Biological Treatment Of Azo Dye Wastewater With High Salt Concentration

Because of their chemical stability, ease of synthesis and versatility, azo dyes are widely used in printing, paper-making, cosmetic and textile dyeing industries, which are the vital pollutions in the waste water. Azo dye wastewater is one of the industrial wastewater to be hardly treated with high salinity. In this paper, properties and treatment methods of azo dye wastewater was reviewed. Some conventional methods of wastewater treatment cannot effectively decolorize water contaminations by azo dyes under hypersaline conditions. Based on that, redox mediator enhancement was believed to be an effective method to increase the performance of anaerobic decolorization. In the A/O biological treatment processes, the presence of activated carbon felt could effectively inhibit autoxidation of intermediate product.The purpose of this paper is to use salt-tolerant microorganism, find the effective substances which enhanced the biological decolorization of azo dyes in the dye waste water and the treatment method of intermediate product. The characteristics of the augmented activated sludge were studied. The effects of several artificial redox mediators were compared. Enhancement of decolorization by adaptive biological carriers was studied.Acid Orange 7 was selected as the representative matter, azo dye wastewater with high salt concentration was treated by the salt-tolerant sludge and GTW at the NaCl concentration of 100 g/L. Enhanced biological decolorization of azo dyes by Acid Red B and several artificial redox mediators was investigated. The results indicated that the decolorization rate of wastewater containing azo dyes was able to be increased when GTW was added to the activated sludge. However, the strengthening effect decreased with continuous operation. The biodecolorization rate of AO7 could be increased when Acid Red B was added to the anaerobic reactor. Anthraquinone-activated sludge self-immobilization system could enhance the biodecolorization of AO7 when anthraquinone was added to the salt-tolerant sludge. The optimum conditions for Acid Orange 7 were as follows: pH 7～9, anthraquinone and initial dye concentrations 100 mg/L and≤600mg/L.Using activated carbon felt as biological carrier in the anaerobic reactor, the decoloration rate could reach over 26.67 mg/L·h under stable operation condition. In the aerobic process, the presence of activated carbon felt could effectively inhibit autoxidation of intermediate product 1-Amino-2-naphthol with a good sludge settlement and over 90% of COD removal. There are two reasons for the good treatment effect: one is the biofilm formation, the other is the good adsorption capacity.