract

Oxidation of microcystin-LR (MCLR) by copper (II) coupled with ascorbic acid (H2A) in the presence of oxygen was investigated in this study. The combination of Cu(II) with H2A in situ generates H2O2 by reducing dissolved oxygen and subsequently produces reactive species through the reaction of Cu(I) and H2O2. A kinetic model was established to successfully describe the kinetics and mechanism for generation of H2O2, and the second-order rate constant between Cu(II) and HA− at neutral pH was determined to be 3.0×103M−1s−1. Furthermore, quenching tests and electron spin resonance (ESR) analysis were used to identify the primary reactive species, and results indicated that HO is the primary reactive species and responsible for MCLR degradation. Batch experiments were further conducted to evaluate the effect of Cu(II) and H2A dosage, solution pH and Cl− concentration on the degradation of MCLR during the Cu(II)/H2A system. The MCLR degradation increased with the increasing Cu(II) and H2A dosages, while decreased with the increasing solution pH. However, addition of Cl− could significantly inhibit the degradation of MCLR. Meanwhile, a possible degradation pathway of MCLR in the Cu(II)/H2A system was proposed. And the toxicity assessment by PP2A test showed that MCLR was readily degraded and the oxidation by-products are not hepatotoxins. Therefore, the Cu(II)/H2A process could be considered as a potential technology to remove MCLR in algae-laden water.