Degradation of azo and anthraquinone dyes by a low-cost Fe0/air process

Degradation of two different kinds of dyes, anthraquinone Reactive Blue 4 (RB4) and azo Reactive Black 5 (RB5), by low-cost zero valent iron (Fe0) in a N2 bubbling system (Fe0/N2 process) and air bubbling system (Fe0/air process) was investigated. The operating parameters, including initial solution pH, dye concentration and Fe0 dose, were also evaluated. The Fe0/air process shows a higher decolorization rate compared to the Fe0/N2 process. Both RB4 and RB5 solutions at 100 mg L−1 were rapidly decolorized by Fe0/air process within 9 and 3 min, respectively, at initial solution pH 3, Fe dose of 50 g L−1 and air flow rate of 5 L min−1. The optimal initial solution pH was 3. The Fe0/N2 process removed only <17% of COD. However, significant COD removals were achieved for RB 4 (87%) and RB5 (43%) by the Fe0/air process after 9 min of treatment. Spectra analysis results indicated that the Fe0/N2 process destroyed only the anthraquinone group (A594) for the RB4 solution and decreased the azo (A596) and naphthalene group (A310) for the RB5 solution. However, the Fe0/air process rapidly removed A594, A370, A296 (anthraquinone group) and A256 (aromatic and dichlorotriazine group) for RB4, and A597 and A310 (naphthalene group) for RB5. The results indicated that the low-cost Fe0/air process is a potential technique for rapid degradation of RB4 and RB5 solutions.