| Azo dye production worldwide has been estimated at 7 × 105 tons per year. Azo dyes are synthesized to be stable in the media to which they are applied, resulting in a molecule that is very stable in light and is resistant to degradation under aerobic conditions. This stability is beneficial to the dye manufacturers, but treatment of azo dye-containing wastes has become a problem, as treatment is ineffective through traditional aerobic processes.; It is hypothesized that zero-valent iron pretreatment converts azo dyes and nitroaromatics (NACs), via chemical reduction, to aerobically biodegradable aromatic amines. Zero-valent iron reduction has been demonstrated for a range of azo dyes and NACs, and a few investigations have been made into reduction product biodegradability. Until now, the two types of investigations have not been integrated. In this research, factors that influence reduction rates and into the biodegradability and toxicity of azo dye and NAC reduction products have been examined. Additionally, the viability of an integrated iron column/activated sludge system for the treatment of azo dye-containing wastewaters has been investigated.; Evaluation of elemental iron for reductive treatment of azo dyes, orange G, orange II, and orange IV, was performed in batch experiments conducted in an anaerobic environment. Reduction rates were determined, products of reduction were confirmed, and solution factors influencing reduction rates were identified. Batch biodegradation assessments and respirometric assays with acclimated microorganisms were performed to quantify enhanced biochemical oxygen demand of iron-treated dyes over the original compounds. Finally, a bench-scale system employing an iron pretreatment column upstream of an activated sludge system was constructed to evaluate the effectiveness of this technology in a continuous-flow system.; Results indicate that low solution pH, the use of cast iron, and the addition of chloride and sulfate ions enhance reduction reaction rates. Other factors, such as elevated solution pH and the presence of phosphate ions inhibit iron corrosion, and therefore dye reduction rates. Results of biodegradability studies illustrate at least one of the reduction products for each dye is biodegradable under aerobic conditions. Finally, the integrated treatment system was effective for the treatment of synthetic wastewaters containing azo dyes. |
