Effect of common metal ions on the rate of degradation of 4-nitrophenol by a laccase-Cu^sup 2+^ synergistic system

Various metal ions are present in industrial wastewater. In this study, the role of Cu^sup 2+^ in pollutant degradation by laccase and the effect of common metal ions such as Na+, K+, Ca^sup 2+^, Mg^sup 2+^, Zn^sup 2+^, Hg^sup 2+^, Mn^sup 2+^, Fe^sup 2+^, Co^sup 2+^, Ni^sup 2+^, Fe^sup 3+^, and Al^sup 3+^ on the degradation velocity of the laccase-Cu^sup 2+^ synergistic system using 4-nitrophenol as the target pollutant were investigated. The results show that the laccase-Cu^sup 2+^ system achieved a higher degradation velocity than the system without Cu^sup 2+^. The activity of the laccase-Cu^sup 2+^ synergistic system was inhibited when a monovalent metal ion (Na+ or K+) was added into the system regardless of the concentration. The addition of relatively low concentrations of any divalent metal ions also resulted in inhibition of the activity. However, increasing concentrations of Ca^sup 2+^ or Fe^sup 2+^ increased the rate of degradation of 4-nitrophenol by the laccase-Cu^sup 2+^ system, whereas increasing concentrations of other divalent metal ions suppressed the system. The inhibition effect of the added trivalent metal ions (Al^sup 3+^ or Fe^sup 3+^) was significant during the entire process, indicating that these trivalent metal ions can be a serious obstacle to the activity of the laccase-Cu^sup 2+^ synergistic system. [PUBLICATION ABSTRACT]