Role of cupric ions in the H2O2/UV oxidation of humic acids

The purpose of this study is to reveal the role of cupric ions as a natural water contaminant in the H2O2/UV oxidation of humic acids. Humic acids are naturally occurring organic matter and exhibit a strong tendency of comple xation with some transition metal ions. Chlorination of humic acids causes potential health hazards due to formation of trihalomethane (THM). The remo val of THM precursors has become an issue of public concern. The H2O2/UV pr ocess is capable of mineralizing humic acids due to formation of a strong o xidant, hydroxyl radicals, in reaction solution. Experiments were conducted in a re-circulated photoreactor. Different cupric concentrations (0-3.8 mg /l) and different pH values (4-9) were controlled to determine their effect s on the degradation of humic acids, I-TV light absorbance at 254 nm, and H 2O2. The presence of cupric ions inhibits humic mineralization and decrease s the rate of destruction of humic acids which absorb UV light at 254 mn. O n the other hand, the higher the cupric concentration, the lower the H2O2 d ecomposition rate. In the studied pH range, the minimum of total organic ca rbon (TOC) removal occurs at pH = 6 in the presence of 2.6 mg/l of cupric i ons; both acidification (pH = 4) and alkaline condition (pH = 9) lead to a better removal of TOC. It is inferred from this study that the cupric-compl exed form of humic acids is more refractory than the non-complexed one. (C) 2001 Elsevier Science Ltd. Ail rights reserved.